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diff --git a/doc/autoconf.info b/doc/autoconf.info new file mode 100644 index 0000000..1ba3bfd --- /dev/null +++ b/doc/autoconf.info @@ -0,0 +1,25690 @@ +This is autoconf.info, produced by makeinfo version 4.13 from +autoconf.texi. + +This manual (24 April 2012) is for GNU Autoconf (version 2.69), a +package for creating scripts to configure source code packages using +templates and an M4 macro package. + + Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.3 or any later version published by the Free Software + Foundation; with no Invariant Sections, no Front-Cover texts, and + no Back-Cover Texts. A copy of the license is included in the + section entitled "GNU Free Documentation License." + +INFO-DIR-SECTION Software development +START-INFO-DIR-ENTRY +* Autoconf: (autoconf). Create source code configuration scripts. +END-INFO-DIR-ENTRY + +INFO-DIR-SECTION Individual utilities +START-INFO-DIR-ENTRY +* autoscan: (autoconf)autoscan Invocation. + Semi-automatic `configure.ac' writing +* ifnames: (autoconf)ifnames Invocation. Listing conditionals in source. +* autoconf-invocation: (autoconf)autoconf Invocation. + How to create configuration scripts +* autoreconf: (autoconf)autoreconf Invocation. + Remaking multiple `configure' scripts +* autoheader: (autoconf)autoheader Invocation. + How to create configuration templates +* autom4te: (autoconf)autom4te Invocation. + The Autoconf executables backbone +* configure: (autoconf)configure Invocation. Configuring a package. +* autoupdate: (autoconf)autoupdate Invocation. + Automatic update of `configure.ac' +* config.status: (autoconf)config.status Invocation. Recreating configurations. +* testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite. +END-INFO-DIR-ENTRY + + +File: autoconf.info, Node: Top, Next: Introduction, Up: (dir) + +Autoconf +******** + +This manual (24 April 2012) is for GNU Autoconf (version 2.69), a +package for creating scripts to configure source code packages using +templates and an M4 macro package. + + Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.3 or any later version published by the Free Software + Foundation; with no Invariant Sections, no Front-Cover texts, and + no Back-Cover Texts. A copy of the license is included in the + section entitled "GNU Free Documentation License." + +* Menu: + +* Introduction:: Autoconf's purpose, strengths, and weaknesses +* The GNU Build System:: A set of tools for portable software packages +* Making configure Scripts:: How to organize and produce Autoconf scripts +* Setup:: Initialization and output +* Existing Tests:: Macros that check for particular features +* Writing Tests:: How to write new feature checks +* Results:: What to do with results from feature checks +* Programming in M4:: Layers on top of which Autoconf is written +* Programming in M4sh:: Shell portability layer +* Writing Autoconf Macros:: Adding new macros to Autoconf +* Portable Shell:: Shell script portability pitfalls +* Portable Make:: Makefile portability pitfalls +* Portable C and C++:: C and C++ portability pitfalls +* Manual Configuration:: Selecting features that can't be guessed +* Site Configuration:: Local defaults for `configure' +* Running configure Scripts:: How to use the Autoconf output +* config.status Invocation:: Recreating a configuration +* Obsolete Constructs:: Kept for backward compatibility +* Using Autotest:: Creating portable test suites +* FAQ:: Frequent Autoconf Questions, with answers +* History:: History of Autoconf +* GNU Free Documentation License:: License for copying this manual +* Indices:: Indices of symbols, concepts, etc. + + --- The Detailed Node Listing --- + +The GNU Build System + +* Automake:: Escaping makefile hell +* Gnulib:: The GNU portability library +* Libtool:: Building libraries portably +* Pointers:: More info on the GNU build system + +Making `configure' Scripts + +* Writing Autoconf Input:: What to put in an Autoconf input file +* autoscan Invocation:: Semi-automatic `configure.ac' writing +* ifnames Invocation:: Listing the conditionals in source code +* autoconf Invocation:: How to create configuration scripts +* autoreconf Invocation:: Remaking multiple `configure' scripts + +Writing `configure.ac' + +* Shell Script Compiler:: Autoconf as solution of a problem +* Autoconf Language:: Programming in Autoconf +* Autoconf Input Layout:: Standard organization of `configure.ac' + +Initialization and Output Files + +* Initializing configure:: Option processing etc. +* Versioning:: Dealing with Autoconf versions +* Notices:: Copyright, version numbers in `configure' +* Input:: Where Autoconf should find files +* Output:: Outputting results from the configuration +* Configuration Actions:: Preparing the output based on results +* Configuration Files:: Creating output files +* Makefile Substitutions:: Using output variables in makefiles +* Configuration Headers:: Creating a configuration header file +* Configuration Commands:: Running arbitrary instantiation commands +* Configuration Links:: Links depending on the configuration +* Subdirectories:: Configuring independent packages together +* Default Prefix:: Changing the default installation prefix + +Substitutions in Makefiles + +* Preset Output Variables:: Output variables that are always set +* Installation Directory Variables:: Other preset output variables +* Changed Directory Variables:: Warnings about `datarootdir' +* Build Directories:: Supporting multiple concurrent compiles +* Automatic Remaking:: Makefile rules for configuring + +Configuration Header Files + +* Header Templates:: Input for the configuration headers +* autoheader Invocation:: How to create configuration templates +* Autoheader Macros:: How to specify CPP templates + +Existing Tests + +* Common Behavior:: Macros' standard schemes +* Alternative Programs:: Selecting between alternative programs +* Files:: Checking for the existence of files +* Libraries:: Library archives that might be missing +* Library Functions:: C library functions that might be missing +* Header Files:: Header files that might be missing +* Declarations:: Declarations that may be missing +* Structures:: Structures or members that might be missing +* Types:: Types that might be missing +* Compilers and Preprocessors:: Checking for compiling programs +* System Services:: Operating system services +* Posix Variants:: Special kludges for specific Posix variants +* Erlang Libraries:: Checking for the existence of Erlang libraries + +Common Behavior + +* Standard Symbols:: Symbols defined by the macros +* Default Includes:: Includes used by the generic macros + +Alternative Programs + +* Particular Programs:: Special handling to find certain programs +* Generic Programs:: How to find other programs + +Library Functions + +* Function Portability:: Pitfalls with usual functions +* Particular Functions:: Special handling to find certain functions +* Generic Functions:: How to find other functions + +Header Files + +* Header Portability:: Collected knowledge on common headers +* Particular Headers:: Special handling to find certain headers +* Generic Headers:: How to find other headers + +Declarations + +* Particular Declarations:: Macros to check for certain declarations +* Generic Declarations:: How to find other declarations + +Structures + +* Particular Structures:: Macros to check for certain structure members +* Generic Structures:: How to find other structure members + +Types + +* Particular Types:: Special handling to find certain types +* Generic Types:: How to find other types + +Compilers and Preprocessors + +* Specific Compiler Characteristics:: Some portability issues +* Generic Compiler Characteristics:: Language independent tests and features +* C Compiler:: Checking its characteristics +* C++ Compiler:: Likewise +* Objective C Compiler:: Likewise +* Objective C++ Compiler:: Likewise +* Erlang Compiler and Interpreter:: Likewise +* Fortran Compiler:: Likewise +* Go Compiler:: Likewise + +Writing Tests + +* Language Choice:: Selecting which language to use for testing +* Writing Test Programs:: Forging source files for compilers +* Running the Preprocessor:: Detecting preprocessor symbols +* Running the Compiler:: Detecting language or header features +* Running the Linker:: Detecting library features +* Runtime:: Testing for runtime features +* Systemology:: A zoology of operating systems +* Multiple Cases:: Tests for several possible values + +Writing Test Programs + +* Guidelines:: General rules for writing test programs +* Test Functions:: Avoiding pitfalls in test programs +* Generating Sources:: Source program boilerplate + +Results of Tests + +* Defining Symbols:: Defining C preprocessor symbols +* Setting Output Variables:: Replacing variables in output files +* Special Chars in Variables:: Characters to beware of in variables +* Caching Results:: Speeding up subsequent `configure' runs +* Printing Messages:: Notifying `configure' users + +Caching Results + +* Cache Variable Names:: Shell variables used in caches +* Cache Files:: Files `configure' uses for caching +* Cache Checkpointing:: Loading and saving the cache file + +Programming in M4 + +* M4 Quotation:: Protecting macros from unwanted expansion +* Using autom4te:: The Autoconf executables backbone +* Programming in M4sugar:: Convenient pure M4 macros +* Debugging via autom4te:: Figuring out what M4 was doing + +M4 Quotation + +* Active Characters:: Characters that change the behavior of M4 +* One Macro Call:: Quotation and one macro call +* Quoting and Parameters:: M4 vs. shell parameters +* Quotation and Nested Macros:: Macros calling macros +* Changequote is Evil:: Worse than INTERCAL: M4 + changequote +* Quadrigraphs:: Another way to escape special characters +* Balancing Parentheses:: Dealing with unbalanced parentheses +* Quotation Rule Of Thumb:: One parenthesis, one quote + +Using `autom4te' + +* autom4te Invocation:: A GNU M4 wrapper +* Customizing autom4te:: Customizing the Autoconf package + +Programming in M4sugar + +* Redefined M4 Macros:: M4 builtins changed in M4sugar +* Diagnostic Macros:: Diagnostic messages from M4sugar +* Diversion support:: Diversions in M4sugar +* Conditional constructs:: Conditions in M4 +* Looping constructs:: Iteration in M4 +* Evaluation Macros:: More quotation and evaluation control +* Text processing Macros:: String manipulation in M4 +* Number processing Macros:: Arithmetic computation in M4 +* Set manipulation Macros:: Set manipulation in M4 +* Forbidden Patterns:: Catching unexpanded macros + +Programming in M4sh + +* Common Shell Constructs:: Portability layer for common shell constructs +* Polymorphic Variables:: Support for indirect variable names +* Initialization Macros:: Macros to establish a sane shell environment +* File Descriptor Macros:: File descriptor macros for input and output + +Writing Autoconf Macros + +* Macro Definitions:: Basic format of an Autoconf macro +* Macro Names:: What to call your new macros +* Reporting Messages:: Notifying `autoconf' users +* Dependencies Between Macros:: What to do when macros depend on other macros +* Obsoleting Macros:: Warning about old ways of doing things +* Coding Style:: Writing Autoconf macros a` la Autoconf + +Dependencies Between Macros + +* Prerequisite Macros:: Ensuring required information +* Suggested Ordering:: Warning about possible ordering problems +* One-Shot Macros:: Ensuring a macro is called only once + +Portable Shell Programming + +* Shellology:: A zoology of shells +* Invoking the Shell:: Invoking the shell as a command +* Here-Documents:: Quirks and tricks +* File Descriptors:: FDs and redirections +* Signal Handling:: Shells, signals, and headaches +* File System Conventions:: File names +* Shell Pattern Matching:: Pattern matching +* Shell Substitutions:: Variable and command expansions +* Assignments:: Varying side effects of assignments +* Parentheses:: Parentheses in shell scripts +* Slashes:: Slashes in shell scripts +* Special Shell Variables:: Variables you should not change +* Shell Functions:: What to look out for if you use them +* Limitations of Builtins:: Portable use of not so portable /bin/sh +* Limitations of Usual Tools:: Portable use of portable tools + +Portable Make Programming + +* $< in Ordinary Make Rules:: $< in ordinary rules +* Failure in Make Rules:: Failing portably in rules +* Special Chars in Names:: Special Characters in Macro Names +* Backslash-Newline-Empty:: Empty lines after backslash-newline +* Backslash-Newline Comments:: Spanning comments across line boundaries +* Long Lines in Makefiles:: Line length limitations +* Macros and Submakes:: `make macro=value' and submakes +* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues +* The Make Macro SHELL:: `$(SHELL)' portability issues +* Parallel Make:: Parallel `make' quirks +* Comments in Make Rules:: Other problems with Make comments +* Newlines in Make Rules:: Using literal newlines in rules +* Comments in Make Macros:: Other problems with Make comments in macros +* Trailing whitespace in Make Macros:: Macro substitution problems +* Command-line Macros and whitespace:: Whitespace trimming of values +* obj/ and Make:: Don't name a subdirectory `obj' +* make -k Status:: Exit status of `make -k' +* VPATH and Make:: `VPATH' woes +* Single Suffix Rules:: Single suffix rules and separated dependencies +* Timestamps and Make:: Subsecond timestamp resolution + +`VPATH' and Make + +* Variables listed in VPATH:: `VPATH' must be literal on ancient hosts +* VPATH and Double-colon:: Problems with `::' on ancient hosts +* $< in Explicit Rules:: `$<' does not work in ordinary rules +* Automatic Rule Rewriting:: `VPATH' goes wild on Solaris +* Tru64 Directory Magic:: `mkdir' goes wild on Tru64 +* Make Target Lookup:: More details about `VPATH' lookup + +Portable C and C++ Programming + +* Varieties of Unportability:: How to make your programs unportable +* Integer Overflow:: When integers get too large +* Preprocessor Arithmetic:: `#if' expression problems +* Null Pointers:: Properties of null pointers +* Buffer Overruns:: Subscript errors and the like +* Volatile Objects:: `volatile' and signals +* Floating Point Portability:: Portable floating-point arithmetic +* Exiting Portably:: Exiting and the exit status + +Integer Overflow + +* Integer Overflow Basics:: Why integer overflow is a problem +* Signed Overflow Examples:: Examples of code assuming wraparound +* Optimization and Wraparound:: Optimizations that break uses of wraparound +* Signed Overflow Advice:: Practical advice for signed overflow issues +* Signed Integer Division:: `INT_MIN / -1' and `INT_MIN % -1' + +Manual Configuration + +* Specifying Target Triplets:: Specifying target triplets +* Canonicalizing:: Getting the canonical system type +* Using System Type:: What to do with the system type + +Site Configuration + +* Help Formatting:: Customizing `configure --help' +* External Software:: Working with other optional software +* Package Options:: Selecting optional features +* Pretty Help Strings:: Formatting help string +* Option Checking:: Controlling checking of `configure' options +* Site Details:: Configuring site details +* Transforming Names:: Changing program names when installing +* Site Defaults:: Giving `configure' local defaults + +Transforming Program Names When Installing + +* Transformation Options:: `configure' options to transform names +* Transformation Examples:: Sample uses of transforming names +* Transformation Rules:: Makefile uses of transforming names + +Running `configure' Scripts + +* Basic Installation:: Instructions for typical cases +* Compilers and Options:: Selecting compilers and optimization +* Multiple Architectures:: Compiling for multiple architectures at once +* Installation Names:: Installing in different directories +* Optional Features:: Selecting optional features +* Particular Systems:: Particular systems +* System Type:: Specifying the system type +* Sharing Defaults:: Setting site-wide defaults for `configure' +* Defining Variables:: Specifying the compiler etc. +* configure Invocation:: Changing how `configure' runs + +Obsolete Constructs + +* Obsolete config.status Use:: Obsolete convention for `config.status' +* acconfig Header:: Additional entries in `config.h.in' +* autoupdate Invocation:: Automatic update of `configure.ac' +* Obsolete Macros:: Backward compatibility macros +* Autoconf 1:: Tips for upgrading your files +* Autoconf 2.13:: Some fresher tips + +Upgrading From Version 1 + +* Changed File Names:: Files you might rename +* Changed Makefiles:: New things to put in `Makefile.in' +* Changed Macros:: Macro calls you might replace +* Changed Results:: Changes in how to check test results +* Changed Macro Writing:: Better ways to write your own macros + +Upgrading From Version 2.13 + +* Changed Quotation:: Broken code which used to work +* New Macros:: Interaction with foreign macros +* Hosts and Cross-Compilation:: Bugward compatibility kludges +* AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token +* AC_ACT_IFELSE vs AC_TRY_ACT:: A more generic scheme for testing sources + +Generating Test Suites with Autotest + +* Using an Autotest Test Suite:: Autotest and the user +* Writing Testsuites:: Autotest macros +* testsuite Invocation:: Running `testsuite' scripts +* Making testsuite Scripts:: Using autom4te to create `testsuite' + +Using an Autotest Test Suite + +* testsuite Scripts:: The concepts of Autotest +* Autotest Logs:: Their contents + +Frequent Autoconf Questions, with answers + +* Distributing:: Distributing `configure' scripts +* Why GNU M4:: Why not use the standard M4? +* Bootstrapping:: Autoconf and GNU M4 require each other? +* Why Not Imake:: Why GNU uses `configure' instead of Imake +* Defining Directories:: Passing `datadir' to program +* Autom4te Cache:: What is it? Can I remove it? +* Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree +* Expanded Before Required:: Expanded Before Required +* Debugging:: Debugging `configure' scripts + +History of Autoconf + +* Genesis:: Prehistory and naming of `configure' +* Exodus:: The plagues of M4 and Perl +* Leviticus:: The priestly code of portability arrives +* Numbers:: Growth and contributors +* Deuteronomy:: Approaching the promises of easy configuration + +Indices + +* Environment Variable Index:: Index of environment variables used +* Output Variable Index:: Index of variables set in output files +* Preprocessor Symbol Index:: Index of C preprocessor symbols defined +* Cache Variable Index:: Index of documented cache variables +* Autoconf Macro Index:: Index of Autoconf macros +* M4 Macro Index:: Index of M4, M4sugar, and M4sh macros +* Autotest Macro Index:: Index of Autotest macros +* Program & Function Index:: Index of those with portability problems +* Concept Index:: General index + + +File: autoconf.info, Node: Introduction, Next: The GNU Build System, Prev: Top, Up: Top + +1 Introduction +************** + + A physicist, an engineer, and a computer scientist were discussing the + nature of God. "Surely a Physicist," said the physicist, "because + early in the Creation, God made Light; and you know, Maxwell's + equations, the dual nature of electromagnetic waves, the relativistic + consequences..." "An Engineer!," said the engineer, "because +before making Light, God split the Chaos into Land and Water; it takes a + hell of an engineer to handle that big amount of mud, and orderly + separation of solids from liquids..." The computer scientist + shouted: "And the Chaos, where do you think it was coming from, hmm?" + + --Anonymous + + Autoconf is a tool for producing shell scripts that automatically +configure software source code packages to adapt to many kinds of +Posix-like systems. The configuration scripts produced by Autoconf are +independent of Autoconf when they are run, so their users do not need +to have Autoconf. + + The configuration scripts produced by Autoconf require no manual user +intervention when run; they do not normally even need an argument +specifying the system type. Instead, they individually test for the +presence of each feature that the software package they are for might +need. (Before each check, they print a one-line message stating what +they are checking for, so the user doesn't get too bored while waiting +for the script to finish.) As a result, they deal well with systems +that are hybrids or customized from the more common Posix variants. +There is no need to maintain files that list the features supported by +each release of each variant of Posix. + + For each software package that Autoconf is used with, it creates a +configuration script from a template file that lists the system features +that the package needs or can use. After the shell code to recognize +and respond to a system feature has been written, Autoconf allows it to +be shared by many software packages that can use (or need) that feature. +If it later turns out that the shell code needs adjustment for some +reason, it needs to be changed in only one place; all of the +configuration scripts can be regenerated automatically to take advantage +of the updated code. + + Those who do not understand Autoconf are condemned to reinvent it, +poorly. The primary goal of Autoconf is making the _user's_ life +easier; making the _maintainer's_ life easier is only a secondary goal. +Put another way, the primary goal is not to make the generation of +`configure' automatic for package maintainers (although patches along +that front are welcome, since package maintainers form the user base of +Autoconf); rather, the goal is to make `configure' painless, portable, +and predictable for the end user of each "autoconfiscated" package. +And to this degree, Autoconf is highly successful at its goal -- most +complaints to the Autoconf list are about difficulties in writing +Autoconf input, and not in the behavior of the resulting `configure'. +Even packages that don't use Autoconf will generally provide a +`configure' script, and the most common complaint about these +alternative home-grown scripts is that they fail to meet one or more of +the GNU Coding Standards (*note Configuration: +(standards)Configuration.) that users have come to expect from +Autoconf-generated `configure' scripts. + + The Metaconfig package is similar in purpose to Autoconf, but the +scripts it produces require manual user intervention, which is quite +inconvenient when configuring large source trees. Unlike Metaconfig +scripts, Autoconf scripts can support cross-compiling, if some care is +taken in writing them. + + Autoconf does not solve all problems related to making portable +software packages--for a more complete solution, it should be used in +concert with other GNU build tools like Automake and Libtool. These +other tools take on jobs like the creation of a portable, recursive +makefile with all of the standard targets, linking of shared libraries, +and so on. *Note The GNU Build System::, for more information. + + Autoconf imposes some restrictions on the names of macros used with +`#if' in C programs (*note Preprocessor Symbol Index::). + + Autoconf requires GNU M4 version 1.4.6 or later in order to generate +the scripts. It uses features that some versions of M4, including GNU +M4 1.3, do not have. Autoconf works better with GNU M4 version 1.4.14 +or later, though this is not required. + + *Note Autoconf 1::, for information about upgrading from version 1. +*Note History::, for the story of Autoconf's development. *Note FAQ::, +for answers to some common questions about Autoconf. + + See the Autoconf web page (http://www.gnu.org/software/autoconf/) +for up-to-date information, details on the mailing lists, pointers to a +list of known bugs, etc. + + Mail suggestions to the Autoconf mailing list <autoconf@gnu.org>. +Past suggestions are archived +(http://lists.gnu.org/archive/html/autoconf/). + + Mail bug reports to the Autoconf Bugs mailing list +<bug-autoconf@gnu.org>. Past bug reports are archived +(http://lists.gnu.org/archive/html/bug-autoconf/). + + If possible, first check that your bug is not already solved in +current development versions, and that it has not been reported yet. +Be sure to include all the needed information and a short +`configure.ac' that demonstrates the problem. + + Autoconf's development tree is accessible via `git'; see the +Autoconf Summary (http://savannah.gnu.org/projects/autoconf/) for +details, or view the actual repository +(http://git.sv.gnu.org/gitweb/?p=autoconf.git). Anonymous CVS access +is also available, see `README' for more details. Patches relative to +the current `git' version can be sent for review to the Autoconf +Patches mailing list <autoconf-patches@gnu.org>, with discussion on +prior patches archived +(http://lists.gnu.org/archive/html/autoconf-patches/); and all commits +are posted in the read-only Autoconf Commit mailing list +<autoconf-commit@gnu.org>, which is also archived +(http://lists.gnu.org/archive/html/autoconf-commit/). + + Because of its mission, the Autoconf package itself includes only a +set of often-used macros that have already demonstrated their +usefulness. Nevertheless, if you wish to share your macros, or find +existing ones, see the Autoconf Macro Archive +(http://www.gnu.org/software/autoconf-archive/), which is kindly run by +Peter Simons <simons@cryp.to>. + + +File: autoconf.info, Node: The GNU Build System, Next: Making configure Scripts, Prev: Introduction, Up: Top + +2 The GNU Build System +********************** + +Autoconf solves an important problem--reliable discovery of +system-specific build and runtime information--but this is only one +piece of the puzzle for the development of portable software. To this +end, the GNU project has developed a suite of integrated utilities to +finish the job Autoconf started: the GNU build system, whose most +important components are Autoconf, Automake, and Libtool. In this +chapter, we introduce you to those tools, point you to sources of more +information, and try to convince you to use the entire GNU build system +for your software. + +* Menu: + +* Automake:: Escaping makefile hell +* Gnulib:: The GNU portability library +* Libtool:: Building libraries portably +* Pointers:: More info on the GNU build system + + +File: autoconf.info, Node: Automake, Next: Gnulib, Up: The GNU Build System + +2.1 Automake +============ + +The ubiquity of `make' means that a makefile is almost the only viable +way to distribute automatic build rules for software, but one quickly +runs into its numerous limitations. Its lack of support for automatic +dependency tracking, recursive builds in subdirectories, reliable +timestamps (e.g., for network file systems), and so on, mean that +developers must painfully (and often incorrectly) reinvent the wheel +for each project. Portability is non-trivial, thanks to the quirks of +`make' on many systems. On top of all this is the manual labor +required to implement the many standard targets that users have come to +expect (`make install', `make distclean', `make uninstall', etc.). +Since you are, of course, using Autoconf, you also have to insert +repetitive code in your `Makefile.in' to recognize `@CC@', `@CFLAGS@', +and other substitutions provided by `configure'. Into this mess steps +"Automake". + + Automake allows you to specify your build needs in a `Makefile.am' +file with a vastly simpler and more powerful syntax than that of a plain +makefile, and then generates a portable `Makefile.in' for use with +Autoconf. For example, the `Makefile.am' to build and install a simple +"Hello world" program might look like: + + bin_PROGRAMS = hello + hello_SOURCES = hello.c + +The resulting `Makefile.in' (~400 lines) automatically supports all the +standard targets, the substitutions provided by Autoconf, automatic +dependency tracking, `VPATH' building, and so on. `make' builds the +`hello' program, and `make install' installs it in `/usr/local/bin' (or +whatever prefix was given to `configure', if not `/usr/local'). + + The benefits of Automake increase for larger packages (especially +ones with subdirectories), but even for small programs the added +convenience and portability can be substantial. And that's not all... + + +File: autoconf.info, Node: Gnulib, Next: Libtool, Prev: Automake, Up: The GNU Build System + +2.2 Gnulib +========== + +GNU software has a well-deserved reputation for running on many +different types of systems. While our primary goal is to write +software for the GNU system, many users and developers have been +introduced to us through the systems that they were already using. + + Gnulib is a central location for common GNU code, intended to be +shared among free software packages. Its components are typically +shared at the source level, rather than being a library that gets built, +installed, and linked against. The idea is to copy files from Gnulib +into your own source tree. There is no distribution tarball; developers +should just grab source modules from the repository. The source files +are available online, under various licenses, mostly GNU GPL or GNU +LGPL. + + Gnulib modules typically contain C source code along with Autoconf +macros used to configure the source code. For example, the Gnulib +`stdbool' module implements a `stdbool.h' header that nearly conforms +to C99, even on old-fashioned hosts that lack `stdbool.h'. This module +contains a source file for the replacement header, along with an +Autoconf macro that arranges to use the replacement header on +old-fashioned systems. + + +File: autoconf.info, Node: Libtool, Next: Pointers, Prev: Gnulib, Up: The GNU Build System + +2.3 Libtool +=========== + +Often, one wants to build not only programs, but libraries, so that +other programs can benefit from the fruits of your labor. Ideally, one +would like to produce _shared_ (dynamically linked) libraries, which +can be used by multiple programs without duplication on disk or in +memory and can be updated independently of the linked programs. +Producing shared libraries portably, however, is the stuff of +nightmares--each system has its own incompatible tools, compiler flags, +and magic incantations. Fortunately, GNU provides a solution: +"Libtool". + + Libtool handles all the requirements of building shared libraries for +you, and at this time seems to be the _only_ way to do so with any +portability. It also handles many other headaches, such as: the +interaction of Make rules with the variable suffixes of shared +libraries, linking reliably with shared libraries before they are +installed by the superuser, and supplying a consistent versioning system +(so that different versions of a library can be installed or upgraded +without breaking binary compatibility). Although Libtool, like +Autoconf, can be used without Automake, it is most simply utilized in +conjunction with Automake--there, Libtool is used automatically +whenever shared libraries are needed, and you need not know its syntax. + + +File: autoconf.info, Node: Pointers, Prev: Libtool, Up: The GNU Build System + +2.4 Pointers +============ + +Developers who are used to the simplicity of `make' for small projects +on a single system might be daunted at the prospect of learning to use +Automake and Autoconf. As your software is distributed to more and +more users, however, you otherwise quickly find yourself putting lots +of effort into reinventing the services that the GNU build tools +provide, and making the same mistakes that they once made and overcame. +(Besides, since you're already learning Autoconf, Automake is a piece +of cake.) + + There are a number of places that you can go to for more information +on the GNU build tools. + + - Web + + The project home pages for Autoconf + (http://www.gnu.org/software/autoconf/), Automake + (http://www.gnu.org/software/automake/), Gnulib + (http://www.gnu.org/software/gnulib/), and Libtool + (http://www.gnu.org/software/libtool/). + + - Automake Manual + + *Note Automake: (automake)Top, for more information on Automake. + + - Books + + The book `GNU Autoconf, Automake and Libtool'(1) describes the + complete GNU build environment. You can also find the entire book + on-line (http://sources.redhat.com/autobook/). + + + ---------- Footnotes ---------- + + (1) `GNU Autoconf, Automake and Libtool', by G. V. Vaughan, B. +Elliston, T. Tromey, and I. L. Taylor. SAMS (originally New Riders), +2000, ISBN 1578701902. + + +File: autoconf.info, Node: Making configure Scripts, Next: Setup, Prev: The GNU Build System, Up: Top + +3 Making `configure' Scripts +**************************** + +The configuration scripts that Autoconf produces are by convention +called `configure'. When run, `configure' creates several files, +replacing configuration parameters in them with appropriate values. +The files that `configure' creates are: + + - one or more `Makefile' files, usually one in each subdirectory of + the package (*note Makefile Substitutions::); + + - optionally, a C header file, the name of which is configurable, + containing `#define' directives (*note Configuration Headers::); + + - a shell script called `config.status' that, when run, recreates + the files listed above (*note config.status Invocation::); + + - an optional shell script normally called `config.cache' (created + when using `configure --config-cache') that saves the results of + running many of the tests (*note Cache Files::); + + - a file called `config.log' containing any messages produced by + compilers, to help debugging if `configure' makes a mistake. + + To create a `configure' script with Autoconf, you need to write an +Autoconf input file `configure.ac' (or `configure.in') and run +`autoconf' on it. If you write your own feature tests to supplement +those that come with Autoconf, you might also write files called +`aclocal.m4' and `acsite.m4'. If you use a C header file to contain +`#define' directives, you might also run `autoheader', and you can +distribute the generated file `config.h.in' with the package. + + Here is a diagram showing how the files that can be used in +configuration are produced. Programs that are executed are suffixed by +`*'. Optional files are enclosed in square brackets (`[]'). +`autoconf' and `autoheader' also read the installed Autoconf macro +files (by reading `autoconf.m4'). + +Files used in preparing a software package for distribution, when using +just Autoconf: + your source files --> [autoscan*] --> [configure.scan] --> configure.ac + + configure.ac --. + | .------> autoconf* -----> configure + [aclocal.m4] --+---+ + | `-----> [autoheader*] --> [config.h.in] + [acsite.m4] ---' + + Makefile.in + +Additionally, if you use Automake, the following additional productions +come into play: + + [acinclude.m4] --. + | + [local macros] --+--> aclocal* --> aclocal.m4 + | + configure.ac ----' + + configure.ac --. + +--> automake* --> Makefile.in + Makefile.am ---' + +Files used in configuring a software package: + .-------------> [config.cache] + configure* ------------+-------------> config.log + | + [config.h.in] -. v .-> [config.h] -. + +--> config.status* -+ +--> make* + Makefile.in ---' `-> Makefile ---' + +* Menu: + +* Writing Autoconf Input:: What to put in an Autoconf input file +* autoscan Invocation:: Semi-automatic `configure.ac' writing +* ifnames Invocation:: Listing the conditionals in source code +* autoconf Invocation:: How to create configuration scripts +* autoreconf Invocation:: Remaking multiple `configure' scripts + + +File: autoconf.info, Node: Writing Autoconf Input, Next: autoscan Invocation, Up: Making configure Scripts + +3.1 Writing `configure.ac' +========================== + +To produce a `configure' script for a software package, create a file +called `configure.ac' that contains invocations of the Autoconf macros +that test the system features your package needs or can use. Autoconf +macros already exist to check for many features; see *note Existing +Tests::, for their descriptions. For most other features, you can use +Autoconf template macros to produce custom checks; see *note Writing +Tests::, for information about them. For especially tricky or +specialized features, `configure.ac' might need to contain some +hand-crafted shell commands; see *note Portable Shell Programming: +Portable Shell. The `autoscan' program can give you a good start in +writing `configure.ac' (*note autoscan Invocation::, for more +information). + + Previous versions of Autoconf promoted the name `configure.in', +which is somewhat ambiguous (the tool needed to process this file is not +described by its extension), and introduces a slight confusion with +`config.h.in' and so on (for which `.in' means "to be processed by +`configure'"). Using `configure.ac' is now preferred. + +* Menu: + +* Shell Script Compiler:: Autoconf as solution of a problem +* Autoconf Language:: Programming in Autoconf +* Autoconf Input Layout:: Standard organization of `configure.ac' + + +File: autoconf.info, Node: Shell Script Compiler, Next: Autoconf Language, Up: Writing Autoconf Input + +3.1.1 A Shell Script Compiler +----------------------------- + +Just as for any other computer language, in order to properly program +`configure.ac' in Autoconf you must understand _what_ problem the +language tries to address and _how_ it does so. + + The problem Autoconf addresses is that the world is a mess. After +all, you are using Autoconf in order to have your package compile +easily on all sorts of different systems, some of them being extremely +hostile. Autoconf itself bears the price for these differences: +`configure' must run on all those systems, and thus `configure' must +limit itself to their lowest common denominator of features. + + Naturally, you might then think of shell scripts; who needs +`autoconf'? A set of properly written shell functions is enough to +make it easy to write `configure' scripts by hand. Sigh! +Unfortunately, even in 2008, where shells without any function support +are far and few between, there are pitfalls to avoid when making use of +them. Also, finding a Bourne shell that accepts shell functions is not +trivial, even though there is almost always one on interesting porting +targets. + + So, what is really needed is some kind of compiler, `autoconf', that +takes an Autoconf program, `configure.ac', and transforms it into a +portable shell script, `configure'. + + How does `autoconf' perform this task? + + There are two obvious possibilities: creating a brand new language or +extending an existing one. The former option is attractive: all sorts +of optimizations could easily be implemented in the compiler and many +rigorous checks could be performed on the Autoconf program (e.g., +rejecting any non-portable construct). Alternatively, you can extend +an existing language, such as the `sh' (Bourne shell) language. + + Autoconf does the latter: it is a layer on top of `sh'. It was +therefore most convenient to implement `autoconf' as a macro expander: +a program that repeatedly performs "macro expansions" on text input, +replacing macro calls with macro bodies and producing a pure `sh' +script in the end. Instead of implementing a dedicated Autoconf macro +expander, it is natural to use an existing general-purpose macro +language, such as M4, and implement the extensions as a set of M4 +macros. + + +File: autoconf.info, Node: Autoconf Language, Next: Autoconf Input Layout, Prev: Shell Script Compiler, Up: Writing Autoconf Input + +3.1.2 The Autoconf Language +--------------------------- + +The Autoconf language differs from many other computer languages +because it treats actual code the same as plain text. Whereas in C, +for instance, data and instructions have different syntactic status, in +Autoconf their status is rigorously the same. Therefore, we need a +means to distinguish literal strings from text to be expanded: +quotation. + + When calling macros that take arguments, there must not be any white +space between the macro name and the open parenthesis. + + AC_INIT ([oops], [1.0]) # incorrect + AC_INIT([hello], [1.0]) # good + + Arguments should be enclosed within the quote characters `[' and +`]', and be separated by commas. Any leading blanks or newlines in +arguments are ignored, unless they are quoted. You should always quote +an argument that might contain a macro name, comma, parenthesis, or a +leading blank or newline. This rule applies recursively for every macro +call, including macros called from other macros. For more details on +quoting rules, see *note Programming in M4::. + + For instance: + + AC_CHECK_HEADER([stdio.h], + [AC_DEFINE([HAVE_STDIO_H], [1], + [Define to 1 if you have <stdio.h>.])], + [AC_MSG_ERROR([sorry, can't do anything for you])]) + +is quoted properly. You may safely simplify its quotation to: + + AC_CHECK_HEADER([stdio.h], + [AC_DEFINE([HAVE_STDIO_H], 1, + [Define to 1 if you have <stdio.h>.])], + [AC_MSG_ERROR([sorry, can't do anything for you])]) + +because `1' cannot contain a macro call. Here, the argument of +`AC_MSG_ERROR' must be quoted; otherwise, its comma would be +interpreted as an argument separator. Also, the second and third +arguments of `AC_CHECK_HEADER' must be quoted, since they contain macro +calls. The three arguments `HAVE_STDIO_H', `stdio.h', and `Define to 1 +if you have <stdio.h>.' do not need quoting, but if you unwisely +defined a macro with a name like `Define' or `stdio' then they would +need quoting. Cautious Autoconf users would keep the quotes, but many +Autoconf users find such precautions annoying, and would rewrite the +example as follows: + + AC_CHECK_HEADER(stdio.h, + [AC_DEFINE(HAVE_STDIO_H, 1, + [Define to 1 if you have <stdio.h>.])], + [AC_MSG_ERROR([sorry, can't do anything for you])]) + +This is safe, so long as you adopt good naming conventions and do not +define macros with names like `HAVE_STDIO_H', `stdio', or `h'. Though +it is also safe here to omit the quotes around `Define to 1 if you have +<stdio.h>.' this is not recommended, as message strings are more likely +to inadvertently contain commas. + + The following example is wrong and dangerous, as it is underquoted: + + AC_CHECK_HEADER(stdio.h, + AC_DEFINE(HAVE_STDIO_H, 1, + Define to 1 if you have <stdio.h>.), + AC_MSG_ERROR([sorry, can't do anything for you])) + + In other cases, you may have to use text that also resembles a macro +call. You must quote that text even when it is not passed as a macro +argument. For example, these two approaches in `configure.ac' (quoting +just the potential problems, or quoting the entire line) will protect +your script in case autoconf ever adds a macro `AC_DC': + + echo "Hard rock was here! --[AC_DC]" + [echo "Hard rock was here! --AC_DC"] + +which results in this text in `configure': + + echo "Hard rock was here! --AC_DC" + echo "Hard rock was here! --AC_DC" + +When you use the same text in a macro argument, you must therefore have +an extra quotation level (since one is stripped away by the macro +substitution). In general, then, it is a good idea to _use double +quoting for all literal string arguments_, either around just the +problematic portions, or over the entire argument: + + AC_MSG_WARN([[AC_DC] stinks --Iron Maiden]) + AC_MSG_WARN([[AC_DC stinks --Iron Maiden]]) + + However, the above example triggers a warning about a possibly +unexpanded macro when running `autoconf', because it collides with the +namespace of macros reserved for the Autoconf language. To be really +safe, you can use additional escaping (either a quadrigraph, or +creative shell constructs) to silence that particular warning: + + echo "Hard rock was here! --AC""_DC" + AC_MSG_WARN([[AC@&t@_DC stinks --Iron Maiden]]) + + You are now able to understand one of the constructs of Autoconf that +has been continually misunderstood... The rule of thumb is that +_whenever you expect macro expansion, expect quote expansion_; i.e., +expect one level of quotes to be lost. For instance: + + AC_COMPILE_IFELSE(AC_LANG_SOURCE([char b[10];]), [], + [AC_MSG_ERROR([you lose])]) + +is incorrect: here, the first argument of `AC_LANG_SOURCE' is `char +b[10];' and is expanded once, which results in `char b10;'; and the +`AC_LANG_SOURCE' is also expanded prior to being passed to +`AC_COMPILE_IFELSE'. (There was an idiom common in Autoconf's past to +address this issue via the M4 `changequote' primitive, but do not use +it!) Let's take a closer look: the author meant the first argument to +be understood as a literal, and therefore it must be quoted twice; +likewise, the intermediate `AC_LANG_SOURCE' macro should be quoted once +so that it is only expanded after the rest of the body of +`AC_COMPILE_IFELSE' is in place: + + AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char b[10];]])], [], + [AC_MSG_ERROR([you lose])]) + +Voila`, you actually produce `char b[10];' this time! + + On the other hand, descriptions (e.g., the last parameter of +`AC_DEFINE' or `AS_HELP_STRING') are not literals--they are subject to +line breaking, for example--and should not be double quoted. Even if +these descriptions are short and are not actually broken, double +quoting them yields weird results. + + Some macros take optional arguments, which this documentation +represents as [ARG] (not to be confused with the quote characters). +You may just leave them empty, or use `[]' to make the emptiness of the +argument explicit, or you may simply omit the trailing commas. The +three lines below are equivalent: + + AC_CHECK_HEADERS([stdio.h], [], [], []) + AC_CHECK_HEADERS([stdio.h],,,) + AC_CHECK_HEADERS([stdio.h]) + + It is best to put each macro call on its own line in `configure.ac'. +Most of the macros don't add extra newlines; they rely on the newline +after the macro call to terminate the commands. This approach makes +the generated `configure' script a little easier to read by not +inserting lots of blank lines. It is generally safe to set shell +variables on the same line as a macro call, because the shell allows +assignments without intervening newlines. + + You can include comments in `configure.ac' files by starting them +with the `#'. For example, it is helpful to begin `configure.ac' files +with a line like this: + + # Process this file with autoconf to produce a configure script. + + +File: autoconf.info, Node: Autoconf Input Layout, Prev: Autoconf Language, Up: Writing Autoconf Input + +3.1.3 Standard `configure.ac' Layout +------------------------------------ + +The order in which `configure.ac' calls the Autoconf macros is not +important, with a few exceptions. Every `configure.ac' must contain a +call to `AC_INIT' before the checks, and a call to `AC_OUTPUT' at the +end (*note Output::). Additionally, some macros rely on other macros +having been called first, because they check previously set values of +some variables to decide what to do. These macros are noted in the +individual descriptions (*note Existing Tests::), and they also warn +you when `configure' is created if they are called out of order. + + To encourage consistency, here is a suggested order for calling the +Autoconf macros. Generally speaking, the things near the end of this +list are those that could depend on things earlier in it. For example, +library functions could be affected by types and libraries. + + Autoconf requirements + `AC_INIT(PACKAGE, VERSION, BUG-REPORT-ADDRESS)' + information on the package + checks for programs + checks for libraries + checks for header files + checks for types + checks for structures + checks for compiler characteristics + checks for library functions + checks for system services + `AC_CONFIG_FILES([FILE...])' + `AC_OUTPUT' + + +File: autoconf.info, Node: autoscan Invocation, Next: ifnames Invocation, Prev: Writing Autoconf Input, Up: Making configure Scripts + +3.2 Using `autoscan' to Create `configure.ac' +============================================= + +The `autoscan' program can help you create and/or maintain a +`configure.ac' file for a software package. `autoscan' examines source +files in the directory tree rooted at a directory given as a command +line argument, or the current directory if none is given. It searches +the source files for common portability problems and creates a file +`configure.scan' which is a preliminary `configure.ac' for that +package, and checks a possibly existing `configure.ac' for completeness. + + When using `autoscan' to create a `configure.ac', you should +manually examine `configure.scan' before renaming it to `configure.ac'; +it probably needs some adjustments. Occasionally, `autoscan' outputs a +macro in the wrong order relative to another macro, so that `autoconf' +produces a warning; you need to move such macros manually. Also, if +you want the package to use a configuration header file, you must add a +call to `AC_CONFIG_HEADERS' (*note Configuration Headers::). You might +also have to change or add some `#if' directives to your program in +order to make it work with Autoconf (*note ifnames Invocation::, for +information about a program that can help with that job). + + When using `autoscan' to maintain a `configure.ac', simply consider +adding its suggestions. The file `autoscan.log' contains detailed +information on why a macro is requested. + + `autoscan' uses several data files (installed along with Autoconf) +to determine which macros to output when it finds particular symbols in +a package's source files. These data files all have the same format: +each line consists of a symbol, one or more blanks, and the Autoconf +macro to output if that symbol is encountered. Lines starting with `#' +are comments. + + `autoscan' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Print the names of the files it examines and the potentially + interesting symbols it finds in them. This output can be + voluminous. + +`--debug' +`-d' + Don't remove temporary files. + +`--include=DIR' +`-I DIR' + Append DIR to the include path. Multiple invocations accumulate. + +`--prepend-include=DIR' +`-B DIR' + Prepend DIR to the include path. Multiple invocations accumulate. + + +File: autoconf.info, Node: ifnames Invocation, Next: autoconf Invocation, Prev: autoscan Invocation, Up: Making configure Scripts + +3.3 Using `ifnames' to List Conditionals +======================================== + +`ifnames' can help you write `configure.ac' for a software package. It +prints the identifiers that the package already uses in C preprocessor +conditionals. If a package has already been set up to have some +portability, `ifnames' can thus help you figure out what its +`configure' needs to check for. It may help fill in some gaps in a +`configure.ac' generated by `autoscan' (*note autoscan Invocation::). + + `ifnames' scans all of the C source files named on the command line +(or the standard input, if none are given) and writes to the standard +output a sorted list of all the identifiers that appear in those files +in `#if', `#elif', `#ifdef', or `#ifndef' directives. It prints each +identifier on a line, followed by a space-separated list of the files +in which that identifier occurs. + +`ifnames' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + + +File: autoconf.info, Node: autoconf Invocation, Next: autoreconf Invocation, Prev: ifnames Invocation, Up: Making configure Scripts + +3.4 Using `autoconf' to Create `configure' +========================================== + +To create `configure' from `configure.ac', run the `autoconf' program +with no arguments. `autoconf' processes `configure.ac' with the M4 +macro processor, using the Autoconf macros. If you give `autoconf' an +argument, it reads that file instead of `configure.ac' and writes the +configuration script to the standard output instead of to `configure'. +If you give `autoconf' the argument `-', it reads from the standard +input instead of `configure.ac' and writes the configuration script to +the standard output. + + The Autoconf macros are defined in several files. Some of the files +are distributed with Autoconf; `autoconf' reads them first. Then it +looks for the optional file `acsite.m4' in the directory that contains +the distributed Autoconf macro files, and for the optional file +`aclocal.m4' in the current directory. Those files can contain your +site's or the package's own Autoconf macro definitions (*note Writing +Autoconf Macros::, for more information). If a macro is defined in +more than one of the files that `autoconf' reads, the last definition +it reads overrides the earlier ones. + + `autoconf' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Report processing steps. + +`--debug' +`-d' + Don't remove the temporary files. + +`--force' +`-f' + Remake `configure' even if newer than its input files. + +`--include=DIR' +`-I DIR' + Append DIR to the include path. Multiple invocations accumulate. + +`--prepend-include=DIR' +`-B DIR' + Prepend DIR to the include path. Multiple invocations accumulate. + +`--output=FILE' +`-o FILE' + Save output (script or trace) to FILE. The file `-' stands for + the standard output. + +`--warnings=CATEGORY' +`-W CATEGORY' + Report the warnings related to CATEGORY (which can actually be a + comma separated list). *Note Reporting Messages::, macro + `AC_DIAGNOSE', for a comprehensive list of categories. Special + values include: + + `all' + report all the warnings + + `none' + report none + + `error' + treats warnings as errors + + `no-CATEGORY' + disable warnings falling into CATEGORY + + Warnings about `syntax' are enabled by default, and the environment + variable `WARNINGS', a comma separated list of categories, is + honored as well. Passing `-W CATEGORY' actually behaves as if you + had passed `--warnings syntax,$WARNINGS,CATEGORY'. To disable the + defaults and `WARNINGS', and then enable warnings about obsolete + constructs, use `-W none,obsolete'. + + Because `autoconf' uses `autom4te' behind the scenes, it displays + a back trace for errors, but not for warnings; if you want them, + just pass `-W error'. *Note autom4te Invocation::, for some + examples. + +`--trace=MACRO[:FORMAT]' +`-t MACRO[:FORMAT]' + Do not create the `configure' script, but list the calls to MACRO + according to the FORMAT. Multiple `--trace' arguments can be used + to list several macros. Multiple `--trace' arguments for a single + macro are not cumulative; instead, you should just make FORMAT as + long as needed. + + The FORMAT is a regular string, with newlines if desired, and + several special escape codes. It defaults to `$f:$l:$n:$%'; see + *note autom4te Invocation::, for details on the FORMAT. + +`--initialization' +`-i' + By default, `--trace' does not trace the initialization of the + Autoconf macros (typically the `AC_DEFUN' definitions). This + results in a noticeable speedup, but can be disabled by this + option. + + It is often necessary to check the content of a `configure.ac' file, +but parsing it yourself is extremely fragile and error-prone. It is +suggested that you rely upon `--trace' to scan `configure.ac'. For +instance, to find the list of variables that are substituted, use: + + $ autoconf -t AC_SUBST + configure.ac:2:AC_SUBST:ECHO_C + configure.ac:2:AC_SUBST:ECHO_N + configure.ac:2:AC_SUBST:ECHO_T + More traces deleted + +The example below highlights the difference between `$@', `$*', and +`$%'. + + $ cat configure.ac + AC_DEFINE(This, is, [an + [example]]) + $ autoconf -t 'AC_DEFINE:@: $@ + *: $* + %: $%' + @: [This],[is],[an + [example]] + *: This,is,an + [example] + %: This:is:an [example] + +The FORMAT gives you a lot of freedom: + + $ autoconf -t 'AC_SUBST:$$ac_subst{"$1"} = "$f:$l";' + $ac_subst{"ECHO_C"} = "configure.ac:2"; + $ac_subst{"ECHO_N"} = "configure.ac:2"; + $ac_subst{"ECHO_T"} = "configure.ac:2"; + More traces deleted + +A long SEPARATOR can be used to improve the readability of complex +structures, and to ease their parsing (for instance when no single +character is suitable as a separator): + + $ autoconf -t 'AM_MISSING_PROG:${|:::::|}*' + ACLOCAL|:::::|aclocal|:::::|$missing_dir + AUTOCONF|:::::|autoconf|:::::|$missing_dir + AUTOMAKE|:::::|automake|:::::|$missing_dir + More traces deleted + + +File: autoconf.info, Node: autoreconf Invocation, Prev: autoconf Invocation, Up: Making configure Scripts + +3.5 Using `autoreconf' to Update `configure' Scripts +==================================================== + +Installing the various components of the GNU Build System can be +tedious: running `autopoint' for Gettext, `automake' for `Makefile.in' +etc. in each directory. It may be needed either because some tools +such as `automake' have been updated on your system, or because some of +the sources such as `configure.ac' have been updated, or finally, +simply in order to install the GNU Build System in a fresh tree. + + `autoreconf' runs `autoconf', `autoheader', `aclocal', `automake', +`libtoolize', and `autopoint' (when appropriate) repeatedly to update +the GNU Build System in the specified directories and their +subdirectories (*note Subdirectories::). By default, it only remakes +those files that are older than their sources. The environment +variables `AUTOM4TE', `AUTOCONF', `AUTOHEADER', `AUTOMAKE', `ACLOCAL', +`AUTOPOINT', `LIBTOOLIZE', `M4', and `MAKE' may be used to override the +invocation of the respective tools. + + If you install a new version of some tool, you can make `autoreconf' +remake _all_ of the files by giving it the `--force' option. + + *Note Automatic Remaking::, for Make rules to automatically rebuild +`configure' scripts when their source files change. That method +handles the timestamps of configuration header templates properly, but +does not pass `--autoconf-dir=DIR' or `--localdir=DIR'. + + Gettext supplies the `autopoint' command to add translation +infrastructure to a source package. If you use `autopoint', your +`configure.ac' should invoke both `AM_GNU_GETTEXT' and +`AM_GNU_GETTEXT_VERSION(GETTEXT-VERSION)'. *Note Invoking the +`autopoint' Program: (gettext)autopoint Invocation, for further details. + +`autoreconf' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Print the name of each directory `autoreconf' examines and the + commands it runs. If given two or more times, pass `--verbose' to + subordinate tools that support it. + +`--debug' +`-d' + Don't remove the temporary files. + +`--force' +`-f' + Remake even `configure' scripts and configuration headers that are + newer than their input files (`configure.ac' and, if present, + `aclocal.m4'). + +`--install' +`-i' + Install the missing auxiliary files in the package. By default, + files are copied; this can be changed with `--symlink'. + + If deemed appropriate, this option triggers calls to `automake + --add-missing', `libtoolize', `autopoint', etc. + +`--no-recursive' + Do not rebuild files in subdirectories to configure (see *note + Subdirectories::, macro `AC_CONFIG_SUBDIRS'). + +`--symlink' +`-s' + When used with `--install', install symbolic links to the missing + auxiliary files instead of copying them. + +`--make' +`-m' + When the directories were configured, update the configuration by + running `./config.status --recheck && ./config.status', and then + run `make'. + +`--include=DIR' +`-I DIR' + Append DIR to the include path. Multiple invocations accumulate. + Passed on to `aclocal', `autoconf' and `autoheader' internally. + +`--prepend-include=DIR' +`-B DIR' + Prepend DIR to the include path. Multiple invocations accumulate. + Passed on to `autoconf' and `autoheader' internally. + +`--warnings=CATEGORY' +`-W CATEGORY' + Report the warnings related to CATEGORY (which can actually be a + comma separated list). + + `cross' + related to cross compilation issues. + + `obsolete' + report the uses of obsolete constructs. + + `portability' + portability issues + + `syntax' + dubious syntactic constructs. + + `all' + report all the warnings + + `none' + report none + + `error' + treats warnings as errors + + `no-CATEGORY' + disable warnings falling into CATEGORY + + Warnings about `syntax' are enabled by default, and the environment + variable `WARNINGS', a comma separated list of categories, is + honored as well. Passing `-W CATEGORY' actually behaves as if you + had passed `--warnings syntax,$WARNINGS,CATEGORY'. To disable the + defaults and `WARNINGS', and then enable warnings about obsolete + constructs, use `-W none,obsolete'. + + If you want `autoreconf' to pass flags that are not listed here on +to `aclocal', set `ACLOCAL_AMFLAGS' in your `Makefile.am'. Due to a +limitation in the Autoconf implementation these flags currently must be +set on a single line in `Makefile.am', without any backslash-newlines. + + +File: autoconf.info, Node: Setup, Next: Existing Tests, Prev: Making configure Scripts, Up: Top + +4 Initialization and Output Files +********************************* + +Autoconf-generated `configure' scripts need some information about how +to initialize, such as how to find the package's source files and about +the output files to produce. The following sections describe the +initialization and the creation of output files. + +* Menu: + +* Initializing configure:: Option processing etc. +* Versioning:: Dealing with Autoconf versions +* Notices:: Copyright, version numbers in `configure' +* Input:: Where Autoconf should find files +* Output:: Outputting results from the configuration +* Configuration Actions:: Preparing the output based on results +* Configuration Files:: Creating output files +* Makefile Substitutions:: Using output variables in makefiles +* Configuration Headers:: Creating a configuration header file +* Configuration Commands:: Running arbitrary instantiation commands +* Configuration Links:: Links depending on the configuration +* Subdirectories:: Configuring independent packages together +* Default Prefix:: Changing the default installation prefix + + +File: autoconf.info, Node: Initializing configure, Next: Versioning, Up: Setup + +4.1 Initializing `configure' +============================ + +Every `configure' script must call `AC_INIT' before doing anything else +that produces output. Calls to silent macros, such as `AC_DEFUN', may +also occur prior to `AC_INIT', although these are generally used via +`aclocal.m4', since that is implicitly included before the start of +`configure.ac'. The only other required macro is `AC_OUTPUT' (*note +Output::). + + -- Macro: AC_INIT (PACKAGE, VERSION, [BUG-REPORT], [TARNAME], [URL]) + Process any command-line arguments and perform initialization and + verification. + + Set the name of the PACKAGE and its VERSION. These are typically + used in `--version' support, including that of `configure'. The + optional argument BUG-REPORT should be the email to which users + should send bug reports. The package TARNAME differs from + PACKAGE: the latter designates the full package name (e.g., `GNU + Autoconf'), while the former is meant for distribution tar ball + names (e.g., `autoconf'). It defaults to PACKAGE with `GNU ' + stripped, lower-cased, and all characters other than alphanumerics + and underscores are changed to `-'. If provided, URL should be + the home page for the package. + + The arguments of `AC_INIT' must be static, i.e., there should not + be any shell computation, quotes, or newlines, but they can be + computed by M4. This is because the package information strings + are expanded at M4 time into several contexts, and must give the + same text at shell time whether used in single-quoted strings, + double-quoted strings, quoted here-documents, or unquoted + here-documents. It is permissible to use `m4_esyscmd' or + `m4_esyscmd_s' for computing a version string that changes with + every commit to a version control system (in fact, Autoconf does + just that, for all builds of the development tree made between + releases). + + The following M4 macros (e.g., `AC_PACKAGE_NAME'), output variables + (e.g., `PACKAGE_NAME'), and preprocessor symbols (e.g., + `PACKAGE_NAME'), are defined by `AC_INIT': + + `AC_PACKAGE_NAME', `PACKAGE_NAME' + Exactly PACKAGE. + + `AC_PACKAGE_TARNAME', `PACKAGE_TARNAME' + Exactly TARNAME, possibly generated from PACKAGE. + + `AC_PACKAGE_VERSION', `PACKAGE_VERSION' + Exactly VERSION. + + `AC_PACKAGE_STRING', `PACKAGE_STRING' + Exactly `PACKAGE VERSION'. + + `AC_PACKAGE_BUGREPORT', `PACKAGE_BUGREPORT' + Exactly BUG-REPORT, if one was provided. Typically an email + address, or URL to a bug management web page. + + `AC_PACKAGE_URL', `PACKAGE_URL' + Exactly URL, if one was provided. If URL was empty, but + PACKAGE begins with `GNU ', then this defaults to + `http://www.gnu.org/software/TARNAME/', otherwise, no URL is + assumed. + + If your `configure' script does its own option processing, it should +inspect `$@' or `$*' immediately after calling `AC_INIT', because other +Autoconf macros liberally use the `set' command to process strings, and +this has the side effect of updating `$@' and `$*'. However, we +suggest that you use standard macros like `AC_ARG_ENABLE' instead of +attempting to implement your own option processing. *Note Site +Configuration::. + + +File: autoconf.info, Node: Versioning, Next: Notices, Prev: Initializing configure, Up: Setup + +4.2 Dealing with Autoconf versions +================================== + +The following optional macros can be used to help choose the minimum +version of Autoconf that can successfully compile a given +`configure.ac'. + + -- Macro: AC_PREREQ (VERSION) + Ensure that a recent enough version of Autoconf is being used. If + the version of Autoconf being used to create `configure' is + earlier than VERSION, print an error message to the standard error + output and exit with failure (exit status is 63). For example: + + AC_PREREQ([2.69]) + + This macro may be used before `AC_INIT'. + + -- Macro: AC_AUTOCONF_VERSION + This macro was introduced in Autoconf 2.62. It identifies the + version of Autoconf that is currently parsing the input file, in a + format suitable for `m4_version_compare' (*note + m4_version_compare::); in other words, for this release of + Autoconf, its value is `2.69'. One potential use of this macro is + for writing conditional fallbacks based on when a feature was + added to Autoconf, rather than using `AC_PREREQ' to require the + newer version of Autoconf. However, remember that the Autoconf + philosophy favors feature checks over version checks. + + You should not expand this macro directly; use + `m4_defn([AC_AUTOCONF_VERSION])' instead. This is because some + users might have a beta version of Autoconf installed, with + arbitrary letters included in its version string. This means it + is possible for the version string to contain the name of a + defined macro, such that expanding `AC_AUTOCONF_VERSION' would + trigger the expansion of that macro during rescanning, and change + the version string to be different than what you intended to check. + + +File: autoconf.info, Node: Notices, Next: Input, Prev: Versioning, Up: Setup + +4.3 Notices in `configure' +========================== + +The following macros manage version numbers for `configure' scripts. +Using them is optional. + + -- Macro: AC_COPYRIGHT (COPYRIGHT-NOTICE) + State that, in addition to the Free Software Foundation's + copyright on the Autoconf macros, parts of your `configure' are + covered by the COPYRIGHT-NOTICE. + + The COPYRIGHT-NOTICE shows up in both the head of `configure' and + in `configure --version'. + + -- Macro: AC_REVISION (REVISION-INFO) + Copy revision stamp REVISION-INFO into the `configure' script, + with any dollar signs or double-quotes removed. This macro lets + you put a revision stamp from `configure.ac' into `configure' + without RCS or CVS changing it when you check in `configure'. + That way, you can determine easily which revision of + `configure.ac' a particular `configure' corresponds to. + + For example, this line in `configure.ac': + + AC_REVISION([$Revision: 1.30 $]) + + produces this in `configure': + + #!/bin/sh + # From configure.ac Revision: 1.30 + + +File: autoconf.info, Node: Input, Next: Output, Prev: Notices, Up: Setup + +4.4 Finding `configure' Input +============================= + + -- Macro: AC_CONFIG_SRCDIR (UNIQUE-FILE-IN-SOURCE-DIR) + UNIQUE-FILE-IN-SOURCE-DIR is some file that is in the package's + source directory; `configure' checks for this file's existence to + make sure that the directory that it is told contains the source + code in fact does. Occasionally people accidentally specify the + wrong directory with `--srcdir'; this is a safety check. *Note + configure Invocation::, for more information. + + Packages that do manual configuration or use the `install' program +might need to tell `configure' where to find some other shell scripts +by calling `AC_CONFIG_AUX_DIR', though the default places it looks are +correct for most cases. + + -- Macro: AC_CONFIG_AUX_DIR (DIR) + Use the auxiliary build tools (e.g., `install-sh', `config.sub', + `config.guess', Cygnus `configure', Automake and Libtool scripts, + etc.) that are in directory DIR. These are auxiliary files used + in configuration. DIR can be either absolute or relative to + `SRCDIR'. The default is `SRCDIR' or `SRCDIR/..' or + `SRCDIR/../..', whichever is the first that contains `install-sh'. + The other files are not checked for, so that using + `AC_PROG_INSTALL' does not automatically require distributing the + other auxiliary files. It checks for `install.sh' also, but that + name is obsolete because some `make' have a rule that creates + `install' from it if there is no makefile. + + The auxiliary directory is commonly named `build-aux'. If you + need portability to DOS variants, do not name the auxiliary + directory `aux'. *Note File System Conventions::. + + -- Macro: AC_REQUIRE_AUX_FILE (FILE) + Declares that FILE is expected in the directory defined above. In + Autoconf proper, this macro does nothing: its sole purpose is to be + traced by third-party tools to produce a list of expected auxiliary + files. For instance it is called by macros like `AC_PROG_INSTALL' + (*note Particular Programs::) or `AC_CANONICAL_BUILD' (*note + Canonicalizing::) to register the auxiliary files they need. + + Similarly, packages that use `aclocal' should declare where local +macros can be found using `AC_CONFIG_MACRO_DIR'. + + -- Macro: AC_CONFIG_MACRO_DIR (DIR) + Specify DIR as the location of additional local Autoconf macros. + This macro is intended for use by future versions of commands like + `autoreconf' that trace macro calls. It should be called directly + from `configure.ac' so that tools that install macros for + `aclocal' can find the macros' declarations. + + Note that if you use `aclocal' from Automake to generate + `aclocal.m4', you must also set `ACLOCAL_AMFLAGS = -I DIR' in your + top-level `Makefile.am'. Due to a limitation in the Autoconf + implementation of `autoreconf', these include directives currently + must be set on a single line in `Makefile.am', without any + backslash-newlines. + + +File: autoconf.info, Node: Output, Next: Configuration Actions, Prev: Input, Up: Setup + +4.5 Outputting Files +==================== + +Every Autoconf script, e.g., `configure.ac', should finish by calling +`AC_OUTPUT'. That is the macro that generates and runs +`config.status', which in turn creates the makefiles and any other +files resulting from configuration. This is the only required macro +besides `AC_INIT' (*note Input::). + + -- Macro: AC_OUTPUT + Generate `config.status' and launch it. Call this macro once, at + the end of `configure.ac'. + + `config.status' performs all the configuration actions: all the + output files (see *note Configuration Files::, macro + `AC_CONFIG_FILES'), header files (see *note Configuration + Headers::, macro `AC_CONFIG_HEADERS'), commands (see *note + Configuration Commands::, macro `AC_CONFIG_COMMANDS'), links (see + *note Configuration Links::, macro `AC_CONFIG_LINKS'), + subdirectories to configure (see *note Subdirectories::, macro + `AC_CONFIG_SUBDIRS') are honored. + + The location of your `AC_OUTPUT' invocation is the exact point + where configuration actions are taken: any code afterwards is + executed by `configure' once `config.status' was run. If you want + to bind actions to `config.status' itself (independently of + whether `configure' is being run), see *note Running Arbitrary + Configuration Commands: Configuration Commands. + + Historically, the usage of `AC_OUTPUT' was somewhat different. +*Note Obsolete Macros::, for a description of the arguments that +`AC_OUTPUT' used to support. + + If you run `make' in subdirectories, you should run it using the +`make' variable `MAKE'. Most versions of `make' set `MAKE' to the name +of the `make' program plus any options it was given. (But many do not +include in it the values of any variables set on the command line, so +those are not passed on automatically.) Some old versions of `make' do +not set this variable. The following macro allows you to use it even +with those versions. + + -- Macro: AC_PROG_MAKE_SET + If the Make command, `$MAKE' if set or else `make', predefines + `$(MAKE)', define output variable `SET_MAKE' to be empty. + Otherwise, define `SET_MAKE' to a macro definition that sets + `$(MAKE)', such as `MAKE=make'. Calls `AC_SUBST' for `SET_MAKE'. + + If you use this macro, place a line like this in each `Makefile.in' +that runs `MAKE' on other directories: + + @SET_MAKE@ + + +File: autoconf.info, Node: Configuration Actions, Next: Configuration Files, Prev: Output, Up: Setup + +4.6 Performing Configuration Actions +==================================== + +`configure' is designed so that it appears to do everything itself, but +there is actually a hidden slave: `config.status'. `configure' is in +charge of examining your system, but it is `config.status' that +actually takes the proper actions based on the results of `configure'. +The most typical task of `config.status' is to _instantiate_ files. + + This section describes the common behavior of the four standard +instantiating macros: `AC_CONFIG_FILES', `AC_CONFIG_HEADERS', +`AC_CONFIG_COMMANDS' and `AC_CONFIG_LINKS'. They all have this +prototype: + + AC_CONFIG_ITEMS(TAG..., [COMMANDS], [INIT-CMDS]) + +where the arguments are: + +TAG... + A blank-or-newline-separated list of tags, which are typically the + names of the files to instantiate. + + You are encouraged to use literals as TAGS. In particular, you + should avoid + + ... && my_foos="$my_foos fooo" + ... && my_foos="$my_foos foooo" + AC_CONFIG_ITEMS([$my_foos]) + + and use this instead: + + ... && AC_CONFIG_ITEMS([fooo]) + ... && AC_CONFIG_ITEMS([foooo]) + + The macros `AC_CONFIG_FILES' and `AC_CONFIG_HEADERS' use special + TAG values: they may have the form `OUTPUT' or `OUTPUT:INPUTS'. + The file OUTPUT is instantiated from its templates, INPUTS + (defaulting to `OUTPUT.in'). + + `AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk])', for + example, asks for the creation of the file `Makefile' that + contains the expansion of the output variables in the + concatenation of `boiler/top.mk' and `boiler/bot.mk'. + + The special value `-' might be used to denote the standard output + when used in OUTPUT, or the standard input when used in the + INPUTS. You most probably don't need to use this in + `configure.ac', but it is convenient when using the command line + interface of `./config.status', see *note config.status + Invocation::, for more details. + + The INPUTS may be absolute or relative file names. In the latter + case they are first looked for in the build tree, and then in the + source tree. Input files should be text files, and a line length + below 2000 bytes should be safe. + +COMMANDS + Shell commands output literally into `config.status', and + associated with a tag that the user can use to tell `config.status' + which commands to run. The commands are run each time a TAG + request is given to `config.status', typically each time the file + `TAG' is created. + + The variables set during the execution of `configure' are _not_ + available here: you first need to set them via the INIT-CMDS. + Nonetheless the following variables are precomputed: + + `srcdir' + The name of the top source directory, assuming that the + working directory is the top build directory. This is what + the `configure' option `--srcdir' sets. + + `ac_top_srcdir' + The name of the top source directory, assuming that the + working directory is the current build directory. + + `ac_top_build_prefix' + The name of the top build directory, assuming that the working + directory is the current build directory. It can be empty, + or else ends with a slash, so that you may concatenate it. + + `ac_srcdir' + The name of the corresponding source directory, assuming that + the working directory is the current build directory. + + `tmp' + The name of a temporary directory within the build tree, + which you can use if you need to create additional temporary + files. The directory is cleaned up when `config.status' is + done or interrupted. Please use package-specific file name + prefixes to avoid clashing with files that `config.status' + may use internally. + + The "current" directory refers to the directory (or + pseudo-directory) containing the input part of TAGS. For + instance, running + + AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [...], [...]) + + with `--srcdir=../package' produces the following values: + + # Argument of --srcdir + srcdir='../package' + # Reversing deep/dir + ac_top_build_prefix='../../' + # Concatenation of $ac_top_build_prefix and srcdir + ac_top_srcdir='../../../package' + # Concatenation of $ac_top_srcdir and deep/dir + ac_srcdir='../../../package/deep/dir' + + independently of `in/in.in'. + +INIT-CMDS + Shell commands output _unquoted_ near the beginning of + `config.status', and executed each time `config.status' runs + (regardless of the tag). Because they are unquoted, for example, + `$var' is output as the value of `var'. INIT-CMDS is typically + used by `configure' to give `config.status' some variables it + needs to run the COMMANDS. + + You should be extremely cautious in your variable names: all the + INIT-CMDS share the same name space and may overwrite each other + in unpredictable ways. Sorry... + + All these macros can be called multiple times, with different TAG +values, of course! + + +File: autoconf.info, Node: Configuration Files, Next: Makefile Substitutions, Prev: Configuration Actions, Up: Setup + +4.7 Creating Configuration Files +================================ + +Be sure to read the previous section, *note Configuration Actions::. + + -- Macro: AC_CONFIG_FILES (FILE..., [CMDS], [INIT-CMDS]) + Make `AC_OUTPUT' create each `FILE' by copying an input file (by + default `FILE.in'), substituting the output variable values. This + macro is one of the instantiating macros; see *note Configuration + Actions::. *Note Makefile Substitutions::, for more information + on using output variables. *Note Setting Output Variables::, for + more information on creating them. This macro creates the + directory that the file is in if it doesn't exist. Usually, + makefiles are created this way, but other files, such as + `.gdbinit', can be specified as well. + + Typical calls to `AC_CONFIG_FILES' look like this: + + AC_CONFIG_FILES([Makefile src/Makefile man/Makefile X/Imakefile]) + AC_CONFIG_FILES([autoconf], [chmod +x autoconf]) + + You can override an input file name by appending to FILE a + colon-separated list of input files. Examples: + + AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk] + [lib/Makefile:boiler/lib.mk]) + + Doing this allows you to keep your file names acceptable to DOS + variants, or to prepend and/or append boilerplate to the file. + + +File: autoconf.info, Node: Makefile Substitutions, Next: Configuration Headers, Prev: Configuration Files, Up: Setup + +4.8 Substitutions in Makefiles +============================== + +Each subdirectory in a distribution that contains something to be +compiled or installed should come with a file `Makefile.in', from which +`configure' creates a file `Makefile' in that directory. To create +`Makefile', `configure' performs a simple variable substitution, +replacing occurrences of `@VARIABLE@' in `Makefile.in' with the value +that `configure' has determined for that variable. Variables that are +substituted into output files in this way are called "output +variables". They are ordinary shell variables that are set in +`configure'. To make `configure' substitute a particular variable into +the output files, the macro `AC_SUBST' must be called with that +variable name as an argument. Any occurrences of `@VARIABLE@' for +other variables are left unchanged. *Note Setting Output Variables::, +for more information on creating output variables with `AC_SUBST'. + + A software package that uses a `configure' script should be +distributed with a file `Makefile.in', but no makefile; that way, the +user has to properly configure the package for the local system before +compiling it. + + *Note Makefile Conventions: (standards)Makefile Conventions, for +more information on what to put in makefiles. + +* Menu: + +* Preset Output Variables:: Output variables that are always set +* Installation Directory Variables:: Other preset output variables +* Changed Directory Variables:: Warnings about `datarootdir' +* Build Directories:: Supporting multiple concurrent compiles +* Automatic Remaking:: Makefile rules for configuring + + +File: autoconf.info, Node: Preset Output Variables, Next: Installation Directory Variables, Up: Makefile Substitutions + +4.8.1 Preset Output Variables +----------------------------- + +Some output variables are preset by the Autoconf macros. Some of the +Autoconf macros set additional output variables, which are mentioned in +the descriptions for those macros. *Note Output Variable Index::, for a +complete list of output variables. *Note Installation Directory +Variables::, for the list of the preset ones related to installation +directories. Below are listed the other preset ones, many of which are +precious variables (*note Setting Output Variables::, `AC_ARG_VAR'). + + The preset variables which are available during `config.status' +(*note Configuration Actions::) may also be used during `configure' +tests. For example, it is permissible to reference `$srcdir' when +constructing a list of directories to pass via option `-I' during a +compiler feature check. When used in this manner, coupled with the +fact that `configure' is always run from the top build directory, it is +sufficient to use just `$srcdir' instead of `$top_srcdir'. + + -- Variable: CFLAGS + Debugging and optimization options for the C compiler. If it is + not set in the environment when `configure' runs, the default + value is set when you call `AC_PROG_CC' (or empty if you don't). + `configure' uses this variable when compiling or linking programs + to test for C features. + + If a compiler option affects only the behavior of the preprocessor + (e.g., `-DNAME'), it should be put into `CPPFLAGS' instead. If it + affects only the linker (e.g., `-LDIRECTORY'), it should be put + into `LDFLAGS' instead. If it affects only the compiler proper, + `CFLAGS' is the natural home for it. If an option affects + multiple phases of the compiler, though, matters get tricky. One + approach to put such options directly into `CC', e.g., `CC='gcc + -m64''. Another is to put them into both `CPPFLAGS' and + `LDFLAGS', but not into `CFLAGS'. + + However, remember that some `Makefile' variables are reserved by + the GNU Coding Standards for the use of the "user"--the person + building the package. For instance, `CFLAGS' is one such variable. + + Sometimes package developers are tempted to set user variables + such as `CFLAGS' because it appears to make their job easier. + However, the package itself should never set a user variable, + particularly not to include switches that are required for proper + compilation of the package. Since these variables are documented + as being for the package builder, that person rightfully expects + to be able to override any of these variables at build time. If + the package developer needs to add switches without interfering + with the user, the proper way to do that is to introduce an + additional variable. Automake makes this easy by introducing + `AM_CFLAGS' (*note Flag Variables Ordering: (automake)Flag + Variables Ordering.), but the concept is the same even if Automake + is not used. + + -- Variable: configure_input + A comment saying that the file was generated automatically by + `configure' and giving the name of the input file. `AC_OUTPUT' + adds a comment line containing this variable to the top of every + makefile it creates. For other files, you should reference this + variable in a comment at the top of each input file. For example, + an input shell script should begin like this: + + #!/bin/sh + # @configure_input@ + + The presence of that line also reminds people editing the file + that it needs to be processed by `configure' in order to be used. + + -- Variable: CPPFLAGS + Preprocessor options for the C, C++, Objective C, and Objective C++ + preprocessors and compilers. If it is not set in the environment + when `configure' runs, the default value is empty. `configure' + uses this variable when preprocessing or compiling programs to + test for C, C++, Objective C, and Objective C++ features. + + This variable's contents should contain options like `-I', `-D', + and `-U' that affect only the behavior of the preprocessor. + Please see the explanation of `CFLAGS' for what you can do if an + option affects other phases of the compiler as well. + + Currently, `configure' always links as part of a single invocation + of the compiler that also preprocesses and compiles, so it uses + this variable also when linking programs. However, it is unwise to + depend on this behavior because the GNU Coding Standards do not + require it and many packages do not use `CPPFLAGS' when linking + programs. + + *Note Special Chars in Variables::, for limitations that `CPPFLAGS' + might run into. + + -- Variable: CXXFLAGS + Debugging and optimization options for the C++ compiler. It acts + like `CFLAGS', but for C++ instead of C. + + -- Variable: DEFS + `-D' options to pass to the C compiler. If `AC_CONFIG_HEADERS' is + called, `configure' replaces `@DEFS@' with `-DHAVE_CONFIG_H' + instead (*note Configuration Headers::). This variable is not + defined while `configure' is performing its tests, only when + creating the output files. *Note Setting Output Variables::, for + how to check the results of previous tests. + + -- Variable: ECHO_C + -- Variable: ECHO_N + -- Variable: ECHO_T + How does one suppress the trailing newline from `echo' for + question-answer message pairs? These variables provide a way: + + echo $ECHO_N "And the winner is... $ECHO_C" + sleep 100000000000 + echo "${ECHO_T}dead." + + Some old and uncommon `echo' implementations offer no means to + achieve this, in which case `ECHO_T' is set to tab. You might not + want to use it. + + -- Variable: ERLCFLAGS + Debugging and optimization options for the Erlang compiler. If it + is not set in the environment when `configure' runs, the default + value is empty. `configure' uses this variable when compiling + programs to test for Erlang features. + + -- Variable: FCFLAGS + Debugging and optimization options for the Fortran compiler. If it + is not set in the environment when `configure' runs, the default + value is set when you call `AC_PROG_FC' (or empty if you don't). + `configure' uses this variable when compiling or linking programs + to test for Fortran features. + + -- Variable: FFLAGS + Debugging and optimization options for the Fortran 77 compiler. + If it is not set in the environment when `configure' runs, the + default value is set when you call `AC_PROG_F77' (or empty if you + don't). `configure' uses this variable when compiling or linking + programs to test for Fortran 77 features. + + -- Variable: LDFLAGS + Options for the linker. If it is not set in the environment when + `configure' runs, the default value is empty. `configure' uses + this variable when linking programs to test for C, C++, Objective + C, Objective C++, Fortran, and Go features. + + This variable's contents should contain options like `-s' and `-L' + that affect only the behavior of the linker. Please see the + explanation of `CFLAGS' for what you can do if an option also + affects other phases of the compiler. + + Don't use this variable to pass library names (`-l') to the + linker; use `LIBS' instead. + + -- Variable: LIBS + `-l' options to pass to the linker. The default value is empty, + but some Autoconf macros may prepend extra libraries to this + variable if those libraries are found and provide necessary + functions, see *note Libraries::. `configure' uses this variable + when linking programs to test for C, C++, Objective C, Objective + C++, Fortran, and Go features. + + -- Variable: OBJCFLAGS + Debugging and optimization options for the Objective C compiler. + It acts like `CFLAGS', but for Objective C instead of C. + + -- Variable: OBJCXXFLAGS + Debugging and optimization options for the Objective C++ compiler. + It acts like `CXXFLAGS', but for Objective C++ instead of C++. + + -- Variable: GOFLAGS + Debugging and optimization options for the Go compiler. It acts + like `CFLAGS', but for Go instead of C. + + -- Variable: builddir + Rigorously equal to `.'. Added for symmetry only. + + -- Variable: abs_builddir + Absolute name of `builddir'. + + -- Variable: top_builddir + The relative name of the top level of the current build tree. In + the top-level directory, this is the same as `builddir'. + + -- Variable: top_build_prefix + The relative name of the top level of the current build tree with + final slash if nonempty. This is the same as `top_builddir', + except that it contains zero or more runs of `../', so it should + not be appended with a slash for concatenation. This helps for + `make' implementations that otherwise do not treat `./file' and + `file' as equal in the toplevel build directory. + + -- Variable: abs_top_builddir + Absolute name of `top_builddir'. + + -- Variable: srcdir + The name of the directory that contains the source code for that + makefile. + + -- Variable: abs_srcdir + Absolute name of `srcdir'. + + -- Variable: top_srcdir + The name of the top-level source code directory for the package. + In the top-level directory, this is the same as `srcdir'. + + -- Variable: abs_top_srcdir + Absolute name of `top_srcdir'. + + +File: autoconf.info, Node: Installation Directory Variables, Next: Changed Directory Variables, Prev: Preset Output Variables, Up: Makefile Substitutions + +4.8.2 Installation Directory Variables +-------------------------------------- + +The following variables specify the directories for package +installation, see *note Variables for Installation Directories: +(standards)Directory Variables, for more information. Each variable +corresponds to an argument of `configure'; trailing slashes are +stripped so that expressions such as `${prefix}/lib' expand with only +one slash between directory names. See the end of this section for +details on when and how to use these variables. + + -- Variable: bindir + The directory for installing executables that users run. + + -- Variable: datadir + The directory for installing idiosyncratic read-only + architecture-independent data. + + -- Variable: datarootdir + The root of the directory tree for read-only + architecture-independent data files. + + -- Variable: docdir + The directory for installing documentation files (other than Info + and man). + + -- Variable: dvidir + The directory for installing documentation files in DVI format. + + -- Variable: exec_prefix + The installation prefix for architecture-dependent files. By + default it's the same as `prefix'. You should avoid installing + anything directly to `exec_prefix'. However, the default value for + directories containing architecture-dependent files should be + relative to `exec_prefix'. + + -- Variable: htmldir + The directory for installing HTML documentation. + + -- Variable: includedir + The directory for installing C header files. + + -- Variable: infodir + The directory for installing documentation in Info format. + + -- Variable: libdir + The directory for installing object code libraries. + + -- Variable: libexecdir + The directory for installing executables that other programs run. + + -- Variable: localedir + The directory for installing locale-dependent but + architecture-independent data, such as message catalogs. This + directory usually has a subdirectory per locale. + + -- Variable: localstatedir + The directory for installing modifiable single-machine data. + + -- Variable: mandir + The top-level directory for installing documentation in man format. + + -- Variable: oldincludedir + The directory for installing C header files for non-GCC compilers. + + -- Variable: pdfdir + The directory for installing PDF documentation. + + -- Variable: prefix + The common installation prefix for all files. If `exec_prefix' is + defined to a different value, `prefix' is used only for + architecture-independent files. + + -- Variable: psdir + The directory for installing PostScript documentation. + + -- Variable: sbindir + The directory for installing executables that system + administrators run. + + -- Variable: sharedstatedir + The directory for installing modifiable architecture-independent + data. + + -- Variable: sysconfdir + The directory for installing read-only single-machine data. + + Most of these variables have values that rely on `prefix' or +`exec_prefix'. It is deliberate that the directory output variables +keep them unexpanded: typically `@datarootdir@' is replaced by +`${prefix}/share', not `/usr/local/share', and `@datadir@' is replaced +by `${datarootdir}'. + + This behavior is mandated by the GNU Coding Standards, so that when +the user runs: + +`make' + she can still specify a different prefix from the one specified to + `configure', in which case, if needed, the package should hard + code dependencies corresponding to the make-specified prefix. + +`make install' + she can specify a different installation location, in which case + the package _must_ still depend on the location which was compiled + in (i.e., never recompile when `make install' is run). This is an + extremely important feature, as many people may decide to install + all the files of a package grouped together, and then install + links from the final locations to there. + + In order to support these features, it is essential that +`datarootdir' remains defined as `${prefix}/share', so that its value +can be expanded based on the current value of `prefix'. + + A corollary is that you should not use these variables except in +makefiles. For instance, instead of trying to evaluate `datadir' in +`configure' and hard-coding it in makefiles using e.g., +`AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])', you +should add `-DDATADIR='$(datadir)'' to your makefile's definition of +`CPPFLAGS' (`AM_CPPFLAGS' if you are also using Automake). + + Similarly, you should not rely on `AC_CONFIG_FILES' to replace +`bindir' and friends in your shell scripts and other files; instead, +let `make' manage their replacement. For instance Autoconf ships +templates of its shell scripts ending with `.in', and uses a makefile +snippet similar to the following to build scripts like `autoheader' and +`autom4te': + + edit = sed \ + -e 's|@bindir[@]|$(bindir)|g' \ + -e 's|@pkgdatadir[@]|$(pkgdatadir)|g' \ + -e 's|@prefix[@]|$(prefix)|g' + + autoheader autom4te: Makefile + rm -f $@ $@.tmp + srcdir=''; \ + test -f ./$@.in || srcdir=$(srcdir)/; \ + $(edit) $${srcdir}$@.in >$@.tmp + chmod +x $@.tmp + chmod a-w $@.tmp + mv $@.tmp $@ + + autoheader: $(srcdir)/autoheader.in + autom4te: $(srcdir)/autom4te.in + + Some details are noteworthy: + +`@bindir[@]' + The brackets prevent `configure' from replacing `@bindir@' in the + Sed expression itself. Brackets are preferable to a backslash + here, since Posix says `\@' is not portable. + +`$(bindir)' + Don't use `@bindir@'! Use the matching makefile variable instead. + +`$(pkgdatadir)' + The example takes advantage of the variable `$(pkgdatadir)' + provided by Automake; it is equivalent to `$(datadir)/$(PACKAGE)'. + +`/' + Don't use `/' in the Sed expressions that replace file names since + most likely the variables you use, such as `$(bindir)', contain + `/'. Use a shell metacharacter instead, such as `|'. + +special characters + File names, file name components, and the value of `VPATH' should + not contain shell metacharacters or white space. *Note Special + Chars in Variables::. + +dependency on `Makefile' + Since `edit' uses values that depend on the configuration specific + values (`prefix', etc.) and not only on `VERSION' and so forth, + the output depends on `Makefile', not `configure.ac'. + +`$@' + The main rule is generic, and uses `$@' extensively to avoid the + need for multiple copies of the rule. + +Separated dependencies and single suffix rules + You can't use them! The above snippet cannot be (portably) + rewritten as: + + autoconf autoheader: Makefile + .in: + rm -f $@ $@.tmp + $(edit) $< >$@.tmp + chmod +x $@.tmp + mv $@.tmp $@ + + *Note Single Suffix Rules::, for details. + +`$(srcdir)' + Be sure to specify the name of the source directory, otherwise the + package won't support separated builds. + + For the more specific installation of Erlang libraries, the +following variables are defined: + + -- Variable: ERLANG_INSTALL_LIB_DIR + The common parent directory of Erlang library installation + directories. This variable is set by calling the + `AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro in `configure.ac'. + + -- Variable: ERLANG_INSTALL_LIB_DIR_LIBRARY + The installation directory for Erlang library LIBRARY. This + variable is set by using the `AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR' + macro in `configure.ac'. + + *Note Erlang Libraries::, for details. + + +File: autoconf.info, Node: Changed Directory Variables, Next: Build Directories, Prev: Installation Directory Variables, Up: Makefile Substitutions + +4.8.3 Changed Directory Variables +--------------------------------- + +In Autoconf 2.60, the set of directory variables has changed, and the +defaults of some variables have been adjusted (*note Installation +Directory Variables::) to changes in the GNU Coding Standards. +Notably, `datadir', `infodir', and `mandir' are now expressed in terms +of `datarootdir'. If you are upgrading from an earlier Autoconf +version, you may need to adjust your files to ensure that the directory +variables are substituted correctly (*note Defining Directories::), and +that a definition of `datarootdir' is in place. For example, in a +`Makefile.in', adding + + datarootdir = @datarootdir@ + +is usually sufficient. If you use Automake to create `Makefile.in', it +will add this for you. + + To help with the transition, Autoconf warns about files that seem to +use `datarootdir' without defining it. In some cases, it then expands +the value of `$datarootdir' in substitutions of the directory +variables. The following example shows such a warning: + + $ cat configure.ac + AC_INIT + AC_CONFIG_FILES([Makefile]) + AC_OUTPUT + $ cat Makefile.in + prefix = @prefix@ + datadir = @datadir@ + $ autoconf + $ configure + configure: creating ./config.status + config.status: creating Makefile + config.status: WARNING: + Makefile.in seems to ignore the --datarootdir setting + $ cat Makefile + prefix = /usr/local + datadir = ${prefix}/share + + Usually one can easily change the file to accommodate both older and +newer Autoconf releases: + + $ cat Makefile.in + prefix = @prefix@ + datarootdir = @datarootdir@ + datadir = @datadir@ + $ configure + configure: creating ./config.status + config.status: creating Makefile + $ cat Makefile + prefix = /usr/local + datarootdir = ${prefix}/share + datadir = ${datarootdir} + + In some cases, however, the checks may not be able to detect that a +suitable initialization of `datarootdir' is in place, or they may fail +to detect that such an initialization is necessary in the output file. +If, after auditing your package, there are still spurious `configure' +warnings about `datarootdir', you may add the line + + AC_DEFUN([AC_DATAROOTDIR_CHECKED]) + +to your `configure.ac' to disable the warnings. This is an exception +to the usual rule that you should not define a macro whose name begins +with `AC_' (*note Macro Names::). + + +File: autoconf.info, Node: Build Directories, Next: Automatic Remaking, Prev: Changed Directory Variables, Up: Makefile Substitutions + +4.8.4 Build Directories +----------------------- + +You can support compiling a software package for several architectures +simultaneously from the same copy of the source code. The object files +for each architecture are kept in their own directory. + + To support doing this, `make' uses the `VPATH' variable to find the +files that are in the source directory. GNU Make can do this. Most +other recent `make' programs can do this as well, though they may have +difficulties and it is often simpler to recommend GNU `make' (*note +VPATH and Make::). Older `make' programs do not support `VPATH'; when +using them, the source code must be in the same directory as the object +files. + + If you are using GNU Automake, the remaining details in this section +are already covered for you, based on the contents of your +`Makefile.am'. But if you are using Autoconf in isolation, then +supporting `VPATH' requires the following in your `Makefile.in': + + srcdir = @srcdir@ + VPATH = @srcdir@ + + Do not set `VPATH' to the value of another variable (*note Variables +listed in VPATH::. + + `configure' substitutes the correct value for `srcdir' when it +produces `Makefile'. + + Do not use the `make' variable `$<', which expands to the file name +of the file in the source directory (found with `VPATH'), except in +implicit rules. (An implicit rule is one such as `.c.o', which tells +how to create a `.o' file from a `.c' file.) Some versions of `make' +do not set `$<' in explicit rules; they expand it to an empty value. + + Instead, Make command lines should always refer to source files by +prefixing them with `$(srcdir)/'. For example: + + time.info: time.texinfo + $(MAKEINFO) '$(srcdir)/time.texinfo' + + +File: autoconf.info, Node: Automatic Remaking, Prev: Build Directories, Up: Makefile Substitutions + +4.8.5 Automatic Remaking +------------------------ + +You can put rules like the following in the top-level `Makefile.in' for +a package to automatically update the configuration information when +you change the configuration files. This example includes all of the +optional files, such as `aclocal.m4' and those related to configuration +header files. Omit from the `Makefile.in' rules for any of these files +that your package does not use. + + The `$(srcdir)/' prefix is included because of limitations in the +`VPATH' mechanism. + + The `stamp-' files are necessary because the timestamps of +`config.h.in' and `config.h' are not changed if remaking them does not +change their contents. This feature avoids unnecessary recompilation. +You should include the file `stamp-h.in' in your package's +distribution, so that `make' considers `config.h.in' up to date. Don't +use `touch' (*note Limitations of Usual Tools: touch.); instead, use +`echo' (using `date' would cause needless differences, hence CVS +conflicts, etc.). + + $(srcdir)/configure: configure.ac aclocal.m4 + cd '$(srcdir)' && autoconf + + # autoheader might not change config.h.in, so touch a stamp file. + $(srcdir)/config.h.in: stamp-h.in + $(srcdir)/stamp-h.in: configure.ac aclocal.m4 + cd '$(srcdir)' && autoheader + echo timestamp > '$(srcdir)/stamp-h.in' + + config.h: stamp-h + stamp-h: config.h.in config.status + ./config.status + + Makefile: Makefile.in config.status + ./config.status + + config.status: configure + ./config.status --recheck + +(Be careful if you copy these lines directly into your makefile, as you +need to convert the indented lines to start with the tab character.) + + In addition, you should use + + AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h]) + +so `config.status' ensures that `config.h' is considered up to date. +*Note Output::, for more information about `AC_OUTPUT'. + + *Note config.status Invocation::, for more examples of handling +configuration-related dependencies. + + +File: autoconf.info, Node: Configuration Headers, Next: Configuration Commands, Prev: Makefile Substitutions, Up: Setup + +4.9 Configuration Header Files +============================== + +When a package contains more than a few tests that define C preprocessor +symbols, the command lines to pass `-D' options to the compiler can get +quite long. This causes two problems. One is that the `make' output +is hard to visually scan for errors. More seriously, the command lines +can exceed the length limits of some operating systems. As an +alternative to passing `-D' options to the compiler, `configure' +scripts can create a C header file containing `#define' directives. +The `AC_CONFIG_HEADERS' macro selects this kind of output. Though it +can be called anywhere between `AC_INIT' and `AC_OUTPUT', it is +customary to call it right after `AC_INIT'. + + The package should `#include' the configuration header file before +any other header files, to prevent inconsistencies in declarations (for +example, if it redefines `const'). + + To provide for VPATH builds, remember to pass the C compiler a `-I.' +option (or `-I..'; whichever directory contains `config.h'). Even if +you use `#include "config.h"', the preprocessor searches only the +directory of the currently read file, i.e., the source directory, not +the build directory. + + With the appropriate `-I' option, you can use `#include <config.h>'. +Actually, it's a good habit to use it, because in the rare case when +the source directory contains another `config.h', the build directory +should be searched first. + + -- Macro: AC_CONFIG_HEADERS (HEADER ..., [CMDS], [INIT-CMDS]) + This macro is one of the instantiating macros; see *note + Configuration Actions::. Make `AC_OUTPUT' create the file(s) in + the blank-or-newline-separated list HEADER containing C + preprocessor `#define' statements, and replace `@DEFS@' in + generated files with `-DHAVE_CONFIG_H' instead of the value of + `DEFS'. The usual name for HEADER is `config.h'. + + If HEADER already exists and its contents are identical to what + `AC_OUTPUT' would put in it, it is left alone. Doing this allows + making some changes in the configuration without needlessly causing + object files that depend on the header file to be recompiled. + + Usually the input file is named `HEADER.in'; however, you can + override the input file name by appending to HEADER a + colon-separated list of input files. For example, you might need + to make the input file name acceptable to DOS variants: + + AC_CONFIG_HEADERS([config.h:config.hin]) + + + -- Macro: AH_HEADER + This macro is defined as the name of the first declared config + header and undefined if no config headers have been declared up to + this point. A third-party macro may, for example, require use of + a config header without invoking AC_CONFIG_HEADERS twice, like + this: + + AC_CONFIG_COMMANDS_PRE( + [m4_ifndef([AH_HEADER], [AC_CONFIG_HEADERS([config.h])])]) + + + *Note Configuration Actions::, for more details on HEADER. + +* Menu: + +* Header Templates:: Input for the configuration headers +* autoheader Invocation:: How to create configuration templates +* Autoheader Macros:: How to specify CPP templates + + +File: autoconf.info, Node: Header Templates, Next: autoheader Invocation, Up: Configuration Headers + +4.9.1 Configuration Header Templates +------------------------------------ + +Your distribution should contain a template file that looks as you want +the final header file to look, including comments, with `#undef' +statements which are used as hooks. For example, suppose your +`configure.ac' makes these calls: + + AC_CONFIG_HEADERS([conf.h]) + AC_CHECK_HEADERS([unistd.h]) + +Then you could have code like the following in `conf.h.in'. The +`conf.h' created by `configure' defines `HAVE_UNISTD_H' to 1, if and +only if the system has `unistd.h'. + + /* Define as 1 if you have unistd.h. */ + #undef HAVE_UNISTD_H + + The format of the template file is stricter than what the C +preprocessor is required to accept. A directive line should contain +only whitespace, `#undef', and `HAVE_UNISTD_H'. The use of `#define' +instead of `#undef', or of comments on the same line as `#undef', is +strongly discouraged. Each hook should only be listed once. Other +preprocessor lines, such as `#ifdef' or `#include', are copied verbatim +from the template into the generated header. + + Since it is a tedious task to keep a template header up to date, you +may use `autoheader' to generate it, see *note autoheader Invocation::. + + During the instantiation of the header, each `#undef' line in the +template file for each symbol defined by `AC_DEFINE' is changed to an +appropriate `#define'. If the corresponding `AC_DEFINE' has not been +executed during the `configure' run, the `#undef' line is commented +out. (This is important, e.g., for `_POSIX_SOURCE': on many systems, +it can be implicitly defined by the compiler, and undefining it in the +header would then break compilation of subsequent headers.) + + Currently, _all_ remaining `#undef' lines in the header template are +commented out, whether or not there was a corresponding `AC_DEFINE' for +the macro name; but this behavior is not guaranteed for future releases +of Autoconf. + + Generally speaking, since you should not use `#define', and you +cannot guarantee whether a `#undef' directive in the header template +will be converted to a `#define' or commented out in the generated +header file, the template file cannot be used for conditional +definition effects. Consequently, if you need to use the construct + + #ifdef THIS + # define THAT + #endif + +you must place it outside of the template. If you absolutely need to +hook it to the config header itself, please put the directives to a +separate file, and `#include' that file from the config header +template. If you are using `autoheader', you would probably use +`AH_BOTTOM' to append the `#include' directive. + + +File: autoconf.info, Node: autoheader Invocation, Next: Autoheader Macros, Prev: Header Templates, Up: Configuration Headers + +4.9.2 Using `autoheader' to Create `config.h.in' +------------------------------------------------ + +The `autoheader' program can create a template file of C `#define' +statements for `configure' to use. It searches for the first +invocation of `AC_CONFIG_HEADERS' in `configure' sources to determine +the name of the template. (If the first call of `AC_CONFIG_HEADERS' +specifies more than one input file name, `autoheader' uses the first +one.) + + It is recommended that only one input file is used. If you want to +append a boilerplate code, it is preferable to use `AH_BOTTOM([#include +<conf_post.h>])'. File `conf_post.h' is not processed during the +configuration then, which make things clearer. Analogically, `AH_TOP' +can be used to prepend a boilerplate code. + + In order to do its job, `autoheader' needs you to document all of +the symbols that you might use. Typically this is done via an +`AC_DEFINE' or `AC_DEFINE_UNQUOTED' call whose first argument is a +literal symbol and whose third argument describes the symbol (*note +Defining Symbols::). Alternatively, you can use `AH_TEMPLATE' (*note +Autoheader Macros::), or you can supply a suitable input file for a +subsequent configuration header file. Symbols defined by Autoconf's +builtin tests are already documented properly; you need to document +only those that you define yourself. + + You might wonder why `autoheader' is needed: after all, why would +`configure' need to "patch" a `config.h.in' to produce a `config.h' +instead of just creating `config.h' from scratch? Well, when +everything rocks, the answer is just that we are wasting our time +maintaining `autoheader': generating `config.h' directly is all that is +needed. When things go wrong, however, you'll be thankful for the +existence of `autoheader'. + + The fact that the symbols are documented is important in order to +_check_ that `config.h' makes sense. The fact that there is a +well-defined list of symbols that should be defined (or not) is also +important for people who are porting packages to environments where +`configure' cannot be run: they just have to _fill in the blanks_. + + But let's come back to the point: the invocation of `autoheader'... + + If you give `autoheader' an argument, it uses that file instead of +`configure.ac' and writes the header file to the standard output +instead of to `config.h.in'. If you give `autoheader' an argument of +`-', it reads the standard input instead of `configure.ac' and writes +the header file to the standard output. + + `autoheader' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Report processing steps. + +`--debug' +`-d' + Don't remove the temporary files. + +`--force' +`-f' + Remake the template file even if newer than its input files. + +`--include=DIR' +`-I DIR' + Append DIR to the include path. Multiple invocations accumulate. + +`--prepend-include=DIR' +`-B DIR' + Prepend DIR to the include path. Multiple invocations accumulate. + +`--warnings=CATEGORY' +`-W CATEGORY' + Report the warnings related to CATEGORY (which can actually be a + comma separated list). Current categories include: + + `obsolete' + report the uses of obsolete constructs + + `all' + report all the warnings + + `none' + report none + + `error' + treats warnings as errors + + `no-CATEGORY' + disable warnings falling into CATEGORY + + + +File: autoconf.info, Node: Autoheader Macros, Prev: autoheader Invocation, Up: Configuration Headers + +4.9.3 Autoheader Macros +----------------------- + +`autoheader' scans `configure.ac' and figures out which C preprocessor +symbols it might define. It knows how to generate templates for +symbols defined by `AC_CHECK_HEADERS', `AC_CHECK_FUNCS' etc., but if +you `AC_DEFINE' any additional symbol, you must define a template for +it. If there are missing templates, `autoheader' fails with an error +message. + + The template for a SYMBOL is created by `autoheader' from the +DESCRIPTION argument to an `AC_DEFINE'; see *note Defining Symbols::. + + For special needs, you can use the following macros. + + -- Macro: AH_TEMPLATE (KEY, DESCRIPTION) + Tell `autoheader' to generate a template for KEY. This macro + generates standard templates just like `AC_DEFINE' when a + DESCRIPTION is given. + + For example: + + AH_TEMPLATE([CRAY_STACKSEG_END], + [Define to one of _getb67, GETB67, getb67 + for Cray-2 and Cray-YMP systems. This + function is required for alloca.c support + on those systems.]) + + generates the following template, with the description properly + justified. + + /* Define to one of _getb67, GETB67, getb67 for Cray-2 and + Cray-YMP systems. This function is required for alloca.c + support on those systems. */ + #undef CRAY_STACKSEG_END + + -- Macro: AH_VERBATIM (KEY, TEMPLATE) + Tell `autoheader' to include the TEMPLATE as-is in the header + template file. This TEMPLATE is associated with the KEY, which is + used to sort all the different templates and guarantee their + uniqueness. It should be a symbol that can be defined via + `AC_DEFINE'. + + -- Macro: AH_TOP (TEXT) + Include TEXT at the top of the header template file. + + -- Macro: AH_BOTTOM (TEXT) + Include TEXT at the bottom of the header template file. + + Please note that TEXT gets included "verbatim" to the template file, +not to the resulting config header, so it can easily get mangled when +the template is processed. There is rarely a need for something other +than + + AH_BOTTOM([#include <custom.h>]) + + +File: autoconf.info, Node: Configuration Commands, Next: Configuration Links, Prev: Configuration Headers, Up: Setup + +4.10 Running Arbitrary Configuration Commands +============================================= + +You can execute arbitrary commands before, during, and after +`config.status' is run. The three following macros accumulate the +commands to run when they are called multiple times. +`AC_CONFIG_COMMANDS' replaces the obsolete macro `AC_OUTPUT_COMMANDS'; +see *note Obsolete Macros::, for details. + + -- Macro: AC_CONFIG_COMMANDS (TAG..., [CMDS], [INIT-CMDS]) + Specify additional shell commands to run at the end of + `config.status', and shell commands to initialize any variables + from `configure'. Associate the commands with TAG. Since + typically the CMDS create a file, TAG should naturally be the name + of that file. If needed, the directory hosting TAG is created. + This macro is one of the instantiating macros; see *note + Configuration Actions::. + + Here is an unrealistic example: + fubar=42 + AC_CONFIG_COMMANDS([fubar], + [echo this is extra $fubar, and so on.], + [fubar=$fubar]) + + Here is a better one: + AC_CONFIG_COMMANDS([timestamp], [date >timestamp]) + + The following two macros look similar, but in fact they are not of +the same breed: they are executed directly by `configure', so you +cannot use `config.status' to rerun them. + + -- Macro: AC_CONFIG_COMMANDS_PRE (CMDS) + Execute the CMDS right before creating `config.status'. + + This macro presents the last opportunity to call `AC_SUBST', + `AC_DEFINE', or `AC_CONFIG_ITEMS' macros. + + -- Macro: AC_CONFIG_COMMANDS_POST (CMDS) + Execute the CMDS right after creating `config.status'. + + +File: autoconf.info, Node: Configuration Links, Next: Subdirectories, Prev: Configuration Commands, Up: Setup + +4.11 Creating Configuration Links +================================= + +You may find it convenient to create links whose destinations depend +upon results of tests. One can use `AC_CONFIG_COMMANDS' but the +creation of relative symbolic links can be delicate when the package is +built in a directory different from the source directory. + + -- Macro: AC_CONFIG_LINKS (DEST:SOURCE..., [CMDS], [INIT-CMDS]) + Make `AC_OUTPUT' link each of the existing files SOURCE to the + corresponding link name DEST. Makes a symbolic link if possible, + otherwise a hard link if possible, otherwise a copy. The DEST and + SOURCE names should be relative to the top level source or build + directory. This macro is one of the instantiating macros; see + *note Configuration Actions::. + + For example, this call: + + AC_CONFIG_LINKS([host.h:config/$machine.h + object.h:config/$obj_format.h]) + + creates in the current directory `host.h' as a link to + `SRCDIR/config/$machine.h', and `object.h' as a link to + `SRCDIR/config/$obj_format.h'. + + The tempting value `.' for DEST is invalid: it makes it impossible + for `config.status' to guess the links to establish. + + One can then run: + ./config.status host.h object.h + to create the links. + + +File: autoconf.info, Node: Subdirectories, Next: Default Prefix, Prev: Configuration Links, Up: Setup + +4.12 Configuring Other Packages in Subdirectories +================================================= + +In most situations, calling `AC_OUTPUT' is sufficient to produce +makefiles in subdirectories. However, `configure' scripts that control +more than one independent package can use `AC_CONFIG_SUBDIRS' to run +`configure' scripts for other packages in subdirectories. + + -- Macro: AC_CONFIG_SUBDIRS (DIR ...) + Make `AC_OUTPUT' run `configure' in each subdirectory DIR in the + given blank-or-newline-separated list. Each DIR should be a + literal, i.e., please do not use: + + if test "x$package_foo_enabled" = xyes; then + my_subdirs="$my_subdirs foo" + fi + AC_CONFIG_SUBDIRS([$my_subdirs]) + + because this prevents `./configure --help=recursive' from + displaying the options of the package `foo'. Instead, you should + write: + + if test "x$package_foo_enabled" = xyes; then + AC_CONFIG_SUBDIRS([foo]) + fi + + If a given DIR is not found at `configure' run time, a warning is + reported; if the subdirectory is optional, write: + + if test -d "$srcdir/foo"; then + AC_CONFIG_SUBDIRS([foo]) + fi + + If a given DIR contains `configure.gnu', it is run instead of + `configure'. This is for packages that might use a non-Autoconf + script `Configure', which can't be called through a wrapper + `configure' since it would be the same file on case-insensitive + file systems. Likewise, if a DIR contains `configure.in' but no + `configure', the Cygnus `configure' script found by + `AC_CONFIG_AUX_DIR' is used. + + The subdirectory `configure' scripts are given the same command + line options that were given to this `configure' script, with minor + changes if needed, which include: + + - adjusting a relative name for the cache file; + + - adjusting a relative name for the source directory; + + - propagating the current value of `$prefix', including if it + was defaulted, and if the default values of the top level and + of the subdirectory `configure' differ. + + This macro also sets the output variable `subdirs' to the list of + directories `DIR ...'. Make rules can use this variable to + determine which subdirectories to recurse into. + + This macro may be called multiple times. + + +File: autoconf.info, Node: Default Prefix, Prev: Subdirectories, Up: Setup + +4.13 Default Prefix +=================== + +By default, `configure' sets the prefix for files it installs to +`/usr/local'. The user of `configure' can select a different prefix +using the `--prefix' and `--exec-prefix' options. There are two ways +to change the default: when creating `configure', and when running it. + + Some software packages might want to install in a directory other +than `/usr/local' by default. To accomplish that, use the +`AC_PREFIX_DEFAULT' macro. + + -- Macro: AC_PREFIX_DEFAULT (PREFIX) + Set the default installation prefix to PREFIX instead of + `/usr/local'. + + It may be convenient for users to have `configure' guess the +installation prefix from the location of a related program that they +have already installed. If you wish to do that, you can call +`AC_PREFIX_PROGRAM'. + + -- Macro: AC_PREFIX_PROGRAM (PROGRAM) + If the user did not specify an installation prefix (using the + `--prefix' option), guess a value for it by looking for PROGRAM in + `PATH', the way the shell does. If PROGRAM is found, set the + prefix to the parent of the directory containing PROGRAM, else + default the prefix as described above (`/usr/local' or + `AC_PREFIX_DEFAULT'). For example, if PROGRAM is `gcc' and the + `PATH' contains `/usr/local/gnu/bin/gcc', set the prefix to + `/usr/local/gnu'. + + +File: autoconf.info, Node: Existing Tests, Next: Writing Tests, Prev: Setup, Up: Top + +5 Existing Tests +**************** + +These macros test for particular system features that packages might +need or want to use. If you need to test for a kind of feature that +none of these macros check for, you can probably do it by calling +primitive test macros with appropriate arguments (*note Writing +Tests::). + + These tests print messages telling the user which feature they're +checking for, and what they find. They cache their results for future +`configure' runs (*note Caching Results::). + + Some of these macros set output variables. *Note Makefile +Substitutions::, for how to get their values. The phrase "define NAME" +is used below as a shorthand to mean "define the C preprocessor symbol +NAME to the value 1". *Note Defining Symbols::, for how to get those +symbol definitions into your program. + +* Menu: + +* Common Behavior:: Macros' standard schemes +* Alternative Programs:: Selecting between alternative programs +* Files:: Checking for the existence of files +* Libraries:: Library archives that might be missing +* Library Functions:: C library functions that might be missing +* Header Files:: Header files that might be missing +* Declarations:: Declarations that may be missing +* Structures:: Structures or members that might be missing +* Types:: Types that might be missing +* Compilers and Preprocessors:: Checking for compiling programs +* System Services:: Operating system services +* Posix Variants:: Special kludges for specific Posix variants +* Erlang Libraries:: Checking for the existence of Erlang libraries + + +File: autoconf.info, Node: Common Behavior, Next: Alternative Programs, Up: Existing Tests + +5.1 Common Behavior +=================== + +Much effort has been expended to make Autoconf easy to learn. The most +obvious way to reach this goal is simply to enforce standard interfaces +and behaviors, avoiding exceptions as much as possible. Because of +history and inertia, unfortunately, there are still too many exceptions +in Autoconf; nevertheless, this section describes some of the common +rules. + +* Menu: + +* Standard Symbols:: Symbols defined by the macros +* Default Includes:: Includes used by the generic macros + + +File: autoconf.info, Node: Standard Symbols, Next: Default Includes, Up: Common Behavior + +5.1.1 Standard Symbols +---------------------- + +All the generic macros that `AC_DEFINE' a symbol as a result of their +test transform their ARGUMENT values to a standard alphabet. First, +ARGUMENT is converted to upper case and any asterisks (`*') are each +converted to `P'. Any remaining characters that are not alphanumeric +are converted to underscores. + + For instance, + + AC_CHECK_TYPES([struct $Expensive*]) + +defines the symbol `HAVE_STRUCT__EXPENSIVEP' if the check succeeds. + + +File: autoconf.info, Node: Default Includes, Prev: Standard Symbols, Up: Common Behavior + +5.1.2 Default Includes +---------------------- + +Several tests depend upon a set of header files. Since these headers +are not universally available, tests actually have to provide a set of +protected includes, such as: + + #ifdef TIME_WITH_SYS_TIME + # include <sys/time.h> + # include <time.h> + #else + # ifdef HAVE_SYS_TIME_H + # include <sys/time.h> + # else + # include <time.h> + # endif + #endif + +Unless you know exactly what you are doing, you should avoid using +unconditional includes, and check the existence of the headers you +include beforehand (*note Header Files::). + + Most generic macros use the following macro to provide the default +set of includes: + + -- Macro: AC_INCLUDES_DEFAULT ([INCLUDE-DIRECTIVES]) + Expand to INCLUDE-DIRECTIVES if defined, otherwise to: + + #include <stdio.h> + #ifdef HAVE_SYS_TYPES_H + # include <sys/types.h> + #endif + #ifdef HAVE_SYS_STAT_H + # include <sys/stat.h> + #endif + #ifdef STDC_HEADERS + # include <stdlib.h> + # include <stddef.h> + #else + # ifdef HAVE_STDLIB_H + # include <stdlib.h> + # endif + #endif + #ifdef HAVE_STRING_H + # if !defined STDC_HEADERS && defined HAVE_MEMORY_H + # include <memory.h> + # endif + # include <string.h> + #endif + #ifdef HAVE_STRINGS_H + # include <strings.h> + #endif + #ifdef HAVE_INTTYPES_H + # include <inttypes.h> + #endif + #ifdef HAVE_STDINT_H + # include <stdint.h> + #endif + #ifdef HAVE_UNISTD_H + # include <unistd.h> + #endif + + If the default includes are used, then check for the presence of + these headers and their compatibility, i.e., you don't need to run + `AC_HEADER_STDC', nor check for `stdlib.h' etc. + + These headers are checked for in the same order as they are + included. For instance, on some systems `string.h' and + `strings.h' both exist, but conflict. Then `HAVE_STRING_H' is + defined, not `HAVE_STRINGS_H'. + + +File: autoconf.info, Node: Alternative Programs, Next: Files, Prev: Common Behavior, Up: Existing Tests + +5.2 Alternative Programs +======================== + +These macros check for the presence or behavior of particular programs. +They are used to choose between several alternative programs and to +decide what to do once one has been chosen. If there is no macro +specifically defined to check for a program you need, and you don't need +to check for any special properties of it, then you can use one of the +general program-check macros. + +* Menu: + +* Particular Programs:: Special handling to find certain programs +* Generic Programs:: How to find other programs + + +File: autoconf.info, Node: Particular Programs, Next: Generic Programs, Up: Alternative Programs + +5.2.1 Particular Program Checks +------------------------------- + +These macros check for particular programs--whether they exist, and in +some cases whether they support certain features. + + -- Macro: AC_PROG_AWK + Check for `gawk', `mawk', `nawk', and `awk', in that order, and + set output variable `AWK' to the first one that is found. It + tries `gawk' first because that is reported to be the best + implementation. The result can be overridden by setting the + variable `AWK' or the cache variable `ac_cv_prog_AWK'. + + Using this macro is sufficient to avoid the pitfalls of traditional + `awk' (*note Limitations of Usual Tools: awk.). + + -- Macro: AC_PROG_GREP + Look for the best available `grep' or `ggrep' that accepts the + longest input lines possible, and that supports multiple `-e' + options. Set the output variable `GREP' to whatever is chosen. + *Note Limitations of Usual Tools: grep, for more information about + portability problems with the `grep' command family. The result + can be overridden by setting the `GREP' variable and is cached in + the `ac_cv_path_GREP' variable. + + -- Macro: AC_PROG_EGREP + Check whether `$GREP -E' works, or else look for the best available + `egrep' or `gegrep' that accepts the longest input lines possible. + Set the output variable `EGREP' to whatever is chosen. The result + can be overridden by setting the `EGREP' variable and is cached in + the `ac_cv_path_EGREP' variable. + + -- Macro: AC_PROG_FGREP + Check whether `$GREP -F' works, or else look for the best available + `fgrep' or `gfgrep' that accepts the longest input lines possible. + Set the output variable `FGREP' to whatever is chosen. The result + can be overridden by setting the `FGREP' variable and is cached in + the `ac_cv_path_FGREP' variable. + + -- Macro: AC_PROG_INSTALL + Set output variable `INSTALL' to the name of a BSD-compatible + `install' program, if one is found in the current `PATH'. + Otherwise, set `INSTALL' to `DIR/install-sh -c', checking the + directories specified to `AC_CONFIG_AUX_DIR' (or its default + directories) to determine DIR (*note Output::). Also set the + variables `INSTALL_PROGRAM' and `INSTALL_SCRIPT' to `${INSTALL}' + and `INSTALL_DATA' to `${INSTALL} -m 644'. + + `@INSTALL@' is special, as its value may vary for different + configuration files. + + This macro screens out various instances of `install' known not to + work. It prefers to find a C program rather than a shell script, + for speed. Instead of `install-sh', it can also use `install.sh', + but that name is obsolete because some `make' programs have a rule + that creates `install' from it if there is no makefile. Further, + this macro requires `install' to be able to install multiple files + into a target directory in a single invocation. + + Autoconf comes with a copy of `install-sh' that you can use. If + you use `AC_PROG_INSTALL', you must include either `install-sh' or + `install.sh' in your distribution; otherwise `configure' produces + an error message saying it can't find them--even if the system + you're on has a good `install' program. This check is a safety + measure to prevent you from accidentally leaving that file out, + which would prevent your package from installing on systems that + don't have a BSD-compatible `install' program. + + If you need to use your own installation program because it has + features not found in standard `install' programs, there is no + reason to use `AC_PROG_INSTALL'; just put the file name of your + program into your `Makefile.in' files. + + The result of the test can be overridden by setting the variable + `INSTALL' or the cache variable `ac_cv_path_install'. + + -- Macro: AC_PROG_MKDIR_P + Set output variable `MKDIR_P' to a program that ensures that for + each argument, a directory named by this argument exists, creating + it and its parent directories if needed, and without race + conditions when two instances of the program attempt to make the + same directory at nearly the same time. + + This macro uses the `mkdir -p' command if possible. Otherwise, it + falls back on invoking `install-sh' with the `-d' option, so your + package should contain `install-sh' as described under + `AC_PROG_INSTALL'. An `install-sh' file that predates Autoconf + 2.60 or Automake 1.10 is vulnerable to race conditions, so if you + want to support parallel installs from different packages into the + same directory you need to make sure you have an up-to-date + `install-sh'. In particular, be careful about using `autoreconf + -if' if your Automake predates Automake 1.10. + + This macro is related to the `AS_MKDIR_P' macro (*note Programming + in M4sh::), but it sets an output variable intended for use in + other files, whereas `AS_MKDIR_P' is intended for use in scripts + like `configure'. Also, `AS_MKDIR_P' does not accept options, but + `MKDIR_P' supports the `-m' option, e.g., a makefile might invoke + `$(MKDIR_P) -m 0 dir' to create an inaccessible directory, and + conversely a makefile should use `$(MKDIR_P) -- $(FOO)' if FOO + might yield a value that begins with `-'. Finally, `AS_MKDIR_P' + does not check for race condition vulnerability, whereas + `AC_PROG_MKDIR_P' does. + + `@MKDIR_P@' is special, as its value may vary for different + configuration files. + + The result of the test can be overridden by setting the variable + `MKDIR_P' or the cache variable `ac_cv_path_mkdir'. + + -- Macro: AC_PROG_LEX + If `flex' is found, set output variable `LEX' to `flex' and + `LEXLIB' to `-lfl', if that library is in a standard place. + Otherwise set `LEX' to `lex' and `LEXLIB' to `-ll', if found. If + neither variant is available, set `LEX' to `:'; for packages that + ship the generated `file.yy.c' alongside the source `file.l', this + default allows users without a lexer generator to still build the + package even if the timestamp for `file.l' is inadvertently + changed. + + Define `YYTEXT_POINTER' if `yytext' defaults to `char *' instead + of to `char []'. Also set output variable `LEX_OUTPUT_ROOT' to + the base of the file name that the lexer generates; usually + `lex.yy', but sometimes something else. These results vary + according to whether `lex' or `flex' is being used. + + You are encouraged to use Flex in your sources, since it is both + more pleasant to use than plain Lex and the C source it produces + is portable. In order to ensure portability, however, you must + either provide a function `yywrap' or, if you don't use it (e.g., + your scanner has no `#include'-like feature), simply include a + `%noyywrap' statement in the scanner's source. Once this done, + the scanner is portable (unless _you_ felt free to use nonportable + constructs) and does not depend on any library. In this case, and + in this case only, it is suggested that you use this Autoconf + snippet: + + AC_PROG_LEX + if test "x$LEX" != xflex; then + LEX="$SHELL $missing_dir/missing flex" + AC_SUBST([LEX_OUTPUT_ROOT], [lex.yy]) + AC_SUBST([LEXLIB], ['']) + fi + + The shell script `missing' can be found in the Automake + distribution. + + Remember that the user may have supplied an alternate location in + `LEX', so if Flex is required, it is better to check that the user + provided something sufficient by parsing the output of `$LEX + --version' than by simply relying on `test "x$LEX" = xflex'. + + To ensure backward compatibility, Automake's `AM_PROG_LEX' invokes + (indirectly) this macro twice, which causes an annoying but benign + "`AC_PROG_LEX' invoked multiple times" warning. Future versions + of Automake will fix this issue; meanwhile, just ignore this + message. + + As part of running the test, this macro may delete any file in the + configuration directory named `lex.yy.c' or `lexyy.c'. + + The result of this test can be influenced by setting the variable + `LEX' or the cache variable `ac_cv_prog_LEX'. + + -- Macro: AC_PROG_LN_S + If `ln -s' works on the current file system (the operating system + and file system support symbolic links), set the output variable + `LN_S' to `ln -s'; otherwise, if `ln' works, set `LN_S' to `ln', + and otherwise set it to `cp -pR'. + + If you make a link in a directory other than the current + directory, its meaning depends on whether `ln' or `ln -s' is used. + To safely create links using `$(LN_S)', either find out which form + is used and adjust the arguments, or always invoke `ln' in the + directory where the link is to be created. + + In other words, it does not work to do: + $(LN_S) foo /x/bar + + Instead, do: + + (cd /x && $(LN_S) foo bar) + + -- Macro: AC_PROG_RANLIB + Set output variable `RANLIB' to `ranlib' if `ranlib' is found, and + otherwise to `:' (do nothing). + + -- Macro: AC_PROG_SED + Set output variable `SED' to a Sed implementation that conforms to + Posix and does not have arbitrary length limits. Report an error + if no acceptable Sed is found. *Note Limitations of Usual Tools: + sed, for more information about portability problems with Sed. + + The result of this test can be overridden by setting the `SED' + variable and is cached in the `ac_cv_path_SED' variable. + + -- Macro: AC_PROG_YACC + If `bison' is found, set output variable `YACC' to `bison -y'. + Otherwise, if `byacc' is found, set `YACC' to `byacc'. Otherwise + set `YACC' to `yacc'. The result of this test can be influenced + by setting the variable `YACC' or the cache variable + `ac_cv_prog_YACC'. + + +File: autoconf.info, Node: Generic Programs, Prev: Particular Programs, Up: Alternative Programs + +5.2.2 Generic Program and File Checks +------------------------------------- + +These macros are used to find programs not covered by the "particular" +test macros. If you need to check the behavior of a program as well as +find out whether it is present, you have to write your own test for it +(*note Writing Tests::). By default, these macros use the environment +variable `PATH'. If you need to check for a program that might not be +in the user's `PATH', you can pass a modified path to use instead, like +this: + + AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd], + [$PATH$PATH_SEPARATOR/usr/libexec$PATH_SEPARATOR]dnl + [/usr/sbin$PATH_SEPARATOR/usr/etc$PATH_SEPARATOR/etc]) + + You are strongly encouraged to declare the VARIABLE passed to +`AC_CHECK_PROG' etc. as precious. *Note Setting Output Variables::, +`AC_ARG_VAR', for more details. + + -- Macro: AC_CHECK_PROG (VARIABLE, PROG-TO-CHECK-FOR, VALUE-IF-FOUND, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH'], [REJECT]) + Check whether program PROG-TO-CHECK-FOR exists in PATH. If it is + found, set VARIABLE to VALUE-IF-FOUND, otherwise to + VALUE-IF-NOT-FOUND, if given. Always pass over REJECT (an + absolute file name) even if it is the first found in the search + path; in that case, set VARIABLE using the absolute file name of + the PROG-TO-CHECK-FOR found that is not REJECT. If VARIABLE was + already set, do nothing. Calls `AC_SUBST' for VARIABLE. The + result of this test can be overridden by setting the VARIABLE + variable or the cache variable `ac_cv_prog_VARIABLE'. + + -- Macro: AC_CHECK_PROGS (VARIABLE, PROGS-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Check for each program in the blank-separated list + PROGS-TO-CHECK-FOR existing in the PATH. If one is found, set + VARIABLE to the name of that program. Otherwise, continue + checking the next program in the list. If none of the programs in + the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if + VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not + changed. Calls `AC_SUBST' for VARIABLE. The result of this test + can be overridden by setting the VARIABLE variable or the cache + variable `ac_cv_prog_VARIABLE'. + + -- Macro: AC_CHECK_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a + prefix of the target type as determined by `AC_CANONICAL_TARGET', + followed by a dash (*note Canonicalizing::). If the tool cannot + be found with a prefix, and if the build and target types are + equal, then it is also searched for without a prefix. + + As noted in *note Specifying Target Triplets::, the target is + rarely specified, because most of the time it is the same as the + host: it is the type of system for which any compiler tool in the + package produces code. What this macro looks for is, for example, + _a tool (assembler, linker, etc.) that the compiler driver (`gcc' + for the GNU C Compiler) uses to produce objects, archives or + executables_. + + -- Macro: AC_CHECK_TOOL (VARIABLE, PROG-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_PROG', but first looks for PROG-TO-CHECK-FOR with a + prefix of the host type as specified by `--host', followed by a + dash. For example, if the user runs `configure --build=x86_64-gnu + --host=i386-gnu', then this call: + AC_CHECK_TOOL([RANLIB], [ranlib], [:]) + sets `RANLIB' to `i386-gnu-ranlib' if that program exists in PATH, + or otherwise to `ranlib' if that program exists in PATH, or to `:' + if neither program exists. + + When cross-compiling, this macro will issue a warning if no program + prefixed with the host type could be found. For more information, + see *note Specifying Target Triplets::. + + -- Macro: AC_CHECK_TARGET_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_TARGET_TOOL', each of the tools in the list + PROGS-TO-CHECK-FOR are checked with a prefix of the target type as + determined by `AC_CANONICAL_TARGET', followed by a dash (*note + Canonicalizing::). If none of the tools can be found with a + prefix, and if the build and target types are equal, then the + first one without a prefix is used. If a tool is found, set + VARIABLE to the name of that program. If none of the tools in the + list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if + VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not + changed. Calls `AC_SUBST' for VARIABLE. + + -- Macro: AC_CHECK_TOOLS (VARIABLE, PROGS-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_TOOL', each of the tools in the list + PROGS-TO-CHECK-FOR are checked with a prefix of the host type as + determined by `AC_CANONICAL_HOST', followed by a dash (*note + Canonicalizing::). If none of the tools can be found with a + prefix, then the first one without a prefix is used. If a tool is + found, set VARIABLE to the name of that program. If none of the + tools in the list are found, set VARIABLE to VALUE-IF-NOT-FOUND; if + VALUE-IF-NOT-FOUND is not specified, the value of VARIABLE is not + changed. Calls `AC_SUBST' for VARIABLE. + + When cross-compiling, this macro will issue a warning if no program + prefixed with the host type could be found. For more information, + see *note Specifying Target Triplets::. + + -- Macro: AC_PATH_PROG (VARIABLE, PROG-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_PROG', but set VARIABLE to the absolute name of + PROG-TO-CHECK-FOR if found. The result of this test can be + overridden by setting the VARIABLE variable. A positive result of + this test is cached in the `ac_cv_path_VARIABLE' variable. + + -- Macro: AC_PATH_PROGS (VARIABLE, PROGS-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_PROGS', but if any of PROGS-TO-CHECK-FOR are found, + set VARIABLE to the absolute name of the program found. The + result of this test can be overridden by setting the VARIABLE + variable. A positive result of this test is cached in the + `ac_cv_path_VARIABLE' variable. + + -- Macro: AC_PATH_PROGS_FEATURE_CHECK (VARIABLE, PROGS-TO-CHECK-FOR, + FEATURE-TEST, [ACTION-IF-NOT-FOUND], [PATH = `$PATH']) + This macro was introduced in Autoconf 2.62. If VARIABLE is not + empty, then set the cache variable `ac_cv_path_VARIABLE' to its + value. Otherwise, check for each program in the blank-separated + list PROGS-TO-CHECK-FOR existing in PATH. For each program found, + execute FEATURE-TEST with `ac_path_VARIABLE' set to the absolute + name of the candidate program. If no invocation of FEATURE-TEST + sets the shell variable `ac_cv_path_VARIABLE', then + ACTION-IF-NOT-FOUND is executed. FEATURE-TEST will be run even + when `ac_cv_path_VARIABLE' is set, to provide the ability to + choose a better candidate found later in PATH; to accept the + current setting and bypass all further checks, FEATURE-TEST can + execute `ac_path_VARIABLE_found=:'. + + Note that this macro has some subtle differences from + `AC_CHECK_PROGS'. It is designed to be run inside `AC_CACHE_VAL', + therefore, it should have no side effects. In particular, + VARIABLE is not set to the final value of `ac_cv_path_VARIABLE', + nor is `AC_SUBST' automatically run. Also, on failure, any action + can be performed, whereas `AC_CHECK_PROGS' only performs + `VARIABLE=VALUE-IF-NOT-FOUND'. + + Here is an example, similar to what Autoconf uses in its own + configure script. It will search for an implementation of `m4' + that supports the `indir' builtin, even if it goes by the name + `gm4' or is not the first implementation on `PATH'. + + AC_CACHE_CHECK([for m4 that supports indir], [ac_cv_path_M4], + [AC_PATH_PROGS_FEATURE_CHECK([M4], [m4 gm4], + [[m4out=`echo 'changequote([,])indir([divnum])' | $ac_path_M4` + test "x$m4out" = x0 \ + && ac_cv_path_M4=$ac_path_M4 ac_path_M4_found=:]], + [AC_MSG_ERROR([could not find m4 that supports indir])])]) + AC_SUBST([M4], [$ac_cv_path_M4]) + + -- Macro: AC_PATH_TARGET_TOOL (VARIABLE, PROG-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_TARGET_TOOL', but set VARIABLE to the absolute name + of the program if it is found. + + -- Macro: AC_PATH_TOOL (VARIABLE, PROG-TO-CHECK-FOR, + [VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Like `AC_CHECK_TOOL', but set VARIABLE to the absolute name of the + program if it is found. + + When cross-compiling, this macro will issue a warning if no program + prefixed with the host type could be found. For more information, + see *note Specifying Target Triplets::. + + +File: autoconf.info, Node: Files, Next: Libraries, Prev: Alternative Programs, Up: Existing Tests + +5.3 Files +========= + +You might also need to check for the existence of files. Before using +these macros, ask yourself whether a runtime test might not be a better +solution. Be aware that, like most Autoconf macros, they test a feature +of the host machine, and therefore, they die when cross-compiling. + + -- Macro: AC_CHECK_FILE (FILE, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + Check whether file FILE exists on the native system. If it is + found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, + if given. The result of this test is cached in the + `ac_cv_file_FILE' variable, with characters not suitable for a + variable name mapped to underscores. + + -- Macro: AC_CHECK_FILES (FILES, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + Executes `AC_CHECK_FILE' once for each file listed in FILES. + Additionally, defines `HAVE_FILE' (*note Standard Symbols::) for + each file found. The results of each test are cached in the + `ac_cv_file_FILE' variable, with characters not suitable for a + variable name mapped to underscores. + + +File: autoconf.info, Node: Libraries, Next: Library Functions, Prev: Files, Up: Existing Tests + +5.4 Library Files +================= + +The following macros check for the presence of certain C, C++, Fortran, +or Go library archive files. + + -- Macro: AC_CHECK_LIB (LIBRARY, FUNCTION, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES]) + Test whether the library LIBRARY is available by trying to link a + test program that calls function FUNCTION with the library. + FUNCTION should be a function provided by the library. Use the + base name of the library; e.g., to check for `-lmp', use `mp' as + the LIBRARY argument. + + ACTION-IF-FOUND is a list of shell commands to run if the link + with the library succeeds; ACTION-IF-NOT-FOUND is a list of shell + commands to run if the link fails. If ACTION-IF-FOUND is not + specified, the default action prepends `-lLIBRARY' to `LIBS' and + defines `HAVE_LIBLIBRARY' (in all capitals). This macro is + intended to support building `LIBS' in a right-to-left + (least-dependent to most-dependent) fashion such that library + dependencies are satisfied as a natural side effect of consecutive + tests. Linkers are sensitive to library ordering so the order in + which `LIBS' is generated is important to reliable detection of + libraries. + + If linking with LIBRARY results in unresolved symbols that would + be resolved by linking with additional libraries, give those + libraries as the OTHER-LIBRARIES argument, separated by spaces: + e.g., `-lXt -lX11'. Otherwise, this macro may fail to detect that + LIBRARY is present, because linking the test program can fail with + unresolved symbols. The OTHER-LIBRARIES argument should be + limited to cases where it is desirable to test for one library in + the presence of another that is not already in `LIBS'. + + `AC_CHECK_LIB' requires some care in usage, and should be avoided + in some common cases. Many standard functions like `gethostbyname' + appear in the standard C library on some hosts, and in special + libraries like `nsl' on other hosts. On some hosts the special + libraries contain variant implementations that you may not want to + use. These days it is normally better to use + `AC_SEARCH_LIBS([gethostbyname], [nsl])' instead of + `AC_CHECK_LIB([nsl], [gethostbyname])'. + + The result of this test is cached in the + `ac_cv_lib_LIBRARY_FUNCTION' variable. + + -- Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES]) + Search for a library defining FUNCTION if it's not already + available. This equates to calling + `AC_LINK_IFELSE([AC_LANG_CALL([], [FUNCTION])])' first with no + libraries, then for each library listed in SEARCH-LIBS. + + Prepend `-lLIBRARY' to `LIBS' for the first library found to + contain FUNCTION, and run ACTION-IF-FOUND. If the function is not + found, run ACTION-IF-NOT-FOUND. + + If linking with LIBRARY results in unresolved symbols that would + be resolved by linking with additional libraries, give those + libraries as the OTHER-LIBRARIES argument, separated by spaces: + e.g., `-lXt -lX11'. Otherwise, this macro fails to detect that + FUNCTION is present, because linking the test program always fails + with unresolved symbols. + + The result of this test is cached in the `ac_cv_search_FUNCTION' + variable as `none required' if FUNCTION is already available, as + `no' if no library containing FUNCTION was found, otherwise as the + `-lLIBRARY' option that needs to be prepended to `LIBS'. + + +File: autoconf.info, Node: Library Functions, Next: Header Files, Prev: Libraries, Up: Existing Tests + +5.5 Library Functions +===================== + +The following macros check for particular C library functions. If +there is no macro specifically defined to check for a function you need, +and you don't need to check for any special properties of it, then you +can use one of the general function-check macros. + +* Menu: + +* Function Portability:: Pitfalls with usual functions +* Particular Functions:: Special handling to find certain functions +* Generic Functions:: How to find other functions + + +File: autoconf.info, Node: Function Portability, Next: Particular Functions, Up: Library Functions + +5.5.1 Portability of C Functions +-------------------------------- + +Most usual functions can either be missing, or be buggy, or be limited +on some architectures. This section tries to make an inventory of these +portability issues. By definition, this list always requires +additions. A much more complete list is maintained by the Gnulib +project (*note Gnulib::), covering *note Current Posix Functions: +(gnulib)Function Substitutes, *note Legacy Functions: (gnulib)Legacy +Function Substitutes, and *note Glibc Functions: (gnulib)Glibc Function +Substitutes. Please help us keep the gnulib list as complete as +possible. + +`exit' + On ancient hosts, `exit' returned `int'. This is because `exit' + predates `void', and there was a long tradition of it returning + `int'. + + On current hosts, the problem more likely is that `exit' is not + declared, due to C++ problems of some sort or another. For this + reason we suggest that test programs not invoke `exit', but return + from `main' instead. + +`free' + The C standard says a call `free (NULL)' does nothing, but some + old systems don't support this (e.g., NextStep). + +`isinf' +`isnan' + The C99 standard says that `isinf' and `isnan' are macros. On + some systems just macros are available (e.g., HP-UX and Solaris + 10), on some systems both macros and functions (e.g., glibc + 2.3.2), and on some systems only functions (e.g., IRIX 6 and + Solaris 9). In some cases these functions are declared in + nonstandard headers like `<sunmath.h>' and defined in non-default + libraries like `-lm' or `-lsunmath'. + + The C99 `isinf' and `isnan' macros work correctly with `long + double' arguments, but pre-C99 systems that use functions + typically assume `double' arguments. On such a system, `isinf' + incorrectly returns true for a finite `long double' argument that + is outside the range of `double'. + + The best workaround for these issues is to use gnulib modules + `isinf' and `isnan' (*note Gnulib::). But a lighter weight + solution involves code like the following. + + #include <math.h> + + #ifndef isnan + # define isnan(x) \ + (sizeof (x) == sizeof (long double) ? isnan_ld (x) \ + : sizeof (x) == sizeof (double) ? isnan_d (x) \ + : isnan_f (x)) + static inline int isnan_f (float x) { return x != x; } + static inline int isnan_d (double x) { return x != x; } + static inline int isnan_ld (long double x) { return x != x; } + #endif + + #ifndef isinf + # define isinf(x) \ + (sizeof (x) == sizeof (long double) ? isinf_ld (x) \ + : sizeof (x) == sizeof (double) ? isinf_d (x) \ + : isinf_f (x)) + static inline int isinf_f (float x) + { return !isnan (x) && isnan (x - x); } + static inline int isinf_d (double x) + { return !isnan (x) && isnan (x - x); } + static inline int isinf_ld (long double x) + { return !isnan (x) && isnan (x - x); } + #endif + + Use `AC_C_INLINE' (*note C Compiler::) so that this code works on + compilers that lack the `inline' keyword. Some optimizing + compilers mishandle these definitions, but systems with that bug + typically have many other floating point corner-case compliance + problems anyway, so it's probably not worth worrying about. + +`malloc' + The C standard says a call `malloc (0)' is implementation + dependent. It can return either `NULL' or a new non-null pointer. + The latter is more common (e.g., the GNU C Library) but is by no + means universal. `AC_FUNC_MALLOC' can be used to insist on + non-`NULL' (*note Particular Functions::). + +`putenv' + Posix prefers `setenv' to `putenv'; among other things, `putenv' + is not required of all Posix implementations, but `setenv' is. + + Posix specifies that `putenv' puts the given string directly in + `environ', but some systems make a copy of it instead (e.g., glibc + 2.0, or BSD). And when a copy is made, `unsetenv' might not free + it, causing a memory leak (e.g., FreeBSD 4). + + On some systems `putenv ("FOO")' removes `FOO' from the + environment, but this is not standard usage and it dumps core on + some systems (e.g., AIX). + + On MinGW, a call `putenv ("FOO=")' removes `FOO' from the + environment, rather than inserting it with an empty value. + +`realloc' + The C standard says a call `realloc (NULL, size)' is equivalent to + `malloc (size)', but some old systems don't support this (e.g., + NextStep). + +`signal' handler + Normally `signal' takes a handler function with a return type of + `void', but some old systems required `int' instead. Any actual + `int' value returned is not used; this is only a difference in the + function prototype demanded. + + All systems we know of in current use return `void'. The `int' + was to support K&R C, where of course `void' is not available. + The obsolete macro `AC_TYPE_SIGNAL' (*note AC_TYPE_SIGNAL::) can + be used to establish the correct type in all cases. + + In most cases, it is more robust to use `sigaction' when it is + available, rather than `signal'. + +`snprintf' + The C99 standard says that if the output array isn't big enough + and if no other errors occur, `snprintf' and `vsnprintf' truncate + the output and return the number of bytes that ought to have been + produced. Some older systems return the truncated length (e.g., + GNU C Library 2.0.x or IRIX 6.5), some a negative value (e.g., + earlier GNU C Library versions), and some the buffer length + without truncation (e.g., 32-bit Solaris 7). Also, some buggy + older systems ignore the length and overrun the buffer (e.g., + 64-bit Solaris 7). + +`sprintf' + The C standard says `sprintf' and `vsprintf' return the number of + bytes written. On some ancient systems (SunOS 4 for instance) + they return the buffer pointer instead, but these no longer need + to be worried about. + +`sscanf' + On various old systems, e.g., HP-UX 9, `sscanf' requires that its + input string be writable (though it doesn't actually change it). + This can be a problem when using `gcc' since it normally puts + constant strings in read-only memory (*note Incompatibilities of + GCC: (gcc)Incompatibilities.). Apparently in some cases even + having format strings read-only can be a problem. + +`strerror_r' + Posix specifies that `strerror_r' returns an `int', but many + systems (e.g., GNU C Library version 2.2.4) provide a different + version returning a `char *'. `AC_FUNC_STRERROR_R' can detect + which is in use (*note Particular Functions::). + +`strnlen' + AIX 4.3 provides a broken version which produces the following + results: + + strnlen ("foobar", 0) = 0 + strnlen ("foobar", 1) = 3 + strnlen ("foobar", 2) = 2 + strnlen ("foobar", 3) = 1 + strnlen ("foobar", 4) = 0 + strnlen ("foobar", 5) = 6 + strnlen ("foobar", 6) = 6 + strnlen ("foobar", 7) = 6 + strnlen ("foobar", 8) = 6 + strnlen ("foobar", 9) = 6 + +`sysconf' + `_SC_PAGESIZE' is standard, but some older systems (e.g., HP-UX 9) + have `_SC_PAGE_SIZE' instead. This can be tested with `#ifdef'. + +`unlink' + The Posix spec says that `unlink' causes the given file to be + removed only after there are no more open file handles for it. + Some non-Posix hosts have trouble with this requirement, though, + and some DOS variants even corrupt the file system. + +`unsetenv' + On MinGW, `unsetenv' is not available, but a variable `FOO' can be + removed with a call `putenv ("FOO=")', as described under `putenv' + above. + +`va_copy' + The C99 standard provides `va_copy' for copying `va_list' + variables. It may be available in older environments too, though + possibly as `__va_copy' (e.g., `gcc' in strict pre-C99 mode). + These can be tested with `#ifdef'. A fallback to `memcpy (&dst, + &src, sizeof (va_list))' gives maximum portability. + +`va_list' + `va_list' is not necessarily just a pointer. It can be a `struct' + (e.g., `gcc' on Alpha), which means `NULL' is not portable. Or it + can be an array (e.g., `gcc' in some PowerPC configurations), + which means as a function parameter it can be effectively + call-by-reference and library routines might modify the value back + in the caller (e.g., `vsnprintf' in the GNU C Library 2.1). + +Signed `>>' + Normally the C `>>' right shift of a signed type replicates the + high bit, giving a so-called "arithmetic" shift. But care should + be taken since Standard C doesn't require that behavior. On those + few processors without a native arithmetic shift (for instance Cray + vector systems) zero bits may be shifted in, the same as a shift + of an unsigned type. + +Integer `/' + C divides signed integers by truncating their quotient toward zero, + yielding the same result as Fortran. However, before C99 the + standard allowed C implementations to take the floor or ceiling of + the quotient in some cases. Hardly any implementations took + advantage of this freedom, though, and it's probably not worth + worrying about this issue nowadays. + + +File: autoconf.info, Node: Particular Functions, Next: Generic Functions, Prev: Function Portability, Up: Library Functions + +5.5.2 Particular Function Checks +-------------------------------- + +These macros check for particular C functions--whether they exist, and +in some cases how they respond when given certain arguments. + + -- Macro: AC_FUNC_ALLOCA + Check how to get `alloca'. Tries to get a builtin version by + checking for `alloca.h' or the predefined C preprocessor macros + `__GNUC__' and `_AIX'. If this macro finds `alloca.h', it defines + `HAVE_ALLOCA_H'. + + If those attempts fail, it looks for the function in the standard C + library. If any of those methods succeed, it defines + `HAVE_ALLOCA'. Otherwise, it sets the output variable `ALLOCA' to + `${LIBOBJDIR}alloca.o' and defines `C_ALLOCA' (so programs can + periodically call `alloca (0)' to garbage collect). This variable + is separate from `LIBOBJS' so multiple programs can share the + value of `ALLOCA' without needing to create an actual library, in + case only some of them use the code in `LIBOBJS'. The + `${LIBOBJDIR}' prefix serves the same purpose as in `LIBOBJS' + (*note AC_LIBOBJ vs LIBOBJS::). + + This macro does not try to get `alloca' from the System V R3 + `libPW' or the System V R4 `libucb' because those libraries + contain some incompatible functions that cause trouble. Some + versions do not even contain `alloca' or contain a buggy version. + If you still want to use their `alloca', use `ar' to extract + `alloca.o' from them instead of compiling `alloca.c'. + + Source files that use `alloca' should start with a piece of code + like the following, to declare it properly. + + #ifdef STDC_HEADERS + # include <stdlib.h> + # include <stddef.h> + #else + # ifdef HAVE_STDLIB_H + # include <stdlib.h> + # endif + #endif + #ifdef HAVE_ALLOCA_H + # include <alloca.h> + #elif !defined alloca + # ifdef __GNUC__ + # define alloca __builtin_alloca + # elif defined _AIX + # define alloca __alloca + # elif defined _MSC_VER + # include <malloc.h> + # define alloca _alloca + # elif !defined HAVE_ALLOCA + # ifdef __cplusplus + extern "C" + # endif + void *alloca (size_t); + # endif + #endif + + -- Macro: AC_FUNC_CHOWN + If the `chown' function is available and works (in particular, it + should accept `-1' for `uid' and `gid'), define `HAVE_CHOWN'. The + result of this macro is cached in the `ac_cv_func_chown_works' + variable. + + -- Macro: AC_FUNC_CLOSEDIR_VOID + If the `closedir' function does not return a meaningful value, + define `CLOSEDIR_VOID'. Otherwise, callers ought to check its + return value for an error indicator. + + Currently this test is implemented by running a test program. When + cross compiling the pessimistic assumption that `closedir' does not + return a meaningful value is made. + + The result of this macro is cached in the + `ac_cv_func_closedir_void' variable. + + This macro is obsolescent, as `closedir' returns a meaningful value + on current systems. New programs need not use this macro. + + -- Macro: AC_FUNC_ERROR_AT_LINE + If the `error_at_line' function is not found, require an + `AC_LIBOBJ' replacement of `error'. + + The result of this macro is cached in the `ac_cv_lib_error_at_line' + variable. + + The `AC_FUNC_ERROR_AT_LINE' macro is obsolescent. New programs + should use Gnulib's `error' module. *Note Gnulib::. + + -- Macro: AC_FUNC_FNMATCH + If the `fnmatch' function conforms to Posix, define + `HAVE_FNMATCH'. Detect common implementation bugs, for example, + the bugs in Solaris 2.4. + + Unlike the other specific `AC_FUNC' macros, `AC_FUNC_FNMATCH' does + not replace a broken/missing `fnmatch'. This is for historical + reasons. See `AC_REPLACE_FNMATCH' below. + + The result of this macro is cached in the + `ac_cv_func_fnmatch_works' variable. + + This macro is obsolescent. New programs should use Gnulib's + `fnmatch-posix' module. *Note Gnulib::. + + -- Macro: AC_FUNC_FNMATCH_GNU + Behave like `AC_REPLACE_FNMATCH' (_replace_) but also test whether + `fnmatch' supports GNU extensions. Detect common implementation + bugs, for example, the bugs in the GNU C Library 2.1. + + The result of this macro is cached in the `ac_cv_func_fnmatch_gnu' + variable. + + This macro is obsolescent. New programs should use Gnulib's + `fnmatch-gnu' module. *Note Gnulib::. + + -- Macro: AC_FUNC_FORK + This macro checks for the `fork' and `vfork' functions. If a + working `fork' is found, define `HAVE_WORKING_FORK'. This macro + checks whether `fork' is just a stub by trying to run it. + + If `vfork.h' is found, define `HAVE_VFORK_H'. If a working + `vfork' is found, define `HAVE_WORKING_VFORK'. Otherwise, define + `vfork' to be `fork' for backward compatibility with previous + versions of `autoconf'. This macro checks for several known + errors in implementations of `vfork' and considers the system to + not have a working `vfork' if it detects any of them. It is not + considered to be an implementation error if a child's invocation + of `signal' modifies the parent's signal handler, since child + processes rarely change their signal handlers. + + Since this macro defines `vfork' only for backward compatibility + with previous versions of `autoconf' you're encouraged to define it + yourself in new code: + #ifndef HAVE_WORKING_VFORK + # define vfork fork + #endif + + The results of this macro are cached in the `ac_cv_func_fork_works' + and `ac_cv_func_vfork_works' variables. In order to override the + test, you also need to set the `ac_cv_func_fork' and + `ac_cv_func_vfork' variables. + + -- Macro: AC_FUNC_FSEEKO + If the `fseeko' function is available, define `HAVE_FSEEKO'. + Define `_LARGEFILE_SOURCE' if necessary to make the prototype + visible on some systems (e.g., glibc 2.2). Otherwise linkage + problems may occur when compiling with `AC_SYS_LARGEFILE' on + largefile-sensitive systems where `off_t' does not default to a + 64bit entity. All systems with `fseeko' also supply `ftello'. + + -- Macro: AC_FUNC_GETGROUPS + If the `getgroups' function is available and works (unlike on + Ultrix 4.3, where `getgroups (0, 0)' always fails), define + `HAVE_GETGROUPS'. Set `GETGROUPS_LIBS' to any libraries needed to + get that function. This macro runs `AC_TYPE_GETGROUPS'. + + -- Macro: AC_FUNC_GETLOADAVG + Check how to get the system load averages. To perform its tests + properly, this macro needs the file `getloadavg.c'; therefore, be + sure to set the `AC_LIBOBJ' replacement directory properly (see + *note Generic Functions::, `AC_CONFIG_LIBOBJ_DIR'). + + If the system has the `getloadavg' function, define + `HAVE_GETLOADAVG', and set `GETLOADAVG_LIBS' to any libraries + necessary to get that function. Also add `GETLOADAVG_LIBS' to + `LIBS'. Otherwise, require an `AC_LIBOBJ' replacement for + `getloadavg' with source code in `DIR/getloadavg.c', and possibly + define several other C preprocessor macros and output variables: + + 1. Define `C_GETLOADAVG'. + + 2. Define `SVR4', `DGUX', `UMAX', or `UMAX4_3' if on those + systems. + + 3. If `nlist.h' is found, define `HAVE_NLIST_H'. + + 4. If `struct nlist' has an `n_un.n_name' member, define + `HAVE_STRUCT_NLIST_N_UN_N_NAME'. The obsolete symbol + `NLIST_NAME_UNION' is still defined, but do not depend upon + it. + + 5. Programs may need to be installed set-group-ID (or + set-user-ID) for `getloadavg' to work. In this case, define + `GETLOADAVG_PRIVILEGED', set the output variable `NEED_SETGID' + to `true' (and otherwise to `false'), and set `KMEM_GROUP' to + the name of the group that should own the installed program. + + The `AC_FUNC_GETLOADAVG' macro is obsolescent. New programs should + use Gnulib's `getloadavg' module. *Note Gnulib::. + + -- Macro: AC_FUNC_GETMNTENT + Check for `getmntent' in the standard C library, and then in the + `sun', `seq', and `gen' libraries, for UNICOS, IRIX 4, PTX, and + UnixWare, respectively. Then, if `getmntent' is available, define + `HAVE_GETMNTENT' and set `ac_cv_func_getmntent' to `yes'. + Otherwise set `ac_cv_func_getmntent' to `no'. + + The result of this macro can be overridden by setting the cache + variable `ac_cv_search_getmntent'. + + -- Macro: AC_FUNC_GETPGRP + Define `GETPGRP_VOID' if it is an error to pass 0 to `getpgrp'; + this is the Posix behavior. On older BSD systems, you must pass 0 + to `getpgrp', as it takes an argument and behaves like Posix's + `getpgid'. + + #ifdef GETPGRP_VOID + pid = getpgrp (); + #else + pid = getpgrp (0); + #endif + + This macro does not check whether `getpgrp' exists at all; if you + need to work in that situation, first call `AC_CHECK_FUNC' for + `getpgrp'. + + The result of this macro is cached in the `ac_cv_func_getpgrp_void' + variable. + + This macro is obsolescent, as current systems have a `getpgrp' + whose signature conforms to Posix. New programs need not use this + macro. + + -- Macro: AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK + If `link' is a symbolic link, then `lstat' should treat `link/' + the same as `link/.'. However, many older `lstat' implementations + incorrectly ignore trailing slashes. + + It is safe to assume that if `lstat' incorrectly ignores trailing + slashes, then other symbolic-link-aware functions like `unlink' + also incorrectly ignore trailing slashes. + + If `lstat' behaves properly, define + `LSTAT_FOLLOWS_SLASHED_SYMLINK', otherwise require an `AC_LIBOBJ' + replacement of `lstat'. + + The result of this macro is cached in the + `ac_cv_func_lstat_dereferences_slashed_symlink' variable. + + The `AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK' macro is obsolescent. + New programs should use Gnulib's `lstat' module. *Note Gnulib::. + + -- Macro: AC_FUNC_MALLOC + If the `malloc' function is compatible with the GNU C library + `malloc' (i.e., `malloc (0)' returns a valid pointer), define + `HAVE_MALLOC' to 1. Otherwise define `HAVE_MALLOC' to 0, ask for + an `AC_LIBOBJ' replacement for `malloc', and define `malloc' to + `rpl_malloc' so that the native `malloc' is not used in the main + project. + + Typically, the replacement file `malloc.c' should look like (note + the `#undef malloc'): + + #include <config.h> + #undef malloc + + #include <sys/types.h> + + void *malloc (); + + /* Allocate an N-byte block of memory from the heap. + If N is zero, allocate a 1-byte block. */ + + void * + rpl_malloc (size_t n) + { + if (n == 0) + n = 1; + return malloc (n); + } + + The result of this macro is cached in the + `ac_cv_func_malloc_0_nonnull' variable. + + -- Macro: AC_FUNC_MBRTOWC + Define `HAVE_MBRTOWC' to 1 if the function `mbrtowc' and the type + `mbstate_t' are properly declared. + + The result of this macro is cached in the `ac_cv_func_mbrtowc' + variable. + + -- Macro: AC_FUNC_MEMCMP + If the `memcmp' function is not available, or does not work on + 8-bit data (like the one on SunOS 4.1.3), or fails when comparing + 16 bytes or more and with at least one buffer not starting on a + 4-byte boundary (such as the one on NeXT x86 OpenStep), require an + `AC_LIBOBJ' replacement for `memcmp'. + + The result of this macro is cached in the + `ac_cv_func_memcmp_working' variable. + + This macro is obsolescent, as current systems have a working + `memcmp'. New programs need not use this macro. + + -- Macro: AC_FUNC_MKTIME + If the `mktime' function is not available, or does not work + correctly, require an `AC_LIBOBJ' replacement for `mktime'. For + the purposes of this test, `mktime' should conform to the Posix + standard and should be the inverse of `localtime'. + + The result of this macro is cached in the + `ac_cv_func_working_mktime' variable. + + The `AC_FUNC_MKTIME' macro is obsolescent. New programs should + use Gnulib's `mktime' module. *Note Gnulib::. + + -- Macro: AC_FUNC_MMAP + If the `mmap' function exists and works correctly, define + `HAVE_MMAP'. This checks only private fixed mapping of + already-mapped memory. + + The result of this macro is cached in the + `ac_cv_func_mmap_fixed_mapped' variable. + + -- Macro: AC_FUNC_OBSTACK + If the obstacks are found, define `HAVE_OBSTACK', else require an + `AC_LIBOBJ' replacement for `obstack'. + + The result of this macro is cached in the `ac_cv_func_obstack' + variable. + + -- Macro: AC_FUNC_REALLOC + If the `realloc' function is compatible with the GNU C library + `realloc' (i.e., `realloc (NULL, 0)' returns a valid pointer), + define `HAVE_REALLOC' to 1. Otherwise define `HAVE_REALLOC' to 0, + ask for an `AC_LIBOBJ' replacement for `realloc', and define + `realloc' to `rpl_realloc' so that the native `realloc' is not + used in the main project. See `AC_FUNC_MALLOC' for details. + + The result of this macro is cached in the + `ac_cv_func_realloc_0_nonnull' variable. + + -- Macro: AC_FUNC_SELECT_ARGTYPES + Determines the correct type to be passed for each of the `select' + function's arguments, and defines those types in + `SELECT_TYPE_ARG1', `SELECT_TYPE_ARG234', and `SELECT_TYPE_ARG5' + respectively. `SELECT_TYPE_ARG1' defaults to `int', + `SELECT_TYPE_ARG234' defaults to `int *', and `SELECT_TYPE_ARG5' + defaults to `struct timeval *'. + + This macro is obsolescent, as current systems have a `select' whose + signature conforms to Posix. New programs need not use this macro. + + -- Macro: AC_FUNC_SETPGRP + If `setpgrp' takes no argument (the Posix version), define + `SETPGRP_VOID'. Otherwise, it is the BSD version, which takes two + process IDs as arguments. This macro does not check whether + `setpgrp' exists at all; if you need to work in that situation, + first call `AC_CHECK_FUNC' for `setpgrp'. + + The result of this macro is cached in the `ac_cv_func_setpgrp_void' + variable. + + This macro is obsolescent, as current systems have a `setpgrp' + whose signature conforms to Posix. New programs need not use this + macro. + + -- Macro: AC_FUNC_STAT + -- Macro: AC_FUNC_LSTAT + Determine whether `stat' or `lstat' have the bug that it succeeds + when given the zero-length file name as argument. The `stat' and + `lstat' from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do this. + + If it does, then define `HAVE_STAT_EMPTY_STRING_BUG' (or + `HAVE_LSTAT_EMPTY_STRING_BUG') and ask for an `AC_LIBOBJ' + replacement of it. + + The results of these macros are cached in the + `ac_cv_func_stat_empty_string_bug' and the + `ac_cv_func_lstat_empty_string_bug' variables, respectively. + + These macros are obsolescent, as no current systems have the bug. + New programs need not use these macros. + + -- Macro: AC_FUNC_STRCOLL + If the `strcoll' function exists and works correctly, define + `HAVE_STRCOLL'. This does a bit more than + `AC_CHECK_FUNCS(strcoll)', because some systems have incorrect + definitions of `strcoll' that should not be used. + + The result of this macro is cached in the + `ac_cv_func_strcoll_works' variable. + + -- Macro: AC_FUNC_STRERROR_R + If `strerror_r' is available, define `HAVE_STRERROR_R', and if it + is declared, define `HAVE_DECL_STRERROR_R'. If it returns a `char + *' message, define `STRERROR_R_CHAR_P'; otherwise it returns an + `int' error number. The Thread-Safe Functions option of Posix + requires `strerror_r' to return `int', but many systems + (including, for example, version 2.2.4 of the GNU C Library) + return a `char *' value that is not necessarily equal to the + buffer argument. + + The result of this macro is cached in the + `ac_cv_func_strerror_r_char_p' variable. + + -- Macro: AC_FUNC_STRFTIME + Check for `strftime' in the `intl' library, for SCO Unix. Then, + if `strftime' is available, define `HAVE_STRFTIME'. + + This macro is obsolescent, as no current systems require the `intl' + library for `strftime'. New programs need not use this macro. + + -- Macro: AC_FUNC_STRTOD + If the `strtod' function does not exist or doesn't work correctly, + ask for an `AC_LIBOBJ' replacement of `strtod'. In this case, + because `strtod.c' is likely to need `pow', set the output + variable `POW_LIB' to the extra library needed. + + This macro caches its result in the `ac_cv_func_strtod' variable + and depends upon the result in the `ac_cv_func_pow' variable. + + The `AC_FUNC_STRTOD' macro is obsolescent. New programs should + use Gnulib's `strtod' module. *Note Gnulib::. + + -- Macro: AC_FUNC_STRTOLD + If the `strtold' function exists and conforms to C99, define + `HAVE_STRTOLD'. + + This macro caches its result in the `ac_cv_func_strtold' variable. + + -- Macro: AC_FUNC_STRNLEN + If the `strnlen' function is not available, or is buggy (like the + one from AIX 4.3), require an `AC_LIBOBJ' replacement for it. + + This macro caches its result in the `ac_cv_func_strnlen_working' + variable. + + -- Macro: AC_FUNC_UTIME_NULL + If `utime (FILE, NULL)' sets FILE's timestamp to the present, + define `HAVE_UTIME_NULL'. + + This macro caches its result in the `ac_cv_func_utime_null' + variable. + + This macro is obsolescent, as all current systems have a `utime' + that behaves this way. New programs need not use this macro. + + -- Macro: AC_FUNC_VPRINTF + If `vprintf' is found, define `HAVE_VPRINTF'. Otherwise, if + `_doprnt' is found, define `HAVE_DOPRNT'. (If `vprintf' is + available, you may assume that `vfprintf' and `vsprintf' are also + available.) + + This macro is obsolescent, as all current systems have `vprintf'. + New programs need not use this macro. + + -- Macro: AC_REPLACE_FNMATCH + If the `fnmatch' function does not conform to Posix (see + `AC_FUNC_FNMATCH'), ask for its `AC_LIBOBJ' replacement. + + The files `fnmatch.c', `fnmatch_loop.c', and `fnmatch_.h' in the + `AC_LIBOBJ' replacement directory are assumed to contain a copy of + the source code of GNU `fnmatch'. If necessary, this source code + is compiled as an `AC_LIBOBJ' replacement, and the `fnmatch_.h' + file is linked to `fnmatch.h' so that it can be included in place + of the system `<fnmatch.h>'. + + This macro caches its result in the `ac_cv_func_fnmatch_works' + variable. + + This macro is obsolescent, as it assumes the use of particular + source files. New programs should use Gnulib's `fnmatch-posix' + module, which provides this macro along with the source files. + *Note Gnulib::. + + +File: autoconf.info, Node: Generic Functions, Prev: Particular Functions, Up: Library Functions + +5.5.3 Generic Function Checks +----------------------------- + +These macros are used to find functions not covered by the "particular" +test macros. If the functions might be in libraries other than the +default C library, first call `AC_CHECK_LIB' for those libraries. If +you need to check the behavior of a function as well as find out +whether it is present, you have to write your own test for it (*note +Writing Tests::). + + -- Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + If C function FUNCTION is available, run shell commands + ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND. If you just want + to define a symbol if the function is available, consider using + `AC_CHECK_FUNCS' instead. This macro checks for functions with C + linkage even when `AC_LANG(C++)' has been called, since C is more + standardized than C++. (*note Language Choice::, for more + information about selecting the language for checks.) + + This macro caches its result in the `ac_cv_func_FUNCTION' variable. + + -- Macro: AC_CHECK_FUNCS (FUNCTION..., [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + For each FUNCTION enumerated in the blank-or-newline-separated + argument list, define `HAVE_FUNCTION' (in all capitals) if it is + available. If ACTION-IF-FOUND is given, it is additional shell + code to execute when one of the functions is found. You can give + it a value of `break' to break out of the loop on the first match. + If ACTION-IF-NOT-FOUND is given, it is executed when one of the + functions is not found. + + Results are cached for each FUNCTION as in `AC_CHECK_FUNC'. + + -- Macro: AC_CHECK_FUNCS_ONCE (FUNCTION...) + For each FUNCTION enumerated in the blank-or-newline-separated + argument list, define `HAVE_FUNCTION' (in all capitals) if it is + available. This is a once-only variant of `AC_CHECK_FUNCS'. It + generates the checking code at most once, so that `configure' is + smaller and faster; but the checks cannot be conditionalized and + are always done once, early during the `configure' run. + + + Autoconf follows a philosophy that was formed over the years by those +who have struggled for portability: isolate the portability issues in +specific files, and then program as if you were in a Posix environment. +Some functions may be missing or unfixable, and your package must be +ready to replace them. + + Suitable replacements for many such problem functions are available +from Gnulib (*note Gnulib::). + + -- Macro: AC_LIBOBJ (FUNCTION) + Specify that `FUNCTION.c' must be included in the executables to + replace a missing or broken implementation of FUNCTION. + + Technically, it adds `FUNCTION.$ac_objext' to the output variable + `LIBOBJS' if it is not already in, and calls `AC_LIBSOURCE' for + `FUNCTION.c'. You should not directly change `LIBOBJS', since + this is not traceable. + + -- Macro: AC_LIBSOURCE (FILE) + Specify that FILE might be needed to compile the project. If you + need to know what files might be needed by a `configure.ac', you + should trace `AC_LIBSOURCE'. FILE must be a literal. + + This macro is called automatically from `AC_LIBOBJ', but you must + call it explicitly if you pass a shell variable to `AC_LIBOBJ'. In + that case, since shell variables cannot be traced statically, you + must pass to `AC_LIBSOURCE' any possible files that the shell + variable might cause `AC_LIBOBJ' to need. For example, if you + want to pass a variable `$foo_or_bar' to `AC_LIBOBJ' that holds + either `"foo"' or `"bar"', you should do: + + AC_LIBSOURCE([foo.c]) + AC_LIBSOURCE([bar.c]) + AC_LIBOBJ([$foo_or_bar]) + + There is usually a way to avoid this, however, and you are + encouraged to simply call `AC_LIBOBJ' with literal arguments. + + Note that this macro replaces the obsolete `AC_LIBOBJ_DECL', with + slightly different semantics: the old macro took the function name, + e.g., `foo', as its argument rather than the file name. + + -- Macro: AC_LIBSOURCES (FILES) + Like `AC_LIBSOURCE', but accepts one or more FILES in a + comma-separated M4 list. Thus, the above example might be + rewritten: + + AC_LIBSOURCES([foo.c, bar.c]) + AC_LIBOBJ([$foo_or_bar]) + + -- Macro: AC_CONFIG_LIBOBJ_DIR (DIRECTORY) + Specify that `AC_LIBOBJ' replacement files are to be found in + DIRECTORY, a name relative to the top level of the source tree. + The replacement directory defaults to `.', the top level + directory, and the most typical value is `lib', corresponding to + `AC_CONFIG_LIBOBJ_DIR([lib])'. + + `configure' might need to know the replacement directory for the + following reasons: (i) some checks use the replacement files, (ii) + some macros bypass broken system headers by installing links to the + replacement headers (iii) when used in conjunction with Automake, + within each makefile, DIRECTORY is used as a relative path from + `$(top_srcdir)' to each object named in `LIBOBJS' and `LTLIBOBJS', + etc. + + + It is common to merely check for the existence of a function, and ask +for its `AC_LIBOBJ' replacement if missing. The following macro is a +convenient shorthand. + + -- Macro: AC_REPLACE_FUNCS (FUNCTION...) + Like `AC_CHECK_FUNCS', but uses `AC_LIBOBJ(FUNCTION)' as + ACTION-IF-NOT-FOUND. You can declare your replacement function by + enclosing the prototype in `#ifndef HAVE_FUNCTION'. If the system + has the function, it probably declares it in a header file you + should be including, so you shouldn't redeclare it lest your + declaration conflict. + + +File: autoconf.info, Node: Header Files, Next: Declarations, Prev: Library Functions, Up: Existing Tests + +5.6 Header Files +================ + +The following macros check for the presence of certain C header files. +If there is no macro specifically defined to check for a header file +you need, and you don't need to check for any special properties of it, +then you can use one of the general header-file check macros. + +* Menu: + +* Header Portability:: Collected knowledge on common headers +* Particular Headers:: Special handling to find certain headers +* Generic Headers:: How to find other headers + + +File: autoconf.info, Node: Header Portability, Next: Particular Headers, Up: Header Files + +5.6.1 Portability of Headers +---------------------------- + +This section documents some collected knowledge about common headers, +and the problems they cause. By definition, this list always requires +additions. A much more complete list is maintained by the Gnulib +project (*note Gnulib::), covering *note Posix Headers: (gnulib)Header +File Substitutes. and *note Glibc Headers: (gnulib)Glibc Header File +Substitutes. Please help us keep the gnulib list as complete as +possible. + +`limits.h' + C99 says that `limits.h' defines `LLONG_MIN', `LLONG_MAX', and + `ULLONG_MAX', but many almost-C99 environments (e.g., default GCC + 4.0.2 + glibc 2.4) do not define them. + +`inttypes.h' vs. `stdint.h' + The C99 standard says that `inttypes.h' includes `stdint.h', so + there's no need to include `stdint.h' separately in a standard + environment. Some implementations have `inttypes.h' but not + `stdint.h' (e.g., Solaris 7), but we don't know of any + implementation that has `stdint.h' but not `inttypes.h'. + +`linux/irda.h' + It requires `linux/types.h' and `sys/socket.h'. + +`linux/random.h' + It requires `linux/types.h'. + +`net/if.h' + On Darwin, this file requires that `sys/socket.h' be included + beforehand. One should run: + + AC_CHECK_HEADERS([sys/socket.h]) + AC_CHECK_HEADERS([net/if.h], [], [], + [#include <stdio.h> + #ifdef STDC_HEADERS + # include <stdlib.h> + # include <stddef.h> + #else + # ifdef HAVE_STDLIB_H + # include <stdlib.h> + # endif + #endif + #ifdef HAVE_SYS_SOCKET_H + # include <sys/socket.h> + #endif + ]) + +`netinet/if_ether.h' + On Darwin, this file requires that `stdio.h' and `sys/socket.h' be + included beforehand. One should run: + + AC_CHECK_HEADERS([sys/socket.h]) + AC_CHECK_HEADERS([netinet/if_ether.h], [], [], + [#include <stdio.h> + #ifdef STDC_HEADERS + # include <stdlib.h> + # include <stddef.h> + #else + # ifdef HAVE_STDLIB_H + # include <stdlib.h> + # endif + #endif + #ifdef HAVE_SYS_SOCKET_H + # include <sys/socket.h> + #endif + ]) + +`stdint.h' + See above, item `inttypes.h' vs. `stdint.h'. + +`stdlib.h' + On many systems (e.g., Darwin), `stdio.h' is a prerequisite. + +`sys/mount.h' + On FreeBSD 4.8 on ia32 and using gcc version 2.95.4, + `sys/params.h' is a prerequisite. + +`sys/ptem.h' + On Solaris 8, `sys/stream.h' is a prerequisite. + +`sys/socket.h' + On Darwin, `stdlib.h' is a prerequisite. + +`sys/ucred.h' + On Tru64 5.1, `sys/types.h' is a prerequisite. + +`X11/extensions/scrnsaver.h' + Using XFree86, this header requires `X11/Xlib.h', which is probably + so required that you might not even consider looking for it. + + AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [], + [[#include <X11/Xlib.h> + ]]) + + +File: autoconf.info, Node: Particular Headers, Next: Generic Headers, Prev: Header Portability, Up: Header Files + +5.6.2 Particular Header Checks +------------------------------ + +These macros check for particular system header files--whether they +exist, and in some cases whether they declare certain symbols. + + -- Macro: AC_CHECK_HEADER_STDBOOL + Check whether `stdbool.h' exists and conforms to C99, and cache the + result in the `ac_cv_header_stdbool_h' variable. If the type + `_Bool' is defined, define `HAVE__BOOL' to 1. + + This macro is intended for use by Gnulib (*note Gnulib::) and other + packages that supply a substitute `stdbool.h' on platforms lacking + a conforming one. The `AC_HEADER_STDBOOL' macro is better for code + that explicitly checks for `stdbool.h'. + + -- Macro: AC_HEADER_ASSERT + Check whether to enable assertions in the style of `assert.h'. + Assertions are enabled by default, but the user can override this + by invoking `configure' with the `--disable-assert' option. + + -- Macro: AC_HEADER_DIRENT + Check for the following header files. For the first one that is + found and defines `DIR', define the listed C preprocessor macro: + + `dirent.h' `HAVE_DIRENT_H' + `sys/ndir.h' `HAVE_SYS_NDIR_H' + `sys/dir.h' `HAVE_SYS_DIR_H' + `ndir.h' `HAVE_NDIR_H' + + The directory-library declarations in your source code should look + something like the following: + + #include <sys/types.h> + #ifdef HAVE_DIRENT_H + # include <dirent.h> + # define NAMLEN(dirent) strlen ((dirent)->d_name) + #else + # define dirent direct + # define NAMLEN(dirent) ((dirent)->d_namlen) + # ifdef HAVE_SYS_NDIR_H + # include <sys/ndir.h> + # endif + # ifdef HAVE_SYS_DIR_H + # include <sys/dir.h> + # endif + # ifdef HAVE_NDIR_H + # include <ndir.h> + # endif + #endif + + Using the above declarations, the program would declare variables + to be of type `struct dirent', not `struct direct', and would + access the length of a directory entry name by passing a pointer + to a `struct dirent' to the `NAMLEN' macro. + + This macro also checks for the SCO Xenix `dir' and `x' libraries. + + This macro is obsolescent, as all current systems with directory + libraries have `<dirent.h>'. New programs need not use this macro. + + Also see `AC_STRUCT_DIRENT_D_INO' and `AC_STRUCT_DIRENT_D_TYPE' + (*note Particular Structures::). + + -- Macro: AC_HEADER_MAJOR + If `sys/types.h' does not define `major', `minor', and `makedev', + but `sys/mkdev.h' does, define `MAJOR_IN_MKDEV'; otherwise, if + `sys/sysmacros.h' does, define `MAJOR_IN_SYSMACROS'. + + -- Macro: AC_HEADER_RESOLV + Checks for header `resolv.h', checking for prerequisites first. + To properly use `resolv.h', your code should contain something like + the following: + + #ifdef HAVE_SYS_TYPES_H + # include <sys/types.h> + #endif + #ifdef HAVE_NETINET_IN_H + # include <netinet/in.h> /* inet_ functions / structs */ + #endif + #ifdef HAVE_ARPA_NAMESER_H + # include <arpa/nameser.h> /* DNS HEADER struct */ + #endif + #ifdef HAVE_NETDB_H + # include <netdb.h> + #endif + #include <resolv.h> + + -- Macro: AC_HEADER_STAT + If the macros `S_ISDIR', `S_ISREG', etc. defined in `sys/stat.h' + do not work properly (returning false positives), define + `STAT_MACROS_BROKEN'. This is the case on Tektronix UTekV, Amdahl + UTS and Motorola System V/88. + + This macro is obsolescent, as no current systems have the bug. + New programs need not use this macro. + + -- Macro: AC_HEADER_STDBOOL + If `stdbool.h' exists and conforms to C99, define `HAVE_STDBOOL_H' + to 1; if the type `_Bool' is defined, define `HAVE__BOOL' to 1. + To fulfill the C99 requirements, your program could contain the + following code: + + #ifdef HAVE_STDBOOL_H + # include <stdbool.h> + #else + # ifndef HAVE__BOOL + # ifdef __cplusplus + typedef bool _Bool; + # else + # define _Bool signed char + # endif + # endif + # define bool _Bool + # define false 0 + # define true 1 + # define __bool_true_false_are_defined 1 + #endif + + Alternatively you can use the `stdbool' package of Gnulib (*note + Gnulib::). It simplifies your code so that it can say just + `#include <stdbool.h>', and it adds support for less-common + platforms. + + This macro caches its result in the `ac_cv_header_stdbool_h' + variable. + + This macro differs from `AC_CHECK_HEADER_STDBOOL' only in that it + defines `HAVE_STDBOOL_H' whereas `AC_CHECK_HEADER_STDBOOL' does + not. + + -- Macro: AC_HEADER_STDC + Define `STDC_HEADERS' if the system has C header files conforming + to ANSI C89 (ISO C90). Specifically, this macro checks for + `stdlib.h', `stdarg.h', `string.h', and `float.h'; if the system + has those, it probably has the rest of the C89 header files. This + macro also checks whether `string.h' declares `memchr' (and thus + presumably the other `mem' functions), whether `stdlib.h' declare + `free' (and thus presumably `malloc' and other related functions), + and whether the `ctype.h' macros work on characters with the high + bit set, as the C standard requires. + + If you use this macro, your code can refer to `STDC_HEADERS' to + determine whether the system has conforming header files (and + probably C library functions). + + This macro caches its result in the `ac_cv_header_stdc' variable. + + This macro is obsolescent, as current systems have conforming + header files. New programs need not use this macro. + + Nowadays `string.h' is part of the C standard and declares + functions like `strcpy', and `strings.h' is standardized by Posix + and declares BSD functions like `bcopy'; but historically, string + functions were a major sticking point in this area. If you still + want to worry about portability to ancient systems without + standard headers, there is so much variation that it is probably + easier to declare the functions you use than to figure out exactly + what the system header files declare. Some ancient systems + contained a mix of functions from the C standard and from BSD; + some were mostly standard but lacked `memmove'; some defined the + BSD functions as macros in `string.h' or `strings.h'; some had + only the BSD functions but `string.h'; some declared the memory + functions in `memory.h', some in `string.h'; etc. It is probably + sufficient to check for one string function and one memory + function; if the library had the standard versions of those then + it probably had most of the others. If you put the following in + `configure.ac': + + # This example is obsolescent. + # Nowadays you can omit these macro calls. + AC_HEADER_STDC + AC_CHECK_FUNCS([strchr memcpy]) + + then, in your code, you can use declarations like this: + + /* This example is obsolescent. + Nowadays you can just #include <string.h>. */ + #ifdef STDC_HEADERS + # include <string.h> + #else + # ifndef HAVE_STRCHR + # define strchr index + # define strrchr rindex + # endif + char *strchr (), *strrchr (); + # ifndef HAVE_MEMCPY + # define memcpy(d, s, n) bcopy ((s), (d), (n)) + # define memmove(d, s, n) bcopy ((s), (d), (n)) + # endif + #endif + + If you use a function like `memchr', `memset', `strtok', or + `strspn', which have no BSD equivalent, then macros don't suffice + to port to ancient hosts; you must provide an implementation of + each function. An easy way to incorporate your implementations + only when needed (since the ones in system C libraries may be hand + optimized) is to, taking `memchr' for example, put it in + `memchr.c' and use `AC_REPLACE_FUNCS([memchr])'. + + -- Macro: AC_HEADER_SYS_WAIT + If `sys/wait.h' exists and is compatible with Posix, define + `HAVE_SYS_WAIT_H'. Incompatibility can occur if `sys/wait.h' does + not exist, or if it uses the old BSD `union wait' instead of `int' + to store a status value. If `sys/wait.h' is not Posix compatible, + then instead of including it, define the Posix macros with their + usual interpretations. Here is an example: + + #include <sys/types.h> + #ifdef HAVE_SYS_WAIT_H + # include <sys/wait.h> + #endif + #ifndef WEXITSTATUS + # define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8) + #endif + #ifndef WIFEXITED + # define WIFEXITED(stat_val) (((stat_val) & 255) == 0) + #endif + + This macro caches its result in the `ac_cv_header_sys_wait_h' + variable. + + This macro is obsolescent, as current systems are compatible with + Posix. New programs need not use this macro. + + `_POSIX_VERSION' is defined when `unistd.h' is included on Posix +systems. If there is no `unistd.h', it is definitely not a Posix +system. However, some non-Posix systems do have `unistd.h'. + + The way to check whether the system supports Posix is: + + #ifdef HAVE_UNISTD_H + # include <sys/types.h> + # include <unistd.h> + #endif + + #ifdef _POSIX_VERSION + /* Code for Posix systems. */ + #endif + + -- Macro: AC_HEADER_TIME + If a program may include both `time.h' and `sys/time.h', define + `TIME_WITH_SYS_TIME'. On some ancient systems, `sys/time.h' + included `time.h', but `time.h' was not protected against multiple + inclusion, so programs could not explicitly include both files. + This macro is useful in programs that use, for example, `struct + timeval' as well as `struct tm'. It is best used in conjunction + with `HAVE_SYS_TIME_H', which can be checked for using + `AC_CHECK_HEADERS([sys/time.h])'. + + #ifdef TIME_WITH_SYS_TIME + # include <sys/time.h> + # include <time.h> + #else + # ifdef HAVE_SYS_TIME_H + # include <sys/time.h> + # else + # include <time.h> + # endif + #endif + + This macro caches its result in the `ac_cv_header_time' variable. + + This macro is obsolescent, as current systems can include both + files when they exist. New programs need not use this macro. + + -- Macro: AC_HEADER_TIOCGWINSZ + If the use of `TIOCGWINSZ' requires `<sys/ioctl.h>', then define + `GWINSZ_IN_SYS_IOCTL'. Otherwise `TIOCGWINSZ' can be found in + `<termios.h>'. + + Use: + + #ifdef HAVE_TERMIOS_H + # include <termios.h> + #endif + + #ifdef GWINSZ_IN_SYS_IOCTL + # include <sys/ioctl.h> + #endif + + +File: autoconf.info, Node: Generic Headers, Prev: Particular Headers, Up: Header Files + +5.6.3 Generic Header Checks +--------------------------- + +These macros are used to find system header files not covered by the +"particular" test macros. If you need to check the contents of a header +as well as find out whether it is present, you have to write your own +test for it (*note Writing Tests::). + + -- Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES]) + If the system header file HEADER-FILE is compilable, execute shell + commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND. + If you just want to define a symbol if the header file is + available, consider using `AC_CHECK_HEADERS' instead. + + INCLUDES is decoded to determine the appropriate include + directives. If omitted or empty, `configure' will check for both + header existence (with the preprocessor) and usability (with the + compiler), using `AC_INCLUDES_DEFAULT' for the compile test. If + there is a discrepancy between the results, a warning is issued to + the user, and the compiler results are favored (*note Present But + Cannot Be Compiled::). In general, favoring the compiler results + means that a header will be treated as not found even though the + file exists, because you did not provide enough prerequisites. + + Providing a non-empty INCLUDES argument allows the code to provide + any prerequisites prior to including the header under test; it is + common to use the argument `AC_INCLUDES_DEFAULT' (*note Default + Includes::). With an explicit fourth argument, no preprocessor + test is needed. As a special case, an INCLUDES of exactly `-' + triggers the older preprocessor check, which merely determines + existence of the file in the preprocessor search path; this should + only be used as a last resort (it is safer to determine the actual + prerequisites and perform a compiler check, or else use + `AC_PREPROC_IFELSE' to make it obvious that only a preprocessor + check is desired). + + This macro caches its result in the `ac_cv_header_HEADER-FILE' + variable, with characters not suitable for a variable name mapped + to underscores. + + -- Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES]) + For each given system header file HEADER-FILE in the + blank-separated argument list that exists, define + `HAVE_HEADER-FILE' (in all capitals). If ACTION-IF-FOUND is + given, it is additional shell code to execute when one of the + header files is found. You can give it a value of `break' to + break out of the loop on the first match. If ACTION-IF-NOT-FOUND + is given, it is executed when one of the header files is not found. + + INCLUDES is interpreted as in `AC_CHECK_HEADER', in order to + choose the set of preprocessor directives supplied before the + header under test. + + This macro caches its result in the `ac_cv_header_HEADER-FILE' + variable, with characters not suitable for a variable name mapped + to underscores. + + Previous versions of Autoconf merely checked whether the header was +accepted by the preprocessor. This was changed because the old test was +inappropriate for typical uses. Headers are typically used to compile, +not merely to preprocess, and the old behavior sometimes accepted +headers that clashed at compile-time (*note Present But Cannot Be +Compiled::). If you need to check whether a header is preprocessable, +you can use `AC_PREPROC_IFELSE' (*note Running the Preprocessor::). + + Actually requiring a header to compile improves the robustness of the +test, but it also requires that you make sure that headers that must be +included before the HEADER-FILE be part of the INCLUDES, (*note Default +Includes::). If looking for `bar.h', which requires that `foo.h' be +included before if it exists, we suggest the following scheme: + +AC_CHECK_HEADERS([foo.h]) +AC_CHECK_HEADERS([bar.h], [], [], +[#ifdef HAVE_FOO_H +# include <foo.h> +#endif +]) + + The following variant generates smaller, faster `configure' files if +you do not need the full power of `AC_CHECK_HEADERS'. + + -- Macro: AC_CHECK_HEADERS_ONCE (HEADER-FILE...) + For each given system header file HEADER-FILE in the + blank-separated argument list that exists, define + `HAVE_HEADER-FILE' (in all capitals). This is a once-only variant + of `AC_CHECK_HEADERS'. It generates the checking code at most + once, so that `configure' is smaller and faster; but the checks + cannot be conditionalized and are always done once, early during + the `configure' run. Thus, this macro is only safe for checking + headers that do not have prerequisites beyond what + `AC_INCLUDES_DEFAULT' provides. + + +File: autoconf.info, Node: Declarations, Next: Structures, Prev: Header Files, Up: Existing Tests + +5.7 Declarations +================ + +The following macros check for the declaration of variables and +functions. If there is no macro specifically defined to check for a +symbol you need, then you can use the general macros (*note Generic +Declarations::) or, for more complex tests, you may use +`AC_COMPILE_IFELSE' (*note Running the Compiler::). + +* Menu: + +* Particular Declarations:: Macros to check for certain declarations +* Generic Declarations:: How to find other declarations + + +File: autoconf.info, Node: Particular Declarations, Next: Generic Declarations, Up: Declarations + +5.7.1 Particular Declaration Checks +----------------------------------- + +There are no specific macros for declarations. + + +File: autoconf.info, Node: Generic Declarations, Prev: Particular Declarations, Up: Declarations + +5.7.2 Generic Declaration Checks +-------------------------------- + +These macros are used to find declarations not covered by the +"particular" test macros. + + -- Macro: AC_CHECK_DECL (SYMBOL, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + If SYMBOL (a function, variable, or constant) is not declared in + INCLUDES and a declaration is needed, run the shell commands + ACTION-IF-NOT-FOUND, otherwise ACTION-IF-FOUND. INCLUDES is a + series of include directives, defaulting to `AC_INCLUDES_DEFAULT' + (*note Default Includes::), which are used prior to the + declaration under test. + + This macro actually tests whether SYMBOL is defined as a macro or + can be used as an r-value, not whether it is really declared, + because it is much safer to avoid introducing extra declarations + when they are not needed. In order to facilitate use of C++ and + overloaded function declarations, it is possible to specify + function argument types in parentheses for types which can be + zero-initialized: + + AC_CHECK_DECL([basename(char *)]) + + This macro caches its result in the `ac_cv_have_decl_SYMBOL' + variable, with characters not suitable for a variable name mapped + to underscores. + + -- Macro: AC_CHECK_DECLS (SYMBOLS, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + For each of the SYMBOLS (_comma_-separated list with optional + function argument types for C++ overloads), define + `HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared, + otherwise to `0'. If ACTION-IF-NOT-FOUND is given, it is + additional shell code to execute when one of the function + declarations is needed, otherwise ACTION-IF-FOUND is executed. + + INCLUDES is a series of include directives, defaulting to + `AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used + prior to the declarations under test. + + This macro uses an M4 list as first argument: + AC_CHECK_DECLS([strdup]) + AC_CHECK_DECLS([strlen]) + AC_CHECK_DECLS([malloc, realloc, calloc, free]) + AC_CHECK_DECLS([j0], [], [], [[#include <math.h>]]) + AC_CHECK_DECLS([[basename(char *)], [dirname(char *)]]) + + Unlike the other `AC_CHECK_*S' macros, when a SYMBOL is not + declared, `HAVE_DECL_SYMBOL' is defined to `0' instead of leaving + `HAVE_DECL_SYMBOL' undeclared. When you are _sure_ that the check + was performed, use `HAVE_DECL_SYMBOL' in `#if': + + #if !HAVE_DECL_SYMBOL + extern char *symbol; + #endif + + If the test may have not been performed, however, because it is + safer _not_ to declare a symbol than to use a declaration that + conflicts with the system's one, you should use: + + #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC + void *malloc (size_t *s); + #endif + + You fall into the second category only in extreme situations: + either your files may be used without being configured, or they + are used during the configuration. In most cases the traditional + approach is enough. + + This macro caches its results in `ac_cv_have_decl_SYMBOL' + variables, with characters not suitable for a variable name mapped + to underscores. + + -- Macro: AC_CHECK_DECLS_ONCE (SYMBOLS) + For each of the SYMBOLS (_comma_-separated list), define + `HAVE_DECL_SYMBOL' (in all capitals) to `1' if SYMBOL is declared + in the default include files, otherwise to `0'. This is a + once-only variant of `AC_CHECK_DECLS'. It generates the checking + code at most once, so that `configure' is smaller and faster; but + the checks cannot be conditionalized and are always done once, + early during the `configure' run. + + +File: autoconf.info, Node: Structures, Next: Types, Prev: Declarations, Up: Existing Tests + +5.8 Structures +============== + +The following macros check for the presence of certain members in C +structures. If there is no macro specifically defined to check for a +member you need, then you can use the general structure-member macros +(*note Generic Structures::) or, for more complex tests, you may use +`AC_COMPILE_IFELSE' (*note Running the Compiler::). + +* Menu: + +* Particular Structures:: Macros to check for certain structure members +* Generic Structures:: How to find other structure members + + +File: autoconf.info, Node: Particular Structures, Next: Generic Structures, Up: Structures + +5.8.1 Particular Structure Checks +--------------------------------- + +The following macros check for certain structures or structure members. + + -- Macro: AC_STRUCT_DIRENT_D_INO + Perform all the actions of `AC_HEADER_DIRENT' (*note Particular + Headers::). Then, if `struct dirent' contains a `d_ino' member, + define `HAVE_STRUCT_DIRENT_D_INO'. + + `HAVE_STRUCT_DIRENT_D_INO' indicates only the presence of `d_ino', + not whether its contents are always reliable. Traditionally, a + zero `d_ino' indicated a deleted directory entry, though current + systems hide this detail from the user and never return zero + `d_ino' values. Many current systems report an incorrect `d_ino' + for a directory entry that is a mount point. + + -- Macro: AC_STRUCT_DIRENT_D_TYPE + Perform all the actions of `AC_HEADER_DIRENT' (*note Particular + Headers::). Then, if `struct dirent' contains a `d_type' member, + define `HAVE_STRUCT_DIRENT_D_TYPE'. + + -- Macro: AC_STRUCT_ST_BLOCKS + If `struct stat' contains an `st_blocks' member, define + `HAVE_STRUCT_STAT_ST_BLOCKS'. Otherwise, require an `AC_LIBOBJ' + replacement of `fileblocks'. The former name, `HAVE_ST_BLOCKS' is + to be avoided, as its support will cease in the future. + + This macro caches its result in the + `ac_cv_member_struct_stat_st_blocks' variable. + + -- Macro: AC_STRUCT_TM + If `time.h' does not define `struct tm', define `TM_IN_SYS_TIME', + which means that including `sys/time.h' had better define `struct + tm'. + + This macro is obsolescent, as `time.h' defines `struct tm' in + current systems. New programs need not use this macro. + + -- Macro: AC_STRUCT_TIMEZONE + Figure out how to get the current timezone. If `struct tm' has a + `tm_zone' member, define `HAVE_STRUCT_TM_TM_ZONE' (and the + obsoleted `HAVE_TM_ZONE'). Otherwise, if the external array + `tzname' is found, define `HAVE_TZNAME'; if it is declared, define + `HAVE_DECL_TZNAME'. + + +File: autoconf.info, Node: Generic Structures, Prev: Particular Structures, Up: Structures + +5.8.2 Generic Structure Checks +------------------------------ + +These macros are used to find structure members not covered by the +"particular" test macros. + + -- Macro: AC_CHECK_MEMBER (AGGREGATE.MEMBER, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + Check whether MEMBER is a member of the aggregate AGGREGATE. If + no INCLUDES are specified, the default includes are used (*note + Default Includes::). + + AC_CHECK_MEMBER([struct passwd.pw_gecos], [], + [AC_MSG_ERROR([we need `passwd.pw_gecos'])], + [[#include <pwd.h>]]) + + You can use this macro for submembers: + + AC_CHECK_MEMBER(struct top.middle.bot) + + This macro caches its result in the + `ac_cv_member_AGGREGATE_MEMBER' variable, with characters not + suitable for a variable name mapped to underscores. + + -- Macro: AC_CHECK_MEMBERS (MEMBERS, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + Check for the existence of each `AGGREGATE.MEMBER' of MEMBERS + using the previous macro. When MEMBER belongs to AGGREGATE, + define `HAVE_AGGREGATE_MEMBER' (in all capitals, with spaces and + dots replaced by underscores). If ACTION-IF-FOUND is given, it is + executed for each of the found members. If ACTION-IF-NOT-FOUND is + given, it is executed for each of the members that could not be + found. + + INCLUDES is a series of include directives, defaulting to + `AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used + prior to the members under test. + + This macro uses M4 lists: + AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize]) + + +File: autoconf.info, Node: Types, Next: Compilers and Preprocessors, Prev: Structures, Up: Existing Tests + +5.9 Types +========= + +The following macros check for C types, either builtin or typedefs. If +there is no macro specifically defined to check for a type you need, and +you don't need to check for any special properties of it, then you can +use a general type-check macro. + +* Menu: + +* Particular Types:: Special handling to find certain types +* Generic Types:: How to find other types + + +File: autoconf.info, Node: Particular Types, Next: Generic Types, Up: Types + +5.9.1 Particular Type Checks +---------------------------- + +These macros check for particular C types in `sys/types.h', `stdlib.h', +`stdint.h', `inttypes.h' and others, if they exist. + + The Gnulib `stdint' module is an alternate way to define many of +these symbols; it is useful if you prefer your code to assume a +C99-or-better environment. *Note Gnulib::. + + -- Macro: AC_TYPE_GETGROUPS + Define `GETGROUPS_T' to be whichever of `gid_t' or `int' is the + base type of the array argument to `getgroups'. + + This macro caches the base type in the `ac_cv_type_getgroups' + variable. + + -- Macro: AC_TYPE_INT8_T + If `stdint.h' or `inttypes.h' does not define the type `int8_t', + define `int8_t' to a signed integer type that is exactly 8 bits + wide and that uses two's complement representation, if such a type + exists. If you are worried about porting to hosts that lack such + a type, you can use the results of this macro in C89-or-later code + as follows: + + #if HAVE_STDINT_H + # include <stdint.h> + #endif + #if defined INT8_MAX || defined int8_t + _code using int8_t_ + #else + _complicated alternative using >8-bit 'signed char'_ + #endif + + This macro caches the type in the `ac_cv_c_int8_t' variable. + + -- Macro: AC_TYPE_INT16_T + This is like `AC_TYPE_INT8_T', except for 16-bit integers. + + -- Macro: AC_TYPE_INT32_T + This is like `AC_TYPE_INT8_T', except for 32-bit integers. + + -- Macro: AC_TYPE_INT64_T + This is like `AC_TYPE_INT8_T', except for 64-bit integers. + + -- Macro: AC_TYPE_INTMAX_T + If `stdint.h' or `inttypes.h' defines the type `intmax_t', define + `HAVE_INTMAX_T'. Otherwise, define `intmax_t' to the widest + signed integer type. + + -- Macro: AC_TYPE_INTPTR_T + If `stdint.h' or `inttypes.h' defines the type `intptr_t', define + `HAVE_INTPTR_T'. Otherwise, define `intptr_t' to a signed integer + type wide enough to hold a pointer, if such a type exists. + + -- Macro: AC_TYPE_LONG_DOUBLE + If the C compiler supports a working `long double' type, define + `HAVE_LONG_DOUBLE'. The `long double' type might have the same + range and precision as `double'. + + This macro caches its result in the `ac_cv_type_long_double' + variable. + + This macro is obsolescent, as current C compilers support `long + double'. New programs need not use this macro. + + -- Macro: AC_TYPE_LONG_DOUBLE_WIDER + If the C compiler supports a working `long double' type with more + range or precision than the `double' type, define + `HAVE_LONG_DOUBLE_WIDER'. + + This macro caches its result in the `ac_cv_type_long_double_wider' + variable. + + -- Macro: AC_TYPE_LONG_LONG_INT + If the C compiler supports a working `long long int' type, define + `HAVE_LONG_LONG_INT'. However, this test does not test `long long + int' values in preprocessor `#if' expressions, because too many + compilers mishandle such expressions. *Note Preprocessor + Arithmetic::. + + This macro caches its result in the `ac_cv_type_long_long_int' + variable. + + -- Macro: AC_TYPE_MBSTATE_T + Define `HAVE_MBSTATE_T' if `<wchar.h>' declares the `mbstate_t' + type. Also, define `mbstate_t' to be a type if `<wchar.h>' does + not declare it. + + This macro caches its result in the `ac_cv_type_mbstate_t' + variable. + + -- Macro: AC_TYPE_MODE_T + Define `mode_t' to a suitable type, if standard headers do not + define it. + + This macro caches its result in the `ac_cv_type_mode_t' variable. + + -- Macro: AC_TYPE_OFF_T + Define `off_t' to a suitable type, if standard headers do not + define it. + + This macro caches its result in the `ac_cv_type_off_t' variable. + + -- Macro: AC_TYPE_PID_T + Define `pid_t' to a suitable type, if standard headers do not + define it. + + This macro caches its result in the `ac_cv_type_pid_t' variable. + + -- Macro: AC_TYPE_SIZE_T + Define `size_t' to a suitable type, if standard headers do not + define it. + + This macro caches its result in the `ac_cv_type_size_t' variable. + + -- Macro: AC_TYPE_SSIZE_T + Define `ssize_t' to a suitable type, if standard headers do not + define it. + + This macro caches its result in the `ac_cv_type_ssize_t' variable. + + -- Macro: AC_TYPE_UID_T + Define `uid_t' and `gid_t' to suitable types, if standard headers + do not define them. + + This macro caches its result in the `ac_cv_type_uid_t' variable. + + -- Macro: AC_TYPE_UINT8_T + If `stdint.h' or `inttypes.h' does not define the type `uint8_t', + define `uint8_t' to an unsigned integer type that is exactly 8 + bits wide, if such a type exists. This is like `AC_TYPE_INT8_T', + except for unsigned integers. + + -- Macro: AC_TYPE_UINT16_T + This is like `AC_TYPE_UINT8_T', except for 16-bit integers. + + -- Macro: AC_TYPE_UINT32_T + This is like `AC_TYPE_UINT8_T', except for 32-bit integers. + + -- Macro: AC_TYPE_UINT64_T + This is like `AC_TYPE_UINT8_T', except for 64-bit integers. + + -- Macro: AC_TYPE_UINTMAX_T + If `stdint.h' or `inttypes.h' defines the type `uintmax_t', define + `HAVE_UINTMAX_T'. Otherwise, define `uintmax_t' to the widest + unsigned integer type. + + -- Macro: AC_TYPE_UINTPTR_T + If `stdint.h' or `inttypes.h' defines the type `uintptr_t', define + `HAVE_UINTPTR_T'. Otherwise, define `uintptr_t' to an unsigned + integer type wide enough to hold a pointer, if such a type exists. + + -- Macro: AC_TYPE_UNSIGNED_LONG_LONG_INT + If the C compiler supports a working `unsigned long long int' type, + define `HAVE_UNSIGNED_LONG_LONG_INT'. However, this test does not + test `unsigned long long int' values in preprocessor `#if' + expressions, because too many compilers mishandle such expressions. + *Note Preprocessor Arithmetic::. + + This macro caches its result in the + `ac_cv_type_unsigned_long_long_int' variable. + + +File: autoconf.info, Node: Generic Types, Prev: Particular Types, Up: Types + +5.9.2 Generic Type Checks +------------------------- + +These macros are used to check for types not covered by the "particular" +test macros. + + -- Macro: AC_CHECK_TYPE (TYPE, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + Check whether TYPE is defined. It may be a compiler builtin type + or defined by the INCLUDES. INCLUDES is a series of include + directives, defaulting to `AC_INCLUDES_DEFAULT' (*note Default + Includes::), which are used prior to the type under test. + + In C, TYPE must be a type-name, so that the expression `sizeof + (TYPE)' is valid (but `sizeof ((TYPE))' is not). The same test is + applied when compiling for C++, which means that in C++ TYPE + should be a type-id and should not be an anonymous `struct' or + `union'. + + This macro caches its result in the `ac_cv_type_TYPE' variable, + with `*' mapped to `p' and other characters not suitable for a + variable name mapped to underscores. + + -- Macro: AC_CHECK_TYPES (TYPES, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [INCLUDES = `AC_INCLUDES_DEFAULT']) + For each TYPE of the TYPES that is defined, define `HAVE_TYPE' (in + all capitals). Each TYPE must follow the rules of + `AC_CHECK_TYPE'. If no INCLUDES are specified, the default + includes are used (*note Default Includes::). If ACTION-IF-FOUND + is given, it is additional shell code to execute when one of the + types is found. If ACTION-IF-NOT-FOUND is given, it is executed + when one of the types is not found. + + This macro uses M4 lists: + AC_CHECK_TYPES([ptrdiff_t]) + AC_CHECK_TYPES([unsigned long long int, uintmax_t]) + AC_CHECK_TYPES([float_t], [], [], [[#include <math.h>]]) + + + Autoconf, up to 2.13, used to provide to another version of +`AC_CHECK_TYPE', broken by design. In order to keep backward +compatibility, a simple heuristic, quite safe but not totally, is +implemented. In case of doubt, read the documentation of the former +`AC_CHECK_TYPE', see *note Obsolete Macros::. + + +File: autoconf.info, Node: Compilers and Preprocessors, Next: System Services, Prev: Types, Up: Existing Tests + +5.10 Compilers and Preprocessors +================================ + +All the tests for compilers (`AC_PROG_CC', `AC_PROG_CXX', +`AC_PROG_F77') define the output variable `EXEEXT' based on the output +of the compiler, typically to the empty string if Posix and `.exe' if a +DOS variant. + + They also define the output variable `OBJEXT' based on the output of +the compiler, after `.c' files have been excluded, typically to `o' if +Posix, `obj' if a DOS variant. + + If the compiler being used does not produce executables, the tests +fail. If the executables can't be run, and cross-compilation is not +enabled, they fail too. *Note Manual Configuration::, for more on +support for cross compiling. + +* Menu: + +* Specific Compiler Characteristics:: Some portability issues +* Generic Compiler Characteristics:: Language independent tests and features +* C Compiler:: Checking its characteristics +* C++ Compiler:: Likewise +* Objective C Compiler:: Likewise +* Objective C++ Compiler:: Likewise +* Erlang Compiler and Interpreter:: Likewise +* Fortran Compiler:: Likewise +* Go Compiler:: Likewise + + +File: autoconf.info, Node: Specific Compiler Characteristics, Next: Generic Compiler Characteristics, Up: Compilers and Preprocessors + +5.10.1 Specific Compiler Characteristics +---------------------------------------- + +Some compilers exhibit different behaviors. + +Static/Dynamic Expressions + Autoconf relies on a trick to extract one bit of information from + the C compiler: using negative array sizes. For instance the + following excerpt of a C source demonstrates how to test whether + `int' objects are 4 bytes wide: + + static int test_array[sizeof (int) == 4 ? 1 : -1]; + + To our knowledge, there is a single compiler that does not support + this trick: the HP C compilers (the real ones, not only the + "bundled") on HP-UX 11.00. They incorrectly reject the above + program with the diagnostic "Variable-length arrays cannot have + static storage." This bug comes from HP compilers' mishandling of + `sizeof (int)', not from the `? 1 : -1', and Autoconf works around + this problem by casting `sizeof (int)' to `long int' before + comparing it. + + +File: autoconf.info, Node: Generic Compiler Characteristics, Next: C Compiler, Prev: Specific Compiler Characteristics, Up: Compilers and Preprocessors + +5.10.2 Generic Compiler Characteristics +--------------------------------------- + + -- Macro: AC_CHECK_SIZEOF (TYPE-OR-EXPR, [UNUSED], [INCLUDES = + `AC_INCLUDES_DEFAULT']) + Define `SIZEOF_TYPE-OR-EXPR' (*note Standard Symbols::) to be the + size in bytes of TYPE-OR-EXPR, which may be either a type or an + expression returning a value that has a size. If the expression + `sizeof (TYPE-OR-EXPR)' is invalid, the result is 0. INCLUDES is + a series of include directives, defaulting to + `AC_INCLUDES_DEFAULT' (*note Default Includes::), which are used + prior to the expression under test. + + This macro now works even when cross-compiling. The UNUSED + argument was used when cross-compiling. + + For example, the call + + AC_CHECK_SIZEOF([int *]) + + defines `SIZEOF_INT_P' to be 8 on DEC Alpha AXP systems. + + This macro caches its result in the `ac_cv_sizeof_TYPE-OR-EXPR' + variable, with `*' mapped to `p' and other characters not suitable + for a variable name mapped to underscores. + + -- Macro: AC_CHECK_ALIGNOF (TYPE, [INCLUDES = `AC_INCLUDES_DEFAULT']) + Define `ALIGNOF_TYPE' (*note Standard Symbols::) to be the + alignment in bytes of TYPE. `TYPE y;' must be valid as a + structure member declaration. If `type' is unknown, the result is + 0. If no INCLUDES are specified, the default includes are used + (*note Default Includes::). + + This macro caches its result in the `ac_cv_alignof_TYPE-OR-EXPR' + variable, with `*' mapped to `p' and other characters not suitable + for a variable name mapped to underscores. + + -- Macro: AC_COMPUTE_INT (VAR, EXPRESSION, [INCLUDES = + `AC_INCLUDES_DEFAULT'], [ACTION-IF-FAILS]) + Store into the shell variable VAR the value of the integer + EXPRESSION. The value should fit in an initializer in a C + variable of type `signed long'. To support cross compilation (in + which case, the macro only works on hosts that use twos-complement + arithmetic), it should be possible to evaluate the expression at + compile-time. If no INCLUDES are specified, the default includes + are used (*note Default Includes::). + + Execute ACTION-IF-FAILS if the value cannot be determined + correctly. + + -- Macro: AC_LANG_WERROR + Normally Autoconf ignores warnings generated by the compiler, + linker, and preprocessor. If this macro is used, warnings count + as fatal errors for the current language. This macro is useful + when the results of configuration are used where warnings are + unacceptable; for instance, if parts of a program are built with + the GCC `-Werror' option. If the whole program is built using + `-Werror' it is often simpler to put `-Werror' in the compiler + flags (`CFLAGS', etc.). + + -- Macro: AC_OPENMP + OpenMP (http://www.openmp.org/) specifies extensions of C, C++, + and Fortran that simplify optimization of shared memory + parallelism, which is a common problem on multicore CPUs. + + If the current language is C, the macro `AC_OPENMP' sets the + variable `OPENMP_CFLAGS' to the C compiler flags needed for + supporting OpenMP. `OPENMP_CFLAGS' is set to empty if the + compiler already supports OpenMP, if it has no way to activate + OpenMP support, or if the user rejects OpenMP support by invoking + `configure' with the `--disable-openmp' option. + + `OPENMP_CFLAGS' needs to be used when compiling programs, when + preprocessing program source, and when linking programs. + Therefore you need to add `$(OPENMP_CFLAGS)' to the `CFLAGS' of C + programs that use OpenMP. If you preprocess OpenMP-specific C + code, you also need to add `$(OPENMP_CFLAGS)' to `CPPFLAGS'. The + presence of OpenMP support is revealed at compile time by the + preprocessor macro `_OPENMP'. + + Linking a program with `OPENMP_CFLAGS' typically adds one more + shared library to the program's dependencies, so its use is + recommended only on programs that actually require OpenMP. + + If the current language is C++, `AC_OPENMP' sets the variable + `OPENMP_CXXFLAGS', suitably for the C++ compiler. The same remarks + hold as for C. + + If the current language is Fortran 77 or Fortran, `AC_OPENMP' sets + the variable `OPENMP_FFLAGS' or `OPENMP_FCFLAGS', respectively. + Similar remarks as for C hold, except that `CPPFLAGS' is not used + for Fortran, and no preprocessor macro signals OpenMP support. + + For portability, it is best to avoid spaces between `#' and + `pragma omp'. That is, write `#pragma omp', not `# pragma omp'. + The Sun WorkShop 6.2 C compiler chokes on the latter. + + This macro caches its result in the `ac_cv_prog_c_openmp', + `ac_cv_prog_cxx_openmp', `ac_cv_prog_f77_openmp', or + `ac_cv_prog_fc_openmp' variable, depending on the current language. + + +File: autoconf.info, Node: C Compiler, Next: C++ Compiler, Prev: Generic Compiler Characteristics, Up: Compilers and Preprocessors + +5.10.3 C Compiler Characteristics +--------------------------------- + +The following macros provide ways to find and exercise a C Compiler. +There are a few constructs that ought to be avoided, but do not deserve +being checked for, since they can easily be worked around. + +Don't use lines containing solitary backslashes + They tickle a bug in the HP-UX C compiler (checked on HP-UX 10.20, + 11.00, and 11i). When given the following source: + + #ifdef __STDC__ + /\ + * A comment with backslash-newlines in it. %{ %} *\ + \ + / + char str[] = "\\ + " A string with backslash-newlines in it %{ %} \\ + ""; + char apostrophe = '\\ + \ + '\ + '; + #endif + + the compiler incorrectly fails with the diagnostics + "Non-terminating comment at end of file" and "Missing `#endif' at + end of file." Removing the lines with solitary backslashes solves + the problem. + +Don't compile several files at once if output matters to you + Some compilers, such as HP's, report names of files being compiled + when given more than one file operand. For instance: + + $ cc a.c b.c + a.c: + b.c: + + This can cause problems if you observe the output of the compiler + to detect failures. Invoking `cc -c a.c && cc -c b.c && cc -o c + a.o b.o' solves the issue. + +Don't rely on `#error' failing + The IRIX C compiler does not fail when #error is preprocessed; it + simply emits a diagnostic and continues, exiting successfully. So, + instead of an error directive like `#error "Unsupported word size"' + it is more portable to use an invalid directive like `#Unsupported + word size' in Autoconf tests. In ordinary source code, `#error' is + OK, since installers with inadequate compilers like IRIX can simply + examine these compilers' diagnostic output. + +Don't rely on correct `#line' support + On Solaris, `c89' (at least Sun C 5.3 through 5.8) diagnoses + `#line' directives whose line numbers are greater than 32767. + Nothing in Posix makes this invalid. That is why Autoconf stopped + issuing `#line' directives. + + -- Macro: AC_PROG_CC ([COMPILER-SEARCH-LIST]) + Determine a C compiler to use. If `CC' is not already set in the + environment, check for `gcc' and `cc', then for other C compilers. + Set output variable `CC' to the name of the compiler found. + + This macro may, however, be invoked with an optional first argument + which, if specified, must be a blank-separated list of C compilers + to search for. This just gives the user an opportunity to specify + an alternative search list for the C compiler. For example, if + you didn't like the default order, then you could invoke + `AC_PROG_CC' like this: + + AC_PROG_CC([gcc cl cc]) + + If the C compiler does not handle function prototypes correctly by + default, try to add an option to output variable `CC' to make it + so. This macro tries various options that select + standard-conformance modes on various systems. + + After calling this macro you can check whether the C compiler has + been set to accept ANSI C89 (ISO C90); if not, the shell variable + `ac_cv_prog_cc_c89' is set to `no'. See also `AC_C_PROTOTYPES' + below. + + If using the GNU C compiler, set shell variable `GCC' to `yes'. + If output variable `CFLAGS' was not already set, set it to `-g + -O2' for the GNU C compiler (`-O2' on systems where GCC does not + accept `-g'), or `-g' for other compilers. If your package does + not like this default, then it is acceptable to insert the line `: + ${CFLAGS=""}' after `AC_INIT' and before `AC_PROG_CC' to select an + empty default instead. + + Many Autoconf macros use a compiler, and thus call + `AC_REQUIRE([AC_PROG_CC])' to ensure that the compiler has been + determined before the body of the outermost `AC_DEFUN' macro. + Although `AC_PROG_CC' is safe to directly expand multiple times, it + performs certain checks (such as the proper value of `EXEEXT') only + on the first invocation. Therefore, care must be used when + invoking this macro from within another macro rather than at the + top level (*note Expanded Before Required::). + + -- Macro: AC_PROG_CC_C_O + If the C compiler does not accept the `-c' and `-o' options + simultaneously, define `NO_MINUS_C_MINUS_O'. This macro actually + tests both the compiler found by `AC_PROG_CC', and, if different, + the first `cc' in the path. The test fails if one fails. This + macro was created for GNU Make to choose the default C compilation + rule. + + For the compiler COMPILER, this macro caches its result in the + `ac_cv_prog_cc_COMPILER_c_o' variable. + + -- Macro: AC_PROG_CPP + Set output variable `CPP' to a command that runs the C + preprocessor. If `$CC -E' doesn't work, `/lib/cpp' is used. It + is only portable to run `CPP' on files with a `.c' extension. + + Some preprocessors don't indicate missing include files by the + error status. For such preprocessors an internal variable is set + that causes other macros to check the standard error from the + preprocessor and consider the test failed if any warnings have + been reported. For most preprocessors, though, warnings do not + cause include-file tests to fail unless `AC_PROG_CPP_WERROR' is + also specified. + + -- Macro: AC_PROG_CPP_WERROR + This acts like `AC_PROG_CPP', except it treats warnings from the + preprocessor as errors even if the preprocessor exit status + indicates success. This is useful for avoiding headers that + generate mandatory warnings, such as deprecation notices. + + The following macros check for C compiler or machine architecture +features. To check for characteristics not listed here, use +`AC_COMPILE_IFELSE' (*note Running the Compiler::) or `AC_RUN_IFELSE' +(*note Runtime::). + + -- Macro: AC_PROG_CC_STDC + If the C compiler cannot compile ISO Standard C (currently C99), + try to add an option to output variable `CC' to make it work. If + the compiler does not support C99, fall back to supporting ANSI + C89 (ISO C90). + + After calling this macro you can check whether the C compiler has + been set to accept Standard C; if not, the shell variable + `ac_cv_prog_cc_stdc' is set to `no'. + + -- Macro: AC_PROG_CC_C89 + If the C compiler is not in ANSI C89 (ISO C90) mode by default, + try to add an option to output variable `CC' to make it so. This + macro tries various options that select ANSI C89 on some system or + another, preferring extended functionality modes over strict + conformance modes. It considers the compiler to be in ANSI C89 + mode if it handles function prototypes correctly. + + After calling this macro you can check whether the C compiler has + been set to accept ANSI C89; if not, the shell variable + `ac_cv_prog_cc_c89' is set to `no'. + + This macro is called automatically by `AC_PROG_CC'. + + -- Macro: AC_PROG_CC_C99 + If the C compiler is not in C99 mode by default, try to add an + option to output variable `CC' to make it so. This macro tries + various options that select C99 on some system or another, + preferring extended functionality modes over strict conformance + modes. It considers the compiler to be in C99 mode if it handles + `_Bool', `//' comments, flexible array members, `inline', signed + and unsigned `long long int', mixed code and declarations, named + initialization of structs, `restrict', `va_copy', varargs macros, + variable declarations in `for' loops, and variable length arrays. + + After calling this macro you can check whether the C compiler has + been set to accept C99; if not, the shell variable + `ac_cv_prog_cc_c99' is set to `no'. + + -- Macro: AC_C_BACKSLASH_A + Define `HAVE_C_BACKSLASH_A' to 1 if the C compiler understands + `\a'. + + This macro is obsolescent, as current C compilers understand `\a'. + New programs need not use this macro. + + -- Macro: AC_C_BIGENDIAN ([ACTION-IF-TRUE], [ACTION-IF-FALSE], + [ACTION-IF-UNKNOWN], [ACTION-IF-UNIVERSAL]) + If words are stored with the most significant byte first (like + Motorola and SPARC CPUs), execute ACTION-IF-TRUE. If words are + stored with the least significant byte first (like Intel and VAX + CPUs), execute ACTION-IF-FALSE. + + This macro runs a test-case if endianness cannot be determined + from the system header files. When cross-compiling, the test-case + is not run but grep'ed for some magic values. ACTION-IF-UNKNOWN + is executed if the latter case fails to determine the byte sex of + the host system. + + In some cases a single run of a compiler can generate code for + multiple architectures. This can happen, for example, when + generating Mac OS X universal binary files, which work on both + PowerPC and Intel architectures. In this case, the different + variants might be for different architectures whose endiannesses + differ. If `configure' detects this, it executes + ACTION-IF-UNIVERSAL instead of ACTION-IF-UNKNOWN. + + The default for ACTION-IF-TRUE is to define `WORDS_BIGENDIAN'. + The default for ACTION-IF-FALSE is to do nothing. The default for + ACTION-IF-UNKNOWN is to abort configure and tell the installer how + to bypass this test. And finally, the default for + ACTION-IF-UNIVERSAL is to ensure that `WORDS_BIGENDIAN' is defined + if and only if a universal build is detected and the current code + is big-endian; this default works only if `autoheader' is used + (*note autoheader Invocation::). + + If you use this macro without specifying ACTION-IF-UNIVERSAL, you + should also use `AC_CONFIG_HEADERS'; otherwise `WORDS_BIGENDIAN' + may be set incorrectly for Mac OS X universal binary files. + + -- Macro: AC_C_CONST + If the C compiler does not fully support the `const' keyword, + define `const' to be empty. Some C compilers that do not define + `__STDC__' do support `const'; some compilers that define + `__STDC__' do not completely support `const'. Programs can simply + use `const' as if every C compiler supported it; for those that + don't, the makefile or configuration header file defines it as + empty. + + Occasionally installers use a C++ compiler to compile C code, + typically because they lack a C compiler. This causes problems + with `const', because C and C++ treat `const' differently. For + example: + + const int foo; + + is valid in C but not in C++. These differences unfortunately + cannot be papered over by defining `const' to be empty. + + If `autoconf' detects this situation, it leaves `const' alone, as + this generally yields better results in practice. However, using a + C++ compiler to compile C code is not recommended or supported, and + installers who run into trouble in this area should get a C + compiler like GCC to compile their C code. + + This macro caches its result in the `ac_cv_c_const' variable. + + This macro is obsolescent, as current C compilers support `const'. + New programs need not use this macro. + + -- Macro: AC_C_RESTRICT + If the C compiler recognizes a variant spelling for the `restrict' + keyword (`__restrict', `__restrict__', or `_Restrict'), then + define `restrict' to that; this is more likely to do the right + thing with compilers that support language variants where plain + `restrict' is not a keyword. Otherwise, if the C compiler + recognizes the `restrict' keyword, don't do anything. Otherwise, + define `restrict' to be empty. Thus, programs may simply use + `restrict' as if every C compiler supported it; for those that do + not, the makefile or configuration header defines it away. + + Although support in C++ for the `restrict' keyword is not + required, several C++ compilers do accept the keyword. This macro + works for them, too. + + This macro caches `no' in the `ac_cv_c_restrict' variable if + `restrict' is not supported, and a supported spelling otherwise. + + -- Macro: AC_C_VOLATILE + If the C compiler does not understand the keyword `volatile', + define `volatile' to be empty. Programs can simply use `volatile' + as if every C compiler supported it; for those that do not, the + makefile or configuration header defines it as empty. + + If the correctness of your program depends on the semantics of + `volatile', simply defining it to be empty does, in a sense, break + your code. However, given that the compiler does not support + `volatile', you are at its mercy anyway. At least your program + compiles, when it wouldn't before. *Note Volatile Objects::, for + more about `volatile'. + + In general, the `volatile' keyword is a standard C feature, so you + might expect that `volatile' is available only when `__STDC__' is + defined. However, Ultrix 4.3's native compiler does support + volatile, but does not define `__STDC__'. + + This macro is obsolescent, as current C compilers support + `volatile'. New programs need not use this macro. + + -- Macro: AC_C_INLINE + If the C compiler supports the keyword `inline', do nothing. + Otherwise define `inline' to `__inline__' or `__inline' if it + accepts one of those, otherwise define `inline' to be empty. + + -- Macro: AC_C_CHAR_UNSIGNED + If the C type `char' is unsigned, define `__CHAR_UNSIGNED__', + unless the C compiler predefines it. + + These days, using this macro is not necessary. The same + information can be determined by this portable alternative, thus + avoiding the use of preprocessor macros in the namespace reserved + for the implementation. + + #include <limits.h> + #if CHAR_MIN == 0 + # define CHAR_UNSIGNED 1 + #endif + + -- Macro: AC_C_STRINGIZE + If the C preprocessor supports the stringizing operator, define + `HAVE_STRINGIZE'. The stringizing operator is `#' and is found in + macros such as this: + + #define x(y) #y + + This macro is obsolescent, as current C compilers support the + stringizing operator. New programs need not use this macro. + + -- Macro: AC_C_FLEXIBLE_ARRAY_MEMBER + If the C compiler supports flexible array members, define + `FLEXIBLE_ARRAY_MEMBER' to nothing; otherwise define it to 1. + That way, a declaration like this: + + struct s + { + size_t n_vals; + double val[FLEXIBLE_ARRAY_MEMBER]; + }; + + will let applications use the "struct hack" even with compilers + that do not support flexible array members. To allocate and use + such an object, you can use code like this: + + size_t i; + size_t n = compute_value_count (); + struct s *p = + malloc (offsetof (struct s, val) + + n * sizeof (double)); + p->n_vals = n; + for (i = 0; i < n; i++) + p->val[i] = compute_value (i); + + -- Macro: AC_C_VARARRAYS + If the C compiler supports variable-length arrays, define + `HAVE_C_VARARRAYS'. A variable-length array is an array of + automatic storage duration whose length is determined at run time, + when the array is declared. + + -- Macro: AC_C_TYPEOF + If the C compiler supports GCC's `typeof' syntax either directly or + through a different spelling of the keyword (e.g., `__typeof__'), + define `HAVE_TYPEOF'. If the support is available only through a + different spelling, define `typeof' to that spelling. + + -- Macro: AC_C_PROTOTYPES + If function prototypes are understood by the compiler (as + determined by `AC_PROG_CC'), define `PROTOTYPES' and + `__PROTOTYPES'. Defining `__PROTOTYPES' is for the benefit of + header files that cannot use macros that infringe on user name + space. + + This macro is obsolescent, as current C compilers support + prototypes. New programs need not use this macro. + + -- Macro: AC_PROG_GCC_TRADITIONAL + Add `-traditional' to output variable `CC' if using the GNU C + compiler and `ioctl' does not work properly without + `-traditional'. That usually happens when the fixed header files + have not been installed on an old system. + + This macro is obsolescent, since current versions of the GNU C + compiler fix the header files automatically when installed. + + +File: autoconf.info, Node: C++ Compiler, Next: Objective C Compiler, Prev: C Compiler, Up: Compilers and Preprocessors + +5.10.4 C++ Compiler Characteristics +----------------------------------- + + -- Macro: AC_PROG_CXX ([COMPILER-SEARCH-LIST]) + Determine a C++ compiler to use. Check whether the environment + variable `CXX' or `CCC' (in that order) is set; if so, then set + output variable `CXX' to its value. + + Otherwise, if the macro is invoked without an argument, then + search for a C++ compiler under the likely names (first `g++' and + `c++' then other names). If none of those checks succeed, then as + a last resort set `CXX' to `g++'. + + This macro may, however, be invoked with an optional first argument + which, if specified, must be a blank-separated list of C++ + compilers to search for. This just gives the user an opportunity + to specify an alternative search list for the C++ compiler. For + example, if you didn't like the default order, then you could + invoke `AC_PROG_CXX' like this: + + AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++]) + + If using the GNU C++ compiler, set shell variable `GXX' to `yes'. + If output variable `CXXFLAGS' was not already set, set it to `-g + -O2' for the GNU C++ compiler (`-O2' on systems where G++ does not + accept `-g'), or `-g' for other compilers. If your package does + not like this default, then it is acceptable to insert the line `: + ${CXXFLAGS=""}' after `AC_INIT' and before `AC_PROG_CXX' to select + an empty default instead. + + + -- Macro: AC_PROG_CXXCPP + Set output variable `CXXCPP' to a command that runs the C++ + preprocessor. If `$CXX -E' doesn't work, `/lib/cpp' is used. It + is portable to run `CXXCPP' only on files with a `.c', `.C', + `.cc', or `.cpp' extension. + + Some preprocessors don't indicate missing include files by the + error status. For such preprocessors an internal variable is set + that causes other macros to check the standard error from the + preprocessor and consider the test failed if any warnings have + been reported. However, it is not known whether such broken + preprocessors exist for C++. + + -- Macro: AC_PROG_CXX_C_O + Test whether the C++ compiler accepts the options `-c' and `-o' + simultaneously, and define `CXX_NO_MINUS_C_MINUS_O', if it does + not. + + +File: autoconf.info, Node: Objective C Compiler, Next: Objective C++ Compiler, Prev: C++ Compiler, Up: Compilers and Preprocessors + +5.10.5 Objective C Compiler Characteristics +------------------------------------------- + + -- Macro: AC_PROG_OBJC ([COMPILER-SEARCH-LIST]) + Determine an Objective C compiler to use. If `OBJC' is not already + set in the environment, check for Objective C compilers. Set + output variable `OBJC' to the name of the compiler found. + + This macro may, however, be invoked with an optional first argument + which, if specified, must be a blank-separated list of Objective C + compilers to search for. This just gives the user an opportunity + to specify an alternative search list for the Objective C + compiler. For example, if you didn't like the default order, then + you could invoke `AC_PROG_OBJC' like this: + + AC_PROG_OBJC([gcc objcc objc]) + + If using the GNU Objective C compiler, set shell variable `GOBJC' + to `yes'. If output variable `OBJCFLAGS' was not already set, set + it to `-g -O2' for the GNU Objective C compiler (`-O2' on systems + where `gcc' does not accept `-g'), or `-g' for other compilers. + + -- Macro: AC_PROG_OBJCPP + Set output variable `OBJCPP' to a command that runs the Objective C + preprocessor. If `$OBJC -E' doesn't work, `/lib/cpp' is used. + + +File: autoconf.info, Node: Objective C++ Compiler, Next: Erlang Compiler and Interpreter, Prev: Objective C Compiler, Up: Compilers and Preprocessors + +5.10.6 Objective C++ Compiler Characteristics +--------------------------------------------- + + -- Macro: AC_PROG_OBJCXX ([COMPILER-SEARCH-LIST]) + Determine an Objective C++ compiler to use. If `OBJCXX' is not + already set in the environment, check for Objective C++ compilers. + Set output variable `OBJCXX' to the name of the compiler found. + + This macro may, however, be invoked with an optional first argument + which, if specified, must be a blank-separated list of Objective + C++ compilers to search for. This just gives the user an + opportunity to specify an alternative search list for the + Objective C++ compiler. For example, if you didn't like the + default order, then you could invoke `AC_PROG_OBJCXX' like this: + + AC_PROG_OBJCXX([gcc g++ objcc++ objcxx]) + + If using the GNU Objective C++ compiler, set shell variable + `GOBJCXX' to `yes'. If output variable `OBJCXXFLAGS' was not + already set, set it to `-g -O2' for the GNU Objective C++ compiler + (`-O2' on systems where `gcc' does not accept `-g'), or `-g' for + other compilers. + + -- Macro: AC_PROG_OBJCXXCPP + Set output variable `OBJCXXCPP' to a command that runs the + Objective C++ preprocessor. If `$OBJCXX -E' doesn't work, + `/lib/cpp' is used. + + +File: autoconf.info, Node: Erlang Compiler and Interpreter, Next: Fortran Compiler, Prev: Objective C++ Compiler, Up: Compilers and Preprocessors + +5.10.7 Erlang Compiler and Interpreter Characteristics +------------------------------------------------------ + +Autoconf defines the following macros for determining paths to the +essential Erlang/OTP programs: + + -- Macro: AC_ERLANG_PATH_ERLC ([VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Determine an Erlang compiler to use. If `ERLC' is not already set + in the environment, check for `erlc'. Set output variable `ERLC' + to the complete path of the compiler command found. In addition, + if `ERLCFLAGS' is not set in the environment, set it to an empty + value. + + The two optional arguments have the same meaning as the two last + arguments of macro `AC_PATH_PROG' for looking for the `erlc' + program. For example, to look for `erlc' only in the + `/usr/lib/erlang/bin' directory: + + AC_ERLANG_PATH_ERLC([not found], [/usr/lib/erlang/bin]) + + -- Macro: AC_ERLANG_NEED_ERLC ([PATH = `$PATH']) + A simplified variant of the `AC_ERLANG_PATH_ERLC' macro, that + prints an error message and exits the `configure' script if the + `erlc' program is not found. + + -- Macro: AC_ERLANG_PATH_ERL ([VALUE-IF-NOT-FOUND], [PATH = `$PATH']) + Determine an Erlang interpreter to use. If `ERL' is not already + set in the environment, check for `erl'. Set output variable + `ERL' to the complete path of the interpreter command found. + + The two optional arguments have the same meaning as the two last + arguments of macro `AC_PATH_PROG' for looking for the `erl' + program. For example, to look for `erl' only in the + `/usr/lib/erlang/bin' directory: + + AC_ERLANG_PATH_ERL([not found], [/usr/lib/erlang/bin]) + + -- Macro: AC_ERLANG_NEED_ERL ([PATH = `$PATH']) + A simplified variant of the `AC_ERLANG_PATH_ERL' macro, that + prints an error message and exits the `configure' script if the + `erl' program is not found. + + +File: autoconf.info, Node: Fortran Compiler, Next: Go Compiler, Prev: Erlang Compiler and Interpreter, Up: Compilers and Preprocessors + +5.10.8 Fortran Compiler Characteristics +--------------------------------------- + +The Autoconf Fortran support is divided into two categories: legacy +Fortran 77 macros (`F77'), and modern Fortran macros (`FC'). The +former are intended for traditional Fortran 77 code, and have output +variables like `F77', `FFLAGS', and `FLIBS'. The latter are for newer +programs that can (or must) compile under the newer Fortran standards, +and have output variables like `FC', `FCFLAGS', and `FCLIBS'. + + Except for the macros `AC_FC_SRCEXT', `AC_FC_FREEFORM', +`AC_FC_FIXEDFORM', and `AC_FC_LINE_LENGTH' (see below), the `FC' and +`F77' macros behave almost identically, and so they are documented +together in this section. + + -- Macro: AC_PROG_F77 ([COMPILER-SEARCH-LIST]) + Determine a Fortran 77 compiler to use. If `F77' is not already + set in the environment, then check for `g77' and `f77', and then + some other names. Set the output variable `F77' to the name of + the compiler found. + + This macro may, however, be invoked with an optional first argument + which, if specified, must be a blank-separated list of Fortran 77 + compilers to search for. This just gives the user an opportunity + to specify an alternative search list for the Fortran 77 compiler. + For example, if you didn't like the default order, then you could + invoke `AC_PROG_F77' like this: + + AC_PROG_F77([fl32 f77 fort77 xlf g77 f90 xlf90]) + + If using `g77' (the GNU Fortran 77 compiler), then set the shell + variable `G77' to `yes'. If the output variable `FFLAGS' was not + already set in the environment, then set it to `-g -02' for `g77' + (or `-O2' where `g77' does not accept `-g'). Otherwise, set + `FFLAGS' to `-g' for all other Fortran 77 compilers. + + The result of the GNU test is cached in the + `ac_cv_f77_compiler_gnu' variable, acceptance of `-g' in the + `ac_cv_prog_f77_g' variable. + + -- Macro: AC_PROG_FC ([COMPILER-SEARCH-LIST], [DIALECT]) + Determine a Fortran compiler to use. If `FC' is not already set in + the environment, then `dialect' is a hint to indicate what Fortran + dialect to search for; the default is to search for the newest + available dialect. Set the output variable `FC' to the name of + the compiler found. + + By default, newer dialects are preferred over older dialects, but + if `dialect' is specified then older dialects are preferred + starting with the specified dialect. `dialect' can currently be + one of Fortran 77, Fortran 90, or Fortran 95. However, this is + only a hint of which compiler _name_ to prefer (e.g., `f90' or + `f95'), and no attempt is made to guarantee that a particular + language standard is actually supported. Thus, it is preferable + that you avoid the `dialect' option, and use AC_PROG_FC only for + code compatible with the latest Fortran standard. + + This macro may, alternatively, be invoked with an optional first + argument which, if specified, must be a blank-separated list of + Fortran compilers to search for, just as in `AC_PROG_F77'. + + If using `gfortran' or `g77' (the GNU Fortran compilers), then set + the shell variable `GFC' to `yes'. If the output variable + `FCFLAGS' was not already set in the environment, then set it to + `-g -02' for GNU `g77' (or `-O2' where `g77' does not accept + `-g'). Otherwise, set `FCFLAGS' to `-g' for all other Fortran + compilers. + + The result of the GNU test is cached in the `ac_cv_fc_compiler_gnu' + variable, acceptance of `-g' in the `ac_cv_prog_fc_g' variable. + + -- Macro: AC_PROG_F77_C_O + -- Macro: AC_PROG_FC_C_O + Test whether the Fortran compiler accepts the options `-c' and + `-o' simultaneously, and define `F77_NO_MINUS_C_MINUS_O' or + `FC_NO_MINUS_C_MINUS_O', respectively, if it does not. + + The result of the test is cached in the `ac_cv_prog_f77_c_o' or + `ac_cv_prog_fc_c_o' variable, respectively. + + The following macros check for Fortran compiler characteristics. To +check for characteristics not listed here, use `AC_COMPILE_IFELSE' +(*note Running the Compiler::) or `AC_RUN_IFELSE' (*note Runtime::), +making sure to first set the current language to Fortran 77 or Fortran +via `AC_LANG([Fortran 77])' or `AC_LANG(Fortran)' (*note Language +Choice::). + + -- Macro: AC_F77_LIBRARY_LDFLAGS + -- Macro: AC_FC_LIBRARY_LDFLAGS + Determine the linker flags (e.g., `-L' and `-l') for the "Fortran + intrinsic and runtime libraries" that are required to successfully + link a Fortran program or shared library. The output variable + `FLIBS' or `FCLIBS' is set to these flags (which should be + included after `LIBS' when linking). + + This macro is intended to be used in those situations when it is + necessary to mix, e.g., C++ and Fortran source code in a single + program or shared library (*note Mixing Fortran 77 With C and C++: + (automake)Mixing Fortran 77 With C and C++.). + + For example, if object files from a C++ and Fortran compiler must + be linked together, then the C++ compiler/linker must be used for + linking (since special C++-ish things need to happen at link time + like calling global constructors, instantiating templates, + enabling exception support, etc.). + + However, the Fortran intrinsic and runtime libraries must be + linked in as well, but the C++ compiler/linker doesn't know by + default how to add these Fortran 77 libraries. Hence, this macro + was created to determine these Fortran libraries. + + The macros `AC_F77_DUMMY_MAIN' and `AC_FC_DUMMY_MAIN' or + `AC_F77_MAIN' and `AC_FC_MAIN' are probably also necessary to link + C/C++ with Fortran; see below. Further, it is highly recommended + that you use `AC_CONFIG_HEADERS' (*note Configuration Headers::) + because the complex defines that the function wrapper macros create + may not work with C/C++ compiler drivers. + + These macros internally compute the flag needed to verbose linking + output and cache it in `ac_cv_prog_f77_v' or `ac_cv_prog_fc_v' + variables, respectively. The computed linker flags are cached in + `ac_cv_f77_libs' or `ac_cv_fc_libs', respectively. + + -- Macro: AC_F77_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND = + `AC_MSG_FAILURE']) + -- Macro: AC_FC_DUMMY_MAIN ([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND = + `AC_MSG_FAILURE']) + With many compilers, the Fortran libraries detected by + `AC_F77_LIBRARY_LDFLAGS' or `AC_FC_LIBRARY_LDFLAGS' provide their + own `main' entry function that initializes things like Fortran + I/O, and which then calls a user-provided entry function named + (say) `MAIN__' to run the user's program. The `AC_F77_DUMMY_MAIN' + and `AC_FC_DUMMY_MAIN' or `AC_F77_MAIN' and `AC_FC_MAIN' macros + figure out how to deal with this interaction. + + When using Fortran for purely numerical functions (no I/O, etc.) + often one prefers to provide one's own `main' and skip the Fortran + library initializations. In this case, however, one may still + need to provide a dummy `MAIN__' routine in order to prevent + linking errors on some systems. `AC_F77_DUMMY_MAIN' or + `AC_FC_DUMMY_MAIN' detects whether any such routine is _required_ + for linking, and what its name is; the shell variable + `F77_DUMMY_MAIN' or `FC_DUMMY_MAIN' holds this name, `unknown' + when no solution was found, and `none' when no such dummy main is + needed. + + By default, ACTION-IF-FOUND defines `F77_DUMMY_MAIN' or + `FC_DUMMY_MAIN' to the name of this routine (e.g., `MAIN__') _if_ + it is required. ACTION-IF-NOT-FOUND defaults to exiting with an + error. + + In order to link with Fortran routines, the user's C/C++ program + should then include the following code to define the dummy main if + it is needed: + + #ifdef F77_DUMMY_MAIN + # ifdef __cplusplus + extern "C" + # endif + int F77_DUMMY_MAIN () { return 1; } + #endif + + (Replace `F77' with `FC' for Fortran instead of Fortran 77.) + + Note that this macro is called automatically from `AC_F77_WRAPPERS' + or `AC_FC_WRAPPERS'; there is generally no need to call it + explicitly unless one wants to change the default actions. + + The result of this macro is cached in the `ac_cv_f77_dummy_main' or + `ac_cv_fc_dummy_main' variable, respectively. + + -- Macro: AC_F77_MAIN + -- Macro: AC_FC_MAIN + As discussed above, many Fortran libraries allow you to provide an + entry point called (say) `MAIN__' instead of the usual `main', + which is then called by a `main' function in the Fortran libraries + that initializes things like Fortran I/O. The `AC_F77_MAIN' and + `AC_FC_MAIN' macros detect whether it is _possible_ to utilize + such an alternate main function, and defines `F77_MAIN' and + `FC_MAIN' to the name of the function. (If no alternate main + function name is found, `F77_MAIN' and `FC_MAIN' are simply + defined to `main'.) + + Thus, when calling Fortran routines from C that perform things + like I/O, one should use this macro and declare the "main" + function like so: + + #ifdef __cplusplus + extern "C" + #endif + int F77_MAIN (int argc, char *argv[]); + + (Again, replace `F77' with `FC' for Fortran instead of Fortran 77.) + + The result of this macro is cached in the `ac_cv_f77_main' or + `ac_cv_fc_main' variable, respectively. + + -- Macro: AC_F77_WRAPPERS + -- Macro: AC_FC_WRAPPERS + Defines C macros `F77_FUNC (name, NAME)', `FC_FUNC (name, NAME)', + `F77_FUNC_(name, NAME)', and `FC_FUNC_(name, NAME)' to properly + mangle the names of C/C++ identifiers, and identifiers with + underscores, respectively, so that they match the name-mangling + scheme used by the Fortran compiler. + + Fortran is case-insensitive, and in order to achieve this the + Fortran compiler converts all identifiers into a canonical case + and format. To call a Fortran subroutine from C or to write a C + function that is callable from Fortran, the C program must + explicitly use identifiers in the format expected by the Fortran + compiler. In order to do this, one simply wraps all C identifiers + in one of the macros provided by `AC_F77_WRAPPERS' or + `AC_FC_WRAPPERS'. For example, suppose you have the following + Fortran 77 subroutine: + + subroutine foobar (x, y) + double precision x, y + y = 3.14159 * x + return + end + + You would then declare its prototype in C or C++ as: + + #define FOOBAR_F77 F77_FUNC (foobar, FOOBAR) + #ifdef __cplusplus + extern "C" /* prevent C++ name mangling */ + #endif + void FOOBAR_F77 (double *x, double *y); + + Note that we pass both the lowercase and uppercase versions of the + function name to `F77_FUNC' so that it can select the right one. + Note also that all parameters to Fortran 77 routines are passed as + pointers (*note Mixing Fortran 77 With C and C++: (automake)Mixing + Fortran 77 With C and C++.). + + (Replace `F77' with `FC' for Fortran instead of Fortran 77.) + + Although Autoconf tries to be intelligent about detecting the + name-mangling scheme of the Fortran compiler, there may be Fortran + compilers that it doesn't support yet. In this case, the above + code generates a compile-time error, but some other behavior + (e.g., disabling Fortran-related features) can be induced by + checking whether `F77_FUNC' or `FC_FUNC' is defined. + + Now, to call that routine from a C program, we would do something + like: + + { + double x = 2.7183, y; + FOOBAR_F77 (&x, &y); + } + + If the Fortran identifier contains an underscore (e.g., `foo_bar'), + you should use `F77_FUNC_' or `FC_FUNC_' instead of `F77_FUNC' or + `FC_FUNC' (with the same arguments). This is because some Fortran + compilers mangle names differently if they contain an underscore. + + The name mangling scheme is encoded in the `ac_cv_f77_mangling' or + `ac_cv_fc_mangling' cache variable, respectively, and also used for + the `AC_F77_FUNC' and `AC_FC_FUNC' macros described below. + + -- Macro: AC_F77_FUNC (NAME, [SHELLVAR]) + -- Macro: AC_FC_FUNC (NAME, [SHELLVAR]) + Given an identifier NAME, set the shell variable SHELLVAR to hold + the mangled version NAME according to the rules of the Fortran + linker (see also `AC_F77_WRAPPERS' or `AC_FC_WRAPPERS'). SHELLVAR + is optional; if it is not supplied, the shell variable is simply + NAME. The purpose of this macro is to give the caller a way to + access the name-mangling information other than through the C + preprocessor as above, for example, to call Fortran routines from + some language other than C/C++. + + -- Macro: AC_FC_SRCEXT (EXT, [ACTION-IF-SUCCESS], [ACTION-IF-FAILURE = + `AC_MSG_FAILURE']) + -- Macro: AC_FC_PP_SRCEXT (EXT, [ACTION-IF-SUCCESS], + [ACTION-IF-FAILURE = `AC_MSG_FAILURE']) + By default, the `FC' macros perform their tests using a `.f' + extension for source-code files. Some compilers, however, only + enable newer language features for appropriately named files, + e.g., Fortran 90 features only for `.f90' files, or preprocessing + only with `.F' files or maybe other upper-case extensions. On the + other hand, some other compilers expect all source files to end in + `.f' and require special flags to support other file name + extensions. The `AC_FC_SRCEXT' and `AC_FC_PP_SRCEXT' macros deal + with these issues. + + The `AC_FC_SRCEXT' macro tries to get the `FC' compiler to accept + files ending with the extension `.EXT' (i.e., EXT does _not_ + contain the dot). If any special compiler flags are needed for + this, it stores them in the output variable `FCFLAGS_EXT'. This + extension and these flags are then used for all subsequent `FC' + tests (until `AC_FC_SRCEXT' or `AC_FC_PP_SRCEXT' is called another + time). + + For example, you would use `AC_FC_SRCEXT(f90)' to employ the + `.f90' extension in future tests, and it would set the + `FCFLAGS_f90' output variable with any extra flags that are needed + to compile such files. + + Similarly, the `AC_FC_PP_SRCEXT' macro tries to get the `FC' + compiler to preprocess and compile files with the extension + `.EXT'. When both `fpp' and `cpp' style preprocessing are + provided, the former is preferred, as the latter may treat + continuation lines, `//' tokens, and white space differently from + what some Fortran dialects expect. Conversely, if you do not want + files to be preprocessed, use only lower-case characters in the + file name extension. Like with `AC_FC_SRCEXT(f90)', any needed + flags are stored in the `FCFLAGS_EXT' variable. + + The `FCFLAGS_EXT' flags can _not_ be simply absorbed into + `FCFLAGS', for two reasons based on the limitations of some + compilers. First, only one `FCFLAGS_EXT' can be used at a time, + so files with different extensions must be compiled separately. + Second, `FCFLAGS_EXT' must appear _immediately_ before the + source-code file name when compiling. So, continuing the example + above, you might compile a `foo.f90' file in your makefile with the + command: + + foo.o: foo.f90 + $(FC) -c $(FCFLAGS) $(FCFLAGS_f90) '$(srcdir)/foo.f90' + + If `AC_FC_SRCEXT' or `AC_FC_PP_SRCEXT' succeeds in compiling files + with the EXT extension, it calls ACTION-IF-SUCCESS (defaults to + nothing). If it fails, and cannot find a way to make the `FC' + compiler accept such files, it calls ACTION-IF-FAILURE (defaults + to exiting with an error message). + + The `AC_FC_SRCEXT' and `AC_FC_PP_SRCEXT' macros cache their + results in `ac_cv_fc_srcext_EXT' and `ac_cv_fc_pp_srcext_EXT' + variables, respectively. + + -- Macro: AC_FC_PP_DEFINE ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE = + `AC_MSG_FAILURE']) + Find a flag to specify defines for preprocessed Fortran. Not all + Fortran compilers use `-D'. Substitute `FC_DEFINE' with the + result and call ACTION-IF-SUCCESS (defaults to nothing) if + successful, and ACTION-IF-FAILURE (defaults to failing with an + error message) if not. + + This macro calls `AC_FC_PP_SRCEXT([F])' in order to learn how to + preprocess a `conftest.F' file, but restores a previously used + Fortran source file extension afterwards again. + + The result of this test is cached in the `ac_cv_fc_pp_define' + variable. + + -- Macro: AC_FC_FREEFORM ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE = + `AC_MSG_FAILURE']) + Try to ensure that the Fortran compiler (`$FC') allows free-format + source code (as opposed to the older fixed-format style from + Fortran 77). If necessary, it may add some additional flags to + `FCFLAGS'. + + This macro is most important if you are using the default `.f' + extension, since many compilers interpret this extension as + indicating fixed-format source unless an additional flag is + supplied. If you specify a different extension with + `AC_FC_SRCEXT', such as `.f90', then `AC_FC_FREEFORM' ordinarily + succeeds without modifying `FCFLAGS'. For extensions which the + compiler does not know about, the flag set by the `AC_FC_SRCEXT' + macro might let the compiler assume Fortran 77 by default, however. + + If `AC_FC_FREEFORM' succeeds in compiling free-form source, it + calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it + calls ACTION-IF-FAILURE (defaults to exiting with an error + message). + + The result of this test, or `none' or `unknown', is cached in the + `ac_cv_fc_freeform' variable. + + -- Macro: AC_FC_FIXEDFORM ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE = + `AC_MSG_FAILURE']) + Try to ensure that the Fortran compiler (`$FC') allows the old + fixed-format source code (as opposed to free-format style). If + necessary, it may add some additional flags to `FCFLAGS'. + + This macro is needed for some compilers alias names like `xlf95' + which assume free-form source code by default, and in case you + want to use fixed-form source with an extension like `.f90' which + many compilers interpret as free-form by default. If you specify + a different extension with `AC_FC_SRCEXT', such as `.f', then + `AC_FC_FIXEDFORM' ordinarily succeeds without modifying `FCFLAGS'. + + If `AC_FC_FIXEDFORM' succeeds in compiling fixed-form source, it + calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it + calls ACTION-IF-FAILURE (defaults to exiting with an error + message). + + The result of this test, or `none' or `unknown', is cached in the + `ac_cv_fc_fixedform' variable. + + -- Macro: AC_FC_LINE_LENGTH ([LENGTH], [ACTION-IF-SUCCESS], + [ACTION-IF-FAILURE = `AC_MSG_FAILURE']) + Try to ensure that the Fortran compiler (`$FC') accepts long source + code lines. The LENGTH argument may be given as 80, 132, or + unlimited, and defaults to 132. Note that line lengths above 254 + columns are not portable, and some compilers do not accept more + than 132 columns at least for fixed format source. If necessary, + it may add some additional flags to `FCFLAGS'. + + If `AC_FC_LINE_LENGTH' succeeds in compiling fixed-form source, it + calls ACTION-IF-SUCCESS (defaults to nothing). If it fails, it + calls ACTION-IF-FAILURE (defaults to exiting with an error + message). + + The result of this test, or `none' or `unknown', is cached in the + `ac_cv_fc_line_length' variable. + + -- Macro: AC_FC_CHECK_BOUNDS ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE + = `AC_MSG_FAILURE']) + The `AC_FC_CHECK_BOUNDS' macro tries to enable array bounds + checking in the Fortran compiler. If successful, the + ACTION-IF-SUCCESS is called and any needed flags are added to + `FCFLAGS'. Otherwise, ACTION-IF-FAILURE is called, which defaults + to failing with an error message. The macro currently requires + Fortran 90 or a newer dialect. + + The result of the macro is cached in the `ac_cv_fc_check_bounds' + variable. + + -- Macro: AC_F77_IMPLICIT_NONE ([ACTION-IF-SUCCESS], + [ACTION-IF-FAILURE = `AC_MSG_FAILURE']) + -- Macro: AC_FC_IMPLICIT_NONE ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE + = `AC_MSG_FAILURE']) + Try to disallow implicit declarations in the Fortran compiler. If + successful, ACTION-IF-SUCCESS is called and any needed flags are + added to `FFLAGS' or `FCFLAGS', respectively. Otherwise, + ACTION-IF-FAILURE is called, which defaults to failing with an + error message. + + The result of these macros are cached in the + `ac_cv_f77_implicit_none' and `ac_cv_fc_implicit_none' variables, + respectively. + + -- Macro: AC_FC_MODULE_EXTENSION + Find the Fortran 90 module file name extension. Most Fortran 90 + compilers store module information in files separate from the + object files. The module files are usually named after the name + of the module rather than the source file name, with characters + possibly turned to upper case, plus an extension, often `.mod'. + + Not all compilers use module files at all, or by default. The Cray + Fortran compiler requires `-e m' in order to store and search + module information in `.mod' files rather than in object files. + Likewise, the Fujitsu Fortran compilers uses the `-Am' option to + indicate how module information is stored. + + The `AC_FC_MODULE_EXTENSION' macro computes the module extension + without the leading dot, and stores that in the `FC_MODEXT' + variable. If the compiler does not produce module files, or the + extension cannot be determined, `FC_MODEXT' is empty. Typically, + the result of this macro may be used in cleanup `make' rules as + follows: + + clean-modules: + -test -z "$(FC_MODEXT)" || rm -f *.$(FC_MODEXT) + + The extension, or `unknown', is cached in the + `ac_cv_fc_module_ext' variable. + + -- Macro: AC_FC_MODULE_FLAG ([ACTION-IF-SUCCESS], [ACTION-IF-FAILURE = + `AC_MSG_FAILURE']) + Find the compiler flag to include Fortran 90 module information + from another directory, and store that in the `FC_MODINC' variable. + Call ACTION-IF-SUCCESS (defaults to nothing) if successful, and + set `FC_MODINC' to empty and call ACTION-IF-FAILURE (defaults to + exiting with an error message) if not. + + Most Fortran 90 compilers provide a way to specify module + directories. Some have separate flags for the directory to write + module files to, and directories to search them in, whereas others + only allow writing to the current directory or to the first + directory specified in the include path. Further, with some + compilers, the module search path and the preprocessor search path + can only be modified with the same flag. Thus, for portability, + write module files to the current directory only and list that as + first directory in the search path. + + There may be no whitespace between `FC_MODINC' and the following + directory name, but `FC_MODINC' may contain trailing white space. + For example, if you use Automake and would like to search `../lib' + for module files, you can use the following: + + AM_FCFLAGS = $(FC_MODINC). $(FC_MODINC)../lib + + Inside `configure' tests, you can use: + + if test -n "$FC_MODINC"; then + FCFLAGS="$FCFLAGS $FC_MODINC. $FC_MODINC../lib" + fi + + The flag is cached in the `ac_cv_fc_module_flag' variable. The + substituted value of `FC_MODINC' may refer to the `ac_empty' dummy + placeholder empty variable, to avoid losing the significant + trailing whitespace in a `Makefile'. + + -- Macro: AC_FC_MODULE_OUTPUT_FLAG ([ACTION-IF-SUCCESS], + [ACTION-IF-FAILURE = `AC_MSG_FAILURE']) + Find the compiler flag to write Fortran 90 module information to + another directory, and store that in the `FC_MODOUT' variable. + Call ACTION-IF-SUCCESS (defaults to nothing) if successful, and + set `FC_MODOUT' to empty and call ACTION-IF-FAILURE (defaults to + exiting with an error message) if not. + + Not all Fortran 90 compilers write module files, and of those that + do, not all allow writing to a directory other than the current + one, nor do all have separate flags for writing and reading; see + the description of `AC_FC_MODULE_FLAG' above. If you need to be + able to write to another directory, for maximum portability use + `FC_MODOUT' before any `FC_MODINC' and include both the current + directory and the one you write to in the search path: + + AM_FCFLAGS = $(FC_MODOUT)../mod $(FC_MODINC)../mod $(FC_MODINC). ... + + The flag is cached in the `ac_cv_fc_module_output_flag' variable. + The substituted value of `FC_MODOUT' may refer to the `ac_empty' + dummy placeholder empty variable, to avoid losing the significant + trailing whitespace in a `Makefile'. + + +File: autoconf.info, Node: Go Compiler, Prev: Fortran Compiler, Up: Compilers and Preprocessors + +5.10.9 Go Compiler Characteristics +---------------------------------- + +Autoconf provides basic support for the Go programming language when +using the `gccgo' compiler (there is currently no support for the `6g' +and `8g' compilers). + + -- Macro: AC_PROG_GO ([COMPILER-SEARCH-LIST]) + Find the Go compiler to use. Check whether the environment + variable `GOC' is set; if so, then set output variable `GOC' to its + value. + + Otherwise, if the macro is invoked without an argument, then + search for a Go compiler named `gccgo'. If it is not found, then + as a last resort set `GOC' to `gccgo'. + + This macro may be invoked with an optional first argument which, if + specified, must be a blank-separated list of Go compilers to + search for. + + If output variable `GOFLAGS' was not already set, set it to `-g + -O2'. If your package does not like this default, `GOFLAGS' may + be set before `AC_PROG_GO'. + + +File: autoconf.info, Node: System Services, Next: Posix Variants, Prev: Compilers and Preprocessors, Up: Existing Tests + +5.11 System Services +==================== + +The following macros check for operating system services or +capabilities. + + -- Macro: AC_PATH_X + Try to locate the X Window System include files and libraries. If + the user gave the command line options `--x-includes=DIR' and + `--x-libraries=DIR', use those directories. + + If either or both were not given, get the missing values by running + `xmkmf' (or an executable pointed to by the `XMKMF' environment + variable) on a trivial `Imakefile' and examining the makefile that + it produces. Setting `XMKMF' to `false' disables this method. + + If this method fails to find the X Window System, `configure' + looks for the files in several directories where they often reside. + If either method is successful, set the shell variables + `x_includes' and `x_libraries' to their locations, unless they are + in directories the compiler searches by default. + + If both methods fail, or the user gave the command line option + `--without-x', set the shell variable `no_x' to `yes'; otherwise + set it to the empty string. + + -- Macro: AC_PATH_XTRA + An enhanced version of `AC_PATH_X'. It adds the C compiler flags + that X needs to output variable `X_CFLAGS', and the X linker flags + to `X_LIBS'. Define `X_DISPLAY_MISSING' if X is not available. + + This macro also checks for special libraries that some systems + need in order to compile X programs. It adds any that the system + needs to output variable `X_EXTRA_LIBS'. And it checks for + special X11R6 libraries that need to be linked with before + `-lX11', and adds any found to the output variable `X_PRE_LIBS'. + + + -- Macro: AC_SYS_INTERPRETER + Check whether the system supports starting scripts with a line of + the form `#!/bin/sh' to select the interpreter to use for the + script. After running this macro, shell code in `configure.ac' + can check the shell variable `interpval'; it is set to `yes' if + the system supports `#!', `no' if not. + + -- Macro: AC_SYS_LARGEFILE + Arrange for 64-bit file offsets, known as large-file support + (http://www.unix-systems.org/version2/whatsnew/lfs20mar.html). On + some hosts, one must use special compiler options to build + programs that can access large files. Append any such options to + the output variable `CC'. Define `_FILE_OFFSET_BITS' and + `_LARGE_FILES' if necessary. + + Large-file support can be disabled by configuring with the + `--disable-largefile' option. + + If you use this macro, check that your program works even when + `off_t' is wider than `long int', since this is common when + large-file support is enabled. For example, it is not correct to + print an arbitrary `off_t' value `X' with `printf ("%ld", (long + int) X)'. + + The LFS introduced the `fseeko' and `ftello' functions to replace + their C counterparts `fseek' and `ftell' that do not use `off_t'. + Take care to use `AC_FUNC_FSEEKO' to make their prototypes + available when using them and large-file support is enabled. + + -- Macro: AC_SYS_LONG_FILE_NAMES + If the system supports file names longer than 14 characters, define + `HAVE_LONG_FILE_NAMES'. + + -- Macro: AC_SYS_POSIX_TERMIOS + Check to see if the Posix termios headers and functions are + available on the system. If so, set the shell variable + `ac_cv_sys_posix_termios' to `yes'. If not, set the variable to + `no'. + + +File: autoconf.info, Node: Posix Variants, Next: Erlang Libraries, Prev: System Services, Up: Existing Tests + +5.12 Posix Variants +=================== + +The following macro makes it possible to use features of Posix that are +extensions to C, as well as platform extensions not defined by Posix. + + -- Macro: AC_USE_SYSTEM_EXTENSIONS + This macro was introduced in Autoconf 2.60. If possible, enable + extensions to C or Posix on hosts that normally disable the + extensions, typically due to standards-conformance namespace + issues. This should be called before any macros that run the C + compiler. The following preprocessor macros are defined where + appropriate: + + `_GNU_SOURCE' + Enable extensions on GNU/Linux. + + `__EXTENSIONS__' + Enable general extensions on Solaris. + + `_POSIX_PTHREAD_SEMANTICS' + Enable threading extensions on Solaris. + + `_TANDEM_SOURCE' + Enable extensions for the HP NonStop platform. + + `_ALL_SOURCE' + Enable extensions for AIX 3, and for Interix. + + `_POSIX_SOURCE' + Enable Posix functions for Minix. + + `_POSIX_1_SOURCE' + Enable additional Posix functions for Minix. + + `_MINIX' + Identify Minix platform. This particular preprocessor macro + is obsolescent, and may be removed in a future release of + Autoconf. + + +File: autoconf.info, Node: Erlang Libraries, Prev: Posix Variants, Up: Existing Tests + +5.13 Erlang Libraries +===================== + +The following macros check for an installation of Erlang/OTP, and for +the presence of certain Erlang libraries. All those macros require the +configuration of an Erlang interpreter and an Erlang compiler (*note +Erlang Compiler and Interpreter::). + + -- Macro: AC_ERLANG_SUBST_ERTS_VER + Set the output variable `ERLANG_ERTS_VER' to the version of the + Erlang runtime system (as returned by Erlang's + `erlang:system_info(version)' function). The result of this test + is cached if caching is enabled when running `configure'. The + `ERLANG_ERTS_VER' variable is not intended to be used for testing + for features of specific ERTS versions, but to be used for + substituting the ERTS version in Erlang/OTP release resource files + (`.rel' files), as shown below. + + -- Macro: AC_ERLANG_SUBST_ROOT_DIR + Set the output variable `ERLANG_ROOT_DIR' to the path to the base + directory in which Erlang/OTP is installed (as returned by Erlang's + `code:root_dir/0' function). The result of this test is cached if + caching is enabled when running `configure'. + + -- Macro: AC_ERLANG_SUBST_LIB_DIR + Set the output variable `ERLANG_LIB_DIR' to the path of the library + directory of Erlang/OTP (as returned by Erlang's `code:lib_dir/0' + function), which subdirectories each contain an installed + Erlang/OTP library. The result of this test is cached if caching + is enabled when running `configure'. + + -- Macro: AC_ERLANG_CHECK_LIB (LIBRARY, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + Test whether the Erlang/OTP library LIBRARY is installed by + calling Erlang's `code:lib_dir/1' function. The result of this + test is cached if caching is enabled when running `configure'. + ACTION-IF-FOUND is a list of shell commands to run if the library + is installed; ACTION-IF-NOT-FOUND is a list of shell commands to + run if it is not. Additionally, if the library is installed, the + output variable `ERLANG_LIB_DIR_LIBRARY' is set to the path to the + library installation directory, and the output variable + `ERLANG_LIB_VER_LIBRARY' is set to the version number that is part + of the subdirectory name, if it is in the standard form + (`LIBRARY-VERSION'). If the directory name does not have a + version part, `ERLANG_LIB_VER_LIBRARY' is set to the empty string. + If the library is not installed, `ERLANG_LIB_DIR_LIBRARY' and + `ERLANG_LIB_VER_LIBRARY' are set to `"not found"'. For example, + to check if library `stdlib' is installed: + + AC_ERLANG_CHECK_LIB([stdlib], + [echo "stdlib version \"$ERLANG_LIB_VER_stdlib\"" + echo "is installed in \"$ERLANG_LIB_DIR_stdlib\""], + [AC_MSG_ERROR([stdlib was not found!])]) + + The `ERLANG_LIB_VER_LIBRARY' variables (set by + `AC_ERLANG_CHECK_LIB') and the `ERLANG_ERTS_VER' variable (set by + `AC_ERLANG_SUBST_ERTS_VER') are not intended to be used for + testing for features of specific versions of libraries or of the + Erlang runtime system. Those variables are intended to be + substituted in Erlang release resource files (`.rel' files). For + instance, to generate a `example.rel' file for an application + depending on the `stdlib' library, `configure.ac' could contain: + + AC_ERLANG_SUBST_ERTS_VER + AC_ERLANG_CHECK_LIB([stdlib], + [], + [AC_MSG_ERROR([stdlib was not found!])]) + AC_CONFIG_FILES([example.rel]) + + The `example.rel.in' file used to generate `example.rel' should + contain: + + {release, + {"@PACKAGE@", "@VERSION@"}, + {erts, "@ERLANG_ERTS_VER@"}, + [{stdlib, "@ERLANG_LIB_VER_stdlib@"}, + {@PACKAGE@, "@VERSION@"}]}. + + In addition to the above macros, which test installed Erlang +libraries, the following macros determine the paths to the directories +into which newly built Erlang libraries are to be installed: + + -- Macro: AC_ERLANG_SUBST_INSTALL_LIB_DIR + Set the `ERLANG_INSTALL_LIB_DIR' output variable to the directory + into which every built Erlang library should be installed in a + separate subdirectory. If this variable is not set in the + environment when `configure' runs, its default value is + `${libdir}/erlang/lib'. + + -- Macro: AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR (LIBRARY, VERSION) + Set the `ERLANG_INSTALL_LIB_DIR_LIBRARY' output variable to the + directory into which the built Erlang library LIBRARY version + VERSION should be installed. If this variable is not set in the + environment when `configure' runs, its default value is + `$ERLANG_INSTALL_LIB_DIR/LIBRARY-VERSION', the value of the + `ERLANG_INSTALL_LIB_DIR' variable being set by the + `AC_ERLANG_SUBST_INSTALL_LIB_DIR' macro. + + +File: autoconf.info, Node: Writing Tests, Next: Results, Prev: Existing Tests, Up: Top + +6 Writing Tests +*************** + +If the existing feature tests don't do something you need, you have to +write new ones. These macros are the building blocks. They provide +ways for other macros to check whether various kinds of features are +available and report the results. + + This chapter contains some suggestions and some of the reasons why +the existing tests are written the way they are. You can also learn a +lot about how to write Autoconf tests by looking at the existing ones. +If something goes wrong in one or more of the Autoconf tests, this +information can help you understand the assumptions behind them, which +might help you figure out how to best solve the problem. + + These macros check the output of the compiler system of the current +language (*note Language Choice::). They do not cache the results of +their tests for future use (*note Caching Results::), because they don't +know enough about the information they are checking for to generate a +cache variable name. They also do not print any messages, for the same +reason. The checks for particular kinds of features call these macros +and do cache their results and print messages about what they're +checking for. + + When you write a feature test that could be applicable to more than +one software package, the best thing to do is encapsulate it in a new +macro. *Note Writing Autoconf Macros::, for how to do that. + +* Menu: + +* Language Choice:: Selecting which language to use for testing +* Writing Test Programs:: Forging source files for compilers +* Running the Preprocessor:: Detecting preprocessor symbols +* Running the Compiler:: Detecting language or header features +* Running the Linker:: Detecting library features +* Runtime:: Testing for runtime features +* Systemology:: A zoology of operating systems +* Multiple Cases:: Tests for several possible values + + +File: autoconf.info, Node: Language Choice, Next: Writing Test Programs, Up: Writing Tests + +6.1 Language Choice +=================== + +Autoconf-generated `configure' scripts check for the C compiler and its +features by default. Packages that use other programming languages +(maybe more than one, e.g., C and C++) need to test features of the +compilers for the respective languages. The following macros determine +which programming language is used in the subsequent tests in +`configure.ac'. + + -- Macro: AC_LANG (LANGUAGE) + Do compilation tests using the compiler, preprocessor, and file + extensions for the specified LANGUAGE. + + Supported languages are: + + `C' + Do compilation tests using `CC' and `CPP' and use extension + `.c' for test programs. Use compilation flags: `CPPFLAGS' + with `CPP', and both `CPPFLAGS' and `CFLAGS' with `CC'. + + `C++' + Do compilation tests using `CXX' and `CXXCPP' and use + extension `.C' for test programs. Use compilation flags: + `CPPFLAGS' with `CXXCPP', and both `CPPFLAGS' and `CXXFLAGS' + with `CXX'. + + `Fortran 77' + Do compilation tests using `F77' and use extension `.f' for + test programs. Use compilation flags: `FFLAGS'. + + `Fortran' + Do compilation tests using `FC' and use extension `.f' (or + whatever has been set by `AC_FC_SRCEXT') for test programs. + Use compilation flags: `FCFLAGS'. + + `Erlang' + Compile and execute tests using `ERLC' and `ERL' and use + extension `.erl' for test Erlang modules. Use compilation + flags: `ERLCFLAGS'. + + `Objective C' + Do compilation tests using `OBJC' and `OBJCPP' and use + extension `.m' for test programs. Use compilation flags: + `CPPFLAGS' with `OBJCPP', and both `CPPFLAGS' and `OBJCFLAGS' + with `OBJC'. + + `Objective C++' + Do compilation tests using `OBJCXX' and `OBJCXXCPP' and use + extension `.mm' for test programs. Use compilation flags: + `CPPFLAGS' with `OBJCXXCPP', and both `CPPFLAGS' and + `OBJCXXFLAGS' with `OBJCXX'. + + `Go' + Do compilation tests using `GOC' and use extension `.go' for + test programs. Use compilation flags `GOFLAGS'. + + -- Macro: AC_LANG_PUSH (LANGUAGE) + Remember the current language (as set by `AC_LANG') on a stack, and + then select the LANGUAGE. Use this macro and `AC_LANG_POP' in + macros that need to temporarily switch to a particular language. + + -- Macro: AC_LANG_POP ([LANGUAGE]) + Select the language that is saved on the top of the stack, as set + by `AC_LANG_PUSH', and remove it from the stack. + + If given, LANGUAGE specifies the language we just _quit_. It is a + good idea to specify it when it's known (which should be the + case...), since Autoconf detects inconsistencies. + + AC_LANG_PUSH([Fortran 77]) + # Perform some tests on Fortran 77. + # ... + AC_LANG_POP([Fortran 77]) + + -- Macro: AC_LANG_ASSERT (LANGUAGE) + Check statically that the current language is LANGUAGE. You + should use this in your language specific macros to avoid that + they be called with an inappropriate language. + + This macro runs only at `autoconf' time, and incurs no cost at + `configure' time. Sadly enough and because Autoconf is a two + layer language (1), the macros `AC_LANG_PUSH' and `AC_LANG_POP' + cannot be "optimizing", therefore as much as possible you ought to + avoid using them to wrap your code, rather, require from the user + to run the macro with a correct current language, and check it + with `AC_LANG_ASSERT'. And anyway, that may help the user + understand she is running a Fortran macro while expecting a result + about her Fortran 77 compiler... + + -- Macro: AC_REQUIRE_CPP + Ensure that whichever preprocessor would currently be used for + tests has been found. Calls `AC_REQUIRE' (*note Prerequisite + Macros::) with an argument of either `AC_PROG_CPP' or + `AC_PROG_CXXCPP', depending on which language is current. + + ---------- Footnotes ---------- + + (1) Because M4 is not aware of Sh code, especially conditionals, +some optimizations that look nice statically may produce incorrect +results at runtime. + + +File: autoconf.info, Node: Writing Test Programs, Next: Running the Preprocessor, Prev: Language Choice, Up: Writing Tests + +6.2 Writing Test Programs +========================= + +Autoconf tests follow a common scheme: feed some program with some +input, and most of the time, feed a compiler with some source file. +This section is dedicated to these source samples. + +* Menu: + +* Guidelines:: General rules for writing test programs +* Test Functions:: Avoiding pitfalls in test programs +* Generating Sources:: Source program boilerplate + + +File: autoconf.info, Node: Guidelines, Next: Test Functions, Up: Writing Test Programs + +6.2.1 Guidelines for Test Programs +---------------------------------- + +The most important rule to follow when writing testing samples is: + + _Look for realism._ + + This motto means that testing samples must be written with the same +strictness as real programs are written. In particular, you should +avoid "shortcuts" and simplifications. + + Don't just play with the preprocessor if you want to prepare a +compilation. For instance, using `cpp' to check whether a header is +functional might let your `configure' accept a header which causes some +_compiler_ error. Do not hesitate to check a header with other headers +included before, especially required headers. + + Make sure the symbols you use are properly defined, i.e., refrain +from simply declaring a function yourself instead of including the +proper header. + + Test programs should not write to standard output. They should exit +with status 0 if the test succeeds, and with status 1 otherwise, so +that success can be distinguished easily from a core dump or other +failure; segmentation violations and other failures produce a nonzero +exit status. Unless you arrange for `exit' to be declared, test +programs should `return', not `exit', from `main', because on many +systems `exit' is not declared by default. + + Test programs can use `#if' or `#ifdef' to check the values of +preprocessor macros defined by tests that have already run. For +example, if you call `AC_HEADER_STDBOOL', then later on in +`configure.ac' you can have a test program that includes `stdbool.h' +conditionally: + + #ifdef HAVE_STDBOOL_H + # include <stdbool.h> + #endif + + Both `#if HAVE_STDBOOL_H' and `#ifdef HAVE_STDBOOL_H' will work with +any standard C compiler. Some developers prefer `#if' because it is +easier to read, while others prefer `#ifdef' because it avoids +diagnostics with picky compilers like GCC with the `-Wundef' option. + + If a test program needs to use or create a data file, give it a name +that starts with `conftest', such as `conftest.data'. The `configure' +script cleans up by running `rm -f -r conftest*' after running test +programs and if the script is interrupted. + + +File: autoconf.info, Node: Test Functions, Next: Generating Sources, Prev: Guidelines, Up: Writing Test Programs + +6.2.2 Test Functions +-------------------- + +These days it's safe to assume support for function prototypes +(introduced in C89). + + Functions that test programs declare should also be conditionalized +for C++, which requires `extern "C"' prototypes. Make sure to not +include any header files containing clashing prototypes. + + #ifdef __cplusplus + extern "C" + #endif + void *valloc (size_t); + + If a test program calls a function with invalid parameters (just to +see whether it exists), organize the program to ensure that it never +invokes that function. You can do this by calling it in another +function that is never invoked. You can't do it by putting it after a +call to `exit', because GCC version 2 knows that `exit' never returns +and optimizes out any code that follows it in the same block. + + If you include any header files, be sure to call the functions +relevant to them with the correct number of arguments, even if they are +just 0, to avoid compilation errors due to prototypes. GCC version 2 +has internal prototypes for several functions that it automatically +inlines; for example, `memcpy'. To avoid errors when checking for +them, either pass them the correct number of arguments or redeclare them +with a different return type (such as `char'). + + +File: autoconf.info, Node: Generating Sources, Prev: Test Functions, Up: Writing Test Programs + +6.2.3 Generating Sources +------------------------ + +Autoconf provides a set of macros that can be used to generate test +source files. They are written to be language generic, i.e., they +actually depend on the current language (*note Language Choice::) to +"format" the output properly. + + -- Macro: AC_LANG_CONFTEST (SOURCE) + Save the SOURCE text in the current test source file: + `conftest.EXTENSION' where the EXTENSION depends on the current + language. As of Autoconf 2.63b, the source file also contains the + results of all of the `AC_DEFINE' performed so far. + + Note that the SOURCE is evaluated exactly once, like regular + Autoconf macro arguments, and therefore (i) you may pass a macro + invocation, (ii) if not, be sure to double quote if needed. + + This macro issues a warning during `autoconf' processing if SOURCE + does not include an expansion of the macro + `AC_LANG_DEFINES_PROVIDED' (note that both `AC_LANG_SOURCE' and + `AC_LANG_PROGRAM' call this macro, and thus avoid the warning). + + This macro is seldom called directly, but is used under the hood + by more common macros such as `AC_COMPILE_IFELSE' and + `AC_RUN_IFELSE'. + + -- Macro: AC_LANG_DEFINES_PROVIDED + This macro is called as a witness that the file + `conftest.EXTENSION' appropriate for the current language is + complete, including all previously determined results from + `AC_DEFINE'. This macro is seldom called directly, but exists if + you have a compelling reason to write a conftest file without using + `AC_LANG_SOURCE', yet still want to avoid a syntax warning from + `AC_LANG_CONFTEST'. + + -- Macro: AC_LANG_SOURCE (SOURCE) + Expands into the SOURCE, with the definition of all the + `AC_DEFINE' performed so far. This macro includes an expansion of + `AC_LANG_DEFINES_PROVIDED'. + + In many cases, you may find it more convenient to use the wrapper + `AC_LANG_PROGRAM'. + + For instance, executing (observe the double quotation!): + + AC_INIT([Hello], [1.0], [bug-hello@example.org], [], + [http://www.example.org/]) + AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], + [Greetings string.]) + AC_LANG([C]) + AC_LANG_CONFTEST( + [AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])]) + gcc -E -dD conftest.c + +on a system with `gcc' installed, results in: + + ... + # 1 "conftest.c" + + #define PACKAGE_NAME "Hello" + #define PACKAGE_TARNAME "hello" + #define PACKAGE_VERSION "1.0" + #define PACKAGE_STRING "Hello 1.0" + #define PACKAGE_BUGREPORT "bug-hello@example.org" + #define PACKAGE_URL "http://www.example.org/" + #define HELLO_WORLD "Hello, World\n" + + const char hw[] = "Hello, World\n"; + + When the test language is Fortran, Erlang, or Go, the `AC_DEFINE' +definitions are not automatically translated into constants in the +source code by this macro. + + -- Macro: AC_LANG_PROGRAM (PROLOGUE, BODY) + Expands into a source file which consists of the PROLOGUE, and + then BODY as body of the main function (e.g., `main' in C). Since + it uses `AC_LANG_SOURCE', the features of the latter are available. + + For instance: + + AC_INIT([Hello], [1.0], [bug-hello@example.org], [], + [http://www.example.org/]) + AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], + [Greetings string.]) + AC_LANG_CONFTEST( + [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]], + [[fputs (hw, stdout);]])]) + gcc -E -dD conftest.c + +on a system with `gcc' installed, results in: + + ... + # 1 "conftest.c" + + #define PACKAGE_NAME "Hello" + #define PACKAGE_TARNAME "hello" + #define PACKAGE_VERSION "1.0" + #define PACKAGE_STRING "Hello 1.0" + #define PACKAGE_BUGREPORT "bug-hello@example.org" + #define PACKAGE_URL "http://www.example.org/" + #define HELLO_WORLD "Hello, World\n" + + const char hw[] = "Hello, World\n"; + int + main () + { + fputs (hw, stdout); + ; + return 0; + } + + In Erlang tests, the created source file is that of an Erlang module +called `conftest' (`conftest.erl'). This module defines and exports at +least one `start/0' function, which is called to perform the test. The +PROLOGUE is optional code that is inserted between the module header and +the `start/0' function definition. BODY is the body of the `start/0' +function without the final period (*note Runtime::, about constraints +on this function's behavior). + + For instance: + + AC_INIT([Hello], [1.0], [bug-hello@example.org]) + AC_LANG(Erlang) + AC_LANG_CONFTEST( + [AC_LANG_PROGRAM([[-define(HELLO_WORLD, "Hello, world!").]], + [[io:format("~s~n", [?HELLO_WORLD])]])]) + cat conftest.erl + +results in: + + -module(conftest). + -export([start/0]). + -define(HELLO_WORLD, "Hello, world!"). + start() -> + io:format("~s~n", [?HELLO_WORLD]) + . + + -- Macro: AC_LANG_CALL (PROLOGUE, FUNCTION) + Expands into a source file which consists of the PROLOGUE, and + then a call to the FUNCTION as body of the main function (e.g., + `main' in C). Since it uses `AC_LANG_PROGRAM', the feature of the + latter are available. + + This function will probably be replaced in the future by a version + which would enable specifying the arguments. The use of this + macro is not encouraged, as it violates strongly the typing system. + + This macro cannot be used for Erlang tests. + + -- Macro: AC_LANG_FUNC_LINK_TRY (FUNCTION) + Expands into a source file which uses the FUNCTION in the body of + the main function (e.g., `main' in C). Since it uses + `AC_LANG_PROGRAM', the features of the latter are available. + + As `AC_LANG_CALL', this macro is documented only for completeness. + It is considered to be severely broken, and in the future will be + removed in favor of actual function calls (with properly typed + arguments). + + This macro cannot be used for Erlang tests. + + +File: autoconf.info, Node: Running the Preprocessor, Next: Running the Compiler, Prev: Writing Test Programs, Up: Writing Tests + +6.3 Running the Preprocessor +============================ + +Sometimes one might need to run the preprocessor on some source file. +_Usually it is a bad idea_, as you typically need to _compile_ your +project, not merely run the preprocessor on it; therefore you certainly +want to run the compiler, not the preprocessor. Resist the temptation +of following the easiest path. + + Nevertheless, if you need to run the preprocessor, then use +`AC_PREPROC_IFELSE'. + + The macros described in this section cannot be used for tests in +Erlang, Fortran, or Go, since those languages require no preprocessor. + + -- Macro: AC_PREPROC_IFELSE (INPUT, [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + Run the preprocessor of the current language (*note Language + Choice::) on the INPUT, run the shell commands ACTION-IF-TRUE on + success, ACTION-IF-FALSE otherwise. The INPUT can be made by + `AC_LANG_PROGRAM' and friends. + + This macro uses `CPPFLAGS', but not `CFLAGS', because `-g', `-O', + etc. are not valid options to many C preprocessors. + + It is customary to report unexpected failures with + `AC_MSG_FAILURE'. If needed, ACTION-IF-TRUE can further access + the preprocessed output in the file `conftest.i'. + + For instance: + + AC_INIT([Hello], [1.0], [bug-hello@example.org]) + AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], + [Greetings string.]) + AC_PREPROC_IFELSE( + [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]], + [[fputs (hw, stdout);]])], + [AC_MSG_RESULT([OK])], + [AC_MSG_FAILURE([unexpected preprocessor failure])]) + +results in: + + checking for gcc... gcc + checking for C compiler default output file name... a.out + checking whether the C compiler works... yes + checking whether we are cross compiling... no + checking for suffix of executables... + checking for suffix of object files... o + checking whether we are using the GNU C compiler... yes + checking whether gcc accepts -g... yes + checking for gcc option to accept ISO C89... none needed + checking how to run the C preprocessor... gcc -E + OK + + + The macro `AC_TRY_CPP' (*note Obsolete Macros::) used to play the +role of `AC_PREPROC_IFELSE', but double quotes its argument, making it +impossible to use it to elaborate sources. You are encouraged to get +rid of your old use of the macro `AC_TRY_CPP' in favor of +`AC_PREPROC_IFELSE', but, in the first place, are you sure you need to +run the _preprocessor_ and not the compiler? + + -- Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND, + [ACTION-IF-NOT-FOUND]) + If the output of running the preprocessor on the system header file + HEADER-FILE matches the extended regular expression PATTERN, + execute shell commands ACTION-IF-FOUND, otherwise execute + ACTION-IF-NOT-FOUND. + + -- Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + PROGRAM is the text of a C or C++ program, on which shell + variable, back quote, and backslash substitutions are performed. + If the output of running the preprocessor on PROGRAM matches the + extended regular expression PATTERN, execute shell commands + ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND. + + +File: autoconf.info, Node: Running the Compiler, Next: Running the Linker, Prev: Running the Preprocessor, Up: Writing Tests + +6.4 Running the Compiler +======================== + +To check for a syntax feature of the current language's (*note Language +Choice::) compiler, such as whether it recognizes a certain keyword, or +simply to try some library feature, use `AC_COMPILE_IFELSE' to try to +compile a small program that uses that feature. + + -- Macro: AC_COMPILE_IFELSE (INPUT, [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + Run the compiler and compilation flags of the current language + (*note Language Choice::) on the INPUT, run the shell commands + ACTION-IF-TRUE on success, ACTION-IF-FALSE otherwise. The INPUT + can be made by `AC_LANG_PROGRAM' and friends. + + It is customary to report unexpected failures with + `AC_MSG_FAILURE'. This macro does not try to link; use + `AC_LINK_IFELSE' if you need to do that (*note Running the + Linker::). If needed, ACTION-IF-TRUE can further access the + just-compiled object file `conftest.$OBJEXT'. + + This macro uses `AC_REQUIRE' for the compiler associated with the + current language, which means that if the compiler has not yet been + determined, the compiler determination will be made prior to the + body of the outermost `AC_DEFUN' macro that triggered this macro to + expand (*note Expanded Before Required::). + + For tests in Erlang, the INPUT must be the source code of a module +named `conftest'. `AC_COMPILE_IFELSE' generates a `conftest.beam' file +that can be interpreted by the Erlang virtual machine (`ERL'). It is +recommended to use `AC_LANG_PROGRAM' to specify the test program, to +ensure that the Erlang module has the right name. + + +File: autoconf.info, Node: Running the Linker, Next: Runtime, Prev: Running the Compiler, Up: Writing Tests + +6.5 Running the Linker +====================== + +To check for a library, a function, or a global variable, Autoconf +`configure' scripts try to compile and link a small program that uses +it. This is unlike Metaconfig, which by default uses `nm' or `ar' on +the C library to try to figure out which functions are available. +Trying to link with the function is usually a more reliable approach +because it avoids dealing with the variations in the options and output +formats of `nm' and `ar' and in the location of the standard libraries. +It also allows configuring for cross-compilation or checking a +function's runtime behavior if needed. On the other hand, it can be +slower than scanning the libraries once, but accuracy is more important +than speed. + + `AC_LINK_IFELSE' is used to compile test programs to test for +functions and global variables. It is also used by `AC_CHECK_LIB' to +check for libraries (*note Libraries::), by adding the library being +checked for to `LIBS' temporarily and trying to link a small program. + + -- Macro: AC_LINK_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE]) + Run the compiler (and compilation flags) and the linker of the + current language (*note Language Choice::) on the INPUT, run the + shell commands ACTION-IF-TRUE on success, ACTION-IF-FALSE + otherwise. The INPUT can be made by `AC_LANG_PROGRAM' and + friends. If needed, ACTION-IF-TRUE can further access the + just-linked program file `conftest$EXEEXT'. + + `LDFLAGS' and `LIBS' are used for linking, in addition to the + current compilation flags. + + It is customary to report unexpected failures with + `AC_MSG_FAILURE'. This macro does not try to execute the program; + use `AC_RUN_IFELSE' if you need to do that (*note Runtime::). + + The `AC_LINK_IFELSE' macro cannot be used for Erlang tests, since +Erlang programs are interpreted and do not require linking. + + +File: autoconf.info, Node: Runtime, Next: Systemology, Prev: Running the Linker, Up: Writing Tests + +6.6 Checking Runtime Behavior +============================= + +Sometimes you need to find out how a system performs at runtime, such +as whether a given function has a certain capability or bug. If you +can, make such checks when your program runs instead of when it is +configured. You can check for things like the machine's endianness when +your program initializes itself. + + If you really need to test for a runtime behavior while configuring, +you can write a test program to determine the result, and compile and +run it using `AC_RUN_IFELSE'. Avoid running test programs if possible, +because this prevents people from configuring your package for +cross-compiling. + + -- Macro: AC_RUN_IFELSE (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE], + [ACTION-IF-CROSS-COMPILING = `AC_MSG_FAILURE']) + Run the compiler (and compilation flags) and the linker of the + current language (*note Language Choice::) on the INPUT, then + execute the resulting program. If the program returns an exit + status of 0 when executed, run shell commands ACTION-IF-TRUE. + Otherwise, run shell commands ACTION-IF-FALSE. + + The INPUT can be made by `AC_LANG_PROGRAM' and friends. `LDFLAGS' + and `LIBS' are used for linking, in addition to the compilation + flags of the current language (*note Language Choice::). + Additionally, ACTION-IF-TRUE can run `./conftest$EXEEXT' for + further testing. + + In the ACTION-IF-FALSE section, the failing exit status is + available in the shell variable `$?'. This exit status might be + that of a failed compilation, or it might be that of a failed + program execution. + + If cross-compilation mode is enabled (this is the case if either + the compiler being used does not produce executables that run on + the system where `configure' is being run, or if the options + `--build' and `--host' were both specified and their values are + different), then the test program is not run. If the optional + shell commands ACTION-IF-CROSS-COMPILING are given, those commands + are run instead; typically these commands provide pessimistic + defaults that allow cross-compilation to work even if the guess + was wrong. If the fourth argument is empty or omitted, but + cross-compilation is detected, then `configure' prints an error + message and exits. If you want your package to be useful in a + cross-compilation scenario, you _should_ provide a non-empty + ACTION-IF-CROSS-COMPILING clause, as well as wrap the + `AC_RUN_IFELSE' compilation inside an `AC_CACHE_CHECK' (*note + Caching Results::) which allows the user to override the + pessimistic default if needed. + + It is customary to report unexpected failures with + `AC_MSG_FAILURE'. + + `autoconf' prints a warning message when creating `configure' each +time it encounters a call to `AC_RUN_IFELSE' with no +ACTION-IF-CROSS-COMPILING argument given. If you are not concerned +about users configuring your package for cross-compilation, you may +ignore the warning. A few of the macros distributed with Autoconf +produce this warning message; but if this is a problem for you, please +report it as a bug, along with an appropriate pessimistic guess to use +instead. + + To configure for cross-compiling you can also choose a value for +those parameters based on the canonical system name (*note Manual +Configuration::). Alternatively, set up a test results cache file with +the correct values for the host system (*note Caching Results::). + + To provide a default for calls of `AC_RUN_IFELSE' that are embedded +in other macros, including a few of the ones that come with Autoconf, +you can test whether the shell variable `cross_compiling' is set to +`yes', and then use an alternate method to get the results instead of +calling the macros. + + It is also permissible to temporarily assign to `cross_compiling' in +order to force tests to behave as though they are in a +cross-compilation environment, particularly since this provides a way to +test your ACTION-IF-CROSS-COMPILING even when you are not using a +cross-compiler. + + # We temporarily set cross-compile mode to force AC_COMPUTE_INT + # to use the slow link-only method + save_cross_compiling=$cross_compiling + cross_compiling=yes + AC_COMPUTE_INT([...]) + cross_compiling=$save_cross_compiling + + A C or C++ runtime test should be portable. *Note Portable C and +C++::. + + Erlang tests must exit themselves the Erlang VM by calling the +`halt/1' function: the given status code is used to determine the +success of the test (status is `0') or its failure (status is different +than `0'), as explained above. It must be noted that data output +through the standard output (e.g., using `io:format/2') may be +truncated when halting the VM. Therefore, if a test must output +configuration information, it is recommended to create and to output +data into the temporary file named `conftest.out', using the functions +of module `file'. The `conftest.out' file is automatically deleted by +the `AC_RUN_IFELSE' macro. For instance, a simplified implementation +of Autoconf's `AC_ERLANG_SUBST_LIB_DIR' macro is: + + AC_INIT([LibdirTest], [1.0], [bug-libdirtest@example.org]) + AC_ERLANG_NEED_ERL + AC_LANG(Erlang) + AC_RUN_IFELSE( + [AC_LANG_PROGRAM([], [dnl + file:write_file("conftest.out", code:lib_dir()), + halt(0)])], + [echo "code:lib_dir() returned: `cat conftest.out`"], + [AC_MSG_FAILURE([test Erlang program execution failed])]) + + +File: autoconf.info, Node: Systemology, Next: Multiple Cases, Prev: Runtime, Up: Writing Tests + +6.7 Systemology +=============== + +This section aims at presenting some systems and pointers to +documentation. It may help you addressing particular problems reported +by users. + + Posix-conforming systems (http://www.opengroup.org/susv3) are +derived from the Unix operating system +(http://www.bell-labs.com/history/unix/). + + The Rosetta Stone for Unix (http://bhami.com/rosetta.html) contains +a table correlating the features of various Posix-conforming systems. +Unix History (http://www.levenez.com/unix/) is a simplified diagram of +how many Unix systems were derived from each other. + + The Heirloom Project (http://heirloom.sourceforge.net/) provides +some variants of traditional implementations of Unix utilities. + +Darwin + Darwin is also known as Mac OS X. Beware that the file system + _can_ be case-preserving, but case insensitive. This can cause + nasty problems, since for instance the installation attempt for a + package having an `INSTALL' file can result in `make install' + report that nothing was to be done! + + That's all dependent on whether the file system is a UFS (case + sensitive) or HFS+ (case preserving). By default Apple wants you + to install the OS on HFS+. Unfortunately, there are some pieces of + software which really need to be built on UFS. We may want to + rebuild Darwin to have both UFS and HFS+ available (and put the + /local/build tree on the UFS). + +QNX 4.25 + QNX is a realtime operating system running on Intel architecture + meant to be scalable from the small embedded systems to the hundred + processor super-computer. It claims to be Posix certified. More + information is available on the QNX home page + (http://www.qnx.com/). + +Tru64 + Documentation of several versions of Tru64 + (http://h30097.www3.hp.com/docs/) is available in different + formats. + +Unix version 7 + Officially this was called the "Seventh Edition" of "the UNIX + time-sharing system" but we use the more-common name "Unix version + 7". Documentation is available in the Unix Seventh Edition Manual + (http://plan9.bell-labs.com/7thEdMan/). Previous versions of Unix + are called "Unix version 6", etc., but they were not as widely + used. + + +File: autoconf.info, Node: Multiple Cases, Prev: Systemology, Up: Writing Tests + +6.8 Multiple Cases +================== + +Some operations are accomplished in several possible ways, depending on +the OS variant. Checking for them essentially requires a "case +statement". Autoconf does not directly provide one; however, it is +easy to simulate by using a shell variable to keep track of whether a +way to perform the operation has been found yet. + + Here is an example that uses the shell variable `fstype' to keep +track of whether the remaining cases need to be checked. Note that +since the value of `fstype' is under our control, we don't have to use +the longer `test "x$fstype" = xno'. + + AC_MSG_CHECKING([how to get file system type]) + fstype=no + # The order of these tests is important. + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statvfs.h> + #include <sys/fstyp.h>]])], + [AC_DEFINE([FSTYPE_STATVFS], [1], + [Define if statvfs exists.]) + fstype=SVR4]) + if test $fstype = no; then + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h> + #include <sys/fstyp.h>]])], + [AC_DEFINE([FSTYPE_USG_STATFS], [1], + [Define if USG statfs.]) + fstype=SVR3]) + fi + if test $fstype = no; then + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h> + #include <sys/vmount.h>]])]), + [AC_DEFINE([FSTYPE_AIX_STATFS], [1], + [Define if AIX statfs.]) + fstype=AIX]) + fi + # (more cases omitted here) + AC_MSG_RESULT([$fstype]) + + +File: autoconf.info, Node: Results, Next: Programming in M4, Prev: Writing Tests, Up: Top + +7 Results of Tests +****************** + +Once `configure' has determined whether a feature exists, what can it +do to record that information? There are four sorts of things it can +do: define a C preprocessor symbol, set a variable in the output files, +save the result in a cache file for future `configure' runs, and print +a message letting the user know the result of the test. + +* Menu: + +* Defining Symbols:: Defining C preprocessor symbols +* Setting Output Variables:: Replacing variables in output files +* Special Chars in Variables:: Characters to beware of in variables +* Caching Results:: Speeding up subsequent `configure' runs +* Printing Messages:: Notifying `configure' users + + +File: autoconf.info, Node: Defining Symbols, Next: Setting Output Variables, Up: Results + +7.1 Defining C Preprocessor Symbols +=================================== + +A common action to take in response to a feature test is to define a C +preprocessor symbol indicating the results of the test. That is done by +calling `AC_DEFINE' or `AC_DEFINE_UNQUOTED'. + + By default, `AC_OUTPUT' places the symbols defined by these macros +into the output variable `DEFS', which contains an option +`-DSYMBOL=VALUE' for each symbol defined. Unlike in Autoconf version +1, there is no variable `DEFS' defined while `configure' is running. +To check whether Autoconf macros have already defined a certain C +preprocessor symbol, test the value of the appropriate cache variable, +as in this example: + + AC_CHECK_FUNC([vprintf], [AC_DEFINE([HAVE_VPRINTF], [1], + [Define if vprintf exists.])]) + if test "x$ac_cv_func_vprintf" != xyes; then + AC_CHECK_FUNC([_doprnt], [AC_DEFINE([HAVE_DOPRNT], [1], + [Define if _doprnt exists.])]) + fi + + If `AC_CONFIG_HEADERS' has been called, then instead of creating +`DEFS', `AC_OUTPUT' creates a header file by substituting the correct +values into `#define' statements in a template file. *Note +Configuration Headers::, for more information about this kind of output. + + -- Macro: AC_DEFINE (VARIABLE, VALUE, [DESCRIPTION]) + -- Macro: AC_DEFINE (VARIABLE) + Define VARIABLE to VALUE (verbatim), by defining a C preprocessor + macro for VARIABLE. VARIABLE should be a C identifier, optionally + suffixed by a parenthesized argument list to define a C + preprocessor macro with arguments. The macro argument list, if + present, should be a comma-separated list of C identifiers, + possibly terminated by an ellipsis `...' if C99 syntax is employed. + VARIABLE should not contain comments, white space, trigraphs, + backslash-newlines, universal character names, or non-ASCII + characters. + + VALUE may contain backslash-escaped newlines, which will be + preserved if you use `AC_CONFIG_HEADERS' but flattened if passed + via `@DEFS@' (with no effect on the compilation, since the + preprocessor sees only one line in the first place). VALUE should + not contain raw newlines. If you are not using + `AC_CONFIG_HEADERS', VALUE should not contain any `#' characters, + as `make' tends to eat them. To use a shell variable, use + `AC_DEFINE_UNQUOTED' instead. + + DESCRIPTION is only useful if you are using `AC_CONFIG_HEADERS'. + In this case, DESCRIPTION is put into the generated `config.h.in' + as the comment before the macro define. The following example + defines the C preprocessor variable `EQUATION' to be the string + constant `"$a > $b"': + + AC_DEFINE([EQUATION], ["$a > $b"], + [Equation string.]) + + If neither VALUE nor DESCRIPTION are given, then VALUE defaults to + 1 instead of to the empty string. This is for backwards + compatibility with older versions of Autoconf, but this usage is + obsolescent and may be withdrawn in future versions of Autoconf. + + If the VARIABLE is a literal string, it is passed to + `m4_pattern_allow' (*note Forbidden Patterns::). + + If multiple `AC_DEFINE' statements are executed for the same + VARIABLE name (not counting any parenthesized argument list), the + last one wins. + + -- Macro: AC_DEFINE_UNQUOTED (VARIABLE, VALUE, [DESCRIPTION]) + -- Macro: AC_DEFINE_UNQUOTED (VARIABLE) + Like `AC_DEFINE', but three shell expansions are + performed--once--on VARIABLE and VALUE: variable expansion (`$'), + command substitution (``'), and backslash escaping (`\'), as if in + an unquoted here-document. Single and double quote characters in + the value have no special meaning. Use this macro instead of + `AC_DEFINE' when VARIABLE or VALUE is a shell variable. Examples: + + AC_DEFINE_UNQUOTED([config_machfile], ["$machfile"], + [Configuration machine file.]) + AC_DEFINE_UNQUOTED([GETGROUPS_T], [$ac_cv_type_getgroups], + [getgroups return type.]) + AC_DEFINE_UNQUOTED([$ac_tr_hdr], [1], + [Translated header name.]) + + Due to a syntactical bizarreness of the Bourne shell, do not use +semicolons to separate `AC_DEFINE' or `AC_DEFINE_UNQUOTED' calls from +other macro calls or shell code; that can cause syntax errors in the +resulting `configure' script. Use either blanks or newlines. That is, +do this: + + AC_CHECK_HEADER([elf.h], + [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"]) + +or this: + + AC_CHECK_HEADER([elf.h], + [AC_DEFINE([SVR4], [1], [System V Release 4]) + LIBS="-lelf $LIBS"]) + +instead of this: + + AC_CHECK_HEADER([elf.h], + [AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"]) + + +File: autoconf.info, Node: Setting Output Variables, Next: Special Chars in Variables, Prev: Defining Symbols, Up: Results + +7.2 Setting Output Variables +============================ + +Another way to record the results of tests is to set "output +variables", which are shell variables whose values are substituted into +files that `configure' outputs. The two macros below create new output +variables. *Note Preset Output Variables::, for a list of output +variables that are always available. + + -- Macro: AC_SUBST (VARIABLE, [VALUE]) + Create an output variable from a shell variable. Make `AC_OUTPUT' + substitute the variable VARIABLE into output files (typically one + or more makefiles). This means that `AC_OUTPUT' replaces + instances of `@VARIABLE@' in input files with the value that the + shell variable VARIABLE has when `AC_OUTPUT' is called. The value + can contain any non-`NUL' character, including newline. If you + are using Automake 1.11 or newer, for newlines in values you might + want to consider using `AM_SUBST_NOTMAKE' to prevent `automake' + from adding a line `VARIABLE = @VARIABLE@' to the `Makefile.in' + files (*note Automake: (automake)Optional.). + + Variable occurrences should not overlap: e.g., an input file should + not contain `@VAR1@VAR2@' if VAR1 and VAR2 are variable names. + The substituted value is not rescanned for more output variables; + occurrences of `@VARIABLE@' in the value are inserted literally + into the output file. (The algorithm uses the special marker + `|#_!!_#|' internally, so neither the substituted value nor the + output file may contain `|#_!!_#|'.) + + If VALUE is given, in addition assign it to VARIABLE. + + The string VARIABLE is passed to `m4_pattern_allow' (*note + Forbidden Patterns::). + + -- Macro: AC_SUBST_FILE (VARIABLE) + Another way to create an output variable from a shell variable. + Make `AC_OUTPUT' insert (without substitutions) the contents of + the file named by shell variable VARIABLE into output files. This + means that `AC_OUTPUT' replaces instances of `@VARIABLE@' in + output files (such as `Makefile.in') with the contents of the file + that the shell variable VARIABLE names when `AC_OUTPUT' is called. + Set the variable to `/dev/null' for cases that do not have a file + to insert. This substitution occurs only when the `@VARIABLE@' is + on a line by itself, optionally surrounded by spaces and tabs. The + substitution replaces the whole line, including the spaces, tabs, + and the terminating newline. + + This macro is useful for inserting makefile fragments containing + special dependencies or other `make' directives for particular host + or target types into makefiles. For example, `configure.ac' could + contain: + + AC_SUBST_FILE([host_frag]) + host_frag=$srcdir/conf/sun4.mh + + and then a `Makefile.in' could contain: + + @host_frag@ + + The string VARIABLE is passed to `m4_pattern_allow' (*note + Forbidden Patterns::). + + Running `configure' in varying environments can be extremely +dangerous. If for instance the user runs `CC=bizarre-cc ./configure', +then the cache, `config.h', and many other output files depend upon +`bizarre-cc' being the C compiler. If for some reason the user runs +`./configure' again, or if it is run via `./config.status --recheck', +(*Note Automatic Remaking::, and *note config.status Invocation::), +then the configuration can be inconsistent, composed of results +depending upon two different compilers. + + Environment variables that affect this situation, such as `CC' +above, are called "precious variables", and can be declared as such by +`AC_ARG_VAR'. + + -- Macro: AC_ARG_VAR (VARIABLE, DESCRIPTION) + Declare VARIABLE is a precious variable, and include its + DESCRIPTION in the variable section of `./configure --help'. + + Being precious means that + - VARIABLE is substituted via `AC_SUBST'. + + - The value of VARIABLE when `configure' was launched is saved + in the cache, including if it was not specified on the command + line but via the environment. Indeed, while `configure' can + notice the definition of `CC' in `./configure CC=bizarre-cc', + it is impossible to notice it in `CC=bizarre-cc ./configure', + which, unfortunately, is what most users do. + + We emphasize that it is the _initial_ value of VARIABLE which + is saved, not that found during the execution of `configure'. + Indeed, specifying `./configure FOO=foo' and letting + `./configure' guess that `FOO' is `foo' can be two different + things. + + - VARIABLE is checked for consistency between two `configure' + runs. For instance: + + $ ./configure --silent --config-cache + $ CC=cc ./configure --silent --config-cache + configure: error: `CC' was not set in the previous run + configure: error: changes in the environment can compromise \ + the build + configure: error: run `make distclean' and/or \ + `rm config.cache' and start over + + and similarly if the variable is unset, or if its content is + changed. If the content has white space changes only, then + the error is degraded to a warning only, but the old value is + reused. + + - VARIABLE is kept during automatic reconfiguration (*note + config.status Invocation::) as if it had been passed as a + command line argument, including when no cache is used: + + $ CC=/usr/bin/cc ./configure var=raboof --silent + $ ./config.status --recheck + running CONFIG_SHELL=/bin/sh /bin/sh ./configure var=raboof \ + CC=/usr/bin/cc --no-create --no-recursion + + +File: autoconf.info, Node: Special Chars in Variables, Next: Caching Results, Prev: Setting Output Variables, Up: Results + +7.3 Special Characters in Output Variables +========================================== + +Many output variables are intended to be evaluated both by `make' and +by the shell. Some characters are expanded differently in these two +contexts, so to avoid confusion these variables' values should not +contain any of the following characters: + + " # $ & ' ( ) * ; < > ? [ \ ^ ` | + + Also, these variables' values should neither contain newlines, nor +start with `~', nor contain white space or `:' immediately followed by +`~'. The values can contain nonempty sequences of white space +characters like tabs and spaces, but each such sequence might +arbitrarily be replaced by a single space during substitution. + + These restrictions apply both to the values that `configure' +computes, and to the values set directly by the user. For example, the +following invocations of `configure' are problematic, since they +attempt to use special characters within `CPPFLAGS' and white space +within `$(srcdir)': + + CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure' + + '../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"' + + +File: autoconf.info, Node: Caching Results, Next: Printing Messages, Prev: Special Chars in Variables, Up: Results + +7.4 Caching Results +=================== + +To avoid checking for the same features repeatedly in various +`configure' scripts (or in repeated runs of one script), `configure' +can optionally save the results of many checks in a "cache file" (*note +Cache Files::). If a `configure' script runs with caching enabled and +finds a cache file, it reads the results of previous runs from the +cache and avoids rerunning those checks. As a result, `configure' can +then run much faster than if it had to perform all of the checks every +time. + + -- Macro: AC_CACHE_VAL (CACHE-ID, COMMANDS-TO-SET-IT) + Ensure that the results of the check identified by CACHE-ID are + available. If the results of the check were in the cache file + that was read, and `configure' was not given the `--quiet' or + `--silent' option, print a message saying that the result was + cached; otherwise, run the shell commands COMMANDS-TO-SET-IT. If + the shell commands are run to determine the value, the value is + saved in the cache file just before `configure' creates its output + files. *Note Cache Variable Names::, for how to choose the name + of the CACHE-ID variable. + + The COMMANDS-TO-SET-IT _must have no side effects_ except for + setting the variable CACHE-ID, see below. + + -- Macro: AC_CACHE_CHECK (MESSAGE, CACHE-ID, COMMANDS-TO-SET-IT) + A wrapper for `AC_CACHE_VAL' that takes care of printing the + messages. This macro provides a convenient shorthand for the most + common way to use these macros. It calls `AC_MSG_CHECKING' for + MESSAGE, then `AC_CACHE_VAL' with the CACHE-ID and COMMANDS + arguments, and `AC_MSG_RESULT' with CACHE-ID. + + The COMMANDS-TO-SET-IT _must have no side effects_ except for + setting the variable CACHE-ID, see below. + + It is common to find buggy macros using `AC_CACHE_VAL' or +`AC_CACHE_CHECK', because people are tempted to call `AC_DEFINE' in the +COMMANDS-TO-SET-IT. Instead, the code that _follows_ the call to +`AC_CACHE_VAL' should call `AC_DEFINE', by examining the value of the +cache variable. For instance, the following macro is broken: + + AC_DEFUN([AC_SHELL_TRUE], + [AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works], + [my_cv_shell_true_works=no + (true) 2>/dev/null && my_cv_shell_true_works=yes + if test "x$my_cv_shell_true_works" = xyes; then + AC_DEFINE([TRUE_WORKS], [1], + [Define if `true(1)' works properly.]) + fi]) + ]) + +This fails if the cache is enabled: the second time this macro is run, +`TRUE_WORKS' _will not be defined_. The proper implementation is: + + AC_DEFUN([AC_SHELL_TRUE], + [AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works], + [my_cv_shell_true_works=no + (true) 2>/dev/null && my_cv_shell_true_works=yes]) + if test "x$my_cv_shell_true_works" = xyes; then + AC_DEFINE([TRUE_WORKS], [1], + [Define if `true(1)' works properly.]) + fi + ]) + + Also, COMMANDS-TO-SET-IT should not print any messages, for example +with `AC_MSG_CHECKING'; do that before calling `AC_CACHE_VAL', so the +messages are printed regardless of whether the results of the check are +retrieved from the cache or determined by running the shell commands. + +* Menu: + +* Cache Variable Names:: Shell variables used in caches +* Cache Files:: Files `configure' uses for caching +* Cache Checkpointing:: Loading and saving the cache file + + +File: autoconf.info, Node: Cache Variable Names, Next: Cache Files, Up: Caching Results + +7.4.1 Cache Variable Names +-------------------------- + +The names of cache variables should have the following format: + + PACKAGE-PREFIX_cv_VALUE-TYPE_SPECIFIC-VALUE_[ADDITIONAL-OPTIONS] + +for example, `ac_cv_header_stat_broken' or +`ac_cv_prog_gcc_traditional'. The parts of the variable name are: + +PACKAGE-PREFIX + An abbreviation for your package or organization; the same prefix + you begin local Autoconf macros with, except lowercase by + convention. For cache values used by the distributed Autoconf + macros, this value is `ac'. + +`_cv_' + Indicates that this shell variable is a cache value. This string + _must_ be present in the variable name, including the leading + underscore. + +VALUE-TYPE + A convention for classifying cache values, to produce a rational + naming system. The values used in Autoconf are listed in *note + Macro Names::. + +SPECIFIC-VALUE + Which member of the class of cache values this test applies to. + For example, which function (`alloca'), program (`gcc'), or output + variable (`INSTALL'). + +ADDITIONAL-OPTIONS + Any particular behavior of the specific member that this test + applies to. For example, `broken' or `set'. This part of the + name may be omitted if it does not apply. + + The values assigned to cache variables may not contain newlines. +Usually, their values are Boolean (`yes' or `no') or the names of files +or functions; so this is not an important restriction. *note Cache +Variable Index:: for an index of cache variables with documented +semantics. + + +File: autoconf.info, Node: Cache Files, Next: Cache Checkpointing, Prev: Cache Variable Names, Up: Caching Results + +7.4.2 Cache Files +----------------- + +A cache file is a shell script that caches the results of configure +tests run on one system so they can be shared between configure scripts +and configure runs. It is not useful on other systems. If its contents +are invalid for some reason, the user may delete or edit it, or override +documented cache variables on the `configure' command line. + + By default, `configure' uses no cache file, to avoid problems caused +by accidental use of stale cache files. + + To enable caching, `configure' accepts `--config-cache' (or `-C') to +cache results in the file `config.cache'. Alternatively, +`--cache-file=FILE' specifies that FILE be the cache file. The cache +file is created if it does not exist already. When `configure' calls +`configure' scripts in subdirectories, it uses the `--cache-file' +argument so that they share the same cache. *Note Subdirectories::, +for information on configuring subdirectories with the +`AC_CONFIG_SUBDIRS' macro. + + `config.status' only pays attention to the cache file if it is given +the `--recheck' option, which makes it rerun `configure'. + + It is wrong to try to distribute cache files for particular system +types. There is too much room for error in doing that, and too much +administrative overhead in maintaining them. For any features that +can't be guessed automatically, use the standard method of the canonical +system type and linking files (*note Manual Configuration::). + + The site initialization script can specify a site-wide cache file to +use, instead of the usual per-program cache. In this case, the cache +file gradually accumulates information whenever someone runs a new +`configure' script. (Running `configure' merges the new cache results +with the existing cache file.) This may cause problems, however, if +the system configuration (e.g., the installed libraries or compilers) +changes and the stale cache file is not deleted. + + If `configure' is interrupted at the right time when it updates a +cache file outside of the build directory where the `configure' script +is run, it may leave behind a temporary file named after the cache file +with digits following it. You may safely delete such a file. + + +File: autoconf.info, Node: Cache Checkpointing, Prev: Cache Files, Up: Caching Results + +7.4.3 Cache Checkpointing +------------------------- + +If your configure script, or a macro called from `configure.ac', happens +to abort the configure process, it may be useful to checkpoint the cache +a few times at key points using `AC_CACHE_SAVE'. Doing so reduces the +amount of time it takes to rerun the configure script with (hopefully) +the error that caused the previous abort corrected. + + -- Macro: AC_CACHE_LOAD + Loads values from existing cache file, or creates a new cache file + if a cache file is not found. Called automatically from `AC_INIT'. + + -- Macro: AC_CACHE_SAVE + Flushes all cached values to the cache file. Called automatically + from `AC_OUTPUT', but it can be quite useful to call + `AC_CACHE_SAVE' at key points in `configure.ac'. + + For instance: + + ... AC_INIT, etc. ... + # Checks for programs. + AC_PROG_CC + AC_PROG_AWK + ... more program checks ... + AC_CACHE_SAVE + + # Checks for libraries. + AC_CHECK_LIB([nsl], [gethostbyname]) + AC_CHECK_LIB([socket], [connect]) + ... more lib checks ... + AC_CACHE_SAVE + + # Might abort... + AM_PATH_GTK([1.0.2], [], [AC_MSG_ERROR([GTK not in path])]) + AM_PATH_GTKMM([0.9.5], [], [AC_MSG_ERROR([GTK not in path])]) + ... AC_OUTPUT, etc. ... + + +File: autoconf.info, Node: Printing Messages, Prev: Caching Results, Up: Results + +7.5 Printing Messages +===================== + +`configure' scripts need to give users running them several kinds of +information. The following macros print messages in ways appropriate +for each kind. The arguments to all of them get enclosed in shell +double quotes, so the shell performs variable and back-quote +substitution on them. + + These macros are all wrappers around the `echo' shell command. They +direct output to the appropriate file descriptor (*note File Descriptor +Macros::). `configure' scripts should rarely need to run `echo' +directly to print messages for the user. Using these macros makes it +easy to change how and when each kind of message is printed; such +changes need only be made to the macro definitions and all the callers +change automatically. + + To diagnose static issues, i.e., when `autoconf' is run, see *note +Diagnostic Macros::. + + -- Macro: AC_MSG_CHECKING (FEATURE-DESCRIPTION) + Notify the user that `configure' is checking for a particular + feature. This macro prints a message that starts with `checking ' + and ends with `...' and no newline. It must be followed by a call + to `AC_MSG_RESULT' to print the result of the check and the + newline. The FEATURE-DESCRIPTION should be something like + `whether the Fortran compiler accepts C++ comments' or `for c89'. + + This macro prints nothing if `configure' is run with the `--quiet' + or `--silent' option. + + -- Macro: AC_MSG_RESULT (RESULT-DESCRIPTION) + Notify the user of the results of a check. RESULT-DESCRIPTION is + almost always the value of the cache variable for the check, + typically `yes', `no', or a file name. This macro should follow a + call to `AC_MSG_CHECKING', and the RESULT-DESCRIPTION should be + the completion of the message printed by the call to + `AC_MSG_CHECKING'. + + This macro prints nothing if `configure' is run with the `--quiet' + or `--silent' option. + + -- Macro: AC_MSG_NOTICE (MESSAGE) + Deliver the MESSAGE to the user. It is useful mainly to print a + general description of the overall purpose of a group of feature + checks, e.g., + + AC_MSG_NOTICE([checking if stack overflow is detectable]) + + This macro prints nothing if `configure' is run with the `--quiet' + or `--silent' option. + + -- Macro: AC_MSG_ERROR (ERROR-DESCRIPTION, [EXIT-STATUS = `$?/1']) + Notify the user of an error that prevents `configure' from + completing. This macro prints an error message to the standard + error output and exits `configure' with EXIT-STATUS (`$?' by + default, except that `0' is converted to `1'). ERROR-DESCRIPTION + should be something like `invalid value $HOME for \$HOME'. + + The ERROR-DESCRIPTION should start with a lower-case letter, and + "cannot" is preferred to "can't". + + -- Macro: AC_MSG_FAILURE (ERROR-DESCRIPTION, [EXIT-STATUS]) + This `AC_MSG_ERROR' wrapper notifies the user of an error that + prevents `configure' from completing _and_ that additional details + are provided in `config.log'. This is typically used when + abnormal results are found during a compilation. + + -- Macro: AC_MSG_WARN (PROBLEM-DESCRIPTION) + Notify the `configure' user of a possible problem. This macro + prints the message to the standard error output; `configure' + continues running afterward, so macros that call `AC_MSG_WARN' + should provide a default (back-up) behavior for the situations + they warn about. PROBLEM-DESCRIPTION should be something like `ln + -s seems to make hard links'. + + +File: autoconf.info, Node: Programming in M4, Next: Programming in M4sh, Prev: Results, Up: Top + +8 Programming in M4 +******************* + +Autoconf is written on top of two layers: "M4sugar", which provides +convenient macros for pure M4 programming, and "M4sh", which provides +macros dedicated to shell script generation. + + As of this version of Autoconf, these two layers still contain +experimental macros, whose interface might change in the future. As a +matter of fact, _anything that is not documented must not be used_. + +* Menu: + +* M4 Quotation:: Protecting macros from unwanted expansion +* Using autom4te:: The Autoconf executables backbone +* Programming in M4sugar:: Convenient pure M4 macros +* Debugging via autom4te:: Figuring out what M4 was doing + + +File: autoconf.info, Node: M4 Quotation, Next: Using autom4te, Up: Programming in M4 + +8.1 M4 Quotation +================ + +The most common problem with existing macros is an improper quotation. +This section, which users of Autoconf can skip, but which macro writers +_must_ read, first justifies the quotation scheme that was chosen for +Autoconf and then ends with a rule of thumb. Understanding the former +helps one to follow the latter. + +* Menu: + +* Active Characters:: Characters that change the behavior of M4 +* One Macro Call:: Quotation and one macro call +* Quoting and Parameters:: M4 vs. shell parameters +* Quotation and Nested Macros:: Macros calling macros +* Changequote is Evil:: Worse than INTERCAL: M4 + changequote +* Quadrigraphs:: Another way to escape special characters +* Balancing Parentheses:: Dealing with unbalanced parentheses +* Quotation Rule Of Thumb:: One parenthesis, one quote + + +File: autoconf.info, Node: Active Characters, Next: One Macro Call, Up: M4 Quotation + +8.1.1 Active Characters +----------------------- + +To fully understand where proper quotation is important, you first need +to know what the special characters are in Autoconf: `#' introduces a +comment inside which no macro expansion is performed, `,' separates +arguments, `[' and `]' are the quotes themselves(1), `(' and `)' (which +M4 tries to match by pairs), and finally `$' inside a macro definition. + + In order to understand the delicate case of macro calls, we first +have to present some obvious failures. Below they are "obvious-ified", +but when you find them in real life, they are usually in disguise. + + Comments, introduced by a hash and running up to the newline, are +opaque tokens to the top level: active characters are turned off, and +there is no macro expansion: + + # define([def], ine) + =># define([def], ine) + + Each time there can be a macro expansion, there is a quotation +expansion, i.e., one level of quotes is stripped: + + int tab[10]; + =>int tab10; + [int tab[10];] + =>int tab[10]; + + Without this in mind, the reader might try hopelessly to use her +macro `array': + + define([array], [int tab[10];]) + array + =>int tab10; + [array] + =>array + +How can you correctly output the intended results(2)? + + ---------- Footnotes ---------- + + (1) By itself, M4 uses ``' and `''; it is the M4sugar layer that +sets up the preferred quotes of `[' and `]'. + + (2) Using `defn'. + + +File: autoconf.info, Node: One Macro Call, Next: Quoting and Parameters, Prev: Active Characters, Up: M4 Quotation + +8.1.2 One Macro Call +-------------------- + +Let's proceed on the interaction between active characters and macros +with this small macro, which just returns its first argument: + + define([car], [$1]) + +The two pairs of quotes above are not part of the arguments of +`define'; rather, they are understood by the top level when it tries to +find the arguments of `define'. Therefore, assuming `car' is not +already defined, it is equivalent to write: + + define(car, $1) + +But, while it is acceptable for a `configure.ac' to avoid unnecessary +quotes, it is bad practice for Autoconf macros which must both be more +robust and also advocate perfect style. + + At the top level, there are only two possibilities: either you quote +or you don't: + + car(foo, bar, baz) + =>foo + [car(foo, bar, baz)] + =>car(foo, bar, baz) + + Let's pay attention to the special characters: + + car(#) + error-->EOF in argument list + + The closing parenthesis is hidden in the comment; with a hypothetical +quoting, the top level understood it this way: + + car([#)] + +Proper quotation, of course, fixes the problem: + + car([#]) + =># + + Here are more examples: + + car(foo, bar) + =>foo + car([foo, bar]) + =>foo, bar + car((foo, bar)) + =>(foo, bar) + car([(foo], [bar)]) + =>(foo + define([a], [b]) + => + car(a) + =>b + car([a]) + =>b + car([[a]]) + =>a + car([[[a]]]) + =>[a] + + +File: autoconf.info, Node: Quoting and Parameters, Next: Quotation and Nested Macros, Prev: One Macro Call, Up: M4 Quotation + +8.1.3 Quoting and Parameters +---------------------------- + +When M4 encounters `$' within a macro definition, followed immediately +by a character it recognizes (`0'...`9', `#', `@', or `*'), it will +perform M4 parameter expansion. This happens regardless of how many +layers of quotes the parameter expansion is nested within, or even if +it occurs in text that will be rescanned as a comment. + + define([none], [$1]) + => + define([one], [[$1]]) + => + define([two], [[[$1]]]) + => + define([comment], [# $1]) + => + define([active], [ACTIVE]) + => + none([active]) + =>ACTIVE + one([active]) + =>active + two([active]) + =>[active] + comment([active]) + =># active + + On the other hand, since autoconf generates shell code, you often +want to output shell variable expansion, rather than performing M4 +parameter expansion. To do this, you must use M4 quoting to separate +the `$' from the next character in the definition of your macro. If +the macro definition occurs in single-quoted text, then insert another +level of quoting; if the usage is already inside a double-quoted +string, then split it into concatenated strings. + + define([single], [a single-quoted $[]1 definition]) + => + define([double], [[a double-quoted $][1 definition]]) + => + single + =>a single-quoted $1 definition + double + =>a double-quoted $1 definition + + Posix states that M4 implementations are free to provide +implementation extensions when `${' is encountered in a macro +definition. Autoconf reserves the longer sequence `${{' for use with +planned extensions that will be available in the future GNU M4 2.0, but +guarantees that all other instances of `${' will be output literally. +Therefore, this idiom can also be used to output shell code parameter +references: + + define([first], [${1}])first + =>${1} + + Posix also states that `$11' should expand to the first parameter +concatenated with a literal `1', although some versions of GNU M4 +expand the eleventh parameter instead. For portability, you should +only use single-digit M4 parameter expansion. + + With this in mind, we can explore the cases where macros invoke +macros... + + +File: autoconf.info, Node: Quotation and Nested Macros, Next: Changequote is Evil, Prev: Quoting and Parameters, Up: M4 Quotation + +8.1.4 Quotation and Nested Macros +--------------------------------- + +The examples below use the following macros: + + define([car], [$1]) + define([active], [ACT, IVE]) + define([array], [int tab[10]]) + + Each additional embedded macro call introduces other possible +interesting quotations: + + car(active) + =>ACT + car([active]) + =>ACT, IVE + car([[active]]) + =>active + + In the first case, the top level looks for the arguments of `car', +and finds `active'. Because M4 evaluates its arguments before applying +the macro, `active' is expanded, which results in: + + car(ACT, IVE) + =>ACT + +In the second case, the top level gives `active' as first and only +argument of `car', which results in: + + active + =>ACT, IVE + +i.e., the argument is evaluated _after_ the macro that invokes it. In +the third case, `car' receives `[active]', which results in: + + [active] + =>active + +exactly as we already saw above. + + The example above, applied to a more realistic example, gives: + + car(int tab[10];) + =>int tab10; + car([int tab[10];]) + =>int tab10; + car([[int tab[10];]]) + =>int tab[10]; + +Huh? The first case is easily understood, but why is the second wrong, +and the third right? To understand that, you must know that after M4 +expands a macro, the resulting text is immediately subjected to macro +expansion and quote removal. This means that the quote removal occurs +twice--first before the argument is passed to the `car' macro, and +second after the `car' macro expands to the first argument. + + As the author of the Autoconf macro `car', you then consider it to +be incorrect that your users have to double-quote the arguments of +`car', so you "fix" your macro. Let's call it `qar' for quoted car: + + define([qar], [[$1]]) + +and check that `qar' is properly fixed: + + qar([int tab[10];]) + =>int tab[10]; + +Ahhh! That's much better. + + But note what you've done: now that the result of `qar' is always a +literal string, the only time a user can use nested macros is if she +relies on an _unquoted_ macro call: + + qar(active) + =>ACT + qar([active]) + =>active + +leaving no way for her to reproduce what she used to do with `car': + + car([active]) + =>ACT, IVE + +Worse yet: she wants to use a macro that produces a set of `cpp' macros: + + define([my_includes], [#include <stdio.h>]) + car([my_includes]) + =>#include <stdio.h> + qar(my_includes) + error-->EOF in argument list + + This macro, `qar', because it double quotes its arguments, forces +its users to leave their macro calls unquoted, which is dangerous. +Commas and other active symbols are interpreted by M4 before they are +given to the macro, often not in the way the users expect. Also, +because `qar' behaves differently from the other macros, it's an +exception that should be avoided in Autoconf. + + +File: autoconf.info, Node: Changequote is Evil, Next: Quadrigraphs, Prev: Quotation and Nested Macros, Up: M4 Quotation + +8.1.5 `changequote' is Evil +--------------------------- + +The temptation is often high to bypass proper quotation, in particular +when it's late at night. Then, many experienced Autoconf hackers +finally surrender to the dark side of the force and use the ultimate +weapon: `changequote'. + + The M4 builtin `changequote' belongs to a set of primitives that +allow one to adjust the syntax of the language to adjust it to one's +needs. For instance, by default M4 uses ``' and `'' as quotes, but in +the context of shell programming (and actually of most programming +languages), that's about the worst choice one can make: because of +strings and back-quoted expressions in shell code (such as `'this'' and +``that`'), and because of literal characters in usual programming +languages (as in `'0''), there are many unbalanced ``' and `''. Proper +M4 quotation then becomes a nightmare, if not impossible. In order to +make M4 useful in such a context, its designers have equipped it with +`changequote', which makes it possible to choose another pair of +quotes. M4sugar, M4sh, Autoconf, and Autotest all have chosen to use +`[' and `]'. Not especially because they are unlikely characters, but +_because they are characters unlikely to be unbalanced_. + + There are other magic primitives, such as `changecom' to specify +what syntactic forms are comments (it is common to see `changecom(<!--, +-->)' when M4 is used to produce HTML pages), `changeword' and +`changesyntax' to change other syntactic details (such as the character +to denote the Nth argument, `$' by default, the parentheses around +arguments, etc.). + + These primitives are really meant to make M4 more useful for specific +domains: they should be considered like command line options: +`--quotes', `--comments', `--words', and `--syntax'. Nevertheless, +they are implemented as M4 builtins, as it makes M4 libraries self +contained (no need for additional options). + + There lies the problem... + + + The problem is that it is then tempting to use them in the middle of +an M4 script, as opposed to its initialization. This, if not carefully +thought out, can lead to disastrous effects: _you are changing the +language in the middle of the execution_. Changing and restoring the +syntax is often not enough: if you happened to invoke macros in between, +these macros are lost, as the current syntax is probably not the one +they were implemented with. + + +File: autoconf.info, Node: Quadrigraphs, Next: Balancing Parentheses, Prev: Changequote is Evil, Up: M4 Quotation + +8.1.6 Quadrigraphs +------------------ + +When writing an Autoconf macro you may occasionally need to generate +special characters that are difficult to express with the standard +Autoconf quoting rules. For example, you may need to output the regular +expression `[^[]', which matches any character other than `['. This +expression contains unbalanced brackets so it cannot be put easily into +an M4 macro. + + Additionally, there are a few m4sugar macros (such as `m4_split' and +`m4_expand') which internally use special markers in addition to the +regular quoting characters. If the arguments to these macros contain +the literal strings `-=<{(' or `)}>=-', the macros might behave +incorrectly. + + You can work around these problems by using one of the following +"quadrigraphs": + +`@<:@' + `[' + +`@:>@' + `]' + +`@S|@' + `$' + +`@%:@' + `#' + +`@{:@' + `(' + +`@:}@' + `)' + +`@&t@' + Expands to nothing. + + Quadrigraphs are replaced at a late stage of the translation process, +after `m4' is run, so they do not get in the way of M4 quoting. For +example, the string `^@<:@', independently of its quotation, appears as +`^[' in the output. + + The empty quadrigraph can be used: + + - to mark trailing spaces explicitly + + Trailing spaces are smashed by `autom4te'. This is a feature. + + - to produce quadrigraphs and other strings reserved by m4sugar + + For instance `@<@&t@:@' produces `@<:@'. For a more contrived + example: + + m4_define([a], [A])m4_define([b], [B])m4_define([c], [C])dnl + m4_split([a )}>=- b -=<{( c]) + =>[a], [], [B], [], [c] + m4_split([a )}@&t@>=- b -=<@&t@{( c]) + =>[a], [)}>=-], [b], [-=<{(], [c] + + - to escape _occurrences_ of forbidden patterns + + For instance you might want to mention `AC_FOO' in a comment, while + still being sure that `autom4te' still catches unexpanded `AC_*'. + Then write `AC@&t@_FOO'. + + The name `@&t@' was suggested by Paul Eggert: + + I should give some credit to the `@&t@' pun. The `&' is my own + invention, but the `t' came from the source code of the ALGOL68C + compiler, written by Steve Bourne (of Bourne shell fame), and + which used `mt' to denote the empty string. In C, it would have + looked like something like: + + char const mt[] = ""; + + but of course the source code was written in Algol 68. + + I don't know where he got `mt' from: it could have been his own + invention, and I suppose it could have been a common pun around the + Cambridge University computer lab at the time. + + +File: autoconf.info, Node: Balancing Parentheses, Next: Quotation Rule Of Thumb, Prev: Quadrigraphs, Up: M4 Quotation + +8.1.7 Dealing with unbalanced parentheses +----------------------------------------- + +One of the pitfalls of portable shell programming is that `case' +statements require unbalanced parentheses (*note Limitations of Shell +Builtins: case.). With syntax highlighting editors, the presence of +unbalanced `)' can interfere with editors that perform syntax +highlighting of macro contents based on finding the matching `('. +Another concern is how much editing must be done when transferring code +snippets between shell scripts and macro definitions. But most +importantly, the presence of unbalanced parentheses can introduce +expansion bugs. + + For an example, here is an underquoted attempt to use the macro +`my_case', which happens to expand to a portable `case' statement: + + AC_DEFUN([my_case], + [case $file_name in + *.c) echo "C source code";; + esac]) + AS_IF(:, my_case) + +In the above example, the `AS_IF' call underquotes its arguments. As a +result, the unbalanced `)' generated by the premature expansion of +`my_case' results in expanding `AS_IF' with a truncated parameter, and +the expansion is syntactically invalid: + + if :; then + case $file_name in + *.c + fi echo "C source code";; + esac) + + If nothing else, this should emphasize the importance of the quoting +arguments to macro calls. On the other hand, there are several +variations for defining `my_case' to be more robust, even when used +without proper quoting, each with some benefits and some drawbacks. + + Creative literal shell comment + AC_DEFUN([my_case], + [case $file_name in #( + *.c) echo "C source code";; + esac]) + This version provides balanced parentheses to several editors, and + can be copied and pasted into a terminal as is. Unfortunately, it + is still unbalanced as an Autoconf argument, since `#(' is an M4 + comment that masks the normal properties of `('. + + Quadrigraph shell comment + AC_DEFUN([my_case], + [case $file_name in @%:@( + *.c) echo "C source code";; + esac]) + This version provides balanced parentheses to even more editors, + and can be used as a balanced Autoconf argument. Unfortunately, + it requires some editing before it can be copied and pasted into a + terminal, and the use of the quadrigraph `@%:@' for `#' reduces + readability. + + Quoting just the parenthesis + AC_DEFUN([my_case], + [case $file_name in + *.c[)] echo "C source code";; + esac]) + This version quotes the `)', so that it can be used as a balanced + Autoconf argument. As written, this is not balanced to an editor, + but it can be coupled with `[#(]' to meet that need, too. + However, it still requires some edits before it can be copied and + pasted into a terminal. + + Double-quoting the entire statement + AC_DEFUN([my_case], + [[case $file_name in #( + *.c) echo "C source code";; + esac]]) + Since the entire macro is double-quoted, there is no problem with + using this as an Autoconf argument; and since the double-quoting + is over the entire statement, this code can be easily copied and + pasted into a terminal. However, the double quoting prevents the + expansion of any macros inside the case statement, which may cause + its own set of problems. + + Using `AS_CASE' + AC_DEFUN([my_case], + [AS_CASE([$file_name], + [*.c], [echo "C source code"])]) + This version avoids the balancing issue altogether, by relying on + `AS_CASE' (*note Common Shell Constructs::); it also allows for the + expansion of `AC_REQUIRE' to occur prior to the entire case + statement, rather than within a branch of the case statement that + might not be taken. However, the abstraction comes with a penalty + that it is no longer a quick copy, paste, and edit to get back to + shell code. + + +File: autoconf.info, Node: Quotation Rule Of Thumb, Prev: Balancing Parentheses, Up: M4 Quotation + +8.1.8 Quotation Rule Of Thumb +----------------------------- + +To conclude, the quotation rule of thumb is: + + _One pair of quotes per pair of parentheses._ + + Never over-quote, never under-quote, in particular in the definition +of macros. In the few places where the macros need to use brackets +(usually in C program text or regular expressions), properly quote _the +arguments_! + + It is common to read Autoconf programs with snippets like: + + AC_TRY_LINK( + changequote(<<, >>)dnl + <<#include <time.h> + #ifndef tzname /* For SGI. */ + extern char *tzname[]; /* RS6000 and others reject char **tzname. */ + #endif>>, + changequote([, ])dnl + [atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no) + +which is incredibly useless since `AC_TRY_LINK' is _already_ double +quoting, so you just need: + + AC_TRY_LINK( + [#include <time.h> + #ifndef tzname /* For SGI. */ + extern char *tzname[]; /* RS6000 and others reject char **tzname. */ + #endif], + [atoi (*tzname);], + [ac_cv_var_tzname=yes], + [ac_cv_var_tzname=no]) + +The M4-fluent reader might note that these two examples are rigorously +equivalent, since M4 swallows both the `changequote(<<, >>)' and `<<' +`>>' when it "collects" the arguments: these quotes are not part of the +arguments! + + Simplified, the example above is just doing this: + + changequote(<<, >>)dnl + <<[]>> + changequote([, ])dnl + +instead of simply: + + [[]] + + With macros that do not double quote their arguments (which is the +rule), double-quote the (risky) literals: + + AC_LINK_IFELSE([AC_LANG_PROGRAM( + [[#include <time.h> + #ifndef tzname /* For SGI. */ + extern char *tzname[]; /* RS6000 and others reject char **tzname. */ + #endif]], + [atoi (*tzname);])], + [ac_cv_var_tzname=yes], + [ac_cv_var_tzname=no]) + + Please note that the macro `AC_TRY_LINK' is obsolete, so you really +should be using `AC_LINK_IFELSE' instead. + + *Note Quadrigraphs::, for what to do if you run into a hopeless case +where quoting does not suffice. + + When you create a `configure' script using newly written macros, +examine it carefully to check whether you need to add more quotes in +your macros. If one or more words have disappeared in the M4 output, +you need more quotes. When in doubt, quote. + + However, it's also possible to put on too many layers of quotes. If +this happens, the resulting `configure' script may contain unexpanded +macros. The `autoconf' program checks for this problem by looking for +the string `AC_' in `configure'. However, this heuristic does not work +in general: for example, it does not catch overquoting in `AC_DEFINE' +descriptions. + + +File: autoconf.info, Node: Using autom4te, Next: Programming in M4sugar, Prev: M4 Quotation, Up: Programming in M4 + +8.2 Using `autom4te' +==================== + +The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition +to Autoconf per se, heavily rely on M4. All these different uses +revealed common needs factored into a layer over M4: `autom4te'(1). + + `autom4te' is a preprocessor that is like `m4'. It supports M4 +extensions designed for use in tools like Autoconf. + +* Menu: + +* autom4te Invocation:: A GNU M4 wrapper +* Customizing autom4te:: Customizing the Autoconf package + + ---------- Footnotes ---------- + + (1) Yet another great name from Lars J. Aas. + + +File: autoconf.info, Node: autom4te Invocation, Next: Customizing autom4te, Up: Using autom4te + +8.2.1 Invoking `autom4te' +------------------------- + +The command line arguments are modeled after M4's: + + autom4te OPTIONS FILES + +where the FILES are directly passed to `m4'. By default, GNU M4 is +found during configuration, but the environment variable `M4' can be +set to tell `autom4te' where to look. In addition to the regular +expansion, it handles the replacement of the quadrigraphs (*note +Quadrigraphs::), and of `__oline__', the current line in the output. +It supports an extended syntax for the FILES: + +`FILE.m4f' + This file is an M4 frozen file. Note that _all the previous files + are ignored_. See the option `--melt' for the rationale. + +`FILE?' + If found in the library path, the FILE is included for expansion, + otherwise it is ignored instead of triggering a failure. + + + Of course, it supports the Autoconf common subset of options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Report processing steps. + +`--debug' +`-d' + Don't remove the temporary files and be even more verbose. + +`--include=DIR' +`-I DIR' + Also look for input files in DIR. Multiple invocations accumulate. + +`--output=FILE' +`-o FILE' + Save output (script or trace) to FILE. The file `-' stands for + the standard output. + + + As an extension of `m4', it includes the following options: + +`--warnings=CATEGORY' +`-W CATEGORY' + Report the warnings related to CATEGORY (which can actually be a + comma separated list). *Note Reporting Messages::, macro + `AC_DIAGNOSE', for a comprehensive list of categories. Special + values include: + + `all' + report all the warnings + + `none' + report none + + `error' + treats warnings as errors + + `no-CATEGORY' + disable warnings falling into CATEGORY + + Warnings about `syntax' are enabled by default, and the environment + variable `WARNINGS', a comma separated list of categories, is + honored. `autom4te -W CATEGORY' actually behaves as if you had + run: + + autom4te --warnings=syntax,$WARNINGS,CATEGORY + + For example, if you want to disable defaults and `WARNINGS' of + `autom4te', but enable the warnings about obsolete constructs, you + would use `-W none,obsolete'. + + `autom4te' displays a back trace for errors, but not for warnings; + if you want them, just pass `-W error'. + +`--melt' +`-M' + Do not use frozen files. Any argument `FILE.m4f' is replaced by + `FILE.m4'. This helps tracing the macros which are executed only + when the files are frozen, typically `m4_define'. For instance, + running: + + autom4te --melt 1.m4 2.m4f 3.m4 4.m4f input.m4 + + is roughly equivalent to running: + + m4 1.m4 2.m4 3.m4 4.m4 input.m4 + + while + + autom4te 1.m4 2.m4f 3.m4 4.m4f input.m4 + + is equivalent to: + + m4 --reload-state=4.m4f input.m4 + +`--freeze' +`-F' + Produce a frozen state file. `autom4te' freezing is stricter than + M4's: it must produce no warnings, and no output other than empty + lines (a line with white space is _not_ empty) and comments + (starting with `#'). Unlike `m4''s similarly-named option, this + option takes no argument: + + autom4te 1.m4 2.m4 3.m4 --freeze --output=3.m4f + + corresponds to + + m4 1.m4 2.m4 3.m4 --freeze-state=3.m4f + +`--mode=OCTAL-MODE' +`-m OCTAL-MODE' + Set the mode of the non-traces output to OCTAL-MODE; by default + `0666'. + + + As another additional feature over `m4', `autom4te' caches its +results. GNU M4 is able to produce a regular output and traces at the +same time. Traces are heavily used in the GNU Build System: +`autoheader' uses them to build `config.h.in', `autoreconf' to +determine what GNU Build System components are used, `automake' to +"parse" `configure.ac' etc. To avoid recomputation, traces are cached +while performing regular expansion, and conversely. This cache is +(actually, the caches are) stored in the directory `autom4te.cache'. +_It can safely be removed_ at any moment (especially if for some reason +`autom4te' considers it trashed). + +`--cache=DIRECTORY' +`-C DIRECTORY' + Specify the name of the directory where the result should be + cached. Passing an empty value disables caching. Be sure to pass + a relative file name, as for the time being, global caches are not + supported. + +`--no-cache' + Don't cache the results. + +`--force' +`-f' + If a cache is used, consider it obsolete (but update it anyway). + + + Because traces are so important to the GNU Build System, `autom4te' +provides high level tracing features as compared to M4, and helps +exploiting the cache: + +`--trace=MACRO[:FORMAT]' +`-t MACRO[:FORMAT]' + Trace the invocations of MACRO according to the FORMAT. Multiple + `--trace' arguments can be used to list several macros. Multiple + `--trace' arguments for a single macro are not cumulative; + instead, you should just make FORMAT as long as needed. + + The FORMAT is a regular string, with newlines if desired, and + several special escape codes. It defaults to `$f:$l:$n:$%'. It + can use the following special escapes: + + `$$' + The character `$'. + + `$f' + The file name from which MACRO is called. + + `$l' + The line number from which MACRO is called. + + `$d' + The depth of the MACRO call. This is an M4 technical detail + that you probably don't want to know about. + + `$n' + The name of the MACRO. + + `$NUM' + The NUMth argument of the call to MACRO. + + `$@' + `$SEP@' + `${SEPARATOR}@' + All the arguments passed to MACRO, separated by the character + SEP or the string SEPARATOR (`,' by default). Each argument + is quoted, i.e., enclosed in a pair of square brackets. + + `$*' + `$SEP*' + `${SEPARATOR}*' + As above, but the arguments are not quoted. + + `$%' + `$SEP%' + `${SEPARATOR}%' + As above, but the arguments are not quoted, all new line + characters in the arguments are smashed, and the default + separator is `:'. + + The escape `$%' produces single-line trace outputs (unless + you put newlines in the `separator'), while `$@' and `$*' do + not. + + *Note autoconf Invocation::, for examples of trace uses. + +`--preselect=MACRO' +`-p MACRO' + Cache the traces of MACRO, but do not enable traces. This is + especially important to save CPU cycles in the future. For + instance, when invoked, `autoconf' preselects all the macros that + `autoheader', `automake', `autoreconf', etc., trace, so that + running `m4' is not needed to trace them: the cache suffices. + This results in a huge speed-up. + + + Finally, `autom4te' introduces the concept of "Autom4te libraries". +They consists in a powerful yet extremely simple feature: sets of +combined command line arguments: + +`--language=LANGUAGE' +`-l LANGUAGE' + Use the LANGUAGE Autom4te library. Current languages include: + + `M4sugar' + create M4sugar output. + + `M4sh' + create M4sh executable shell scripts. + + `Autotest' + create Autotest executable test suites. + + `Autoconf-without-aclocal-m4' + create Autoconf executable configure scripts without reading + `aclocal.m4'. + + `Autoconf' + create Autoconf executable configure scripts. This language + inherits all the characteristics of + `Autoconf-without-aclocal-m4' and additionally reads + `aclocal.m4'. + +`--prepend-include=DIR' +`-B DIR' + Prepend directory DIR to the search path. This is used to include + the language-specific files before any third-party macros. + + + As an example, if Autoconf is installed in its default location, +`/usr/local', the command `autom4te -l m4sugar foo.m4' is strictly +equivalent to the command: + + autom4te --prepend-include /usr/local/share/autoconf \ + m4sugar/m4sugar.m4f --warnings syntax foo.m4 + +Recursive expansion applies here: the command `autom4te -l m4sh foo.m4' +is the same as `autom4te --language M4sugar m4sugar/m4sh.m4f foo.m4', +i.e.: + + autom4te --prepend-include /usr/local/share/autoconf \ + m4sugar/m4sugar.m4f m4sugar/m4sh.m4f --mode 777 foo.m4 + +The definition of the languages is stored in `autom4te.cfg'. + + +File: autoconf.info, Node: Customizing autom4te, Prev: autom4te Invocation, Up: Using autom4te + +8.2.2 Customizing `autom4te' +---------------------------- + +One can customize `autom4te' via `~/.autom4te.cfg' (i.e., as found in +the user home directory), and `./.autom4te.cfg' (i.e., as found in the +directory from which `autom4te' is run). The order is first reading +`autom4te.cfg', then `~/.autom4te.cfg', then `./.autom4te.cfg', and +finally the command line arguments. + + In these text files, comments are introduced with `#', and empty +lines are ignored. Customization is performed on a per-language basis, +wrapped in between a `begin-language: "LANGUAGE"', `end-language: +"LANGUAGE"' pair. + + Customizing a language stands for appending options (*note autom4te +Invocation::) to the current definition of the language. Options, and +more generally arguments, are introduced by `args: ARGUMENTS'. You may +use the traditional shell syntax to quote the ARGUMENTS. + + As an example, to disable Autoconf caches (`autom4te.cache') +globally, include the following lines in `~/.autom4te.cfg': + +## ------------------ ## +## User Preferences. ## +## ------------------ ## + +begin-language: "Autoconf-without-aclocal-m4" +args: --no-cache +end-language: "Autoconf-without-aclocal-m4" + + +File: autoconf.info, Node: Programming in M4sugar, Next: Debugging via autom4te, Prev: Using autom4te, Up: Programming in M4 + +8.3 Programming in M4sugar +========================== + +M4 by itself provides only a small, but sufficient, set of all-purpose +macros. M4sugar introduces additional generic macros. Its name was +coined by Lars J. Aas: "Readability And Greater Understanding Stands 4 +M4sugar". + + M4sugar reserves the macro namespace `^_m4_' for internal use, and +the macro namespace `^m4_' for M4sugar macros. You should not define +your own macros into these namespaces. + +* Menu: + +* Redefined M4 Macros:: M4 builtins changed in M4sugar +* Diagnostic Macros:: Diagnostic messages from M4sugar +* Diversion support:: Diversions in M4sugar +* Conditional constructs:: Conditions in M4 +* Looping constructs:: Iteration in M4 +* Evaluation Macros:: More quotation and evaluation control +* Text processing Macros:: String manipulation in M4 +* Number processing Macros:: Arithmetic computation in M4 +* Set manipulation Macros:: Set manipulation in M4 +* Forbidden Patterns:: Catching unexpanded macros + + +File: autoconf.info, Node: Redefined M4 Macros, Next: Diagnostic Macros, Up: Programming in M4sugar + +8.3.1 Redefined M4 Macros +------------------------- + +With a few exceptions, all the M4 native macros are moved in the `m4_' +pseudo-namespace, e.g., M4sugar renames `define' as `m4_define' etc. + + The list of macros unchanged from M4, except for their name, is: + - m4_builtin + + - m4_changecom + + - m4_changequote + + - m4_debugfile + + - m4_debugmode + + - m4_decr + + - m4_define + + - m4_divnum + + - m4_errprint + + - m4_esyscmd + + - m4_eval + + - m4_format + + - m4_ifdef + + - m4_incr + + - m4_index + + - m4_indir + + - m4_len + + - m4_pushdef + + - m4_shift + + - m4_substr + + - m4_syscmd + + - m4_sysval + + - m4_traceoff + + - m4_traceon + + - m4_translit + + Some M4 macros are redefined, and are slightly incompatible with +their native equivalent. + + -- Macro: __file__ + -- Macro: __line__ + All M4 macros starting with `__' retain their original name: for + example, no `m4__file__' is defined. + + -- Macro: __oline__ + This is not technically a macro, but a feature of Autom4te. The + sequence `__oline__' can be used similarly to the other m4sugar + location macros, but rather than expanding to the location of the + input file, it is translated to the line number where it appears + in the output file after all other M4 expansions. + + -- Macro: dnl + This macro kept its original name: no `m4_dnl' is defined. + + -- Macro: m4_bpatsubst (STRING, REGEXP, [REPLACEMENT]) + This macro corresponds to `patsubst'. The name `m4_patsubst' is + kept for future versions of M4sugar, once GNU M4 2.0 is released + and supports extended regular expression syntax. + + -- Macro: m4_bregexp (STRING, REGEXP, [REPLACEMENT]) + This macro corresponds to `regexp'. The name `m4_regexp' is kept + for future versions of M4sugar, once GNU M4 2.0 is released and + supports extended regular expression syntax. + + -- Macro: m4_copy (SOURCE, DEST) + -- Macro: m4_copy_force (SOURCE, DEST) + -- Macro: m4_rename (SOURCE, DEST) + -- Macro: m4_rename_force (SOURCE, DEST) + These macros aren't directly builtins, but are closely related to + `m4_pushdef' and `m4_defn'. `m4_copy' and `m4_rename' ensure that + DEST is undefined, while `m4_copy_force' and `m4_rename_force' + overwrite any existing definition. All four macros then proceed + to copy the entire pushdef stack of definitions of SOURCE over to + DEST. `m4_copy' and `m4_copy_force' preserve the source + (including in the special case where SOURCE is undefined), while + `m4_rename' and `m4_rename_force' undefine the original macro name + (making it an error to rename an undefined SOURCE). + + Note that attempting to invoke a renamed macro might not work, + since the macro may have a dependence on helper macros accessed + via composition of `$0' but that were not also renamed; likewise, + other macros may have a hard-coded dependence on SOURCE and could + break if SOURCE has been deleted. On the other hand, it is always + safe to rename a macro to temporarily move it out of the way, then + rename it back later to restore original semantics. + + -- Macro: m4_defn (MACRO...) + This macro fails if MACRO is not defined, even when using older + versions of M4 that did not warn. See `m4_undefine'. + Unfortunately, in order to support these older versions of M4, + there are some situations involving unbalanced quotes where + concatenating multiple macros together will work in newer M4 but + not in m4sugar; use quadrigraphs to work around this. + + -- Macro: m4_divert (DIVERSION) + M4sugar relies heavily on diversions, so rather than behaving as a + primitive, `m4_divert' behaves like: + m4_divert_pop()m4_divert_push([DIVERSION]) + *Note Diversion support::, for more details about the use of the + diversion stack. In particular, this implies that DIVERSION + should be a named diversion rather than a raw number. But be + aware that it is seldom necessary to explicitly change the + diversion stack, and that when done incorrectly, it can lead to + syntactically invalid scripts. + + -- Macro: m4_dumpdef (NAME...) + -- Macro: m4_dumpdefs (NAME...) + `m4_dumpdef' is like the M4 builtin, except that this version + requires at least one argument, output always goes to standard + error rather than the current debug file, no sorting is done on + multiple arguments, and an error is issued if any NAME is + undefined. `m4_dumpdefs' is a convenience macro that calls + `m4_dumpdef' for all of the `m4_pushdef' stack of definitions, + starting with the current, and silently does nothing if NAME is + undefined. + + Unfortunately, due to a limitation in M4 1.4.x, any macro defined + as a builtin is output as the empty string. This behavior is + rectified by using M4 1.6 or newer. However, this behavior + difference means that `m4_dumpdef' should only be used while + developing m4sugar macros, and never in the final published form + of a macro. + + -- Macro: m4_esyscmd_s (COMMAND) + Like `m4_esyscmd', this macro expands to the result of running + COMMAND in a shell. The difference is that any trailing newlines + are removed, so that the output behaves more like shell command + substitution. + + -- Macro: m4_exit (EXIT-STATUS) + This macro corresponds to `m4exit'. + + -- Macro: m4_if (COMMENT) + -- Macro: m4_if (STRING-1, STRING-2, EQUAL, [NOT-EQUAL]) + -- Macro: m4_if (STRING-1, STRING-2, EQUAL-1, STRING-3, STRING-4, + EQUAL-2, ..., [NOT-EQUAL]) + This macro corresponds to `ifelse'. STRING-1 and STRING-2 are + compared literally, so usually one of the two arguments is passed + unquoted. *Note Conditional constructs::, for more conditional + idioms. + + -- Macro: m4_include (FILE) + -- Macro: m4_sinclude (FILE) + Like the M4 builtins, but warn against multiple inclusions of FILE. + + -- Macro: m4_mkstemp (TEMPLATE) + -- Macro: m4_maketemp (TEMPLATE) + Posix requires `maketemp' to replace the trailing `X' characters + in TEMPLATE with the process id, without regards to the existence + of a file by that name, but this a security hole. When this was + pointed out to the Posix folks, they agreed to invent a new macro + `mkstemp' that always creates a uniquely named file, but not all + versions of GNU M4 support the new macro. In M4sugar, + `m4_maketemp' and `m4_mkstemp' are synonyms for each other, and + both have the secure semantics regardless of which macro the + underlying M4 provides. + + -- Macro: m4_popdef (MACRO...) + This macro fails if MACRO is not defined, even when using older + versions of M4 that did not warn. See `m4_undefine'. + + -- Macro: m4_undefine (MACRO...) + This macro fails if MACRO is not defined, even when using older + versions of M4 that did not warn. Use + + m4_ifdef([MACRO], [m4_undefine([MACRO])]) + + if you are not sure whether MACRO is defined. + + -- Macro: m4_undivert (DIVERSION...) + Unlike the M4 builtin, at least one DIVERSION must be specified. + Also, since the M4sugar diversion stack prefers named diversions, + the use of `m4_undivert' to include files is risky. *Note + Diversion support::, for more details about the use of the + diversion stack. But be aware that it is seldom necessary to + explicitly change the diversion stack, and that when done + incorrectly, it can lead to syntactically invalid scripts. + + -- Macro: m4_wrap (TEXT) + -- Macro: m4_wrap_lifo (TEXT) + These macros correspond to `m4wrap'. Posix requires arguments of + multiple wrap calls to be reprocessed at EOF in the same order as + the original calls (first-in, first-out). GNU M4 versions through + 1.4.10, however, reprocess them in reverse order (last-in, + first-out). Both orders are useful, therefore, you can rely on + `m4_wrap' to provide FIFO semantics and `m4_wrap_lifo' for LIFO + semantics, regardless of the underlying GNU M4 version. + + Unlike the GNU M4 builtin, these macros only recognize one + argument, and avoid token pasting between consecutive invocations. + On the other hand, nested calls to `m4_wrap' from within wrapped + text work just as in the builtin. + + +File: autoconf.info, Node: Diagnostic Macros, Next: Diversion support, Prev: Redefined M4 Macros, Up: Programming in M4sugar + +8.3.2 Diagnostic messages from M4sugar +-------------------------------------- + +When macros statically diagnose abnormal situations, benign or fatal, +they should report them using these macros. For issuing dynamic issues, +i.e., when `configure' is run, see *note Printing Messages::. + + -- Macro: m4_assert (EXPRESSION, [EXIT-STATUS = `1']) + Assert that the arithmetic EXPRESSION evaluates to non-zero. + Otherwise, issue a fatal error, and exit `autom4te' with + EXIT-STATUS. + + -- Macro: m4_errprintn (MESSAGE) + Similar to the builtin `m4_errprint', except that a newline is + guaranteed after MESSAGE. + + -- Macro: m4_fatal (MESSAGE) + Report a severe error MESSAGE prefixed with the current location, + and have `autom4te' die. + + -- Macro: m4_location + Useful as a prefix in a message line. Short for: + __file__:__line__ + + -- Macro: m4_warn (CATEGORY, MESSAGE) + Report MESSAGE as a warning (or as an error if requested by the + user) if warnings of the CATEGORY are turned on. If the message + is emitted, it is prefixed with the current location, and followed + by a call trace of all macros defined via `AC_DEFUN' used to get + to the current expansion. You are encouraged to use standard + categories, which currently include: + + `all' + messages that don't fall into one of the following + categories. Use of an empty CATEGORY is equivalent. + + `cross' + related to cross compilation issues. + + `obsolete' + use of an obsolete construct. + + `syntax' + dubious syntactic constructs, incorrectly ordered macro calls. + + +File: autoconf.info, Node: Diversion support, Next: Conditional constructs, Prev: Diagnostic Macros, Up: Programming in M4sugar + +8.3.3 Diversion support +----------------------- + +M4sugar makes heavy use of diversions under the hood, because it is +often the case that text that must appear early in the output is not +discovered until late in the input. Additionally, some of the +topological sorting algorithms used in resolving macro dependencies use +diversions. However, most macros should not need to change diversions +directly, but rather rely on higher-level M4sugar macros to manage +diversions transparently. If you change diversions improperly, you +risk generating a syntactically invalid script, because an incorrect +diversion will violate assumptions made by many macros about whether +prerequisite text has been previously output. In short, if you +manually change the diversion, you should not expect any macros +provided by the Autoconf package to work until you have restored the +diversion stack back to its original state. + + In the rare case that it is necessary to write a macro that +explicitly outputs text to a different diversion, it is important to be +aware of an M4 limitation regarding diversions: text only goes to a +diversion if it is not part of argument collection. Therefore, any +macro that changes the current diversion cannot be used as an unquoted +argument to another macro, but must be expanded at the top level. The +macro `m4_expand' will diagnose any attempt to change diversions, since +it is generally useful only as an argument to another macro. The +following example shows what happens when diversion manipulation is +attempted within macro arguments: + + m4_do([normal text] + m4_divert_push([KILL])unwanted[]m4_divert_pop([KILL]) + [m4_divert_push([KILL])discarded[]m4_divert_pop([KILL])])dnl + =>normal text + =>unwanted + +Notice that the unquoted text `unwanted' is output, even though it was +processed while the current diversion was `KILL', because it was +collected as part of the argument to `m4_do'. However, the text +`discarded' disappeared as desired, because the diversion changes were +single-quoted, and were not expanded until the top-level rescan of the +output of `m4_do'. + + To make diversion management easier, M4sugar uses the concept of +named diversions. Rather than using diversion numbers directly, it is +nicer to associate a name with each diversion. The diversion number +associated with a particular diversion name is an implementation +detail, and a syntax warning is issued if a diversion number is used +instead of a name. In general, you should not output text to a named +diversion until after calling the appropriate initialization routine +for your language (`m4_init', `AS_INIT', `AT_INIT', ...), although +there are some exceptions documented below. + + M4sugar defines two named diversions. +`KILL' + Text written to this diversion is discarded. This is the default + diversion once M4sugar is initialized. + +`GROW' + This diversion is used behind the scenes by topological sorting + macros, such as `AC_REQUIRE'. + + M4sh adds several more named diversions. +`BINSH' + This diversion is reserved for the `#!' interpreter line. + +`HEADER-REVISION' + This diversion holds text from `AC_REVISION'. + +`HEADER-COMMENT' + This diversion holds comments about the purpose of a file. + +`HEADER-COPYRIGHT' + This diversion is managed by `AC_COPYRIGHT'. + +`M4SH-SANITIZE' + This diversion contains M4sh sanitization code, used to ensure + M4sh is executing in a reasonable shell environment. + +`M4SH-INIT' + This diversion contains M4sh initialization code, initializing + variables that are required by other M4sh macros. + +`BODY' + This diversion contains the body of the shell code, and is the + default diversion once M4sh is initialized. + + Autotest inherits diversions from M4sh, and changes the default +diversion from `BODY' back to `KILL'. It also adds several more named +diversions, with the following subset designed for developer use. +`PREPARE_TESTS' + This diversion contains initialization sequences which are executed + after `atconfig' and `atlocal', and after all command line + arguments have been parsed, but prior to running any tests. It + can be used to set up state that is required across all tests. + This diversion will work even before `AT_INIT'. + + Autoconf inherits diversions from M4sh, and adds the following named +diversions which developers can utilize. +`DEFAULTS' + This diversion contains shell variable assignments to set defaults + that must be in place before arguments are parsed. This diversion + is placed early enough in `configure' that it is unsafe to expand + any autoconf macros into this diversion. + +`HELP_ENABLE' + If `AC_PRESERVE_HELP_ORDER' was used, then text placed in this + diversion will be included as part of a quoted here-doc providing + all of the `--help' output of `configure' related to options + created by `AC_ARG_WITH' and `AC_ARG_ENABLE'. + +`INIT_PREPARE' + This diversion occurs after all command line options have been + parsed, but prior to the main body of the `configure' script. This + diversion is the last chance to insert shell code such as variable + assignments or shell function declarations that will used by the + expansion of other macros. + + For now, the remaining named diversions of Autoconf, Autoheader, and +Autotest are not documented. In other words, intentionally outputting +text into an undocumented diversion is subject to breakage in a future +release of Autoconf. + + -- Macro: m4_cleardivert (DIVERSION...) + Permanently discard any text that has been diverted into DIVERSION. + + -- Macro: m4_divert_once (DIVERSION, [CONTENT]) + Similar to `m4_divert_text', except that CONTENT is only output to + DIVERSION if this is the first time that `m4_divert_once' has been + called with its particular arguments. + + -- Macro: m4_divert_pop ([DIVERSION]) + If provided, check that the current diversion is indeed DIVERSION. + Then change to the diversion located earlier on the stack, giving + an error if an attempt is made to pop beyond the initial m4sugar + diversion of `KILL'. + + -- Macro: m4_divert_push (DIVERSION) + Remember the former diversion on the diversion stack, and output + subsequent text into DIVERSION. M4sugar maintains a diversion + stack, and issues an error if there is not a matching pop for every + push. + + -- Macro: m4_divert_text (DIVERSION, [CONTENT]) + Output CONTENT and a newline into DIVERSION, without affecting the + current diversion. Shorthand for: + m4_divert_push([DIVERSION])CONTENT + m4_divert_pop([DIVERSION])dnl + + One use of `m4_divert_text' is to develop two related macros, where + macro `MY_A' does the work, but adjusts what work is performed + based on whether the optional macro `MY_B' has also been expanded. + Of course, it is possible to use `AC_BEFORE' within `MY_A' to + require that `MY_B' occurs first, if it occurs at all. But this + imposes an ordering restriction on the user; it would be nicer if + macros `MY_A' and `MY_B' can be invoked in either order. The trick + is to let `MY_B' leave a breadcrumb in an early diversion, which + `MY_A' can then use to determine whether `MY_B' has been expanded. + + AC_DEFUN([MY_A], + [# various actions + if test -n "$b_was_used"; then + # extra action + fi]) + AC_DEFUN([MY_B], + [AC_REQUIRE([MY_A])dnl + m4_divert_text([INIT_PREPARE], [b_was_used=true])]) + + + -- Macro: m4_init + Initialize the M4sugar environment, setting up the default named + diversion to be `KILL'. + + +File: autoconf.info, Node: Conditional constructs, Next: Looping constructs, Prev: Diversion support, Up: Programming in M4sugar + +8.3.4 Conditional constructs +---------------------------- + +The following macros provide additional conditional constructs as +convenience wrappers around `m4_if'. + + -- Macro: m4_bmatch (STRING, REGEX-1, VALUE-1, [REGEX-2], [VALUE-2], + ..., [DEFAULT]) + The string STRING is repeatedly compared against a series of REGEX + arguments; if a match is found, the expansion is the corresponding + VALUE, otherwise, the macro moves on to the next REGEX. If no + REGEX match, then the result is the optional DEFAULT, or nothing. + + -- Macro: m4_bpatsubsts (STRING, REGEX-1, SUBST-1, [REGEX-2], + [SUBST-2], ...) + The string STRING is altered by REGEX-1 and SUBST-1, as if by: + m4_bpatsubst([[STRING]], [REGEX], [SUBST]) + + The result of the substitution is then passed through the next set + of REGEX and SUBST, and so forth. An empty SUBST implies deletion + of any matched portions in the current string. Note that this + macro over-quotes STRING; this behavior is intentional, so that + the result of each step of the recursion remains as a quoted + string. However, it means that anchors (`^' and `$' in the REGEX + will line up with the extra quotations, and not the characters of + the original string. The overquoting is removed after the final + substitution. + + -- Macro: m4_case (STRING, VALUE-1, IF-VALUE-1, [VALUE-2], + [IF-VALUE-2], ..., [DEFAULT]) + Test STRING against multiple VALUE possibilities, resulting in the + first IF-VALUE for a match, or in the optional DEFAULT. This is + shorthand for: + m4_if([STRING], [VALUE-1], [IF-VALUE-1], + [STRING], [VALUE-2], [IF-VALUE-2], ..., + [DEFAULT]) + + -- Macro: m4_cond (TEST-1, VALUE-1, IF-VALUE-1, [TEST-2], [VALUE-2], + [IF-VALUE-2], ..., [DEFAULT]) + This macro was introduced in Autoconf 2.62. Similar to `m4_if', + except that each TEST is expanded only when it is encountered. + This is useful for short-circuiting expensive tests; while `m4_if' + requires all its strings to be expanded up front before doing + comparisons, `m4_cond' only expands a TEST when all earlier tests + have failed. + + For an example, these two sequences give the same result, but in + the case where `$1' does not contain a backslash, the `m4_cond' + version only expands `m4_index' once, instead of five times, for + faster computation if this is a common case for `$1'. Notice that + every third argument is unquoted for `m4_if', and quoted for + `m4_cond': + + m4_if(m4_index([$1], [\]), [-1], [$2], + m4_eval(m4_index([$1], [\\]) >= 0), [1], [$2], + m4_eval(m4_index([$1], [\$]) >= 0), [1], [$2], + m4_eval(m4_index([$1], [\`]) >= 0), [1], [$3], + m4_eval(m4_index([$1], [\"]) >= 0), [1], [$3], + [$2]) + m4_cond([m4_index([$1], [\])], [-1], [$2], + [m4_eval(m4_index([$1], [\\]) >= 0)], [1], [$2], + [m4_eval(m4_index([$1], [\$]) >= 0)], [1], [$2], + [m4_eval(m4_index([$1], [\`]) >= 0)], [1], [$3], + [m4_eval(m4_index([$1], [\"]) >= 0)], [1], [$3], + [$2]) + + -- Macro: m4_default (EXPR-1, EXPR-2) + -- Macro: m4_default_quoted (EXPR-1, EXPR-2) + -- Macro: m4_default_nblank (EXPR-1, [EXPR-2]) + -- Macro: m4_default_nblank_quoted (EXPR-1, [EXPR-2]) + If EXPR-1 contains text, use it. Otherwise, select EXPR-2. + `m4_default' expands the result, while `m4_default_quoted' does + not. Useful for providing a fixed default if the expression that + results in EXPR-1 would otherwise be empty. The difference + between `m4_default' and `m4_default_nblank' is whether an + argument consisting of just blanks (space, tab, newline) is + significant. When using the expanding versions, note that an + argument may contain text but still expand to an empty string. + + m4_define([active], [ACTIVE])dnl + m4_define([empty], [])dnl + m4_define([demo1], [m4_default([$1], [$2])])dnl + m4_define([demo2], [m4_default_quoted([$1], [$2])])dnl + m4_define([demo3], [m4_default_nblank([$1], [$2])])dnl + m4_define([demo4], [m4_default_nblank_quoted([$1], [$2])])dnl + demo1([active], [default]) + =>ACTIVE + demo1([], [active]) + =>ACTIVE + demo1([empty], [text]) + => + -demo1([ ], [active])- + =>- - + demo2([active], [default]) + =>active + demo2([], [active]) + =>active + demo2([empty], [text]) + =>empty + -demo2([ ], [active])- + =>- - + demo3([active], [default]) + =>ACTIVE + demo3([], [active]) + =>ACTIVE + demo3([empty], [text]) + => + -demo3([ ], [active])- + =>-ACTIVE- + demo4([active], [default]) + =>active + demo4([], [active]) + =>active + demo4([empty], [text]) + =>empty + -demo4([ ], [active])- + =>-active- + + -- Macro: m4_define_default (MACRO, [DEFAULT-DEFINITION]) + If MACRO does not already have a definition, then define it to + DEFAULT-DEFINITION. + + -- Macro: m4_ifblank (COND, [IF-BLANK], [IF-TEXT]) + -- Macro: m4_ifnblank (COND, [IF-TEXT], [IF-BLANK]) + If COND is empty or consists only of blanks (space, tab, newline), + then expand IF-BLANK; otherwise, expand IF-TEXT. Two variants + exist, in order to make it easier to select the correct logical + sense when using only two parameters. Note that this is more + efficient than the equivalent behavior of: + m4_ifval(m4_normalize([COND]), IF-TEXT, IF-BLANK) + + -- Macro: m4_ifndef (MACRO, IF-NOT-DEFINED, [IF-DEFINED]) + This is shorthand for: + m4_ifdef([MACRO], [IF-DEFINED], [IF-NOT-DEFINED]) + + -- Macro: m4_ifset (MACRO, [IF-TRUE], [IF-FALSE]) + If MACRO is undefined, or is defined as the empty string, expand + to IF-FALSE. Otherwise, expands to IF-TRUE. Similar to: + m4_ifval(m4_defn([MACRO]), [IF-TRUE], [IF-FALSE]) + except that it is not an error if MACRO is undefined. + + -- Macro: m4_ifval (COND, [IF-TRUE], [IF-FALSE]) + Expands to IF-TRUE if COND is not empty, otherwise to IF-FALSE. + This is shorthand for: + m4_if([COND], [], [IF-FALSE], [IF-TRUE]) + + -- Macro: m4_ifvaln (COND, [IF-TRUE], [IF-FALSE]) + Similar to `m4_ifval', except guarantee that a newline is present + after any non-empty expansion. Often followed by `dnl'. + + -- Macro: m4_n (TEXT) + Expand to TEXT, and add a newline if TEXT is not empty. Often + followed by `dnl'. + + +File: autoconf.info, Node: Looping constructs, Next: Evaluation Macros, Prev: Conditional constructs, Up: Programming in M4sugar + +8.3.5 Looping constructs +------------------------ + +The following macros are useful in implementing recursive algorithms in +M4, including loop operations. An M4 list is formed by quoting a list +of quoted elements; generally the lists are comma-separated, although +`m4_foreach_w' is whitespace-separated. For example, the list `[[a], +[b,c]]' contains two elements: `[a]' and `[b,c]'. It is common to see +lists with unquoted elements when those elements are not likely to be +macro names, as in `[fputc_unlocked, fgetc_unlocked]'. + + Although not generally recommended, it is possible for quoted lists +to have side effects; all side effects are expanded only once, and +prior to visiting any list element. On the other hand, the fact that +unquoted macros are expanded exactly once means that macros without +side effects can be used to generate lists. For example, + + m4_foreach([i], [[1], [2], [3]m4_errprintn([hi])], [i]) + error-->hi + =>123 + m4_define([list], [[1], [2], [3]]) + => + m4_foreach([i], [list], [i]) + =>123 + + -- Macro: m4_argn (N, [ARG]...) + Extracts argument N (larger than 0) from the remaining arguments. + If there are too few arguments, the empty string is used. For any + N besides 1, this is more efficient than the similar + `m4_car(m4_shiftn([N], [], [ARG...]))'. + + -- Macro: m4_car (ARG...) + Expands to the quoted first ARG. Can be used with `m4_cdr' to + recursively iterate through a list. Generally, when using quoted + lists of quoted elements, `m4_car' should be called without any + extra quotes. + + -- Macro: m4_cdr (ARG...) + Expands to a quoted list of all but the first ARG, or the empty + string if there was only one argument. Generally, when using + quoted lists of quoted elements, `m4_cdr' should be called without + any extra quotes. + + For example, this is a simple implementation of `m4_map'; note how + each iteration checks for the end of recursion, then merely + applies the first argument to the first element of the list, then + repeats with the rest of the list. (The actual implementation in + M4sugar is a bit more involved, to gain some speed and share code + with `m4_map_sep', and also to avoid expanding side effects in + `$2' twice). + m4_define([m4_map], [m4_ifval([$2], + [m4_apply([$1], m4_car($2))[]$0([$1], m4_cdr($2))])])dnl + m4_map([ m4_eval], [[[1]], [[1+1]], [[10],[16]]]) + => 1 2 a + + -- Macro: m4_for (VAR, FIRST, LAST, [STEP], EXPRESSION) + Loop over the numeric values between FIRST and LAST including + bounds by increments of STEP. For each iteration, expand + EXPRESSION with the numeric value assigned to VAR. If STEP is + omitted, it defaults to `1' or `-1' depending on the order of the + limits. If given, STEP has to match this order. The number of + iterations is determined independently from definition of VAR; + iteration cannot be short-circuited or lengthened by modifying VAR + from within EXPRESSION. + + -- Macro: m4_foreach (VAR, LIST, EXPRESSION) + Loop over the comma-separated M4 list LIST, assigning each value + to VAR, and expand EXPRESSION. The following example outputs two + lines: + + m4_foreach([myvar], [[foo], [bar, baz]], + [echo myvar + ])dnl + =>echo foo + =>echo bar, baz + + Note that for some forms of EXPRESSION, it may be faster to use + `m4_map_args'. + + -- Macro: m4_foreach_w (VAR, LIST, EXPRESSION) + Loop over the white-space-separated list LIST, assigning each value + to VAR, and expand EXPRESSION. If VAR is only referenced once in + EXPRESSION, it is more efficient to use `m4_map_args_w'. + + The deprecated macro `AC_FOREACH' is an alias of `m4_foreach_w'. + + -- Macro: m4_map (MACRO, LIST) + -- Macro: m4_mapall (MACRO, LIST) + -- Macro: m4_map_sep (MACRO, SEPARATOR, LIST) + -- Macro: m4_mapall_sep (MACRO, SEPARATOR, LIST) + Loop over the comma separated quoted list of argument descriptions + in LIST, and invoke MACRO with the arguments. An argument + description is in turn a comma-separated quoted list of quoted + elements, suitable for `m4_apply'. The macros `m4_map' and + `m4_map_sep' ignore empty argument descriptions, while `m4_mapall' + and `m4_mapall_sep' invoke MACRO with no arguments. The macros + `m4_map_sep' and `m4_mapall_sep' additionally expand SEPARATOR + between invocations of MACRO. + + Note that SEPARATOR is expanded, unlike in `m4_join'. When + separating output with commas, this means that the map result can + be used as a series of arguments, by using a single-quoted comma as + SEPARATOR, or as a single string, by using a double-quoted comma. + + m4_map([m4_count], []) + => + m4_map([ m4_count], [[], + [[1]], + [[1], [2]]]) + => 1 2 + m4_mapall([ m4_count], [[], + [[1]], + [[1], [2]]]) + => 0 1 2 + m4_map_sep([m4_eval], [,], [[[1+2]], + [[10], [16]]]) + =>3,a + m4_map_sep([m4_echo], [,], [[[a]], [[b]]]) + =>a,b + m4_count(m4_map_sep([m4_echo], [,], [[[a]], [[b]]])) + =>2 + m4_map_sep([m4_echo], [[,]], [[[a]], [[b]]]) + =>a,b + m4_count(m4_map_sep([m4_echo], [[,]], [[[a]], [[b]]])) + =>1 + + -- Macro: m4_map_args (MACRO, ARG...) + Repeatedly invoke MACRO with each successive ARG as its only + argument. In the following example, three solutions are presented + with the same expansion; the solution using `m4_map_args' is the + most efficient. + m4_define([active], [ACTIVE])dnl + m4_foreach([var], [[plain], [active]], [ m4_echo(m4_defn([var]))]) + => plain active + m4_map([ m4_echo], [[[plain]], [[active]]]) + => plain active + m4_map_args([ m4_echo], [plain], [active]) + => plain active + + In cases where it is useful to operate on additional parameters + besides the list elements, the macro `m4_curry' can be used in + MACRO to supply the argument currying necessary to generate the + desired argument list. In the following example, `list_add_n' is + more efficient than `list_add_x'. On the other hand, using + `m4_map_args_sep' can be even more efficient. + + m4_define([list], [[1], [2], [3]])dnl + m4_define([add], [m4_eval(([$1]) + ([$2]))])dnl + dnl list_add_n(N, ARG...) + dnl Output a list consisting of each ARG added to N + m4_define([list_add_n], + [m4_shift(m4_map_args([,m4_curry([add], [$1])], m4_shift($@)))])dnl + list_add_n([1], list) + =>2,3,4 + list_add_n([2], list) + =>3,4,5 + m4_define([list_add_x], + [m4_shift(m4_foreach([var], m4_dquote(m4_shift($@)), + [,add([$1],m4_defn([var]))]))])dnl + list_add_x([1], list) + =>2,3,4 + + -- Macro: m4_map_args_pair (MACRO, [MACRO-END = `macro'], ARG...) + For every pair of arguments ARG, invoke MACRO with two arguments. + If there is an odd number of arguments, invoke MACRO-END, which + defaults to MACRO, with the remaining argument. + + m4_map_args_pair([, m4_reverse], [], [1], [2], [3]) + =>, 2, 1, 3 + m4_map_args_pair([, m4_reverse], [, m4_dquote], [1], [2], [3]) + =>, 2, 1, [3] + m4_map_args_pair([, m4_reverse], [, m4_dquote], [1], [2], [3], [4]) + =>, 2, 1, 4, 3 + + -- Macro: m4_map_args_sep ([PRE], [POST], [SEP], ARG...) + Expand the sequence `PRE[ARG]POST' for each argument, additionally + expanding SEP between arguments. One common use of this macro is + constructing a macro call, where the opening and closing + parentheses are split between PRE and POST; in particular, + `m4_map_args([MACRO], [ARG])' is equivalent to + `m4_map_args_sep([MACRO(], [)], [], [ARG])'. This macro provides + the most efficient means for iterating over an arbitrary list of + arguments, particularly when repeatedly constructing a macro call + with more arguments than ARG. + + -- Macro: m4_map_args_w (STRING, [PRE], [POST], [SEP]) + Expand the sequence `PRE[word]POST' for each word in the + whitespace-separated STRING, additionally expanding SEP between + words. This macro provides the most efficient means for iterating + over a whitespace-separated string. In particular, + `m4_map_args_w([STRING], [ACTION(], [)])' is more efficient than + `m4_foreach_w([var], [STRING], [ACTION(m4_defn([var]))])'. + + -- Macro: m4_shiftn (COUNT, ...) + -- Macro: m4_shift2 (...) + -- Macro: m4_shift3 (...) + `m4_shiftn' performs COUNT iterations of `m4_shift', along with + validation that enough arguments were passed in to match the shift + count, and that the count is positive. `m4_shift2' and + `m4_shift3' are specializations of `m4_shiftn', introduced in + Autoconf 2.62, and are more efficient for two and three shifts, + respectively. + + -- Macro: m4_stack_foreach (MACRO, ACTION) + -- Macro: m4_stack_foreach_lifo (MACRO, ACTION) + For each of the `m4_pushdef' definitions of MACRO, expand ACTION + with the single argument of a definition of MACRO. + `m4_stack_foreach' starts with the oldest definition, while + `m4_stack_foreach_lifo' starts with the current definition. + ACTION should not push or pop definitions of MACRO, nor is there + any guarantee that the current definition of MACRO matches the + argument that was passed to ACTION. The macro `m4_curry' can be + used if ACTION needs more than one argument, although in that case + it is more efficient to use M4_STACK_FOREACH_SEP. + + Due to technical limitations, there are a few low-level m4sugar + functions, such as `m4_pushdef', that cannot be used as the MACRO + argument. + + m4_pushdef([a], [1])m4_pushdef([a], [2])dnl + m4_stack_foreach([a], [ m4_incr]) + => 2 3 + m4_stack_foreach_lifo([a], [ m4_curry([m4_substr], [abcd])]) + => cd bcd + + -- Macro: m4_stack_foreach_sep (MACRO, [PRE], [POST], [SEP]) + -- Macro: m4_stack_foreach_sep_lifo (MACRO, [PRE], [POST], [SEP]) + Expand the sequence `PRE[definition]POST' for each `m4_pushdef' + definition of MACRO, additionally expanding SEP between + definitions. `m4_stack_foreach_sep' visits the oldest definition + first, while `m4_stack_foreach_sep_lifo' visits the current + definition first. This macro provides the most efficient means + for iterating over a pushdef stack. In particular, + `m4_stack_foreach([MACRO], [ACTION])' is short for + `m4_stack_foreach_sep([MACRO], [ACTION(], [)])'. + + +File: autoconf.info, Node: Evaluation Macros, Next: Text processing Macros, Prev: Looping constructs, Up: Programming in M4sugar + +8.3.6 Evaluation Macros +----------------------- + +The following macros give some control over the order of the evaluation +by adding or removing levels of quotes. + + -- Macro: m4_apply (MACRO, LIST) + Apply the elements of the quoted, comma-separated LIST as the + arguments to MACRO. If LIST is empty, invoke MACRO without + arguments. Note the difference between `m4_indir', which expects + its first argument to be a macro name but can use names that are + otherwise invalid, and `m4_apply', where MACRO can contain other + text, but must end in a valid macro name. + m4_apply([m4_count], []) + =>0 + m4_apply([m4_count], [[]]) + =>1 + m4_apply([m4_count], [[1], [2]]) + =>2 + m4_apply([m4_join], [[|], [1], [2]]) + =>1|2 + + -- Macro: m4_count (ARG, ...) + This macro returns the decimal count of the number of arguments it + was passed. + + -- Macro: m4_curry (MACRO, ARG...) + This macro performs argument currying. The expansion of this + macro is another macro name that expects exactly one argument; + that argument is then appended to the ARG list, and then MACRO is + expanded with the resulting argument list. + + m4_curry([m4_curry], [m4_reverse], [1])([2])([3]) + =>3, 2, 1 + + Unfortunately, due to a limitation in M4 1.4.x, it is not possible + to pass the definition of a builtin macro as the argument to the + output of `m4_curry'; the empty string is used instead of the + builtin token. This behavior is rectified by using M4 1.6 or + newer. + + -- Macro: m4_do (ARG, ...) + This macro loops over its arguments and expands each ARG in + sequence. Its main use is for readability; it allows the use of + indentation and fewer `dnl' to result in the same expansion. This + macro guarantees that no expansion will be concatenated with + subsequent text; to achieve full concatenation, use + `m4_unquote(m4_join([], ARG...))'. + + m4_define([ab],[1])m4_define([bc],[2])m4_define([abc],[3])dnl + m4_do([a],[b])c + =>abc + m4_unquote(m4_join([],[a],[b]))c + =>3 + m4_define([a],[A])m4_define([b],[B])m4_define([c],[C])dnl + m4_define([AB],[4])m4_define([BC],[5])m4_define([ABC],[6])dnl + m4_do([a],[b])c + =>ABC + m4_unquote(m4_join([],[a],[b]))c + =>3 + + -- Macro: m4_dquote (ARG, ...) + Return the arguments as a quoted list of quoted arguments. + Conveniently, if there is just one ARG, this effectively adds a + level of quoting. + + -- Macro: m4_dquote_elt (ARG, ...) + Return the arguments as a series of double-quoted arguments. + Whereas `m4_dquote' returns a single argument, `m4_dquote_elt' + returns as many arguments as it was passed. + + -- Macro: m4_echo (ARG, ...) + Return the arguments, with the same level of quoting. Other than + discarding whitespace after unquoted commas, this macro is a no-op. + + -- Macro: m4_expand (ARG) + Return the expansion of ARG as a quoted string. Whereas + `m4_quote' is designed to collect expanded text into a single + argument, `m4_expand' is designed to perform one level of expansion + on quoted text. One distinction is in the treatment of whitespace + following a comma in the original ARG. Any time multiple + arguments are collected into one with `m4_quote', the M4 argument + collection rules discard the whitespace. However, with + `m4_expand', whitespace is preserved, even after the expansion of + macros contained in ARG. Additionally, `m4_expand' is able to + expand text that would involve an unterminated comment, whereas + expanding that same text as the argument to `m4_quote' runs into + difficulty in finding the end of the argument. Since manipulating + diversions during argument collection is inherently unsafe, + `m4_expand' issues an error if ARG attempts to change the current + diversion (*note Diversion support::). + + m4_define([active], [ACT, IVE])dnl + m4_define([active2], [[ACT, IVE]])dnl + m4_quote(active, active) + =>ACT,IVE,ACT,IVE + m4_expand([active, active]) + =>ACT, IVE, ACT, IVE + m4_quote(active2, active2) + =>ACT, IVE,ACT, IVE + m4_expand([active2, active2]) + =>ACT, IVE, ACT, IVE + m4_expand([# m4_echo]) + =># m4_echo + m4_quote(# m4_echo) + ) + =># m4_echo) + => + + Note that `m4_expand' cannot handle an ARG that expands to literal + unbalanced quotes, but that quadrigraphs can be used when + unbalanced output is necessary. Likewise, unbalanced parentheses + should be supplied with double quoting or a quadrigraph. + + m4_define([pattern], [[!@<:@]])dnl + m4_define([bar], [BAR])dnl + m4_expand([case $foo in + m4_defn([pattern])@:}@ bar ;; + *[)] blah ;; + esac]) + =>case $foo in + => [![]) BAR ;; + => *) blah ;; + =>esac + + -- Macro: m4_ignore (...) + This macro was introduced in Autoconf 2.62. Expands to nothing, + ignoring all of its arguments. By itself, this isn't very useful. + However, it can be used to conditionally ignore an arbitrary + number of arguments, by deciding which macro name to apply to a + list of arguments. + dnl foo outputs a message only if [debug] is defined. + m4_define([foo], + [m4_ifdef([debug],[AC_MSG_NOTICE],[m4_ignore])([debug message])]) + + Note that for earlier versions of Autoconf, the macro `__gnu__' can + serve the same purpose, although it is less readable. + + -- Macro: m4_make_list (ARG, ...) + This macro exists to aid debugging of M4sugar algorithms. Its net + effect is similar to `m4_dquote'--it produces a quoted list of + quoted arguments, for each ARG. The difference is that this + version uses a comma-newline separator instead of just comma, to + improve readability of the list; with the result that it is less + efficient than `m4_dquote'. + m4_define([zero],[0])m4_define([one],[1])m4_define([two],[2])dnl + m4_dquote(zero, [one], [[two]]) + =>[0],[one],[[two]] + m4_make_list(zero, [one], [[two]]) + =>[0], + =>[one], + =>[[two]] + m4_foreach([number], m4_dquote(zero, [one], [[two]]), [ number]) + => 0 1 two + m4_foreach([number], m4_make_list(zero, [one], [[two]]), [ number]) + => 0 1 two + + -- Macro: m4_quote (ARG, ...) + Return the arguments as a single entity, i.e., wrap them into a + pair of quotes. This effectively collapses multiple arguments + into one, although it loses whitespace after unquoted commas in + the process. + + -- Macro: m4_reverse (ARG, ...) + Outputs each argument with the same level of quoting, but in + reverse order, and with space following each comma for readability. + + m4_define([active], [ACT,IVE]) + => + m4_reverse(active, [active]) + =>active, IVE, ACT + + -- Macro: m4_unquote (ARG, ...) + This macro was introduced in Autoconf 2.62. Expand each argument, + separated by commas. For a single ARG, this effectively removes a + layer of quoting, and `m4_unquote([ARG])' is more efficient than + the equivalent `m4_do([ARG])'. For multiple arguments, this + results in an unquoted list of expansions. This is commonly used + with `m4_split', in order to convert a single quoted list into a + series of quoted elements. + + The following example aims at emphasizing the difference between +several scenarios: not using these macros, using `m4_defn', using +`m4_quote', using `m4_dquote', and using `m4_expand'. + + $ cat example.m4 + dnl Overquote, so that quotes are visible. + m4_define([show], [$[]1 = [$1], $[]@ = [$@]]) + m4_define([a], [A]) + m4_define([mkargs], [1, 2[,] 3]) + m4_define([arg1], [[$1]]) + m4_divert([0])dnl + show(a, b) + show([a, b]) + show(m4_quote(a, b)) + show(m4_dquote(a, b)) + show(m4_expand([a, b])) + + arg1(mkargs) + arg1([mkargs]) + arg1(m4_defn([mkargs])) + arg1(m4_quote(mkargs)) + arg1(m4_dquote(mkargs)) + arg1(m4_expand([mkargs])) + $ autom4te -l m4sugar example.m4 + $1 = A, $@ = [A],[b] + $1 = a, b, $@ = [a, b] + $1 = A,b, $@ = [A,b] + $1 = [A],[b], $@ = [[A],[b]] + $1 = A, b, $@ = [A, b] + + 1 + mkargs + 1, 2[,] 3 + 1,2, 3 + [1],[2, 3] + 1, 2, 3 + + +File: autoconf.info, Node: Text processing Macros, Next: Number processing Macros, Prev: Evaluation Macros, Up: Programming in M4sugar + +8.3.7 String manipulation in M4 +------------------------------- + +The following macros may be used to manipulate strings in M4. Many of +the macros in this section intentionally result in quoted strings as +output, rather than subjecting the arguments to further expansions. As +a result, if you are manipulating text that contains active M4 +characters, the arguments are passed with single quoting rather than +double. + + -- Macro: m4_append (MACRO-NAME, STRING, [SEPARATOR]) + -- Macro: m4_append_uniq (MACRO-NAME, STRING, [SEPARATOR] [IF-UNIQ], + [IF-DUPLICATE]) + Redefine MACRO-NAME to its former contents with SEPARATOR and + STRING added at the end. If MACRO-NAME was undefined before (but + not if it was defined but empty), then no SEPARATOR is added. As + of Autoconf 2.62, neither STRING nor SEPARATOR are expanded during + this macro; instead, they are expanded when MACRO-NAME is invoked. + + `m4_append' can be used to grow strings, and `m4_append_uniq' to + grow strings without duplicating substrings. Additionally, + `m4_append_uniq' takes two optional parameters as of Autoconf 2.62; + IF-UNIQ is expanded if STRING was appended, and IF-DUPLICATE is + expanded if STRING was already present. Also, `m4_append_uniq' + warns if SEPARATOR is not empty, but occurs within STRING, since + that can lead to duplicates. + + Note that `m4_append' can scale linearly in the length of the final + string, depending on the quality of the underlying M4 + implementation, while `m4_append_uniq' has an inherent quadratic + scaling factor. If an algorithm can tolerate duplicates in the + final string, use the former for speed. If duplicates must be + avoided, consider using `m4_set_add' instead (*note Set + manipulation Macros::). + + m4_define([active], [ACTIVE])dnl + m4_append([sentence], [This is an])dnl + m4_append([sentence], [ active ])dnl + m4_append([sentence], [symbol.])dnl + sentence + =>This is an ACTIVE symbol. + m4_undefine([active])dnl + =>This is an active symbol. + m4_append_uniq([list], [one], [, ], [new], [existing]) + =>new + m4_append_uniq([list], [one], [, ], [new], [existing]) + =>existing + m4_append_uniq([list], [two], [, ], [new], [existing]) + =>new + m4_append_uniq([list], [three], [, ], [new], [existing]) + =>new + m4_append_uniq([list], [two], [, ], [new], [existing]) + =>existing + list + =>one, two, three + m4_dquote(list) + =>[one],[two],[three] + m4_append([list2], [one], [[, ]])dnl + m4_append_uniq([list2], [two], [[, ]])dnl + m4_append([list2], [three], [[, ]])dnl + list2 + =>one, two, three + m4_dquote(list2) + =>[one, two, three] + + -- Macro: m4_append_uniq_w (MACRO-NAME, STRINGS) + This macro was introduced in Autoconf 2.62. It is similar to + `m4_append_uniq', but treats STRINGS as a whitespace separated + list of words to append, and only appends unique words. + MACRO-NAME is updated with a single space between new words. + m4_append_uniq_w([numbers], [1 1 2])dnl + m4_append_uniq_w([numbers], [ 2 3 ])dnl + numbers + =>1 2 3 + + -- Macro: m4_chomp (STRING) + -- Macro: m4_chomp_all (STRING) + Output STRING in quotes, but without a trailing newline. The + macro `m4_chomp' is slightly faster, and removes at most one + newline; the macro `m4_chomp_all' removes all consecutive trailing + newlines. Unlike `m4_flatten', embedded newlines are left intact, + and backslash does not influence the result. + + -- Macro: m4_combine ([SEPARATOR], PREFIX-LIST, [INFIX], SUFFIX-1, + [SUFFIX-2], ...) + This macro produces a quoted string containing the pairwise + combination of every element of the quoted, comma-separated + PREFIX-LIST, and every element from the SUFFIX arguments. Each + pairwise combination is joined with INFIX in the middle, and + successive pairs are joined by SEPARATOR. No expansion occurs on + any of the arguments. No output occurs if either the PREFIX or + SUFFIX list is empty, but the lists can contain empty elements. + m4_define([a], [oops])dnl + m4_combine([, ], [[a], [b], [c]], [-], [1], [2], [3]) + =>a-1, a-2, a-3, b-1, b-2, b-3, c-1, c-2, c-3 + m4_combine([, ], [[a], [b]], [-]) + => + m4_combine([, ], [[a], [b]], [-], []) + =>a-, b- + m4_combine([, ], [], [-], [1], [2]) + => + m4_combine([, ], [[]], [-], [1], [2]) + =>-1, -2 + + -- Macro: m4_escape (STRING) + Convert all instances of `[', `]', `#', and `$' within STRING into + their respective quadrigraphs. The result is still a quoted + string. + + -- Macro: m4_flatten (STRING) + Flatten STRING into a single line. Delete all backslash-newline + pairs, and replace all remaining newlines with a space. The + result is still a quoted string. + + -- Macro: m4_join ([SEPARATOR], ARGS...) + -- Macro: m4_joinall ([SEPARATOR], ARGS...) + Concatenate each ARG, separated by SEPARATOR. `joinall' uses + every argument, while `join' omits empty arguments so that there + are no back-to-back separators in the output. The result is a + quoted string. + m4_define([active], [ACTIVE])dnl + m4_join([|], [one], [], [active], [two]) + =>one|active|two + m4_joinall([|], [one], [], [active], [two]) + =>one||active|two + + Note that if all you intend to do is join ARGS with commas between + them, to form a quoted list suitable for `m4_foreach', it is more + efficient to use `m4_dquote'. + + -- Macro: m4_newline ([TEXT]) + This macro was introduced in Autoconf 2.62, and expands to a + newline, followed by any TEXT. It is primarily useful for + maintaining macro formatting, and ensuring that M4 does not + discard leading whitespace during argument collection. + + -- Macro: m4_normalize (STRING) + Remove leading and trailing spaces and tabs, sequences of + backslash-then-newline, and replace multiple spaces, tabs, and + newlines with a single space. This is a combination of + `m4_flatten' and `m4_strip'. To determine if STRING consists only + of bytes that would be removed by `m4_normalize', you can use + `m4_ifblank'. + + -- Macro: m4_re_escape (STRING) + Backslash-escape all characters in STRING that are active in + regexps. + + -- Macro: m4_split (STRING, [REGEXP = `[\t ]+']) + Split STRING into an M4 list of elements quoted by `[' and `]', + while keeping white space at the beginning and at the end. If + REGEXP is given, use it instead of `[\t ]+' for splitting. If + STRING is empty, the result is an empty list. + + -- Macro: m4_strip (STRING) + Strip whitespace from STRING. Sequences of spaces and tabs are + reduced to a single space, then leading and trailing spaces are + removed. The result is still a quoted string. Note that this + does not interfere with newlines; if you want newlines stripped as + well, consider `m4_flatten', or do it all at once with + `m4_normalize'. To quickly test if STRING has only whitespace, + use `m4_ifblank'. + + -- Macro: m4_text_box (MESSAGE, [FRAME = `-']) + Add a text box around MESSAGE, using FRAME as the border character + above and below the message. The FRAME argument must be a single + byte, and does not support quadrigraphs. The frame correctly + accounts for the subsequent expansion of MESSAGE. For example: + m4_define([macro], [abc])dnl + m4_text_box([macro]) + =>## --- ## + =>## abc ## + =>## --- ## + + The MESSAGE must contain balanced quotes and parentheses, although + quadrigraphs can be used to work around this. + + -- Macro: m4_text_wrap (STRING, [PREFIX], [PREFIX1 = `PREFIX'], [WIDTH + = `79']) + Break STRING into a series of whitespace-separated words, then + output those words separated by spaces, and wrapping lines any + time the output would exceed WIDTH columns. If given, PREFIX1 + begins the first line, and PREFIX begins all wrapped lines. If + PREFIX1 is longer than PREFIX, then the first line consists of + just PREFIX1. If PREFIX is longer than PREFIX1, padding is + inserted so that the first word of STRING begins at the same + indentation as all wrapped lines. Note that using literal tab + characters in any of the arguments will interfere with the + calculation of width. No expansions occur on PREFIX, PREFIX1, or + the words of STRING, although quadrigraphs are recognized. + + For some examples: + m4_text_wrap([Short string */], [ ], [/* ], [20]) + =>/* Short string */ + m4_text_wrap([Much longer string */], [ ], [/* ], [20]) + =>/* Much longer + => string */ + m4_text_wrap([Short doc.], [ ], [ --short ], [30]) + => --short Short doc. + m4_text_wrap([Short doc.], [ ], [ --too-wide ], [30]) + => --too-wide + => Short doc. + m4_text_wrap([Super long documentation.], [ ], + [ --too-wide ], 30) + => --too-wide + => Super long + => documentation. + + -- Macro: m4_tolower (STRING) + -- Macro: m4_toupper (STRING) + Return STRING with letters converted to upper or lower case, + respectively. + + +File: autoconf.info, Node: Number processing Macros, Next: Set manipulation Macros, Prev: Text processing Macros, Up: Programming in M4sugar + +8.3.8 Arithmetic computation in M4 +---------------------------------- + +The following macros facilitate integer arithmetic operations. Where a +parameter is documented as taking an arithmetic expression, you can use +anything that can be parsed by `m4_eval'. + + -- Macro: m4_cmp (EXPR-1, EXPR-2) + Compare the arithmetic expressions EXPR-1 and EXPR-2, and expand + to `-1' if EXPR-1 is smaller, `0' if they are equal, and `1' if + EXPR-1 is larger. + + -- Macro: m4_list_cmp (LIST-1, LIST-2) + Compare the two M4 lists consisting of comma-separated arithmetic + expressions, left to right. Expand to `-1' for the first element + pairing where the value from LIST-1 is smaller, `1' where the + value from LIST-2 is smaller, or `0' if both lists have the same + values. If one list is shorter than the other, the remaining + elements of the longer list are compared against zero. + m4_list_cmp([1, 0], [1]) + =>0 + m4_list_cmp([1, [1 * 0]], [1, 0]) + =>0 + m4_list_cmp([1, 2], [1, 0]) + =>1 + m4_list_cmp([1, [1+1], 3],[1, 2]) + =>1 + m4_list_cmp([1, 2, -3], [1, 2]) + =>-1 + m4_list_cmp([1, 0], [1, 2]) + =>-1 + m4_list_cmp([1], [1, 2]) + =>-1 + + -- Macro: m4_max (ARG, ...) + This macro was introduced in Autoconf 2.62. Expand to the decimal + value of the maximum arithmetic expression among all the arguments. + + -- Macro: m4_min (ARG, ...) + This macro was introduced in Autoconf 2.62. Expand to the decimal + value of the minimum arithmetic expression among all the arguments. + + -- Macro: m4_sign (EXPR) + Expand to `-1' if the arithmetic expression EXPR is negative, `1' + if it is positive, and `0' if it is zero. + + -- Macro: m4_version_compare (VERSION-1, VERSION-2) + This macro was introduced in Autoconf 2.53, but had a number of + usability limitations that were not lifted until Autoconf 2.62. + Compare the version strings VERSION-1 and VERSION-2, and expand to + `-1' if VERSION-1 is smaller, `0' if they are the same, or `1' + VERSION-2 is smaller. Version strings must be a list of elements + separated by `.', `,' or `-', where each element is a number along + with optional case-insensitive letters designating beta releases. + The comparison stops at the leftmost element that contains a + difference, although a 0 element compares equal to a missing + element. + + It is permissible to include commit identifiers in VERSION, such + as an abbreviated SHA1 of the commit, provided there is still a + monotonically increasing prefix to allow for accurate version-based + comparisons. For example, this paragraph was written when the + development snapshot of autoconf claimed to be at version + `2.61a-248-dc51', or 248 commits after the 2.61a release, with an + abbreviated commit identification of `dc51'. + + m4_version_compare([1.1], [2.0]) + =>-1 + m4_version_compare([2.0b], [2.0a]) + =>1 + m4_version_compare([1.1.1], [1.1.1a]) + =>-1 + m4_version_compare([1.2], [1.1.1a]) + =>1 + m4_version_compare([1.0], [1]) + =>0 + m4_version_compare([1.1pre], [1.1PRE]) + =>0 + m4_version_compare([1.1a], [1,10]) + =>-1 + m4_version_compare([2.61a], [2.61a-248-dc51]) + =>-1 + m4_version_compare([2.61b], [2.61a-248-dc51]) + =>1 + + -- Macro: m4_version_prereq (VERSION, [IF-NEW-ENOUGH], [IF-OLD = + `m4_fatal']) + Compares VERSION against the version of Autoconf currently + running. If the running version is at VERSION or newer, expand + IF-NEW-ENOUGH, but if VERSION is larger than the version currently + executing, expand IF-OLD, which defaults to printing an error + message and exiting m4sugar with status 63. When given only one + argument, this behaves like `AC_PREREQ' (*note Versioning::). + Remember that the autoconf philosophy favors feature checks over + version checks. + + +File: autoconf.info, Node: Set manipulation Macros, Next: Forbidden Patterns, Prev: Number processing Macros, Up: Programming in M4sugar + +8.3.9 Set manipulation in M4 +---------------------------- + +Sometimes, it is necessary to track a set of data, where the order does +not matter and where there are no duplicates in the set. The following +macros facilitate set manipulations. Each set is an opaque object, +which can only be accessed via these basic operations. The underlying +implementation guarantees linear scaling for set creation, which is more +efficient than using the quadratic `m4_append_uniq'. Both set names +and values can be arbitrary strings, except for unbalanced quotes. +This implementation ties up memory for removed elements until the next +operation that must traverse all the elements of a set; and although +that may slow down some operations until the memory for removed elements +is pruned, it still guarantees linear performance. + + -- Macro: m4_set_add (SET, VALUE, [IF-UNIQ], [IF-DUP]) + Adds the string VALUE as a member of set SET. Expand IF-UNIQ if + the element was added, or IF-DUP if it was previously in the set. + Operates in amortized constant time, so that set creation scales + linearly. + + -- Macro: m4_set_add_all (SET, VALUE...) + Adds each VALUE to the set SET. This is slightly more efficient + than repeatedly invoking `m4_set_add'. + + -- Macro: m4_set_contains (SET, VALUE, [IF-PRESENT], [IF-ABSENT]) + Expands IF-PRESENT if the string VALUE is a member of SET, + otherwise IF-ABSENT. + + m4_set_contains([a], [1], [yes], [no]) + =>no + m4_set_add([a], [1], [added], [dup]) + =>added + m4_set_add([a], [1], [added], [dup]) + =>dup + m4_set_contains([a], [1], [yes], [no]) + =>yes + m4_set_remove([a], [1], [removed], [missing]) + =>removed + m4_set_contains([a], [1], [yes], [no]) + =>no + m4_set_remove([a], [1], [removed], [missing]) + =>missing + + -- Macro: m4_set_contents (SET, [SEP]) + -- Macro: m4_set_dump (SET, [SEP]) + Expands to a single string consisting of all the members of the set + SET, each separated by SEP, which is not expanded. + `m4_set_contents' leaves the elements in SET but reclaims any + memory occupied by removed elements, while `m4_set_dump' is a + faster one-shot action that also deletes the set. No provision is + made for disambiguating members that contain a non-empty SEP as a + substring; use `m4_set_empty' to distinguish between an empty set + and the set containing only the empty string. The order of the + output is unspecified; in the current implementation, part of the + speed of `m4_set_dump' results from using a different output order + than `m4_set_contents'. These macros scale linearly in the size + of the set before memory pruning, and `m4_set_contents([SET], + [SEP])' is faster than `m4_joinall([SEP]m4_set_listc([SET]))'. + + m4_set_add_all([a], [1], [2], [3]) + => + m4_set_contents([a], [-]) + =>1-2-3 + m4_joinall([-]m4_set_listc([a])) + =>1-2-3 + m4_set_dump([a], [-]) + =>3-2-1 + m4_set_contents([a]) + => + m4_set_add([a], []) + => + m4_set_contents([a], [-]) + => + + -- Macro: m4_set_delete (SET) + Delete all elements and memory associated with SET. This is + linear in the set size, and faster than removing one element at a + time. + + -- Macro: m4_set_difference (SETA, SETB) + -- Macro: m4_set_intersection (SETA, SETB) + -- Macro: m4_set_union (SETA, SETB) + Compute the relation between SETA and SETB, and output the result + as a list of quoted arguments without duplicates and with a + leading comma. Set difference selects the elements in SETA but + not SETB, intersection selects only elements in both sets, and + union selects elements in either set. These actions are linear in + the sum of the set sizes. The leading comma is necessary to + distinguish between no elements and the empty string as the only + element. + + m4_set_add_all([a], [1], [2], [3]) + => + m4_set_add_all([b], [3], [], [4]) + => + m4_set_difference([a], [b]) + =>,1,2 + m4_set_difference([b], [a]) + =>,,4 + m4_set_intersection([a], [b]) + =>,3 + m4_set_union([a], [b]) + =>,1,2,3,,4 + + -- Macro: m4_set_empty (SET, [IF-EMPTY], [IF-ELEMENTS]) + Expand IF-EMPTY if the set SET has no elements, otherwise expand + IF-ELEMENTS. This macro operates in constant time. Using this + macro can help disambiguate output from `m4_set_contents' or + `m4_set_list'. + + -- Macro: m4_set_foreach (SET, VARIABLE, ACTION) + For each element in the set SET, expand ACTION with the macro + VARIABLE defined as the set element. Behavior is unspecified if + ACTION recursively lists the contents of SET (although listing + other sets is acceptable), or if it modifies the set in any way + other than removing the element currently contained in VARIABLE. + This macro is faster than the corresponding `m4_foreach([VARIABLE], + m4_indir([m4_dquote]m4_set_listc([SET])), [ACTION])', although + `m4_set_map' might be faster still. + + m4_set_add_all([a]m4_for([i], [1], [5], [], [,i])) + => + m4_set_contents([a]) + =>12345 + m4_set_foreach([a], [i], + [m4_if(m4_eval(i&1), [0], [m4_set_remove([a], i, [i])])]) + =>24 + m4_set_contents([a]) + =>135 + + -- Macro: m4_set_list (SET) + -- Macro: m4_set_listc (SET) + Produce a list of arguments, where each argument is a quoted + element from the set SET. The variant `m4_set_listc' is + unambiguous, by adding a leading comma if there are any set + elements, whereas the variant `m4_set_list' cannot distinguish + between an empty set and a set containing only the empty string. + These can be directly used in macros that take multiple arguments, + such as `m4_join' or `m4_set_add_all', or wrapped by `m4_dquote' + for macros that take a quoted list, such as `m4_map' or + `m4_foreach'. Any memory occupied by removed elements is + reclaimed during these macros. + + m4_set_add_all([a], [1], [2], [3]) + => + m4_set_list([a]) + =>1,2,3 + m4_set_list([b]) + => + m4_set_listc([b]) + => + m4_count(m4_set_list([b])) + =>1 + m4_set_empty([b], [0], [m4_count(m4_set_list([b]))]) + =>0 + m4_set_add([b], []) + => + m4_set_list([b]) + => + m4_set_listc([b]) + =>, + m4_count(m4_set_list([b])) + =>1 + m4_set_empty([b], [0], [m4_count(m4_set_list([b]))]) + =>1 + + -- Macro: m4_set_map (SET, ACTION) + For each element in the set SET, expand ACTION with a single + argument of the set element. Behavior is unspecified if ACTION + recursively lists the contents of SET (although listing other sets + is acceptable), or if it modifies the set in any way other than + removing the element passed as an argument. This macro is faster + than either corresponding counterpart of + `m4_map_args([ACTION]m4_set_listc([SET]))' or + `m4_set_foreach([SET], [var], [ACTION(m4_defn([var]))])'. It is + possible to use `m4_curry' if more than one argument is needed for + ACTION, although it is more efficient to use `m4_set_map_sep' in + that case. + + -- Macro: m4_set_map_sep (SET, [PRE], [POST], [SEP]) + For each element in the set SET, expand `PRE[element]POST', + additionally expanding SEP between elements. Behavior is + unspecified if the expansion recursively lists the contents of SET + (although listing other sets is acceptable), or if it modifies the + set in any way other than removing the element visited by the + expansion. This macro provides the most efficient means for + non-destructively visiting the elements of a set; in particular, + `m4_set_map([SET], [ACTION])' is equivalent to + `m4_set_map_sep([SET], [ACTION(], [)])'. + + -- Macro: m4_set_remove (SET, VALUE, [IF-PRESENT], [IF-ABSENT]) + If VALUE is an element in the set SET, then remove it and expand + IF-PRESENT. Otherwise expand IF-ABSENT. This macro operates in + constant time so that multiple removals will scale linearly rather + than quadratically; but when used outside of `m4_set_foreach' or + `m4_set_map', it leaves memory occupied until the set is later + compacted by `m4_set_contents' or `m4_set_list'. Several other + set operations are then less efficient between the time of element + removal and subsequent memory compaction, but still maintain their + guaranteed scaling performance. + + -- Macro: m4_set_size (SET) + Expand to the size of the set SET. This implementation operates + in constant time, and is thus more efficient than + `m4_eval(m4_count(m4_set_listc([set])) - 1)'. + + +File: autoconf.info, Node: Forbidden Patterns, Prev: Set manipulation Macros, Up: Programming in M4sugar + +8.3.10 Forbidden Patterns +------------------------- + +M4sugar provides a means to define suspicious patterns, patterns +describing tokens which should not be found in the output. For +instance, if an Autoconf `configure' script includes tokens such as +`AC_DEFINE', or `dnl', then most probably something went wrong +(typically a macro was not evaluated because of overquotation). + + M4sugar forbids all the tokens matching `^_?m4_' and `^dnl$'. +Additional layers, such as M4sh and Autoconf, add additional forbidden +patterns to the list. + + -- Macro: m4_pattern_forbid (PATTERN) + Declare that no token matching PATTERN must be found in the output. + Comments are not checked; this can be a problem if, for instance, + you have some macro left unexpanded after an `#include'. No + consensus is currently found in the Autoconf community, as some + people consider it should be valid to name macros in comments + (which doesn't make sense to the authors of this documentation: + input, such as macros, should be documented by `dnl' comments; + reserving `#'-comments to document the output). + + Of course, you might encounter exceptions to these generic rules, for +instance you might have to refer to `$m4_flags'. + + -- Macro: m4_pattern_allow (PATTERN) + Any token matching PATTERN is allowed, including if it matches an + `m4_pattern_forbid' pattern. + + +File: autoconf.info, Node: Debugging via autom4te, Prev: Programming in M4sugar, Up: Programming in M4 + +8.4 Debugging via autom4te +========================== + +At times, it is desirable to see what was happening inside m4, to see +why output was not matching expectations. However, post-processing done +by `autom4te' means that directly using the m4 builtin `m4_traceon' is +likely to interfere with operation. Also, frequent diversion changes +and the concept of forbidden tokens make it difficult to use `m4_defn' +to generate inline comments in the final output. + + There are a couple of tools to help with this. One is the use of the +`--trace' option provided by `autom4te' (as well as each of the +programs that wrap `autom4te', such as `autoconf'), in order to inspect +when a macro is called and with which arguments. For example, when +this paragraph was written, the autoconf version could be found by: + + $ autoconf --trace=AC_INIT + configure.ac:23:AC_INIT:GNU Autoconf:2.63b.95-3963:bug-autoconf@gnu.org + $ autoconf --trace='AC_INIT:version is $2' + version is 2.63b.95-3963 + + Another trick is to print out the expansion of various m4 +expressions to standard error or to an independent file, with no +further m4 expansion, and without interfering with diversion changes or +the post-processing done to standard output. `m4_errprintn' shows a +given expression on standard error. For example, if you want to see +the expansion of an autoconf primitive or of one of your autoconf +macros, you can do it like this: + + $ cat <<\EOF > configure.ac + AC_INIT + m4_errprintn([The definition of AC_DEFINE_UNQUOTED:]) + m4_errprintn(m4_defn([AC_DEFINE_UNQUOTED])) + AC_OUTPUT + EOF + $ autoconf + error-->The definition of AC_DEFINE_UNQUOTED: + error-->_AC_DEFINE_Q([], $@) + + +File: autoconf.info, Node: Programming in M4sh, Next: Writing Autoconf Macros, Prev: Programming in M4, Up: Top + +9 Programming in M4sh +********************* + +M4sh, pronounced "mash", is aiming at producing portable Bourne shell +scripts. This name was coined by Lars J. Aas, who notes that, +according to the Webster's Revised Unabridged Dictionary (1913): + + Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische, + mash, wash, and prob. to AS. miscian to mix. See "Mix".] + + 1. A mass of mixed ingredients reduced to a soft pulpy state by + beating or pressure... + + 2. A mixture of meal or bran and water fed to animals. + + 3. A mess; trouble. [Obs.] -Beau. & Fl. + + M4sh reserves the M4 macro namespace `^_AS_' for internal use, and +the namespace `^AS_' for M4sh macros. It also reserves the shell and +environment variable namespace `^as_', and the here-document delimiter +namespace `^_AS[A-Z]' in the output file. You should not define your +own macros or output shell code that conflicts with these namespaces. + +* Menu: + +* Common Shell Constructs:: Portability layer for common shell constructs +* Polymorphic Variables:: Support for indirect variable names +* Initialization Macros:: Macros to establish a sane shell environment +* File Descriptor Macros:: File descriptor macros for input and output + + +File: autoconf.info, Node: Common Shell Constructs, Next: Polymorphic Variables, Up: Programming in M4sh + +9.1 Common Shell Constructs +=========================== + +M4sh provides portable alternatives for some common shell constructs +that unfortunately are not portable in practice. + + -- Macro: AS_BOX (TEXT, [CHAR = `-']) + Expand into shell code that will output TEXT surrounded by a box + with CHAR in the top and bottom border. TEXT should not contain a + newline, but may contain shell expansions valid for unquoted + here-documents. CHAR defaults to `-', but can be any character + except `/', `'', `"', `\', `&', or ``'. This is useful for + outputting a comment box into log files to separate distinct + phases of script operation. + + -- Macro: AS_CASE (WORD, [PATTERN1], [IF-MATCHED1], ..., [DEFAULT]) + Expand into a shell `case' statement, where WORD is matched + against one or more patterns. IF-MATCHED is run if the + corresponding pattern matched WORD, else DEFAULT is run. Avoids + several portability issues (*note Limitations of Shell Builtins: + case.). + + -- Macro: AS_DIRNAME (FILE-NAME) + Output the directory portion of FILE-NAME. For example, if + `$file' is `/one/two/three', the command + `dir=`AS_DIRNAME(["$file"])`' sets `dir' to `/one/two'. + + This interface may be improved in the future to avoid forks and + losing trailing newlines. + + -- Macro: AS_ECHO (WORD) + Emits WORD to the standard output, followed by a newline. WORD + must be a single shell word (typically a quoted string). The + bytes of WORD are output as-is, even if it starts with "-" or + contains "\". Redirections can be placed outside the macro + invocation. This is much more portable than using `echo' (*note + Limitations of Shell Builtins: echo.). + + -- Macro: AS_ECHO_N (WORD) + Emits WORD to the standard output, without a following newline. + WORD must be a single shell word (typically a quoted string) and, + for portability, should not include more than one newline. The + bytes of WORD are output as-is, even if it starts with "-" or + contains "\". Redirections can be placed outside the macro + invocation. + + -- Macro: AS_ESCAPE (STRING, [CHARS = ``\"$']) + Expands to STRING, with any characters in CHARS escaped with a + backslash (`\'). CHARS should be at most four bytes long, and + only contain characters from the set ``\"$'; however, characters + may be safely listed more than once in CHARS for the sake of + syntax highlighting editors. The current implementation expands + STRING after adding escapes; if STRING contains macro calls that + in turn expand to text needing shell quoting, you can use + `AS_ESCAPE(m4_dquote(m4_expand([string])))'. + + The default for CHARS (`\"$`') is the set of characters needing + escapes when STRING will be used literally within double quotes. + One common variant is the set of characters to protect when STRING + will be used literally within back-ticks or an unquoted + here-document (`\$`'). Another common variant is `""', which can + be used to form a double-quoted string containing the same + expansions that would have occurred if STRING were expanded in an + unquoted here-document; however, when using this variant, care + must be taken that STRING does not use double quotes within + complex variable expansions (such as `${foo-`echo "hi"`}') that + would be broken with improper escapes. + + This macro is often used with `AS_ECHO'. For an example, observe + the output generated by the shell code generated from this snippet: + + foo=bar + AS_ECHO(["AS_ESCAPE(["$foo" = ])AS_ESCAPE(["$foo"], [""])"]) + =>"$foo" = "bar" + m4_define([macro], [a, [\b]]) + AS_ECHO(["AS_ESCAPE([[macro]])"]) + =>macro + AS_ECHO(["AS_ESCAPE([macro])"]) + =>a, b + AS_ECHO(["AS_ESCAPE(m4_dquote(m4_expand([macro])))"]) + =>a, \b + + To escape a string that will be placed within single quotes, use: + + m4_bpatsubst([[STRING]], ['], ['\\'']) + + -- Macro: AS_EXECUTABLE_P (FILE) + Emit code to probe whether FILE is a regular file with executable + permissions (and not a directory with search permissions). The + caller is responsible for quoting FILE. + + -- Macro: AS_EXIT ([STATUS = `$?']) + Emit code to exit the shell with STATUS, defaulting to `$?'. This + macro works around shells that see the exit status of the command + prior to `exit' inside a `trap 0' handler (*note Limitations of + Shell Builtins: trap.). + + -- Macro: AS_IF (TEST1, [RUN-IF-TRUE1], ..., [RUN-IF-FALSE]) + Run shell code TEST1. If TEST1 exits with a zero status then run + shell code RUN-IF-TRUE1, else examine further tests. If no test + exits with a zero status, run shell code RUN-IF-FALSE, with + simplifications if either RUN-IF-TRUE1 or RUN-IF-FALSE is empty. + For example, + + AS_IF([test "x$foo" = xyes], [HANDLE_FOO([yes])], + [test "x$foo" != xno], [HANDLE_FOO([maybe])], + [echo foo not specified]) + + ensures any required macros of `HANDLE_FOO' are expanded before + the first test. + + -- Macro: AS_MKDIR_P (FILE-NAME) + Make the directory FILE-NAME, including intervening directories as + necessary. This is equivalent to `mkdir -p -- FILE-NAME', except + that it is portable to older versions of `mkdir' that lack support + for the `-p' option or for the `--' delimiter (*note Limitations + of Usual Tools: mkdir.). Also, `AS_MKDIR_P' succeeds if FILE-NAME + is a symbolic link to an existing directory, even though Posix is + unclear whether `mkdir -p' should succeed in that case. If + creation of FILE-NAME fails, exit the script. + + Also see the `AC_PROG_MKDIR_P' macro (*note Particular Programs::). + + -- Macro: AS_SET_STATUS (STATUS) + Emit shell code to set the value of `$?' to STATUS, as efficiently + as possible. However, this is not guaranteed to abort a shell + running with `set -e' (*note Limitations of Shell Builtins: set.). + This should also be used at the end of a complex shell function + instead of `return' (*note Shell Functions::) to avoid a DJGPP + shell bug. + + -- Macro: AS_TR_CPP (EXPRESSION) + Transform EXPRESSION into a valid right-hand side for a C + `#define'. For example: + + # This outputs "#define HAVE_CHAR_P 1". + # Notice the m4 quoting around #, to prevent an m4 comment + type="char *" + echo "[#]define AS_TR_CPP([HAVE_$type]) 1" + + -- Macro: AS_TR_SH (EXPRESSION) + Transform EXPRESSION into shell code that generates a valid shell + variable name. The result is literal when possible at m4 time, + but must be used with `eval' if EXPRESSION causes shell + indirections. For example: + + # This outputs "Have it!". + header="sys/some file.h" + eval AS_TR_SH([HAVE_$header])=yes + if test "x$HAVE_sys_some_file_h" = xyes; then echo "Have it!"; fi + + -- Macro: AS_SET_CATFILE (VAR, DIR, FILE) + Set the polymorphic shell variable VAR to DIR/FILE, but optimizing + the common cases (DIR or FILE is `.', FILE is absolute, etc.). + + -- Macro: AS_UNSET (VAR) + Unsets the shell variable VAR, working around bugs in older shells + (*note Limitations of Shell Builtins: unset.). VAR can be a + literal or indirect variable name. + + -- Macro: AS_VERSION_COMPARE (VERSION-1, VERSION-2, [ACTION-IF-LESS], + [ACTION-IF-EQUAL], [ACTION-IF-GREATER]) + Compare two strings VERSION-1 and VERSION-2, possibly containing + shell variables, as version strings, and expand ACTION-IF-LESS, + ACTION-IF-EQUAL, or ACTION-IF-GREATER depending upon the result. + The algorithm to compare is similar to the one used by strverscmp + in glibc (*note String/Array Comparison: (libc)String/Array + Comparison.). + + +File: autoconf.info, Node: Polymorphic Variables, Next: Initialization Macros, Prev: Common Shell Constructs, Up: Programming in M4sh + +9.2 Support for indirect variable names +======================================= + +Often, it is convenient to write a macro that will emit shell code +operating on a shell variable. The simplest case is when the variable +name is known. But a more powerful idiom is writing shell code that can +work through an indirection, where another variable or command +substitution produces the name of the variable to actually manipulate. +M4sh supports the notion of polymorphic shell variables, making it easy +to write a macro that can deal with either literal or indirect variable +names and output shell code appropriate for both use cases. Behavior is +undefined if expansion of an indirect variable does not result in a +literal variable name. + + -- Macro: AS_LITERAL_IF (EXPRESSION, [IF-LITERAL], [IF-NOT], + [IF-SIMPLE-REF = `IF-NOT']) + -- Macro: AS_LITERAL_WORD_IF (EXPRESSION, [IF-LITERAL], [IF-NOT], + [IF-SIMPLE-REF = `IF-NOT']) + If the expansion of EXPRESSION is definitely a shell literal, + expand IF-LITERAL. If the expansion of EXPRESSION looks like it + might contain shell indirections (such as `$var' or ``expr`'), + then IF-NOT is expanded. Sometimes, it is possible to output + optimized code if EXPRESSION consists only of shell variable + expansions (such as `${var}'), in which case IF-SIMPLE-REF can be + provided; but defaulting to IF-NOT should always be safe. + `AS_LITERAL_WORD_IF' only expands IF-LITERAL if EXPRESSION looks + like a single shell word, containing no whitespace; while + `AS_LITERAL_IF' allows whitespace in EXPRESSION. + + In order to reduce the time spent recognizing whether an + EXPRESSION qualifies as a literal or a simple indirection, the + implementation is somewhat conservative: EXPRESSION must be a + single shell word (possibly after stripping whitespace), + consisting only of bytes that would have the same meaning whether + unquoted or enclosed in double quotes (for example, `a.b' results + in IF-LITERAL, even though it is not a valid shell variable name; + while both `'a'' and `[$]' result in IF-NOT, because they behave + differently than `"'a'"' and `"[$]"'). This macro can be used in + contexts for recognizing portable file names (such as in the + implementation of `AC_LIBSOURCE'), or coupled with some + transliterations for forming valid variable names (such as in the + implementation of `AS_TR_SH', which uses an additional + `m4_translit' to convert `.' to `_'). + + This example shows how to read the contents of the shell variable + `bar', exercising all three arguments to `AS_LITERAL_IF'. It + results in a script that will output the line `hello' three times. + + AC_DEFUN([MY_ACTION], + [AS_LITERAL_IF([$1], + [echo "$$1"], + [AS_VAR_COPY([var], [$1]) + echo "$var"], + [eval 'echo "$'"$1"\"])]) + foo=bar bar=hello + MY_ACTION([bar]) + MY_ACTION([`echo bar`]) + MY_ACTION([$foo]) + + -- Macro: AS_VAR_APPEND (VAR, TEXT) + Emit shell code to append the shell expansion of TEXT to the end + of the current contents of the polymorphic shell variable VAR, + taking advantage of shells that provide the `+=' extension for more + efficient scaling. + + For situations where the final contents of VAR are relatively + short (less than 256 bytes), it is more efficient to use the + simpler code sequence of `VAR=${VAR}TEXT' (or its polymorphic + equivalent of `AS_VAR_COPY([t], [VAR])' and `AS_VAR_SET([VAR], + ["$t"TEXT])'). But in the case when the script will be repeatedly + appending text into `var', issues of scaling start to become + apparent. A naive implementation requires execution time linear + to the length of the current contents of VAR as well as the length + of TEXT for a single append, for an overall quadratic scaling with + multiple appends. This macro takes advantage of shells which + provide the extension `VAR+=TEXT', which can provide amortized + constant time for a single append, for an overall linear scaling + with multiple appends. Note that unlike `AS_VAR_SET', this macro + requires that TEXT be quoted properly to avoid field splitting and + file name expansion. + + -- Macro: AS_VAR_ARITH (VAR, EXPRESSION) + Emit shell code to compute the arithmetic expansion of EXPRESSION, + assigning the result as the contents of the polymorphic shell + variable VAR. The code takes advantage of shells that provide + `$(())' for fewer forks, but uses `expr' as a fallback. + Therefore, the syntax for a valid EXPRESSION is rather limited: + all operators must occur as separate shell arguments and with + proper quoting, there is no portable equality operator, all + variables containing numeric values must be expanded prior to the + computation, all numeric values must be provided in decimal + without leading zeroes, and the first shell argument should not be + a negative number. In the following example, this snippet will + print `(2+3)*4 == 20'. + + bar=3 + AS_VAR_ARITH([foo], [\( 2 + $bar \) \* 4]) + echo "(2+$bar)*4 == $foo" + + -- Macro: AS_VAR_COPY (DEST, SOURCE) + Emit shell code to assign the contents of the polymorphic shell + variable SOURCE to the polymorphic shell variable DEST. For + example, executing this M4sh snippet will output `bar hi': + + foo=bar bar=hi + AS_VAR_COPY([a], [foo]) + AS_VAR_COPY([b], [$foo]) + echo "$a $b" + + When it is necessary to access the contents of an indirect variable + inside a shell double-quoted context, the recommended idiom is to + first copy the contents into a temporary literal shell variable. + + for header in stdint_h inttypes_h ; do + AS_VAR_COPY([var], [ac_cv_header_$header]) + echo "$header detected: $var" + done + + -- Macro: AS_VAR_IF (VAR, [WORD], [IF-EQUAL], [IF-NOT-EQUAL]) + Output a shell conditional statement. If the contents of the + polymorphic shell variable VAR match the string WORD, execute + IF-EQUAL; otherwise execute IF-NOT-EQUAL. WORD must be a single + shell word (typically a quoted string). Avoids shell bugs if an + interrupt signal arrives while a command substitution in VAR is + being expanded. + + -- Macro: AS_VAR_PUSHDEF (M4-NAME, VALUE) + -- Macro: AS_VAR_POPDEF (M4-NAME) + A common M4sh idiom involves composing shell variable names from + an m4 argument (for example, writing a macro that uses a cache + variable). VALUE can be an arbitrary string, which will be + transliterated into a valid shell name by `AS_TR_SH'. In order to + access the composed variable name based on VALUE, it is easier to + declare a temporary m4 macro M4-NAME with `AS_VAR_PUSHDEF', then + use that macro as the argument to subsequent `AS_VAR' macros as a + polymorphic variable name, and finally free the temporary macro + with `AS_VAR_POPDEF'. These macros are often followed with `dnl', + to avoid excess newlines in the output. + + Here is an involved example, that shows the power of writing + macros that can handle composed shell variable names: + + m4_define([MY_CHECK_HEADER], + [AS_VAR_PUSHDEF([my_Header], [ac_cv_header_$1])dnl + AS_VAR_IF([my_Header], [yes], [echo "header $1 detected"])dnl + AS_VAR_POPDEF([my_Header])dnl + ]) + MY_CHECK_HEADER([stdint.h]) + for header in inttypes.h stdlib.h ; do + MY_CHECK_HEADER([$header]) + done + + In the above example, `MY_CHECK_HEADER' can operate on polymorphic + variable names. In the first invocation, the m4 argument is + `stdint.h', which transliterates into a literal `stdint_h'. As a + result, the temporary macro `my_Header' expands to the literal + shell name `ac_cv_header_stdint_h'. In the second invocation, the + m4 argument to `MY_CHECK_HEADER' is `$header', and the temporary + macro `my_Header' expands to the indirect shell name + `$as_my_Header'. During the shell execution of the for loop, when + `$header' contains `inttypes.h', then `$as_my_Header' contains + `ac_cv_header_inttypes_h'. If this script is then run on a + platform where all three headers have been previously detected, the + output of the script will include: + + header stdint.h detected + header inttypes.h detected + header stdlib.h detected + + -- Macro: AS_VAR_SET (VAR, [VALUE]) + Emit shell code to assign the contents of the polymorphic shell + variable VAR to the shell expansion of VALUE. VALUE is not + subject to field splitting or file name expansion, so if command + substitution is used, it may be done with ``""`' rather than using + an intermediate variable (*note Shell Substitutions::). However, + VALUE does undergo rescanning for additional macro names; behavior + is unspecified if late expansion results in any shell + meta-characters. + + -- Macro: AS_VAR_SET_IF (VAR, [IF-SET], [IF-UNDEF]) + Emit a shell conditional statement, which executes IF-SET if the + polymorphic shell variable `var' is set to any value, and IF-UNDEF + otherwise. + + -- Macro: AS_VAR_TEST_SET (VAR) + Emit a shell statement that results in a successful exit status + only if the polymorphic shell variable `var' is set. + + +File: autoconf.info, Node: Initialization Macros, Next: File Descriptor Macros, Prev: Polymorphic Variables, Up: Programming in M4sh + +9.3 Initialization Macros +========================= + + -- Macro: AS_BOURNE_COMPATIBLE + Set up the shell to be more compatible with the Bourne shell as + standardized by Posix, if possible. This may involve setting + environment variables, or setting options, or similar + implementation-specific actions. This macro is deprecated, since + `AS_INIT' already invokes it. + + -- Macro: AS_INIT + Initialize the M4sh environment. This macro calls `m4_init', then + outputs the `#! /bin/sh' line, a notice about where the output was + generated from, and code to sanitize the environment for the rest + of the script. Among other initializations, this sets `SHELL' to + the shell chosen to run the script (*note CONFIG_SHELL::), and + `LC_ALL' to ensure the C locale. Finally, it changes the current + diversion to `BODY'. `AS_INIT' is called automatically by + `AC_INIT' and `AT_INIT', so shell code in `configure', + `config.status', and `testsuite' all benefit from a sanitized + shell environment. + + -- Macro: AS_INIT_GENERATED (FILE, [COMMENT]) + Emit shell code to start the creation of a subsidiary shell script + in FILE, including changing FILE to be executable. This macro + populates the child script with information learned from the parent + (thus, the emitted code is equivalent in effect, but more + efficient, than the code output by `AS_INIT', + `AS_BOURNE_COMPATIBLE', and `AS_SHELL_SANITIZE'). If present, + COMMENT is output near the beginning of the child, prior to the + shell initialization code, and is subject to parameter expansion, + command substitution, and backslash quote removal. The parent + script should check the exit status after this macro, in case FILE + could not be properly created (for example, if the disk was full). + If successfully created, the parent script can then proceed to + append additional M4sh constructs into the child script. + + Note that the child script starts life without a log file open, so + if the parent script uses logging (*note AS_MESSAGE_LOG_FD::), you + must temporarily disable any attempts to use the log file until + after emitting code to open a log within the child. On the other + hand, if the parent script has `AS_MESSAGE_FD' redirected + somewhere besides `1', then the child script already has code that + copies stdout to that descriptor. Currently, the suggested idiom + for writing a M4sh shell script from within another script is: + + AS_INIT_GENERATED([FILE], [[# My child script. + ]]) || { AS_ECHO(["Failed to create child script"]); AS_EXIT; } + m4_pushdef([AS_MESSAGE_LOG_FD])dnl + cat >> "FILE" <<\__EOF__ + # Code to initialize AS_MESSAGE_LOG_FD + m4_popdef([AS_MESSAGE_LOG_FD])dnl + # Additional code + __EOF__ + + This, however, may change in the future as the M4sh interface is + stabilized further. + + Also, be aware that use of `LINENO' within the child script may + report line numbers relative to their location in the parent + script, even when using `AS_LINENO_PREPARE', if the parent script + was unable to locate a shell with working `LINENO' support. + + -- Macro: AS_LINENO_PREPARE + Find a shell that supports the special variable `LINENO', which + contains the number of the currently executing line. This macro is + automatically invoked by `AC_INIT' in configure scripts. + + -- Macro: AS_ME_PREPARE + Set up variable `as_me' to be the basename of the currently + executing script. This macro is automatically invoked by + `AC_INIT' in configure scripts. + + -- Macro: AS_TMPDIR (PREFIX, [DIR = `${TMPDIR:=/tmp}']) + Create, as safely as possible, a temporary sub-directory within + DIR with a name starting with PREFIX. PREFIX should be 2-4 + characters, to make it slightly easier to identify the owner of + the directory. If DIR is omitted, then the value of `TMPDIR' will + be used (defaulting to `/tmp'). On success, the name of the newly + created directory is stored in the shell variable `tmp'. On + error, the script is aborted. + + Typically, this macro is coupled with some exit traps to delete + the created directory and its contents on exit or interrupt. + However, there is a slight window between when the directory is + created and when the name is actually known to the shell, so an + interrupt at the right moment might leave the temporary directory + behind. Hence it is important to use a PREFIX that makes it + easier to determine if a leftover temporary directory from an + interrupted script is safe to delete. + + The use of the output variable `$tmp' rather than something in the + `as_' namespace is historical; it has the unfortunate consequence + that reusing this otherwise common name for any other purpose + inside your script has the potential to break any cleanup traps + designed to remove the temporary directory. + + -- Macro: AS_SHELL_SANITIZE + Initialize the shell suitably for `configure' scripts. This has + the effect of `AS_BOURNE_COMPATIBLE', and sets some other + environment variables for predictable results from configuration + tests. For example, it sets `LC_ALL' to change to the default C + locale. *Note Special Shell Variables::. This macro is + deprecated, since `AS_INIT' already invokes it. + + +File: autoconf.info, Node: File Descriptor Macros, Prev: Initialization Macros, Up: Programming in M4sh + +9.4 File Descriptor Macros +========================== + +The following macros define file descriptors used to output messages +(or input values) from `configure' scripts. For example: + + echo "$wombats found" >&AS_MESSAGE_LOG_FD + echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD + read kangaroos <&AS_ORIGINAL_STDIN_FD` + +However doing so is seldom needed, because Autoconf provides higher +level macros as described below. + + -- Macro: AS_MESSAGE_FD + The file descriptor for `checking for...' messages and results. + By default, `AS_INIT' sets this to `1' for standalone M4sh + clients. However, `AC_INIT' shuffles things around to another file + descriptor, in order to allow the `-q' option of `configure' to + choose whether messages should go to the script's standard output + or be discarded. + + If you want to display some messages, consider using one of the + printing macros (*note Printing Messages::) instead. Copies of + messages output via these macros are also recorded in `config.log'. + + -- Macro: AS_MESSAGE_LOG_FD + This must either be empty, or expand to a file descriptor for log + messages. By default, `AS_INIT' sets this macro to the empty + string for standalone M4sh clients, thus disabling logging. + However, `AC_INIT' shuffles things around so that both `configure' + and `config.status' use `config.log' for log messages. Macros + that run tools, like `AC_COMPILE_IFELSE' (*note Running the + Compiler::), redirect all output to this descriptor. You may want + to do so if you develop such a low-level macro. + + -- Macro: AS_ORIGINAL_STDIN_FD + This must expand to a file descriptor for the original standard + input. By default, `AS_INIT' sets this macro to `0' for standalone + M4sh clients. However, `AC_INIT' shuffles things around for + safety. + + When `configure' runs, it may accidentally execute an interactive + command that has the same name as the non-interactive meant to be + used or checked. If the standard input was the terminal, such + interactive programs would cause `configure' to stop, pending some + user input. Therefore `configure' redirects its standard input + from `/dev/null' during its initialization. This is not normally + a problem, since `configure' normally does not need user input. + + In the extreme case where your `configure' script really needs to + obtain some values from the original standard input, you can read + them explicitly from `AS_ORIGINAL_STDIN_FD'. + + +File: autoconf.info, Node: Writing Autoconf Macros, Next: Portable Shell, Prev: Programming in M4sh, Up: Top + +10 Writing Autoconf Macros +************************** + +When you write a feature test that could be applicable to more than one +software package, the best thing to do is encapsulate it in a new macro. +Here are some instructions and guidelines for writing Autoconf macros. + +* Menu: + +* Macro Definitions:: Basic format of an Autoconf macro +* Macro Names:: What to call your new macros +* Reporting Messages:: Notifying `autoconf' users +* Dependencies Between Macros:: What to do when macros depend on other macros +* Obsoleting Macros:: Warning about old ways of doing things +* Coding Style:: Writing Autoconf macros a` la Autoconf + + +File: autoconf.info, Node: Macro Definitions, Next: Macro Names, Up: Writing Autoconf Macros + +10.1 Macro Definitions +====================== + + -- Macro: AC_DEFUN (NAME, [BODY]) + Autoconf macros are defined using the `AC_DEFUN' macro, which is + similar to the M4 builtin `m4_define' macro; this creates a macro + named NAME and with BODY as its expansion. In addition to + defining a macro, `AC_DEFUN' adds to it some code that is used to + constrain the order in which macros are called, while avoiding + redundant output (*note Prerequisite Macros::). + + An Autoconf macro definition looks like this: + + AC_DEFUN(MACRO-NAME, MACRO-BODY) + + You can refer to any arguments passed to the macro as `$1', `$2', +etc. *Note How to define new macros: (m4.info)Definitions, for more +complete information on writing M4 macros. + + Most macros fall in one of two general categories. The first +category includes macros which take arguments, in order to generate +output parameterized by those arguments. Macros in this category are +designed to be directly expanded, often multiple times, and should not +be used as the argument to `AC_REQUIRE'. The other category includes +macros which are shorthand for a fixed block of text, and therefore do +not take arguments. For this category of macros, directly expanding +the macro multiple times results in redundant output, so it is more +common to use the macro as the argument to `AC_REQUIRE', or to declare +the macro with `AC_DEFUN_ONCE' (*note One-Shot Macros::). + + Be sure to properly quote both the MACRO-BODY _and_ the MACRO-NAME +to avoid any problems if the macro happens to have been previously +defined. + + Each macro should have a header comment that gives its prototype, +and a brief description. When arguments have default values, display +them in the prototype. For example: + + # AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1]) + # -------------------------------------- + m4_define([AC_MSG_ERROR], + [{ AS_MESSAGE([error: $1], [2]) + exit m4_default([$2], [1]); }]) + + Comments about the macro should be left in the header comment. Most +other comments make their way into `configure', so just keep using `#' +to introduce comments. + + If you have some special comments about pure M4 code, comments that +make no sense in `configure' and in the header comment, then use the +builtin `dnl': it causes M4 to discard the text through the next +newline. + + Keep in mind that `dnl' is rarely needed to introduce comments; +`dnl' is more useful to get rid of the newlines following macros that +produce no output, such as `AC_REQUIRE'. + + Public third-party macros need to use `AC_DEFUN', and not +`m4_define', in order to be found by `aclocal' (*note Extending +aclocal: (automake)Extending aclocal.). Additionally, if it is ever +determined that a macro should be made obsolete, it is easy to convert +from `AC_DEFUN' to `AU_DEFUN' in order to have `autoupdate' assist the +user in choosing a better alternative, but there is no corresponding +way to make `m4_define' issue an upgrade notice (*note AU_DEFUN::). + + There is another subtle, but important, difference between using +`m4_define' and `AC_DEFUN': only the former is unaffected by +`AC_REQUIRE'. When writing a file, it is always safe to replace a +block of text with a `m4_define' macro that will expand to the same +text. But replacing a block of text with an `AC_DEFUN' macro with the +same content does not necessarily give the same results, because it +changes the location where any embedded but unsatisfied `AC_REQUIRE' +invocations within the block will be expanded. For an example of this, +see *note Expanded Before Required::. + + +File: autoconf.info, Node: Macro Names, Next: Reporting Messages, Prev: Macro Definitions, Up: Writing Autoconf Macros + +10.2 Macro Names +================ + +All of the public Autoconf macros have all-uppercase names in the +namespace `^AC_' to prevent them from accidentally conflicting with +other text; Autoconf also reserves the namespace `^_AC_' for internal +macros. All shell variables that they use for internal purposes have +mostly-lowercase names starting with `ac_'. Autoconf also uses +here-document delimiters in the namespace `^_AC[A-Z]'. During +`configure', files produced by Autoconf make heavy use of the file +system namespace `^conf'. + + Since Autoconf is built on top of M4sugar (*note Programming in +M4sugar::) and M4sh (*note Programming in M4sh::), you must also be +aware of those namespaces (`^_?\(m4\|AS\)_'). And since `configure.ac' +is also designed to be scanned by Autoheader, Autoscan, Autoupdate, and +Automake, you should be aware of the `^_?A[HNUM]_' namespaces. In +general, you _should not use_ the namespace of a package that does not +own the macro or shell code you are writing. + + To ensure that your macros don't conflict with present or future +Autoconf macros, you should prefix your own macro names and any shell +variables they use with some other sequence. Possibilities include your +initials, or an abbreviation for the name of your organization or +software package. Historically, people have not always followed the +rule of using a namespace appropriate for their package, and this has +made it difficult for determining the origin of a macro (and where to +report bugs about that macro), as well as difficult for the true +namespace owner to add new macros without interference from pre-existing +uses of third-party macros. Perhaps the best example of this confusion +is the `AM_GNU_GETTEXT' macro, which belongs, not to Automake, but to +Gettext. + + Most of the Autoconf macros' names follow a structured naming +convention that indicates the kind of feature check by the name. The +macro names consist of several words, separated by underscores, going +from most general to most specific. The names of their cache variables +use the same convention (*note Cache Variable Names::, for more +information on them). + + The first word of the name after the namespace initials (such as +`AC_') usually tells the category of the feature being tested. Here +are the categories used in Autoconf for specific test macros, the kind +of macro that you are more likely to write. They are also used for +cache variables, in all-lowercase. Use them where applicable; where +they're not, invent your own categories. + +`C' + C language builtin features. + +`DECL' + Declarations of C variables in header files. + +`FUNC' + Functions in libraries. + +`GROUP' + Posix group owners of files. + +`HEADER' + Header files. + +`LIB' + C libraries. + +`PROG' + The base names of programs. + +`MEMBER' + Members of aggregates. + +`SYS' + Operating system features. + +`TYPE' + C builtin or declared types. + +`VAR' + C variables in libraries. + + After the category comes the name of the particular feature being +tested. Any further words in the macro name indicate particular aspects +of the feature. For example, `AC_PROG_CC_STDC' checks whether the C +compiler supports ISO Standard C. + + An internal macro should have a name that starts with an underscore; +Autoconf internals should therefore start with `_AC_'. Additionally, a +macro that is an internal subroutine of another macro should have a +name that starts with an underscore and the name of that other macro, +followed by one or more words saying what the internal macro does. For +example, `AC_PATH_X' has internal macros `_AC_PATH_X_XMKMF' and +`_AC_PATH_X_DIRECT'. + + +File: autoconf.info, Node: Reporting Messages, Next: Dependencies Between Macros, Prev: Macro Names, Up: Writing Autoconf Macros + +10.3 Reporting Messages +======================= + +When macros statically diagnose abnormal situations, benign or fatal, it +is possible to make `autoconf' detect the problem, and refuse to create +`configure' in the case of an error. The macros in this section are +considered obsolescent, and new code should use M4sugar macros for this +purpose, see *note Diagnostic Macros::. + + On the other hand, it is possible to want to detect errors when +`configure' is run, which are dependent on the environment of the user +rather than the maintainer. For dynamic diagnostics, see *note +Printing Messages::. + + -- Macro: AC_DIAGNOSE (CATEGORY, MESSAGE) + Report MESSAGE as a warning (or as an error if requested by the + user) if warnings of the CATEGORY are turned on. This macro is + obsolescent; you are encouraged to use: + m4_warn([CATEGORY], [MESSAGE]) + instead. *Note m4_warn::, for more details, including valid + CATEGORY names. + + -- Macro: AC_WARNING (MESSAGE) + Report MESSAGE as a syntax warning. This macro is obsolescent; + you are encouraged to use: + m4_warn([syntax], [MESSAGE]) + instead. *Note m4_warn::, for more details, as well as better + finer-grained categories of warnings (not all problems have to do + with syntax). + + -- Macro: AC_FATAL (MESSAGE) + Report a severe error MESSAGE, and have `autoconf' die. This + macro is obsolescent; you are encouraged to use: + m4_fatal([MESSAGE]) + instead. *Note m4_fatal::, for more details. + + When the user runs `autoconf -W error', warnings from `m4_warn' +(including those issued through `AC_DIAGNOSE' and `AC_WARNING') are +reported as errors, see *note autoconf Invocation::. + + +File: autoconf.info, Node: Dependencies Between Macros, Next: Obsoleting Macros, Prev: Reporting Messages, Up: Writing Autoconf Macros + +10.4 Dependencies Between Macros +================================ + +Some Autoconf macros depend on other macros having been called first in +order to work correctly. Autoconf provides a way to ensure that certain +macros are called if needed and a way to warn the user if macros are +called in an order that might cause incorrect operation. + +* Menu: + +* Prerequisite Macros:: Ensuring required information +* Suggested Ordering:: Warning about possible ordering problems +* One-Shot Macros:: Ensuring a macro is called only once + + +File: autoconf.info, Node: Prerequisite Macros, Next: Suggested Ordering, Up: Dependencies Between Macros + +10.4.1 Prerequisite Macros +-------------------------- + +A macro that you write might need to use values that have previously +been computed by other macros. For example, `AC_DECL_YYTEXT' examines +the output of `flex' or `lex', so it depends on `AC_PROG_LEX' having +been called first to set the shell variable `LEX'. + + Rather than forcing the user of the macros to keep track of the +dependencies between them, you can use the `AC_REQUIRE' macro to do it +automatically. `AC_REQUIRE' can ensure that a macro is only called if +it is needed, and only called once. + + -- Macro: AC_REQUIRE (MACRO-NAME) + If the M4 macro MACRO-NAME has not already been called, call it + (without any arguments). Make sure to quote MACRO-NAME with + square brackets. MACRO-NAME must have been defined using + `AC_DEFUN' or else contain a call to `AC_PROVIDE' to indicate that + it has been called. + + `AC_REQUIRE' must be used inside a macro defined by `AC_DEFUN'; it + must not be called from the top level. Also, it does not make + sense to require a macro that takes parameters. + + `AC_REQUIRE' is often misunderstood. It really implements +dependencies between macros in the sense that if one macro depends upon +another, the latter is expanded _before_ the body of the former. To be +more precise, the required macro is expanded before the outermost +defined macro in the current expansion stack. In particular, +`AC_REQUIRE([FOO])' is not replaced with the body of `FOO'. For +instance, this definition of macros: + + AC_DEFUN([TRAVOLTA], + [test "$body_temperature_in_celsius" -gt "38" && + dance_floor=occupied]) + AC_DEFUN([NEWTON_JOHN], + [test "x$hair_style" = xcurly && + dance_floor=occupied]) + + AC_DEFUN([RESERVE_DANCE_FLOOR], + [if date | grep '^Sat.*pm' >/dev/null 2>&1; then + AC_REQUIRE([TRAVOLTA]) + AC_REQUIRE([NEWTON_JOHN]) + fi]) + +with this `configure.ac' + + AC_INIT([Dance Manager], [1.0], [bug-dance@example.org]) + RESERVE_DANCE_FLOOR + if test "x$dance_floor" = xoccupied; then + AC_MSG_ERROR([cannot pick up here, let's move]) + fi + +does not leave you with a better chance to meet a kindred soul at other +times than Saturday night since it expands into: + + test "$body_temperature_in_Celsius" -gt "38" && + dance_floor=occupied + test "x$hair_style" = xcurly && + dance_floor=occupied + fi + if date | grep '^Sat.*pm' >/dev/null 2>&1; then + + + fi + + This behavior was chosen on purpose: (i) it prevents messages in +required macros from interrupting the messages in the requiring macros; +(ii) it avoids bad surprises when shell conditionals are used, as in: + + if ...; then + AC_REQUIRE([SOME_CHECK]) + fi + ... + SOME_CHECK + + However, this implementation can lead to another class of problems. +Consider the case where an outer macro first expands, then indirectly +requires, an inner macro: + + AC_DEFUN([TESTA], [[echo in A + if test -n "$SEEN_A" ; then echo duplicate ; fi + SEEN_A=:]]) + AC_DEFUN([TESTB], [AC_REQUIRE([TESTA])[echo in B + if test -z "$SEEN_A" ; then echo bug ; fi]]) + AC_DEFUN([TESTC], [AC_REQUIRE([TESTB])[echo in C]]) + AC_DEFUN([OUTER], [[echo in OUTER] + TESTA + TESTC]) + OUTER + +Prior to Autoconf 2.64, the implementation of `AC_REQUIRE' recognized +that `TESTB' needed to be hoisted prior to the expansion of `OUTER', +but because `TESTA' had already been directly expanded, it failed to +hoist `TESTA'. Therefore, the expansion of `TESTB' occurs prior to its +prerequisites, leading to the following output: + + in B + bug + in OUTER + in A + in C + +Newer Autoconf is smart enough to recognize this situation, and hoists +`TESTA' even though it has already been expanded, but issues a syntax +warning in the process. This is because the hoisted expansion of +`TESTA' defeats the purpose of using `AC_REQUIRE' to avoid redundant +code, and causes its own set of problems if the hoisted macro is not +idempotent: + + in A + in B + in OUTER + in A + duplicate + in C + + The bug is not in Autoconf, but in the macro definitions. If you +ever pass a particular macro name to `AC_REQUIRE', then you are implying +that the macro only needs to be expanded once. But to enforce this, +either the macro must be declared with `AC_DEFUN_ONCE' (although this +only helps in Autoconf 2.64 or newer), or all uses of that macro should +be through `AC_REQUIRE'; directly expanding the macro defeats the point +of using `AC_REQUIRE' to eliminate redundant expansion. In the +example, this rule of thumb was violated because `TESTB' requires +`TESTA' while `OUTER' directly expands it. One way of fixing the bug +is to factor `TESTA' into two macros, the portion designed for direct +and repeated use (here, named `TESTA'), and the portion designed for +one-shot output and used only inside `AC_REQUIRE' (here, named +`TESTA_PREREQ'). Then, by fixing all clients to use the correct +calling convention according to their needs: + + AC_DEFUN([TESTA], [AC_REQUIRE([TESTA_PREREQ])[echo in A]]) + AC_DEFUN([TESTA_PREREQ], [[echo in A_PREREQ + if test -n "$SEEN_A" ; then echo duplicate ; fi + SEEN_A=:]]) + AC_DEFUN([TESTB], [AC_REQUIRE([TESTA_PREREQ])[echo in B + if test -z "$SEEN_A" ; then echo bug ; fi]]) + AC_DEFUN([TESTC], [AC_REQUIRE([TESTB])[echo in C]]) + AC_DEFUN([OUTER], [[echo in OUTER] + TESTA + TESTC]) + OUTER + +the resulting output will then obey all dependency rules and avoid any +syntax warnings, whether the script is built with old or new Autoconf +versions: + + in A_PREREQ + in B + in OUTER + in A + in C + + The helper macros `AS_IF' and `AS_CASE' may be used to enforce +expansion of required macros outside of shell conditional constructs. +You are furthermore encouraged, although not required, to put all +`AC_REQUIRE' calls at the beginning of a macro. You can use `dnl' to +avoid the empty lines they leave. + + +File: autoconf.info, Node: Suggested Ordering, Next: One-Shot Macros, Prev: Prerequisite Macros, Up: Dependencies Between Macros + +10.4.2 Suggested Ordering +------------------------- + +Some macros should be run before another macro if both are called, but +neither _requires_ that the other be called. For example, a macro that +changes the behavior of the C compiler should be called before any +macros that run the C compiler. Many of these dependencies are noted in +the documentation. + + Autoconf provides the `AC_BEFORE' macro to warn users when macros +with this kind of dependency appear out of order in a `configure.ac' +file. The warning occurs when creating `configure' from +`configure.ac', not when running `configure'. + + For example, `AC_PROG_CPP' checks whether the C compiler can run the +C preprocessor when given the `-E' option. It should therefore be +called after any macros that change which C compiler is being used, +such as `AC_PROG_CC'. So `AC_PROG_CC' contains: + + AC_BEFORE([$0], [AC_PROG_CPP])dnl + +This warns the user if a call to `AC_PROG_CPP' has already occurred +when `AC_PROG_CC' is called. + + -- Macro: AC_BEFORE (THIS-MACRO-NAME, CALLED-MACRO-NAME) + Make M4 print a warning message to the standard error output if + CALLED-MACRO-NAME has already been called. THIS-MACRO-NAME should + be the name of the macro that is calling `AC_BEFORE'. The macro + CALLED-MACRO-NAME must have been defined using `AC_DEFUN' or else + contain a call to `AC_PROVIDE' to indicate that it has been called. + + +File: autoconf.info, Node: One-Shot Macros, Prev: Suggested Ordering, Up: Dependencies Between Macros + +10.4.3 One-Shot Macros +---------------------- + +Some macros should be called only once, either because calling them +multiple time is unsafe, or because it is bad style. For instance +Autoconf ensures that `AC_CANONICAL_BUILD' and cousins (*note +Canonicalizing::) are evaluated only once, because it makes no sense to +run these expensive checks more than once. Such one-shot macros can be +defined using `AC_DEFUN_ONCE'. + + -- Macro: AC_DEFUN_ONCE (MACRO-NAME, MACRO-BODY) + Declare macro MACRO-NAME like `AC_DEFUN' would (*note Macro + Definitions::), but add additional logic that guarantees that only + the first use of the macro (whether by direct expansion or + `AC_REQUIRE') causes an expansion of MACRO-BODY; the expansion + will occur before the start of any enclosing macro defined by + `AC_DEFUN'. Subsequent expansions are silently ignored. + Generally, it does not make sense for MACRO-BODY to use parameters + such as `$1'. + + Prior to Autoconf 2.64, a macro defined by `AC_DEFUN_ONCE' would +emit a warning if it was directly expanded a second time, so for +portability, it is better to use `AC_REQUIRE' than direct invocation of +MACRO-NAME inside a macro defined by `AC_DEFUN' (*note Prerequisite +Macros::). + + +File: autoconf.info, Node: Obsoleting Macros, Next: Coding Style, Prev: Dependencies Between Macros, Up: Writing Autoconf Macros + +10.5 Obsoleting Macros +====================== + +Configuration and portability technology has evolved over the years. +Often better ways of solving a particular problem are developed, or +ad-hoc approaches are systematized. This process has occurred in many +parts of Autoconf. One result is that some of the macros are now +considered "obsolete"; they still work, but are no longer considered +the best thing to do, hence they should be replaced with more modern +macros. Ideally, `autoupdate' should replace the old macro calls with +their modern implementation. + + Autoconf provides a simple means to obsolete a macro. + + -- Macro: AU_DEFUN (OLD-MACRO, IMPLEMENTATION, [MESSAGE]) + Define OLD-MACRO as IMPLEMENTATION. The only difference with + `AC_DEFUN' is that the user is warned that OLD-MACRO is now + obsolete. + + If she then uses `autoupdate', the call to OLD-MACRO is replaced + by the modern IMPLEMENTATION. MESSAGE should include information + on what to do after running `autoupdate'; `autoupdate' prints it + as a warning, and includes it in the updated `configure.ac' file. + + The details of this macro are hairy: if `autoconf' encounters an + `AU_DEFUN'ed macro, all macros inside its second argument are + expanded as usual. However, when `autoupdate' is run, only M4 and + M4sugar macros are expanded here, while all other macros are + disabled and appear literally in the updated `configure.ac'. + + -- Macro: AU_ALIAS (OLD-NAME, NEW-NAME) + Used if the OLD-NAME is to be replaced by a call to NEW-MACRO with + the same parameters. This happens for example if the macro was + renamed. + + +File: autoconf.info, Node: Coding Style, Prev: Obsoleting Macros, Up: Writing Autoconf Macros + +10.6 Coding Style +================= + +The Autoconf macros follow a strict coding style. You are encouraged to +follow this style, especially if you intend to distribute your macro, +either by contributing it to Autoconf itself or the Autoconf Macro +Archive (http://www.gnu.org/software/autoconf-archive/), or by other +means. + + The first requirement is to pay great attention to the quotation. +For more details, see *note Autoconf Language::, and *note M4 +Quotation::. + + Do not try to invent new interfaces. It is likely that there is a +macro in Autoconf that resembles the macro you are defining: try to +stick to this existing interface (order of arguments, default values, +etc.). We _are_ conscious that some of these interfaces are not +perfect; nevertheless, when harmless, homogeneity should be preferred +over creativity. + + Be careful about clashes both between M4 symbols and between shell +variables. + + If you stick to the suggested M4 naming scheme (*note Macro Names::), +you are unlikely to generate conflicts. Nevertheless, when you need to +set a special value, _avoid using a regular macro name_; rather, use an +"impossible" name. For instance, up to version 2.13, the macro +`AC_SUBST' used to remember what SYMBOL macros were already defined by +setting `AC_SUBST_SYMBOL', which is a regular macro name. But since +there is a macro named `AC_SUBST_FILE', it was just impossible to +`AC_SUBST(FILE)'! In this case, `AC_SUBST(SYMBOL)' or +`_AC_SUBST(SYMBOL)' should have been used (yes, with the parentheses). + + No Autoconf macro should ever enter the user-variable name space; +i.e., except for the variables that are the actual result of running the +macro, all shell variables should start with `ac_'. In addition, small +macros or any macro that is likely to be embedded in other macros +should be careful not to use obvious names. + + Do not use `dnl' to introduce comments: most of the comments you are +likely to write are either header comments which are not output anyway, +or comments that should make their way into `configure'. There are +exceptional cases where you do want to comment special M4 constructs, +in which case `dnl' is right, but keep in mind that it is unlikely. + + M4 ignores the leading blanks and newlines before each argument. +Use this feature to indent in such a way that arguments are (more or +less) aligned with the opening parenthesis of the macro being called. +For instance, instead of + + AC_CACHE_CHECK(for EMX OS/2 environment, + ac_cv_emxos2, + [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])], + [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) + +write + + AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], + [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], + [ac_cv_emxos2=yes], + [ac_cv_emxos2=no])]) + +or even + + AC_CACHE_CHECK([for EMX OS/2 environment], + [ac_cv_emxos2], + [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], + [return __EMX__;])], + [ac_cv_emxos2=yes], + [ac_cv_emxos2=no])]) + + When using `AC_RUN_IFELSE' or any macro that cannot work when +cross-compiling, provide a pessimistic value (typically `no'). + + Feel free to use various tricks to prevent auxiliary tools, such as +syntax-highlighting editors, from behaving improperly. For instance, +instead of: + + m4_bpatsubst([$1], [$"]) + +use + + m4_bpatsubst([$1], [$""]) + +so that Emacsen do not open an endless "string" at the first quote. +For the same reasons, avoid: + + test $[#] != 0 + +and use: + + test $[@%:@] != 0 + +Otherwise, the closing bracket would be hidden inside a `#'-comment, +breaking the bracket-matching highlighting from Emacsen. Note the +preferred style to escape from M4: `$[1]', `$[@]', etc. Do not escape +when it is unnecessary. Common examples of useless quotation are +`[$]$1' (write `$$1'), `[$]var' (use `$var'), etc. If you add +portability issues to the picture, you'll prefer `${1+"$[@]"}' to +`"[$]@"', and you'll prefer do something better than hacking Autoconf +`:-)'. + + When using `sed', don't use `-e' except for indenting purposes. +With the `s' and `y' commands, the preferred separator is `/' unless +`/' itself might appear in the pattern or replacement, in which case +you should use `|', or optionally `,' if you know the pattern and +replacement cannot contain a file name. If none of these characters +will do, choose a printable character that cannot appear in the pattern +or replacement. Characters from the set `"#$&'()*;<=>?`|~' are good +choices if the pattern or replacement might contain a file name, since +they have special meaning to the shell and are less likely to occur in +file names. + + *Note Macro Definitions::, for details on how to define a macro. If +a macro doesn't use `AC_REQUIRE', is expected to never be the object of +an `AC_REQUIRE' directive, and macros required by other macros inside +arguments do not need to be expanded before this macro, then use +`m4_define'. In case of doubt, use `AC_DEFUN'. Also take into account +that public third-party macros need to use `AC_DEFUN' in order to be +found by `aclocal' (*note Extending aclocal: (automake)Extending +aclocal.). All the `AC_REQUIRE' statements should be at the beginning +of the macro, and each statement should be followed by `dnl'. + + You should not rely on the number of arguments: instead of checking +whether an argument is missing, test that it is not empty. It provides +both a simpler and a more predictable interface to the user, and saves +room for further arguments. + + Unless the macro is short, try to leave the closing `])' at the +beginning of a line, followed by a comment that repeats the name of the +macro being defined. This introduces an additional newline in +`configure'; normally, that is not a problem, but if you want to remove +it you can use `[]dnl' on the last line. You can similarly use `[]dnl' +after a macro call to remove its newline. `[]dnl' is recommended +instead of `dnl' to ensure that M4 does not interpret the `dnl' as +being attached to the preceding text or macro output. For example, +instead of: + + AC_DEFUN([AC_PATH_X], + [AC_MSG_CHECKING([for X]) + AC_REQUIRE_CPP() + # ...omitted... + AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) + fi]) + +you would write: + + AC_DEFUN([AC_PATH_X], + [AC_REQUIRE_CPP()[]dnl + AC_MSG_CHECKING([for X]) + # ...omitted... + AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) + fi[]dnl + ])# AC_PATH_X + + If the macro is long, try to split it into logical chunks. +Typically, macros that check for a bug in a function and prepare its +`AC_LIBOBJ' replacement should have an auxiliary macro to perform this +setup. Do not hesitate to introduce auxiliary macros to factor your +code. + + In order to highlight the recommended coding style, here is a macro +written the old way: + + dnl Check for EMX on OS/2. + dnl _AC_EMXOS2 + AC_DEFUN(_AC_EMXOS2, + [AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2, + [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)], + ac_cv_emxos2=yes, ac_cv_emxos2=no)]) + test "x$ac_cv_emxos2" = xyes && EMXOS2=yes]) + +and the new way: + + # _AC_EMXOS2 + # ---------- + # Check for EMX on OS/2. + m4_define([_AC_EMXOS2], + [AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], + [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], + [ac_cv_emxos2=yes], + [ac_cv_emxos2=no])]) + test "x$ac_cv_emxos2" = xyes && EMXOS2=yes[]dnl + ])# _AC_EMXOS2 + + +File: autoconf.info, Node: Portable Shell, Next: Portable Make, Prev: Writing Autoconf Macros, Up: Top + +11 Portable Shell Programming +***************************** + +When writing your own checks, there are some shell-script programming +techniques you should avoid in order to make your code portable. The +Bourne shell and upward-compatible shells like the Korn shell and Bash +have evolved over the years, and many features added to the original +System7 shell are now supported on all interesting porting targets. +However, the following discussion between Russ Allbery and Robert Lipe +is worth reading: + +Russ Allbery: + + The GNU assumption that `/bin/sh' is the one and only shell leads + to a permanent deadlock. Vendors don't want to break users' + existing shell scripts, and there are some corner cases in the + Bourne shell that are not completely compatible with a Posix + shell. Thus, vendors who have taken this route will _never_ + (OK..."never say never") replace the Bourne shell (as `/bin/sh') + with a Posix shell. + +Robert Lipe: + + This is exactly the problem. While most (at least most System + V's) do have a Bourne shell that accepts shell functions most + vendor `/bin/sh' programs are not the Posix shell. + + So while most modern systems do have a shell _somewhere_ that + meets the Posix standard, the challenge is to find it. + + For this reason, part of the job of M4sh (*note Programming in +M4sh::) is to find such a shell. But to prevent trouble, if you're not +using M4sh you should not take advantage of features that were added +after Unix version 7, circa 1977 (*note Systemology::); you should not +use aliases, negated character classes, or even `unset'. `#' comments, +while not in Unix version 7, were retrofitted in the original Bourne +shell and can be assumed to be part of the least common denominator. + + On the other hand, if you're using M4sh you can assume that the shell +has the features that were added in SVR2 (circa 1984), including shell +functions, `return', `unset', and I/O redirection for builtins. For +more information, refer to `http://www.in-ulm.de/~mascheck/bourne/'. +However, some pitfalls have to be avoided for portable use of these +constructs; these will be documented in the rest of this chapter. See +in particular *note Shell Functions:: and *note Limitations of Shell +Builtins: Limitations of Builtins. + + Some ancient systems have quite small limits on the length of the +`#!' line; for instance, 32 bytes (not including the newline) on SunOS +4. However, these ancient systems are no longer of practical concern. + + The set of external programs you should run in a `configure' script +is fairly small. *Note Utilities in Makefiles: (standards)Utilities in +Makefiles, for the list. This restriction allows users to start out +with a fairly small set of programs and build the rest, avoiding too +many interdependencies between packages. + + Some of these external utilities have a portable subset of features; +see *note Limitations of Usual Tools::. + + There are other sources of documentation about shells. The +specification for the Posix Shell Command Language +(http://www.opengroup.org/susv3/utilities/xcu_chap02.html), though more +generous than the restrictive shell subset described above, is fairly +portable nowadays. Also please see the Shell FAQs +(http://www.faqs.org/faqs/unix-faq/shell/). + +* Menu: + +* Shellology:: A zoology of shells +* Invoking the Shell:: Invoking the shell as a command +* Here-Documents:: Quirks and tricks +* File Descriptors:: FDs and redirections +* Signal Handling:: Shells, signals, and headaches +* File System Conventions:: File names +* Shell Pattern Matching:: Pattern matching +* Shell Substitutions:: Variable and command expansions +* Assignments:: Varying side effects of assignments +* Parentheses:: Parentheses in shell scripts +* Slashes:: Slashes in shell scripts +* Special Shell Variables:: Variables you should not change +* Shell Functions:: What to look out for if you use them +* Limitations of Builtins:: Portable use of not so portable /bin/sh +* Limitations of Usual Tools:: Portable use of portable tools + + +File: autoconf.info, Node: Shellology, Next: Invoking the Shell, Up: Portable Shell + +11.1 Shellology +=============== + +There are several families of shells, most prominently the Bourne family +and the C shell family which are deeply incompatible. If you want to +write portable shell scripts, avoid members of the C shell family. The +the Shell difference FAQ +(http://www.faqs.org/faqs/unix-faq/shell/shell-differences/) includes a +small history of Posix shells, and a comparison between several of them. + + Below we describe some of the members of the Bourne shell family. + +Ash + Ash is often used on GNU/Linux and BSD systems as a light-weight + Bourne-compatible shell. Ash 0.2 has some bugs that are fixed in + the 0.3.x series, but portable shell scripts should work around + them, since version 0.2 is still shipped with many GNU/Linux + distributions. + + To be compatible with Ash 0.2: + + - don't use `$?' after expanding empty or unset variables, or + at the start of an `eval': + + foo= + false + $foo + echo "Do not use it: $?" + false + eval 'echo "Do not use it: $?"' + + - don't use command substitution within variable expansion: + + cat ${FOO=`bar`} + + - beware that single builtin substitutions are not performed by + a subshell, hence their effect applies to the current shell! + *Note Shell Substitutions::, item "Command Substitution". + +Bash + To detect whether you are running Bash, test whether + `BASH_VERSION' is set. To require Posix compatibility, run `set + -o posix'. *Note Bash Posix Mode: (bash)Bash POSIX Mode, for + details. + +Bash 2.05 and later + Versions 2.05 and later of Bash use a different format for the + output of the `set' builtin, designed to make evaluating its + output easier. However, this output is not compatible with earlier + versions of Bash (or with many other shells, probably). So if you + use Bash 2.05 or higher to execute `configure', you'll need to use + Bash 2.05 for all other build tasks as well. + +Ksh + The Korn shell is compatible with the Bourne family and it mostly + conforms to Posix. It has two major variants commonly called + `ksh88' and `ksh93', named after the years of initial release. It + is usually called `ksh', but is called `sh' on some hosts if you + set your path appropriately. + + Solaris systems have three variants: `/usr/bin/ksh' is `ksh88'; it + is standard on Solaris 2.0 and later. `/usr/xpg4/bin/sh' is a + Posix-compliant variant of `ksh88'; it is standard on Solaris 9 + and later. `/usr/dt/bin/dtksh' is `ksh93'. Variants that are not + standard may be parts of optional packages. There is no extra + charge for these packages, but they are not part of a minimal OS + install and therefore some installations may not have it. + + Starting with Tru64 Version 4.0, the Korn shell `/usr/bin/ksh' is + also available as `/usr/bin/posix/sh'. If the environment + variable `BIN_SH' is set to `xpg4', subsidiary invocations of the + standard shell conform to Posix. + +Pdksh + A public-domain clone of the Korn shell called `pdksh' is widely + available: it has most of the `ksh88' features along with a few of + its own. It usually sets `KSH_VERSION', except if invoked as + `/bin/sh' on OpenBSD, and similarly to Bash you can require Posix + compatibility by running `set -o posix'. Unfortunately, with + `pdksh' 5.2.14 (the latest stable version as of January 2007) + Posix mode is buggy and causes `pdksh' to depart from Posix in at + least one respect, see *note Shell Substitutions::. + +Zsh + To detect whether you are running `zsh', test whether + `ZSH_VERSION' is set. By default `zsh' is _not_ compatible with + the Bourne shell: you must execute `emulate sh', and for `zsh' + versions before 3.1.6-dev-18 you must also set `NULLCMD' to `:'. + *Note Compatibility: (zsh)Compatibility, for details. + + The default Mac OS X `sh' was originally Zsh; it was changed to + Bash in Mac OS X 10.2. + + +File: autoconf.info, Node: Invoking the Shell, Next: Here-Documents, Prev: Shellology, Up: Portable Shell + +11.2 Invoking the Shell +======================= + +The Korn shell (up to at least version M-12/28/93d) has a bug when +invoked on a file whose name does not contain a slash. It first +searches for the file's name in `PATH', and if found it executes that +rather than the original file. For example, assuming there is a binary +executable `/usr/bin/script' in your `PATH', the last command in the +following example fails because the Korn shell finds `/usr/bin/script' +and refuses to execute it as a shell script: + + $ touch xxyzzyz script + $ ksh xxyzzyz + $ ksh ./script + $ ksh script + ksh: script: cannot execute + + Bash 2.03 has a bug when invoked with the `-c' option: if the +option-argument ends in backslash-newline, Bash incorrectly reports a +syntax error. The problem does not occur if a character follows the +backslash: + + $ $ bash -c 'echo foo \ + > ' + bash: -c: line 2: syntax error: unexpected end of file + $ bash -c 'echo foo \ + > ' + foo + +*Note Backslash-Newline-Empty::, for how this can cause problems in +makefiles. + + +File: autoconf.info, Node: Here-Documents, Next: File Descriptors, Prev: Invoking the Shell, Up: Portable Shell + +11.3 Here-Documents +=================== + +Don't rely on `\' being preserved just because it has no special +meaning together with the next symbol. In the native `sh' on OpenBSD +2.7 `\"' expands to `"' in here-documents with unquoted delimiter. As +a general rule, if `\\' expands to `\' use `\\' to get `\'. + + With OpenBSD 2.7's `sh' + + $ cat <<EOF + > \" \\ + > EOF + " \ + +and with Bash: + + bash-2.04$ cat <<EOF + > \" \\ + > EOF + \" \ + + Using command substitutions in a here-document that is fed to a shell +function is not portable. For example, with Solaris 10 `/bin/sh': + + $ kitty () { cat; } + $ kitty <<EOF + > `echo ok` + > EOF + /tmp/sh199886: cannot open + $ echo $? + 1 + + Some shells mishandle large here-documents: for example, Solaris 10 +`dtksh' and the UnixWare 7.1.1 Posix shell, which are derived from Korn +shell version M-12/28/93d, mishandle braced variable expansion that +crosses a 1024- or 4096-byte buffer boundary within a here-document. +Only the part of the variable name after the boundary is used. For +example, `${variable}' could be replaced by the expansion of `${ble}'. +If the end of the variable name is aligned with the block boundary, the +shell reports an error, as if you used `${}'. Instead of +`${variable-default}', the shell may expand `${riable-default}', or +even `${fault}'. This bug can often be worked around by omitting the +braces: `$variable'. The bug was fixed in `ksh93g' (1998-04-30) but as +of 2006 many operating systems were still shipping older versions with +the bug. + + Empty here-documents are not portable either; with the following +code, `zsh' up to at least version 4.3.10 creates a file with a single +newline, whereas other shells create an empty file: + + cat >file <<EOF + EOF + + Many shells (including the Bourne shell) implement here-documents +inefficiently. In particular, some shells can be extremely inefficient +when a single statement contains many here-documents. For instance if +your `configure.ac' includes something like: + + if <cross_compiling>; then + assume this and that + else + check this + check that + check something else + ... + on and on forever + ... + fi + + A shell parses the whole `if'/`fi' construct, creating temporary +files for each here-document in it. Some shells create links for such +here-documents on every `fork', so that the clean-up code they had +installed correctly removes them. It is creating the links that can +take the shell forever. + + Moving the tests out of the `if'/`fi', or creating multiple +`if'/`fi' constructs, would improve the performance significantly. +Anyway, this kind of construct is not exactly the typical use of +Autoconf. In fact, it's even not recommended, because M4 macros can't +look into shell conditionals, so we may fail to expand a macro when it +was expanded before in a conditional path, and the condition turned out +to be false at runtime, and we end up not executing the macro at all. + + Be careful with the use of `<<-' to unindent here-documents. The +behavior is only portable for stripping leading <TAB>s, and things can +silently break if an overzealous editor converts to using leading +spaces (not all shells are nice enough to warn about unterminated +here-documents). + + $ printf 'cat <<-x\n\t1\n\t 2\n\tx\n' | bash && echo done + 1 + 2 + done + $ printf 'cat <<-x\n 1\n 2\n x\n' | bash-3.2 && echo done + 1 + 2 + x + done + + +File: autoconf.info, Node: File Descriptors, Next: Signal Handling, Prev: Here-Documents, Up: Portable Shell + +11.4 File Descriptors +===================== + +Most shells, if not all (including Bash, Zsh, Ash), output traces on +stderr, even for subshells. This might result in undesirable content +if you meant to capture the standard-error output of the inner command: + + $ ash -x -c '(eval "echo foo >&2") 2>stderr' + $ cat stderr + + eval echo foo >&2 + + echo foo + foo + $ bash -x -c '(eval "echo foo >&2") 2>stderr' + $ cat stderr + + eval 'echo foo >&2' + ++ echo foo + foo + $ zsh -x -c '(eval "echo foo >&2") 2>stderr' + # Traces on startup files deleted here. + $ cat stderr + +zsh:1> eval echo foo >&2 + +zsh:1> echo foo + foo + +One workaround is to grep out uninteresting lines, hoping not to remove +good ones. + + If you intend to redirect both standard error and standard output, +redirect standard output first. This works better with HP-UX, since +its shell mishandles tracing if standard error is redirected first: + + $ sh -x -c ': 2>err >out' + + : + + 2> err $ cat err + 1> out + + Don't try to redirect the standard error of a command substitution. +It must be done _inside_ the command substitution. When running `: `cd +/zorglub` 2>/dev/null' expect the error message to escape, while `: `cd +/zorglub 2>/dev/null`' works properly. + + On the other hand, some shells, such as Solaris or FreeBSD +`/bin/sh', warn about missing programs before performing redirections. +Therefore, to silently check whether a program exists, it is necessary +to perform redirections on a subshell or brace group: + $ /bin/sh -c 'nosuch 2>/dev/null' + nosuch: not found + $ /bin/sh -c '(nosuch) 2>/dev/null' + $ /bin/sh -c '{ nosuch; } 2>/dev/null' + $ bash -c 'nosuch 2>/dev/null' + + FreeBSD 6.2 sh may mix the trace output lines from the statements in +a shell pipeline. + + It is worth noting that Zsh (but not Ash nor Bash) makes it possible +in assignments though: `foo=`cd /zorglub` 2>/dev/null'. + + Some shells, like `ash', don't recognize bi-directional redirection +(`<>'). And even on shells that recognize it, it is not portable to +use on fifos: Posix does not require read-write support for named +pipes, and Cygwin does not support it: + + $ mkfifo fifo + $ exec 5<>fifo + $ echo hi >&5 + bash: echo: write error: Communication error on send + +Furthermore, versions of `dash' before 0.5.6 mistakenly truncate +regular files when using `<>': + + $ echo a > file + $ bash -c ': 1<>file'; cat file + a + $ dash -c ': 1<>file'; cat file + $ rm a + + When catering to old systems, don't redirect the same file descriptor +several times, as you are doomed to failure under Ultrix. + + ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995 + UWS V4.4 (Rev. 11) + $ eval 'echo matter >fullness' >void + illegal io + $ eval '(echo matter >fullness)' >void + illegal io + $ (eval '(echo matter >fullness)') >void + Ambiguous output redirect. + +In each case the expected result is of course `fullness' containing +`matter' and `void' being empty. However, this bug is probably not of +practical concern to modern platforms. + + Solaris 10 `sh' will try to optimize away a `:' command (even if it +is redirected) in a loop after the first iteration, or in a shell +function after the first call: + + $ for i in 1 2 3 ; do : >x$i; done + $ ls x* + x1 + $ f () { : >$1; }; f y1; f y2; f y3; + $ ls y* + y1 + +As a workaround, `echo' or `eval' can be used. + + Don't rely on file descriptors 0, 1, and 2 remaining closed in a +subsidiary program. If any of these descriptors is closed, the +operating system may open an unspecified file for the descriptor in the +new process image. Posix 2008 says this may be done only if the +subsidiary program is set-user-ID or set-group-ID, but HP-UX 11.23 does +it even for ordinary programs, and the next version of Posix will allow +HP-UX behavior. + + If you want a file descriptor above 2 to be inherited into a child +process, then you must use redirections specific to that command or a +containing subshell or command group, rather than relying on `exec' in +the shell. In `ksh' as well as HP-UX `sh', file descriptors above 2 +which are opened using `exec N>file' are closed by a subsequent `exec' +(such as that involved in the fork-and-exec which runs a program or +script): + + $ echo 'echo hello >&5' >k + $ /bin/sh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t + hello + $ bash -c 'exec 5>t; ksh ./k; exec 5>&-; cat t + hello + $ ksh -c 'exec 5>t; ksh ./k; exec 5>&-; cat t + ./k[1]: 5: cannot open [Bad file number] + $ ksh -c '(ksh ./k) 5>t; cat t' + hello + $ ksh -c '{ ksh ./k; } 5>t; cat t' + hello + $ ksh -c '5>t ksh ./k; cat t + hello + + Don't rely on duplicating a closed file descriptor to cause an +error. With Solaris `/bin/sh', failed duplication is silently ignored, +which can cause unintended leaks to the original file descriptor. In +this example, observe the leak to standard output: + + $ bash -c 'echo hi >&3' 3>&-; echo $? + bash: 3: Bad file descriptor + 1 + $ /bin/sh -c 'echo hi >&3' 3>&-; echo $? + hi + 0 + + Fortunately, an attempt to close an already closed file descriptor +will portably succeed. Likewise, it is safe to use either style of +`N<&-' or `N>&-' for closing a file descriptor, even if it doesn't +match the read/write mode that the file descriptor was opened with. + + DOS variants cannot rename or remove open files, such as in `mv foo +bar >foo' or `rm foo >foo', even though this is perfectly portable +among Posix hosts. + + A few ancient systems reserved some file descriptors. By convention, +file descriptor 3 was opened to `/dev/tty' when you logged into Eighth +Edition (1985) through Tenth Edition Unix (1989). File descriptor 4 +had a special use on the Stardent/Kubota Titan (circa 1990), though we +don't now remember what it was. Both these systems are obsolete, so +it's now safe to treat file descriptors 3 and 4 like any other file +descriptors. + + On the other hand, you can't portably use multi-digit file +descriptors. Solaris `ksh' doesn't understand any file descriptor +larger than `9': + + $ bash -c 'exec 10>&-'; echo $? + 0 + $ ksh -c 'exec 9>&-'; echo $? + 0 + $ ksh -c 'exec 10>&-'; echo $? + ksh[1]: exec: 10: not found + 127 + + +File: autoconf.info, Node: Signal Handling, Next: File System Conventions, Prev: File Descriptors, Up: Portable Shell + +11.5 Signal Handling +==================== + +Portable handling of signals within the shell is another major source of +headaches. This is worsened by the fact that various different, +mutually incompatible approaches are possible in this area, each with +its distinctive merits and demerits. A detailed description of these +possible approaches, as well as of their pros and cons, can be found in +this article (http://www.cons.org/cracauer/sigint.html). + + Solaris 10 `/bin/sh' automatically traps most signals by default; +the shell still exits with error upon termination by one of those +signals, but in such a case the exit status might be somewhat +unexpected (even if allowed by POSIX, strictly speaking): + + $ bash -c 'kill -1 $$'; echo $? # Will exit 128 + (signal number). + Hangup + 129 + $ /bin/ksh -c 'kill -15 $$'; echo $? # Likewise. + Terminated + 143 + $ for sig in 1 2 3 15; do + > echo $sig: + > /bin/sh -c "kill -$s \$\$"; echo $? + > done + signal 1: + Hangup + 129 + signal 2: + 208 + signal 3: + 208 + signal 15: + 208 + + This gets even worse if one is using the POSIX `wait' interface to +get details about the shell process terminations: it will result in the +shell having exited normally, rather than by receiving a signal. + + $ cat > foo.c <<'END' + #include <stdio.h> /* for printf */ + #include <stdlib.h> /* for system */ + #include <sys/wait.h> /* for WIF* macros */ + int main(void) + { + int status = system ("kill -15 $$"); + printf ("Terminated by signal: %s\n", + WIFSIGNALED (status) ? "yes" : "no"); + printf ("Exited normally: %s\n", + WIFEXITED (status) ? "yes" : "no"); + return 0; + } + END + $ cc -o foo foo.c + $ ./a.out # On GNU/Linux + Terminated by signal: no + Exited normally: yes + $ ./a.out # On Solaris 10 + Terminated by signal: yes + Exited normally: no + + Various shells seem to handle `SIGQUIT' specially: they ignore it +even if it is not blocked, and even if the shell is not running +interactively (in fact, even if the shell has no attached tty); among +these shells are at least Bash (from version 2 onwards), Zsh 4.3.12, +Solaris 10 `/bin/ksh' and `/usr/xpg4/bin/sh', and AT&T `ksh93' (2011). +Still, `SIGQUIT' seems to be trappable quite portably within all these +shells. OTOH, some other shells doesn't special-case the handling of +`SIGQUIT'; among these shells are at least `pdksh' 5.2.14, Solaris 10 +and NetBSD 5.1 `/bin/sh', and the Almquist Shell 0.5.5.1. + + Some shells (especially Korn shells and derivatives) might try to +propagate to themselves a signal that has killed a child process; this +is not a bug, but a conscious design choice (although its overall value +might be debatable). The exact details of how this is attained vary +from shell to shell. For example, upon running `perl -e 'kill 2, $$'', +after the perl process has been interrupted AT&T `ksh93' (2011) will +proceed to send itself a `SIGINT', while Solaris 10 `/bin/ksh' and +`/usr/xpg4/bin/sh' will proceed to exit with status 130 (i.e., 128 + +2). In any case, if there is an active trap associated with `SIGINT', +those shells will correctly execute it. + + Some Korn shells, when a child process die due receiving a signal +with signal number N, can leave in `$?' an exit status of 256+N instead +of the more common 128+N. Observe the difference between AT&T `ksh93' +(2011) and `bash' 4.1.5 on Debian: + + $ /bin/ksh -c 'sh -c "kill -1 \$\$"; echo $?' + /bin/ksh: line 1: 7837: Hangup + 257 + $ /bin/bash -c 'sh -c "kill -1 \$\$"; echo $?' + /bin/bash: line 1: 7861 Hangup (sh -c "kill -1 \$\$") + 129 + +This `ksh' behavior is allowed by POSIX, if implemented with due care; +see this Austin Group discussion +(http://www.austingroupbugs.net/view.php?id=51) for more background. +However, if it is not implemented with proper care, such a behavior +might cause problems in some corner cases. To see why, assume we have +a "wrapper" script like this: + + #!/bin/sh + # Ignore some signals in the shell only, not in its child processes. + trap : 1 2 13 15 + wrapped_command "$@" + ret=$? + other_command + exit $ret + +If `wrapped_command' is interrupted by a `SIGHUP' (which has signal +number 1), `ret' will be set to 257. Unless the `exit' shell builtin +is smart enough to understand that such a value can only have +originated from a signal, and adjust the final wait status of the shell +appropriately, the value 257 will just get truncated to 1 by the +closing `exit' call, so that a caller of the script will have no way to +determine that termination by a signal was involved. Observe the +different behavior of AT&T `ksh93' (2011) and `bash' 4.1.5 on Debian: + + $ cat foo.sh + #!/bin/sh + sh -c 'kill -1 $$' + ret=$? + echo $ret + exit $ret + $ /bin/ksh foo.sh; echo $? + foo.sh: line 2: 12479: Hangup + 257 + 1 + $ /bin/bash foo.sh; echo $? + foo.sh: line 2: 12487 Hangup (sh -c 'kill -1 $$') + 129 + 129 + + +File: autoconf.info, Node: File System Conventions, Next: Shell Pattern Matching, Prev: Signal Handling, Up: Portable Shell + +11.6 File System Conventions +============================ + +Autoconf uses shell-script processing extensively, so the file names +that it processes should not contain characters that are special to the +shell. Special characters include space, tab, newline, NUL, and the +following: + + " # $ & ' ( ) * ; < = > ? [ \ ` | + + Also, file names should not begin with `~' or `-', and should +contain neither `-' immediately after `/' nor `~' immediately after +`:'. On Posix-like platforms, directory names should not contain `:', +as this runs afoul of `:' used as the path separator. + + These restrictions apply not only to the files that you distribute, +but also to the absolute file names of your source, build, and +destination directories. + + On some Posix-like platforms, `!' and `^' are special too, so they +should be avoided. + + Posix lets implementations treat leading `//' specially, but +requires leading `///' and beyond to be equivalent to `/'. Most Unix +variants treat `//' like `/'. However, some treat `//' as a +"super-root" that can provide access to files that are not otherwise +reachable from `/'. The super-root tradition began with Apollo +Domain/OS, which died out long ago, but unfortunately Cygwin has +revived it. + + While `autoconf' and friends are usually run on some Posix variety, +they can be used on other systems, most notably DOS variants. This +impacts several assumptions regarding file names. + +For example, the following code: + + case $foo_dir in + /*) # Absolute + ;; + *) + foo_dir=$dots$foo_dir ;; + esac + +fails to properly detect absolute file names on those systems, because +they can use a drivespec, and usually use a backslash as directory +separator. If you want to be portable to DOS variants (at the price of +rejecting valid but oddball Posix file names like `a:\b'), you can +check for absolute file names like this: + + case $foo_dir in + [\\/]* | ?:[\\/]* ) # Absolute + ;; + *) + foo_dir=$dots$foo_dir ;; + esac + +Make sure you quote the brackets if appropriate and keep the backslash +as first character (*note Limitations of Shell Builtins: case.). + + Also, because the colon is used as part of a drivespec, these +systems don't use it as path separator. When creating or accessing +paths, you can use the `PATH_SEPARATOR' output variable instead. +`configure' sets this to the appropriate value for the build system +(`:' or `;') when it starts up. + + File names need extra care as well. While DOS variants that are +Posixy enough to run `autoconf' (such as DJGPP) are usually able to +handle long file names properly, there are still limitations that can +seriously break packages. Several of these issues can be easily +detected by the doschk +(ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz) package. + + A short overview follows; problems are marked with SFN/LFN to +indicate where they apply: SFN means the issues are only relevant to +plain DOS, not to DOS under Microsoft Windows variants, while LFN +identifies problems that exist even under Microsoft Windows variants. + +No multiple dots (SFN) + DOS cannot handle multiple dots in file names. This is an + especially important thing to remember when building a portable + configure script, as `autoconf' uses a .in suffix for template + files. + + This is perfectly OK on Posix variants: + + AC_CONFIG_HEADERS([config.h]) + AC_CONFIG_FILES([source.c foo.bar]) + AC_OUTPUT + + but it causes problems on DOS, as it requires `config.h.in', + `source.c.in' and `foo.bar.in'. To make your package more portable + to DOS-based environments, you should use this instead: + + AC_CONFIG_HEADERS([config.h:config.hin]) + AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in]) + AC_OUTPUT + +No leading dot (SFN) + DOS cannot handle file names that start with a dot. This is + usually not important for `autoconf'. + +Case insensitivity (LFN) + DOS is case insensitive, so you cannot, for example, have both a + file called `INSTALL' and a directory called `install'. This also + affects `make'; if there's a file called `INSTALL' in the + directory, `make install' does nothing (unless the `install' + target is marked as PHONY). + +The 8+3 limit (SFN) + Because the DOS file system only stores the first 8 characters of + the file name and the first 3 of the extension, those must be + unique. That means that `foobar-part1.c', `foobar-part2.c' and + `foobar-prettybird.c' all resolve to the same file name + (`FOOBAR-P.C'). The same goes for `foo.bar' and `foo.bartender'. + + The 8+3 limit is not usually a problem under Microsoft Windows, as + it uses numeric tails in the short version of file names to make + them unique. However, a registry setting can turn this behavior + off. While this makes it possible to share file trees containing + long file names between SFN and LFN environments, it also means + the above problem applies there as well. + +Invalid characters (LFN) + Some characters are invalid in DOS file names, and should therefore + be avoided. In a LFN environment, these are `/', `\', `?', `*', + `:', `<', `>', `|' and `"'. In a SFN environment, other + characters are also invalid. These include `+', `,', `[' and `]'. + +Invalid names (LFN) + Some DOS file names are reserved, and cause problems if you try to + use files with those names. These names include `CON', `AUX', + `COM1', `COM2', `COM3', `COM4', `LPT1', `LPT2', `LPT3', `NUL', and + `PRN'. File names are case insensitive, so even names like + `aux/config.guess' are disallowed. + + + +File: autoconf.info, Node: Shell Pattern Matching, Next: Shell Substitutions, Prev: File System Conventions, Up: Portable Shell + +11.7 Shell Pattern Matching +=========================== + +Nowadays portable patterns can use negated character classes like +`[!-aeiou]'. The older syntax `[^-aeiou]' is supported by some shells +but not others; hence portable scripts should never use `^' as the +first character of a bracket pattern. + + Outside the C locale, patterns like `[a-z]' are problematic since +they may match characters that are not lower-case letters. + + +File: autoconf.info, Node: Shell Substitutions, Next: Assignments, Prev: Shell Pattern Matching, Up: Portable Shell + +11.8 Shell Substitutions +======================== + +Contrary to a persistent urban legend, the Bourne shell does not +systematically split variables and back-quoted expressions, in +particular on the right-hand side of assignments and in the argument of +`case'. For instance, the following code: + + case "$given_srcdir" in + .) top_srcdir="`echo "$dots" | sed 's|/$||'`" ;; + *) top_srcdir="$dots$given_srcdir" ;; + esac + +is more readable when written as: + + case $given_srcdir in + .) top_srcdir=`echo "$dots" | sed 's|/$||'` ;; + *) top_srcdir=$dots$given_srcdir ;; + esac + +and in fact it is even _more_ portable: in the first case of the first +attempt, the computation of `top_srcdir' is not portable, since not all +shells properly understand `"`..."..."...`"', for example Solaris 10 +ksh: + + $ foo="`echo " bar" | sed 's, ,,'`" + ksh: : cannot execute + ksh: bar | sed 's, ,,': cannot execute + +Posix does not specify behavior for this sequence. On the other hand, +behavior for `"`...\"...\"...`"' is specified by Posix, but in +practice, not all shells understand it the same way: pdksh 5.2.14 +prints spurious quotes when in Posix mode: + + $ echo "`echo \"hello\"`" + hello + $ set -o posix + $ echo "`echo \"hello\"`" + "hello" + +There is just no portable way to use double-quoted strings inside +double-quoted back-quoted expressions (pfew!). + + Bash 4.1 has a bug where quoted empty strings adjacent to unquoted +parameter expansions are elided during word splitting. Meanwhile, zsh +does not perform word splitting except when in Bourne compatibility +mode. In the example below, the correct behavior is to have five +arguments to the function, and exactly two spaces on either side of the +middle `-', since word splitting collapses multiple spaces in `$f' but +leaves empty arguments intact. + + $ bash -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -' + 3- - - + $ ksh -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -' + 5- - - + $ zsh -c 'n() { echo "$#$@"; }; f=" - "; n - ""$f"" -' + 3- - - + $ zsh -c 'emulate sh; + > n() { echo "$#$@"; }; f=" - "; n - ""$f"" -' + 5- - - + +You can work around this by doing manual word splitting, such as using +`"$str" $list' rather than `"$str"$list'. + + There are also portability pitfalls with particular expansions: + +`$@' + One of the most famous shell-portability issues is related to + `"$@"'. When there are no positional arguments, Posix says that + `"$@"' is supposed to be equivalent to nothing, but the original + Unix version 7 Bourne shell treated it as equivalent to `""' + instead, and this behavior survives in later implementations like + Digital Unix 5.0. + + The traditional way to work around this portability problem is to + use `${1+"$@"}'. Unfortunately this method does not work with Zsh + (3.x and 4.x), which is used on Mac OS X. When emulating the + Bourne shell, Zsh performs word splitting on `${1+"$@"}': + + zsh $ emulate sh + zsh $ for i in "$@"; do echo $i; done + Hello World + ! + zsh $ for i in ${1+"$@"}; do echo $i; done + Hello + World + ! + + Zsh handles plain `"$@"' properly, but we can't use plain `"$@"' + because of the portability problems mentioned above. One + workaround relies on Zsh's "global aliases" to convert `${1+"$@"}' + into `"$@"' by itself: + + test "${ZSH_VERSION+set}" = set && alias -g '${1+"$@"}'='"$@"' + + Zsh only recognizes this alias when a shell word matches it + exactly; `"foo"${1+"$@"}' remains subject to word splitting. + Since this case always yields at least one shell word, use plain + `"$@"'. + + A more conservative workaround is to avoid `"$@"' if it is + possible that there may be no positional arguments. For example, + instead of: + + cat conftest.c "$@" + + you can use this instead: + + case $# in + 0) cat conftest.c;; + *) cat conftest.c "$@";; + esac + + Autoconf macros often use the `set' command to update `$@', so if + you are writing shell code intended for `configure' you should not + assume that the value of `$@' persists for any length of time. + +`${10}' + The 10th, 11th, ... positional parameters can be accessed only + after a `shift'. The 7th Edition shell reported an error if given + `${10}', and Solaris 10 `/bin/sh' still acts that way: + + $ set 1 2 3 4 5 6 7 8 9 10 + $ echo ${10} + bad substitution + + Conversely, not all shells obey the Posix rule that when braces are + omitted, multiple digits beyond a `$' imply the single-digit + positional parameter expansion concatenated with the remaining + literal digits. To work around the issue, you must use braces. + + $ bash -c 'set a b c d e f g h i j; echo $10 ${1}0' + a0 a0 + $ dash -c 'set a b c d e f g h i j; echo $10 ${1}0' + j a0 + +`${VAR:-VALUE}' + Old BSD shells, including the Ultrix `sh', don't accept the colon + for any shell substitution, and complain and die. Similarly for + ${VAR:=VALUE}, ${VAR:?VALUE}, etc. However, all shells that + support functions allow the use of colon in shell substitution, + and since m4sh requires functions, you can portably use null + variable substitution patterns in configure scripts. + +`${VAR+VALUE}' + When using `${VAR-VALUE}' or `${VAR-VALUE}' for providing + alternate substitutions, VALUE must either be a single shell word, + quoted, or in the context of an unquoted here-document. Solaris + `/bin/sh' complains otherwise. + + $ /bin/sh -c 'echo ${a-b c}' + /bin/sh: bad substitution + $ /bin/sh -c 'echo ${a-'\''b c'\''}' + b c + $ /bin/sh -c 'echo "${a-b c}"' + b c + $ /bin/sh -c 'cat <<EOF + ${a-b c} + EOF + b c + + According to Posix, if an expansion occurs inside double quotes, + then the use of unquoted double quotes within VALUE is + unspecified, and any single quotes become literal characters; in + that case, escaping must be done with backslash. Likewise, the + use of unquoted here-documents is a case where double quotes have + unspecified results: + + $ /bin/sh -c 'echo "${a-"b c"}"' + /bin/sh: bad substitution + $ ksh -c 'echo "${a-"b c"}"' + b c + $ bash -c 'echo "${a-"b c"}"' + b c + $ /bin/sh -c 'a=; echo ${a+'\''b c'\''}' + b c + $ /bin/sh -c 'a=; echo "${a+'\''b c'\''}"' + 'b c' + $ /bin/sh -c 'a=; echo "${a+\"b c\"}"' + "b c" + $ /bin/sh -c 'a=; echo "${a+b c}"' + b c + $ /bin/sh -c 'cat <<EOF + ${a-"b c"} + EOF' + "b c" + $ /bin/sh -c 'cat <<EOF + ${a-'b c'} + EOF' + 'b c' + $ bash -c 'cat <<EOF + ${a-"b c"} + EOF' + b c + $ bash -c 'cat <<EOF + ${a-'b c'} + EOF' + 'b c' + + Perhaps the easiest way to work around quoting issues in a manner + portable to all shells is to place the results in a temporary + variable, then use `$t' as the VALUE, rather than trying to inline + the expression needing quoting. + + $ /bin/sh -c 't="b c\"'\''}\\"; echo "${a-$t}"' + b c"'}\ + $ ksh -c 't="b c\"'\''}\\"; echo "${a-$t}"' + b c"'}\ + $ bash -c 't="b c\"'\''}\\"; echo "${a-$t}"' + b c"'}\ + +`${VAR=VALUE}' + When using `${VAR=VALUE}' to assign a default value to VAR, + remember that even though the assignment to VAR does not undergo + file name expansion, the result of the variable expansion does + unless the expansion occurred within double quotes. In particular, + when using `:' followed by unquoted variable expansion for the + side effect of setting a default value, if the final value of + `$var' contains any globbing characters (either from VALUE or from + prior contents), the shell has to spend time performing file name + expansion and field splitting even though those results will not be + used. Therefore, it is a good idea to consider double quotes when + performing default initialization; while remembering how this + impacts any quoting characters appearing in VALUE. + + $ time bash -c ': "${a=/usr/bin/*}"; echo "$a"' + /usr/bin/* + + real 0m0.005s + user 0m0.002s + sys 0m0.003s + $ time bash -c ': ${a=/usr/bin/*}; echo "$a"' + /usr/bin/* + + real 0m0.039s + user 0m0.026s + sys 0m0.009s + $ time bash -c 'a=/usr/bin/*; : ${a=noglob}; echo "$a"' + /usr/bin/* + + real 0m0.031s + user 0m0.020s + sys 0m0.010s + + $ time bash -c 'a=/usr/bin/*; : "${a=noglob}"; echo "$a"' + /usr/bin/* + + real 0m0.006s + user 0m0.002s + sys 0m0.003s + + As with `+' and `-', you must use quotes when using `=' if the + VALUE contains more than one shell word; either single quotes for + just the VALUE, or double quotes around the entire expansion: + + $ : ${var1='Some words'} + $ : "${var2=like this}" + $ echo $var1 $var2 + Some words like this + + otherwise some shells, such as Solaris `/bin/sh' or on Digital + Unix V 5.0, die because of a "bad substitution". Meanwhile, Posix + requires that with `=', quote removal happens prior to the + assignment, and the expansion be the final contents of VAR without + quoting (and thus subject to field splitting), in contrast to the + behavior with `-' passing the quoting through to the final + expansion. However, `bash' 4.1 does not obey this rule. + + $ ksh -c 'echo ${var-a\ \ b}' + a b + $ ksh -c 'echo ${var=a\ \ b}' + a b + $ bash -c 'echo ${var=a\ \ b}' + a b + + Finally, Posix states that when mixing `${a=b}' with regular + commands, it is unspecified whether the assignments affect the + parent shell environment. It is best to perform assignments + independently from commands, to avoid the problems demonstrated in + this example: + + $ bash -c 'x= y=${x:=b} sh -c "echo +\$x+\$y+";echo -$x-' + +b+b+ + -b- + $ /bin/sh -c 'x= y=${x:=b} sh -c "echo +\$x+\$y+";echo -$x-' + ++b+ + -- + $ ksh -c 'x= y=${x:=b} sh -c "echo +\$x+\$y+";echo -$x-' + +b+b+ + -- + +`${VAR=VALUE}' + Solaris `/bin/sh' has a frightening bug in its handling of literal + assignments. Imagine you need set a variable to a string + containing `}'. This `}' character confuses Solaris `/bin/sh' + when the affected variable was already set. This bug can be + exercised by running: + + $ unset foo + $ foo=${foo='}'} + $ echo $foo + } + $ foo=${foo='}' # no error; this hints to what the bug is + $ echo $foo + } + $ foo=${foo='}'} + $ echo $foo + }} + ^ ugh! + + It seems that `}' is interpreted as matching `${', even though it + is enclosed in single quotes. The problem doesn't happen using + double quotes, or when using a temporary variable holding the + problematic string. + +`${VAR=EXPANDED-VALUE}' + On Ultrix, running + + default="yu,yaa" + : ${var="$default"} + + sets VAR to `M-yM-uM-,M-yM-aM-a', i.e., the 8th bit of each char + is set. You don't observe the phenomenon using a simple `echo + $var' since apparently the shell resets the 8th bit when it + expands $var. Here are two means to make this shell confess its + sins: + + $ cat -v <<EOF + $var + EOF + + and + + $ set | grep '^var=' | cat -v + + One classic incarnation of this bug is: + + default="a b c" + : ${list="$default"} + for c in $list; do + echo $c + done + + You'll get `a b c' on a single line. Why? Because there are no + spaces in `$list': there are `M- ', i.e., spaces with the 8th bit + set, hence no IFS splitting is performed!!! + + One piece of good news is that Ultrix works fine with `: + ${list=$default}'; i.e., if you _don't_ quote. The bad news is + then that QNX 4.25 then sets LIST to the _last_ item of DEFAULT! + + The portable way out consists in using a double assignment, to + switch the 8th bit twice on Ultrix: + + list=${list="$default"} + + ...but beware of the `}' bug from Solaris (see above). For safety, + use: + + test "${var+set}" = set || var={VALUE} + +`${#VAR}' +`${VAR%WORD}' +`${VAR%%WORD}' +`${VAR#WORD}' +`${VAR##WORD}' + Posix requires support for these usages, but they do not work with + many traditional shells, e.g., Solaris 10 `/bin/sh'. + + Also, `pdksh' 5.2.14 mishandles some WORD forms. For example if + `$1' is `a/b' and `$2' is `a', then `${1#$2}' should yield `/b', + but with `pdksh' it yields the empty string. + +``COMMANDS`' + Posix requires shells to trim all trailing newlines from command + output before substituting it, so assignments like `dir=`echo + "$file" | tr a A`' do not work as expected if `$file' ends in a + newline. + + While in general it makes no sense, do not substitute a single + builtin with side effects, because Ash 0.2, trying to optimize, + does not fork a subshell to perform the command. + + For instance, if you wanted to check that `cd' is silent, do not + use `test -z "`cd /`"' because the following can happen: + + $ pwd + /tmp + $ test -z "`cd /`" && pwd + / + + The result of `foo=`exit 1`' is left as an exercise to the reader. + + The MSYS shell leaves a stray byte in the expansion of a + double-quoted command substitution of a native program, if the end + of the substitution is not aligned with the end of the double + quote. This may be worked around by inserting another pair of + quotes: + + $ echo "`printf 'foo\r\n'` bar" > broken + $ echo "`printf 'foo\r\n'`"" bar" | cmp - broken + - broken differ: char 4, line 1 + + Upon interrupt or SIGTERM, some shells may abort a command + substitution, replace it with a null string, and wrongly evaluate + the enclosing command before entering the trap or ending the + script. This can lead to spurious errors: + + $ sh -c 'if test `sleep 5; echo hi` = hi; then echo yes; fi' + $ ^C + sh: test: hi: unexpected operator/operand + + You can avoid this by assigning the command substitution to a + temporary variable: + + $ sh -c 'res=`sleep 5; echo hi` + if test "x$res" = xhi; then echo yes; fi' + $ ^C + +`$(COMMANDS)' + This construct is meant to replace ``COMMANDS`', and it has most + of the problems listed under ``COMMANDS`'. + + This construct can be nested while this is impossible to do + portably with back quotes. Unfortunately it is not yet + universally supported. Most notably, even recent releases of + Solaris don't support it: + + $ showrev -c /bin/sh | grep version + Command version: SunOS 5.10 Generic 121005-03 Oct 2006 + $ echo $(echo blah) + syntax error: `(' unexpected + + nor does IRIX 6.5's Bourne shell: + $ uname -a + IRIX firebird-image 6.5 07151432 IP22 + $ echo $(echo blah) + $(echo blah) + + If you do use `$(COMMANDS)', make sure that the commands do not + start with a parenthesis, as that would cause confusion with a + different notation `$((EXPRESSION))' that in modern shells is an + arithmetic expression not a command. To avoid the confusion, + insert a space between the two opening parentheses. + + Avoid COMMANDS that contain unbalanced parentheses in + here-documents, comments, or case statement patterns, as many + shells mishandle them. For example, Bash 3.1, `ksh88', `pdksh' + 5.2.14, and Zsh 4.2.6 all mishandle the following valid command: + + echo $(case x in x) echo hello;; esac) + +`$((EXPRESSION))' + Arithmetic expansion is not portable as some shells (most notably + Solaris 10 `/bin/sh') don't support it. + + Among shells that do support `$(( ))', not all of them obey the + Posix rule that octal and hexadecimal constants must be recognized: + + $ bash -c 'echo $(( 010 + 0x10 ))' + 24 + $ zsh -c 'echo $(( 010 + 0x10 ))' + 26 + $ zsh -c 'emulate sh; echo $(( 010 + 0x10 ))' + 24 + $ pdksh -c 'echo $(( 010 + 0x10 ))' + pdksh: 010 + 0x10 : bad number `0x10' + $ pdksh -c 'echo $(( 010 ))' + 10 + + When it is available, using arithmetic expansion provides a + noticeable speedup in script execution; but testing for support + requires `eval' to avoid syntax errors. The following construct + is used by `AS_VAR_ARITH' to provide arithmetic computation when + all arguments are provided in decimal and without a leading zero, + and all operators are properly quoted and appear as distinct + arguments: + + if ( eval 'test $(( 1 + 1 )) = 2' ) 2>/dev/null; then + eval 'func_arith () + { + func_arith_result=$(( $* )) + }' + else + func_arith () + { + func_arith_result=`expr "$@"` + } + fi + func_arith 1 + 1 + foo=$func_arith_result + +`^' + Always quote `^', otherwise traditional shells such as `/bin/sh' + on Solaris 10 treat this like `|'. + + + +File: autoconf.info, Node: Assignments, Next: Parentheses, Prev: Shell Substitutions, Up: Portable Shell + +11.9 Assignments +================ + +When setting several variables in a row, be aware that the order of the +evaluation is undefined. For instance `foo=1 foo=2; echo $foo' gives +`1' with Solaris `/bin/sh', but `2' with Bash. You must use `;' to +enforce the order: `foo=1; foo=2; echo $foo'. + + Don't rely on the following to find `subdir/program': + + PATH=subdir$PATH_SEPARATOR$PATH program + +as this does not work with Zsh 3.0.6. Use something like this instead: + + (PATH=subdir$PATH_SEPARATOR$PATH; export PATH; exec program) + + Don't rely on the exit status of an assignment: Ash 0.2 does not +change the status and propagates that of the last statement: + + $ false || foo=bar; echo $? + 1 + $ false || foo=`:`; echo $? + 0 + +and to make things even worse, QNX 4.25 just sets the exit status to 0 +in any case: + + $ foo=`exit 1`; echo $? + 0 + + To assign default values, follow this algorithm: + + 1. If the default value is a literal and does not contain any closing + brace, use: + + : "${var='my literal'}" + + 2. If the default value contains no closing brace, has to be + expanded, and the variable being initialized is not intended to be + IFS-split (i.e., it's not a list), then use: + + : ${var="$default"} + + 3. If the default value contains no closing brace, has to be + expanded, and the variable being initialized is intended to be + IFS-split (i.e., it's a list), then use: + + var=${var="$default"} + + 4. If the default value contains a closing brace, then use: + + test "${var+set}" = set || var="has a '}'" + + In most cases `var=${var="$default"}' is fine, but in case of doubt, +just use the last form. *Note Shell Substitutions::, items +`${VAR:-VALUE}' and `${VAR=VALUE}' for the rationale. + + +File: autoconf.info, Node: Parentheses, Next: Slashes, Prev: Assignments, Up: Portable Shell + +11.10 Parentheses in Shell Scripts +================================== + +Beware of two opening parentheses in a row, as many shell +implementations treat them specially, and Posix says that a portable +script cannot use `((' outside the `$((' form used for shell +arithmetic. In traditional shells, `((cat))' behaves like `(cat)'; but +many shells, including Bash and the Korn shell, treat `((cat))' as an +arithmetic expression equivalent to `let "cat"', and may or may not +report an error when they detect that `cat' is not a number. As another +example, `pdksh' 5.2.14 does not treat the following code as a +traditional shell would: + + if ((true) || false); then + echo ok + fi + +To work around this problem, insert a space between the two opening +parentheses. There is a similar problem and workaround with `$(('; see +*note Shell Substitutions::. + + +File: autoconf.info, Node: Slashes, Next: Special Shell Variables, Prev: Parentheses, Up: Portable Shell + +11.11 Slashes in Shell Scripts +============================== + +Unpatched Tru64 5.1 `sh' omits the last slash of command-line arguments +that contain two trailing slashes: + + $ echo / // /// //// .// //. + / / // /// ./ //. + $ x=// + $ eval "echo \$x" + / + $ set -x + $ echo abc | tr -t ab // + + echo abc + + tr -t ab / + /bc + + Unpatched Tru64 4.0 `sh' adds a slash after `"$var"' if the variable +is empty and the second double-quote is followed by a word that begins +and ends with slash: + + $ sh -xc 'p=; echo "$p"/ouch/' + p= + + echo //ouch/ + //ouch/ + + However, our understanding is that patches are available, so perhaps +it's not worth worrying about working around these horrendous bugs. + + +File: autoconf.info, Node: Special Shell Variables, Next: Shell Functions, Prev: Slashes, Up: Portable Shell + +11.12 Special Shell Variables +============================= + +Some shell variables should not be used, since they can have a deep +influence on the behavior of the shell. In order to recover a sane +behavior from the shell, some variables should be unset; M4sh takes +care of this and provides fallback values, whenever needed, to cater +for a very old `/bin/sh' that does not support `unset'. (*note +Portable Shell Programming: Portable Shell.). + + As a general rule, shell variable names containing a lower-case +letter are safe; you can define and use these variables without +worrying about their effect on the underlying system, and without +worrying about whether the shell changes them unexpectedly. (The +exception is the shell variable `status', as described below.) + + Here is a list of names that are known to cause trouble. This list +is not exhaustive, but you should be safe if you avoid the name +`status' and names containing only upper-case letters and underscores. + +`?' + Not all shells correctly reset `$?' after conditionals (*note + Limitations of Shell Builtins: if.). Not all shells manage `$?' + correctly in shell functions (*note Shell Functions::) or in traps + (*note Limitations of Shell Builtins: trap.). Not all shells reset + `$?' to zero after an empty command. + + $ bash -c 'false; $empty; echo $?' + 0 + $ zsh -c 'false; $empty; echo $?' + 1 + +`_' + Many shells reserve `$_' for various purposes, e.g., the name of + the last command executed. + +`BIN_SH' + In Tru64, if `BIN_SH' is set to `xpg4', subsidiary invocations of + the standard shell conform to Posix. + +`CDPATH' + When this variable is set it specifies a list of directories to + search when invoking `cd' with a relative file name that did not + start with `./' or `../'. Posix 1003.1-2001 says that if a + nonempty directory name from `CDPATH' is used successfully, `cd' + prints the resulting absolute file name. Unfortunately this + output can break idioms like `abs=`cd src && pwd`' because `abs' + receives the name twice. Also, many shells do not conform to this + part of Posix; for example, `zsh' prints the result only if a + directory name other than `.' was chosen from `CDPATH'. + + In practice the shells that have this problem also support + `unset', so you can work around the problem as follows: + + (unset CDPATH) >/dev/null 2>&1 && unset CDPATH + + You can also avoid output by ensuring that your directory name is + absolute or anchored at `./', as in `abs=`cd ./src && pwd`'. + + Configure scripts use M4sh, which automatically unsets `CDPATH' if + possible, so you need not worry about this problem in those + scripts. + +`CLICOLOR_FORCE' + When this variable is set, some implementations of tools like `ls' + attempt to add color to their output via terminal escape + sequences, even when the output is not directed to a terminal, and + can thus cause spurious failures in scripts. Configure scripts + use M4sh, which automatically unsets this variable. + +`DUALCASE' + In the MKS shell, case statements and file name generation are + case-insensitive unless `DUALCASE' is nonzero. Autoconf-generated + scripts export this variable when they start up. + +`ENV' +`MAIL' +`MAILPATH' +`PS1' +`PS2' +`PS4' + These variables should not matter for shell scripts, since they are + supposed to affect only interactive shells. However, at least one + shell (the pre-3.0 UWIN Korn shell) gets confused about whether it + is interactive, which means that (for example) a `PS1' with a side + effect can unexpectedly modify `$?'. To work around this bug, + M4sh scripts (including `configure' scripts) do something like + this: + + (unset ENV) >/dev/null 2>&1 && unset ENV MAIL MAILPATH + PS1='$ ' + PS2='> ' + PS4='+ ' + + (actually, there is some complication due to bugs in `unset'; + *note Limitations of Shell Builtins: unset.). + +`FPATH' + The Korn shell uses `FPATH' to find shell functions, so avoid + `FPATH' in portable scripts. `FPATH' is consulted after `PATH', + but you still need to be wary of tests that use `PATH' to find + whether a command exists, since they might report the wrong result + if `FPATH' is also set. + +`GREP_OPTIONS' + When this variable is set, some implementations of `grep' honor + these options, even if the options include direction to enable + colored output via terminal escape sequences, and the result can + cause spurious failures when the output is not directed to a + terminal. Configure scripts use M4sh, which automatically unsets + this variable. + +`IFS' + Long ago, shell scripts inherited `IFS' from the environment, but + this caused many problems so modern shells ignore any environment + settings for `IFS'. + + Don't set the first character of `IFS' to backslash. Indeed, + Bourne shells use the first character (backslash) when joining the + components in `"$@"' and some shells then reinterpret (!) the + backslash escapes, so you can end up with backspace and other + strange characters. + + The proper value for `IFS' (in regular code, not when performing + splits) is `<SPC><TAB><RET>'. The first character is especially + important, as it is used to join the arguments in `$*'; however, + note that traditional shells, but also bash-2.04, fail to adhere + to this and join with a space anyway. + + M4sh guarantees that `IFS' will have the default value at the + beginning of a script, and many macros within autoconf rely on this + setting. It is okay to use blocks of shell code that temporarily + change the value of `IFS' in order to split on another character, + but remember to restore it before expanding further macros. + + Unsetting `IFS' instead of resetting it to the default sequence is + not suggested, since code that tries to save and restore the + variable's value will incorrectly reset it to an empty value, thus + disabling field splitting: + + unset IFS + # default separators used for field splitting + + save_IFS=$IFS + IFS=: + # ... + IFS=$save_IFS + # no field splitting performed + +`LANG' +`LC_ALL' +`LC_COLLATE' +`LC_CTYPE' +`LC_MESSAGES' +`LC_MONETARY' +`LC_NUMERIC' +`LC_TIME' + You should set all these variables to `C' because so much + configuration code assumes the C locale and Posix requires that + locale environment variables be set to `C' if the C locale is + desired; `configure' scripts and M4sh do that for you. Export + these variables after setting them. + +`LANGUAGE' + `LANGUAGE' is not specified by Posix, but it is a GNU extension + that overrides `LC_ALL' in some cases, so you (or M4sh) should set + it too. + +`LC_ADDRESS' +`LC_IDENTIFICATION' +`LC_MEASUREMENT' +`LC_NAME' +`LC_PAPER' +`LC_TELEPHONE' + These locale environment variables are GNU extensions. They are + treated like their Posix brethren (`LC_COLLATE', etc.) as + described above. + +`LINENO' + Most modern shells provide the current line number in `LINENO'. + Its value is the line number of the beginning of the current + command. M4sh, and hence Autoconf, attempts to execute + `configure' with a shell that supports `LINENO'. If no such shell + is available, it attempts to implement `LINENO' with a Sed prepass + that replaces each instance of the string `$LINENO' (not followed + by an alphanumeric character) with the line's number. In M4sh + scripts you should execute `AS_LINENO_PREPARE' so that these + workarounds are included in your script; configure scripts do this + automatically in `AC_INIT'. + + You should not rely on `LINENO' within `eval' or shell functions, + as the behavior differs in practice. The presence of a quoted + newline within simple commands can alter which line number is used + as the starting point for `$LINENO' substitutions within that + command. Also, the possibility of the Sed prepass means that you + should not rely on `$LINENO' when quoted, when in here-documents, + or when line continuations are used. Subshells should be OK, + though. In the following example, lines 1, 9, and 14 are + portable, but the other instances of `$LINENO' do not have + deterministic values: + + $ cat lineno + echo 1. $LINENO + echo "2. $LINENO + 3. $LINENO" + cat <<EOF + 5. $LINENO + 6. $LINENO + 7. \$LINENO + EOF + ( echo 9. $LINENO ) + eval 'echo 10. $LINENO' + eval 'echo 11. $LINENO + echo 12. $LINENO' + echo 13. '$LINENO' + echo 14. $LINENO ' + 15.' $LINENO + f () { echo $1 $LINENO; + echo $1 $LINENO } + f 18. + echo 19. \ + $LINENO + $ bash-3.2 ./lineno + 1. 1 + 2. 3 + 3. 3 + 5. 4 + 6. 4 + 7. $LINENO + 9. 9 + 10. 10 + 11. 12 + 12. 13 + 13. $LINENO + 14. 14 + 15. 14 + 18. 16 + 18. 17 + 19. 19 + $ zsh-4.3.4 ./lineno + 1. 1 + 2. 2 + 3. 2 + 5. 4 + 6. 4 + 7. $LINENO + 9. 9 + 10. 1 + 11. 1 + 12. 2 + 13. $LINENO + 14. 14 + 15. 14 + 18. 0 + 18. 1 + 19. 19 + $ pdksh-5.2.14 ./lineno + 1. 1 + 2. 2 + 3. 2 + 5. 4 + 6. 4 + 7. $LINENO + 9. 9 + 10. 0 + 11. 0 + 12. 0 + 13. $LINENO + 14. 14 + 15. 14 + 18. 16 + 18. 17 + 19. 19 + $ sed '=' <lineno | + > sed ' + > N + > s,$,-, + > t loop + > :loop + > s,^\([0-9]*\)\(.*\)[$]LINENO\([^a-zA-Z0-9_]\),\1\2\1\3, + > t loop + > s,-$,, + > s,^[0-9]*\n,, + > ' | + > sh + 1. 1 + 2. 2 + 3. 3 + 5. 5 + 6. 6 + 7. \7 + 9. 9 + 10. 10 + 11. 11 + 12. 12 + 13. 13 + 14. 14 + 15. 15 + 18. 16 + 18. 17 + 19. 20 + + In particular, note that `config.status' (and any other subsidiary + script created by `AS_INIT_GENERATED') might report line numbers + relative to the parent script as a result of the potential Sed + pass. + +`NULLCMD' + When executing the command `>foo', `zsh' executes `$NULLCMD >foo' + unless it is operating in Bourne shell compatibility mode and the + `zsh' version is newer than 3.1.6-dev-18. If you are using an + older `zsh' and forget to set `NULLCMD', your script might be + suspended waiting for data on its standard input. + +`options' + For `zsh' 4.3.10, `options' is treated as an associative array + even after `emulate sh', so it should not be used. + +`PATH_SEPARATOR' + On DJGPP systems, the `PATH_SEPARATOR' environment variable can be + set to either `:' or `;' to control the path separator Bash uses + to set up certain environment variables (such as `PATH'). You can + set this variable to `;' if you want `configure' to use `;' as a + separator; this might be useful if you plan to use non-Posix + shells to execute files. *Note File System Conventions::, for + more information about `PATH_SEPARATOR'. + +`POSIXLY_CORRECT' + In the GNU environment, exporting `POSIXLY_CORRECT' with any value + (even empty) causes programs to try harder to conform to Posix. + Autoconf does not directly manipulate this variable, but `bash' + ties the shell variable `POSIXLY_CORRECT' to whether the script is + running in Posix mode. Therefore, take care when exporting or + unsetting this variable, so as not to change whether `bash' is in + Posix mode. + + $ bash --posix -c 'set -o | grep posix + > unset POSIXLY_CORRECT + > set -o | grep posix' + posix on + posix off + +`PWD' + Posix 1003.1-2001 requires that `cd' and `pwd' must update the + `PWD' environment variable to point to the logical name of the + current directory, but traditional shells do not support this. + This can cause confusion if one shell instance maintains `PWD' but + a subsidiary and different shell does not know about `PWD' and + executes `cd'; in this case `PWD' points to the wrong directory. + Use ``pwd`' rather than `$PWD'. + +`RANDOM' + Many shells provide `RANDOM', a variable that returns a different + integer each time it is used. Most of the time, its value does not + change when it is not used, but on IRIX 6.5 the value changes all + the time. This can be observed by using `set'. It is common + practice to use `$RANDOM' as part of a file name, but code + shouldn't rely on `$RANDOM' expanding to a nonempty string. + +`status' + This variable is an alias to `$?' for `zsh' (at least 3.1.6), + hence read-only. Do not use it. + + +File: autoconf.info, Node: Shell Functions, Next: Limitations of Builtins, Prev: Special Shell Variables, Up: Portable Shell + +11.13 Shell Functions +===================== + +Nowadays, it is difficult to find a shell that does not support shell +functions at all. However, some differences should be expected. + + When declaring a shell function, you must include whitespace between +the `)' after the function name and the start of the compound +expression, to avoid upsetting `ksh'. While it is possible to use any +compound command, most scripts use `{...}'. + + $ /bin/sh -c 'a(){ echo hi;}; a' + hi + $ ksh -c 'a(){ echo hi;}; a' + ksh: syntax error at line 1: `}' unexpected + $ ksh -c 'a() { echo hi;}; a' + hi + + Inside a shell function, you should not rely on the error status of a +subshell if the last command of that subshell was `exit' or `trap', as +this triggers bugs in zsh 4.x; while Autoconf tries to find a shell +that does not exhibit the bug, zsh might be the only shell present on +the user's machine. + + Likewise, the state of `$?' is not reliable when entering a shell +function. This has the effect that using a function as the first +command in a `trap' handler can cause problems. + + $ bash -c 'foo() { echo $?; }; trap foo 0; (exit 2); exit 2'; echo $? + 2 + 2 + $ ash -c 'foo() { echo $?; }; trap foo 0; (exit 2); exit 2'; echo $? + 0 + 2 + + DJGPP bash 2.04 has a bug in that `return' from a shell function +which also used a command substitution causes a segmentation fault. To +work around the issue, you can use `return' from a subshell, or +`AS_SET_STATUS' as last command in the execution flow of the function +(*note Common Shell Constructs::). + + Not all shells treat shell functions as simple commands impacted by +`set -e', for example with Solaris 10 `/bin/sh': + + $ bash -c 'f() { return 1; }; set -e; f; echo oops' + $ /bin/sh -c 'f() { return 1; }; set -e; f; echo oops' + oops + + Shell variables and functions may share the same namespace, for +example with Solaris 10 `/bin/sh': + + $ f () { :; }; f=; f + f: not found + +For this reason, Autoconf (actually M4sh, *note Programming in M4sh::) +uses the prefix `as_fn_' for its functions. + + Handling of positional parameters and shell options varies among +shells. For example, Korn shells reset and restore trace output (`set +-x') and other options upon function entry and exit. Inside a function, +IRIX sh sets `$0' to the function name. + + It is not portable to pass temporary environment variables to shell +functions. Solaris `/bin/sh' does not see the variable. Meanwhile, +not all shells follow the Posix rule that the assignment must affect +the current environment in the same manner as special built-ins. + + $ /bin/sh -c 'func() { echo $a;}; a=1 func; echo $a' + => + => + $ ash -c 'func() { echo $a;}; a=1 func; echo $a' + =>1 + => + $ bash -c 'set -o posix; func() { echo $a;}; a=1 func; echo $a' + =>1 + =>1 + + Some ancient Bourne shell variants with function support did not +reset `$I, I >= 0', upon function exit, so effectively the arguments of +the script were lost after the first function invocation. It is +probably not worth worrying about these shells any more. + + With AIX sh, a `trap' on 0 installed in a shell function triggers at +function exit rather than at script exit. *Note Limitations of Shell +Builtins: trap. + + +File: autoconf.info, Node: Limitations of Builtins, Next: Limitations of Usual Tools, Prev: Shell Functions, Up: Portable Shell + +11.14 Limitations of Shell Builtins +=================================== + +No, no, we are serious: some shells do have limitations! :) + + You should always keep in mind that any builtin or command may +support options, and therefore differ in behavior with arguments +starting with a dash. For instance, even the innocent `echo "$word"' +can give unexpected results when `word' starts with a dash. It is +often possible to avoid this problem using `echo "x$word"', taking the +`x' into account later in the pipe. Many of these limitations can be +worked around using M4sh (*note Programming in M4sh::). + +`.' + Use `.' only with regular files (use `test -f'). Bash 2.03, for + instance, chokes on `. /dev/null'. Remember that `.' uses `PATH' + if its argument contains no slashes. Also, some shells, including + bash 3.2, implicitly append the current directory to this `PATH' + search, even though Posix forbids it. So if you want to use `.' + on a file `foo' in the current directory, you must use `. ./foo'. + + Not all shells gracefully handle syntax errors within a sourced + file. On one extreme, some non-interactive shells abort the + entire script. On the other, `zsh' 4.3.10 has a bug where it + fails to react to the syntax error. + + $ echo 'fi' > syntax + $ bash -c '. ./syntax; echo $?' + ./syntax: line 1: syntax error near unexpected token `fi' + ./syntax: line 1: `fi' + 1 + $ ash -c '. ./syntax; echo $?' + ./syntax: 1: Syntax error: "fi" unexpected + $ zsh -c '. ./syntax; echo $?' + ./syntax:1: parse error near `fi' + 0 + +`!' + The Unix version 7 shell did not support negating the exit status + of commands with `!', and this feature is still absent from some + shells (e.g., Solaris `/bin/sh'). Other shells, such as FreeBSD + `/bin/sh' or `ash', have bugs when using `!': + + $ sh -c '! : | :'; echo $? + 1 + $ ash -c '! : | :'; echo $? + 0 + $ sh -c '! { :; }'; echo $? + 1 + $ ash -c '! { :; }'; echo $? + {: not found + Syntax error: "}" unexpected + 2 + + Shell code like this: + + if ! cmp file1 file2 >/dev/null 2>&1; then + echo files differ or trouble + fi + + is therefore not portable in practice. Typically it is easy to + rewrite such code, e.g.: + + cmp file1 file2 >/dev/null 2>&1 || + echo files differ or trouble + + More generally, one can always rewrite `! COMMAND' as: + + if COMMAND; then (exit 1); else :; fi + +`{...}' + Bash 3.2 (and earlier versions) sometimes does not properly set + `$?' when failing to write redirected output of a compound command. + This problem is most commonly observed with `{...}'; it does not + occur with `(...)'. For example: + + $ bash -c '{ echo foo; } >/bad; echo $?' + bash: line 1: /bad: Permission denied + 0 + $ bash -c 'while :; do echo; done >/bad; echo $?' + bash: line 1: /bad: Permission denied + 0 + + To work around the bug, prepend `:;': + + $ bash -c ':;{ echo foo; } >/bad; echo $?' + bash: line 1: /bad: Permission denied + 1 + + Posix requires a syntax error if a brace list has no contents. + However, not all shells obey this rule; and on shells where empty + lists are permitted, the effect on `$?' is inconsistent. To avoid + problems, ensure that a brace list is never empty. + + $ bash -c 'false; { }; echo $?' || echo $? + bash: line 1: syntax error near unexpected token `}' + bash: line 1: `false; { }; echo $?' + 2 + $ zsh -c 'false; { }; echo $?' || echo $? + 1 + $ pdksh -c 'false; { }; echo $?' || echo $? + 0 + +`break' + The use of `break 2' etc. is safe. + +`case' + You don't need to quote the argument; no splitting is performed. + + You don't need the final `;;', but you should use it. + + Posix requires support for `case' patterns with opening + parentheses like this: + + case $file_name in + (*.c) echo "C source code";; + esac + + but the `(' in this example is not portable to many Bourne shell + implementations, which is a pity for those of us using tools that + rely on balanced parentheses. For instance, with Solaris + `/bin/sh': + + $ case foo in (foo) echo foo;; esac + error-->syntax error: `(' unexpected + + The leading `(' can be omitted safely. Unfortunately, there are + contexts where unbalanced parentheses cause other problems, such + as when using a syntax-highlighting editor that searches for the + balancing counterpart, or more importantly, when using a case + statement as an underquoted argument to an Autoconf macro. *Note + Balancing Parentheses::, for tradeoffs involved in various styles + of dealing with unbalanced `)'. + + Zsh handles pattern fragments derived from parameter expansions or + command substitutions as though quoted: + + $ pat=\?; case aa in ?$pat) echo match;; esac + $ pat=\?; case a? in ?$pat) echo match;; esac + match + + Because of a bug in its `fnmatch', Bash fails to properly handle + backslashes in character classes: + + bash-2.02$ case /tmp in [/\\]*) echo OK;; esac + bash-2.02$ + + This is extremely unfortunate, since you are likely to use this + code to handle Posix or MS-DOS absolute file names. To work + around this bug, always put the backslash first: + + bash-2.02$ case '\TMP' in [\\/]*) echo OK;; esac + OK + bash-2.02$ case /tmp in [\\/]*) echo OK;; esac + OK + + Many Bourne shells cannot handle closing brackets in character + classes correctly. + + Some shells also have problems with backslash escaping in case you + do not want to match the backslash: both a backslash and the + escaped character match this pattern. To work around this, + specify the character class in a variable, so that quote removal + does not apply afterwards, and the special characters don't have + to be backslash-escaped: + + $ case '\' in [\<]) echo OK;; esac + OK + $ scanset='[<]'; case '\' in $scanset) echo OK;; esac + $ + + Even with this, Solaris `ksh' matches a backslash if the set + contains any of the characters `|', `&', `(', or `)'. + + Conversely, Tru64 `ksh' (circa 2003) erroneously always matches a + closing parenthesis if not specified in a character class: + + $ case foo in *\)*) echo fail ;; esac + fail + $ case foo in *')'*) echo fail ;; esac + fail + + Some shells, such as Ash 0.3.8, are confused by an empty + `case'/`esac': + + ash-0.3.8 $ case foo in esac; + error-->Syntax error: ";" unexpected (expecting ")") + + Posix requires `case' to give an exit status of 0 if no cases + match. However, `/bin/sh' in Solaris 10 does not obey this rule. + Meanwhile, it is unclear whether a case that matches, but contains + no statements, must also change the exit status to 0. The M4sh + macro `AS_CASE' works around these inconsistencies. + + $ bash -c 'case `false` in ?) ;; esac; echo $?' + 0 + $ /bin/sh -c 'case `false` in ?) ;; esac; echo $?' + 255 + +`cd' + Posix 1003.1-2001 requires that `cd' must support the `-L' + ("logical") and `-P' ("physical") options, with `-L' being the + default. However, traditional shells do not support these + options, and their `cd' command has the `-P' behavior. + + Portable scripts should assume neither option is supported, and + should assume neither behavior is the default. This can be a bit + tricky, since the Posix default behavior means that, for example, + `ls ..' and `cd ..' may refer to different directories if the + current logical directory is a symbolic link. It is safe to use + `cd DIR' if DIR contains no `..' components. Also, + Autoconf-generated scripts check for this problem when computing + variables like `ac_top_srcdir' (*note Configuration Actions::), so + it is safe to `cd' to these variables. + + Posix states that behavior is undefined if `cd' is given an + explicit empty argument. Some shells do nothing, some change to + the first entry in `CDPATH', some change to `HOME', and some exit + the shell rather than returning an error. Unfortunately, this + means that if `$var' is empty, then `cd "$var"' is less predictable + than `cd $var' (at least the latter is well-behaved in all shells + at changing to `HOME', although this is probably not what you + wanted in a script). You should check that a directory name was + supplied before trying to change locations. + + *Note Special Shell Variables::, for portability problems involving + `cd' and the `CDPATH' environment variable. Also please see the + discussion of the `pwd' command. + +`echo' + The simple `echo' is probably the most surprising source of + portability troubles. It is not possible to use `echo' portably + unless both options and escape sequences are omitted. Don't + expect any option. + + Do not use backslashes in the arguments, as there is no consensus + on their handling. For `echo '\n' | wc -l', the `sh' of Solaris + outputs 2, but Bash and Zsh (in `sh' emulation mode) output 1. + The problem is truly `echo': all the shells understand `'\n'' as + the string composed of a backslash and an `n'. Within a command + substitution, `echo 'string\c'' will mess up the internal state of + ksh88 on AIX 6.1 so that it will print the first character `s' + only, followed by a newline, and then entirely drop the output of + the next echo in a command substitution. + + Because of these problems, do not pass a string containing + arbitrary characters to `echo'. For example, `echo "$foo"' is safe + only if you know that FOO's value cannot contain backslashes and + cannot start with `-'. + + If this may not be true, `printf' is in general safer and easier + to use than `echo' and `echo -n'. Thus, scripts where portability + is not a major concern should use `printf '%s\n'' whenever `echo' + could fail, and similarly use `printf %s' instead of `echo -n'. + For portable shell scripts, instead, it is suggested to use a + here-document like this: + + cat <<EOF + $foo + EOF + + Alternatively, M4sh provides `AS_ECHO' and `AS_ECHO_N' macros + which choose between various portable implementations: `echo' or + `print' where they work, `printf' if it is available, or else + other creative tricks in order to work around the above problems. + +`eval' + The `eval' command is useful in limited circumstances, e.g., using + commands like `eval table_$key=\$value' and `eval + value=table_$key' to simulate a hash table when the key is known + to be alphanumeric. + + You should also be wary of common bugs in `eval' implementations. + In some shell implementations (e.g., older `ash', OpenBSD 3.8 + `sh', `pdksh' v5.2.14 99/07/13.2, and `zsh' 4.2.5), the arguments + of `eval' are evaluated in a context where `$?' is 0, so they + exhibit behavior like this: + + $ false; eval 'echo $?' + 0 + + The correct behavior here is to output a nonzero value, but + portable scripts should not rely on this. + + You should not rely on `LINENO' within `eval'. *Note Special + Shell Variables::. + + Note that, even though these bugs are easily avoided, `eval' is + tricky to use on arbitrary arguments. It is obviously unwise to + use `eval $cmd' if the string value of `cmd' was derived from an + untrustworthy source. But even if the string value is valid, + `eval $cmd' might not work as intended, since it causes field + splitting and file name expansion to occur twice, once for the + `eval' and once for the command itself. It is therefore safer to + use `eval "$cmd"'. For example, if CMD has the value `cat + test?.c', `eval $cmd' might expand to the equivalent of `cat + test;.c' if there happens to be a file named `test;.c' in the + current directory; and this in turn mistakenly attempts to invoke + `cat' on the file `test' and then execute the command `.c'. To + avoid this problem, use `eval "$cmd"' rather than `eval $cmd'. + + However, suppose that you want to output the text of the evaluated + command just before executing it. Assuming the previous example, + `echo "Executing: $cmd"' outputs `Executing: cat test?.c', but + this output doesn't show the user that `test;.c' is the actual name + of the copied file. Conversely, `eval "echo Executing: $cmd"' + works on this example, but it fails with `cmd='cat foo >bar'', + since it mistakenly replaces the contents of `bar' by the string + `cat foo'. No simple, general, and portable solution to this + problem is known. + +`exec' + Posix describes several categories of shell built-ins. Special + built-ins (such as `exit') must impact the environment of the + current shell, and need not be available through `exec'. All + other built-ins are regular, and must not propagate variable + assignments to the environment of the current shell. However, the + group of regular built-ins is further distinguished by commands + that do not require a `PATH' search (such as `cd'), in contrast to + built-ins that are offered as a more efficient version of + something that must still be found in a `PATH' search (such as + `echo'). Posix is not clear on whether `exec' must work with the + list of 17 utilities that are invoked without a `PATH' search, and + many platforms lack an executable for some of those built-ins: + + $ sh -c 'exec cd /tmp' + sh: line 0: exec: cd: not found + + All other built-ins that provide utilities specified by Posix must + have a counterpart executable that exists on `PATH', although Posix + allows `exec' to use the built-in instead of the executable. For + example, contrast `bash' 3.2 and `pdksh' 5.2.14: + + $ bash -c 'pwd --version' | head -n1 + bash: line 0: pwd: --: invalid option + pwd: usage: pwd [-LP] + $ bash -c 'exec pwd --version' | head -n1 + pwd (GNU coreutils) 6.10 + $ pdksh -c 'exec pwd --version' | head -n1 + pdksh: pwd: --: unknown option + + When it is desired to avoid a regular shell built-in, the + workaround is to use some other forwarding command, such as `env' + or `nice', that will ensure a path search: + + $ pdksh -c 'exec true --version' | head -n1 + $ pdksh -c 'nice true --version' | head -n1 + true (GNU coreutils) 6.10 + $ pdksh -c 'env true --version' | head -n1 + true (GNU coreutils) 6.10 + +`exit' + The default value of `exit' is supposed to be `$?'; unfortunately, + some shells, such as the DJGPP port of Bash 2.04, just perform + `exit 0'. + + bash-2.04$ foo=`exit 1` || echo fail + fail + bash-2.04$ foo=`(exit 1)` || echo fail + fail + bash-2.04$ foo=`(exit 1); exit` || echo fail + bash-2.04$ + + Using `exit $?' restores the expected behavior. + + Some shell scripts, such as those generated by `autoconf', use a + trap to clean up before exiting. If the last shell command exited + with nonzero status, the trap also exits with nonzero status so + that the invoker can tell that an error occurred. + + Unfortunately, in some shells, such as Solaris `/bin/sh', an exit + trap ignores the `exit' command's argument. In these shells, a + trap cannot determine whether it was invoked by plain `exit' or by + `exit 1'. Instead of calling `exit' directly, use the + `AC_MSG_ERROR' macro that has a workaround for this problem. + +`export' + The builtin `export' dubs a shell variable "environment variable". + Each update of exported variables corresponds to an update of the + environment variables. Conversely, each environment variable + received by the shell when it is launched should be imported as a + shell variable marked as exported. + + Alas, many shells, such as Solaris `/bin/sh', IRIX 6.3, IRIX 5.2, + AIX 4.1.5, and Digital Unix 4.0, forget to `export' the + environment variables they receive. As a result, two variables + coexist: the environment variable and the shell variable. The + following code demonstrates this failure: + + #!/bin/sh + echo $FOO + FOO=bar + echo $FOO + exec /bin/sh $0 + + when run with `FOO=foo' in the environment, these shells print + alternately `foo' and `bar', although they should print only `foo' + and then a sequence of `bar's. + + Therefore you should `export' again each environment variable that + you update; the export can occur before or after the assignment. + + Posix is not clear on whether the `export' of an undefined + variable causes the variable to be defined with the value of an + empty string, or merely marks any future definition of a variable + by that name for export. Various shells behave differently in + this regard: + + $ sh -c 'export foo; env | grep foo' + $ ash -c 'export foo; env | grep foo' + foo= + + Posix requires `export' to honor assignments made as arguments, + but older shells do not support this, including `/bin/sh' in + Solaris 10. Portable scripts should separate assignments and + exports into different statements. + + $ bash -c 'export foo=bar; echo $foo' + bar + $ /bin/sh -c 'export foo=bar; echo $foo' + /bin/sh: foo=bar: is not an identifier + $ /bin/sh -c 'export foo; foo=bar; echo $foo' + bar + +`false' + Don't expect `false' to exit with status 1: in native Solaris + `/bin/false' exits with status 255. + +`for' + To loop over positional arguments, use: + + for arg + do + echo "$arg" + done + + You may _not_ leave the `do' on the same line as `for', since some + shells improperly grok: + + for arg; do + echo "$arg" + done + + If you want to explicitly refer to the positional arguments, given + the `$@' bug (*note Shell Substitutions::), use: + + for arg in ${1+"$@"}; do + echo "$arg" + done + + But keep in mind that Zsh, even in Bourne shell emulation mode, + performs word splitting on `${1+"$@"}'; see *note Shell + Substitutions::, item `$@', for more. + + In Solaris `/bin/sh', when the list of arguments of a `for' loop + starts with _unquoted_ tokens looking like variable assignments, + the loop is not executed on those tokens: + + $ /bin/sh -c 'for v in a=b c=d x e=f; do echo $v; done' + x + e=f + + Thankfully, quoting the assignment-like tokens, or starting the + list with other tokens (including unquoted variable expansion that + results in an assignment-like result), avoids the problem, so it + is easy to work around: + + $ /bin/sh -c 'for v in "a=b"; do echo $v; done' + a=b + $ /bin/sh -c 'x=a=b; for v in $x c=d; do echo $v; done' + a=b + c=d + +`if' + Using `!' is not portable. Instead of: + + if ! cmp -s file file.new; then + mv file.new file + fi + + use: + + if cmp -s file file.new; then :; else + mv file.new file + fi + + Or, especially if the "else" branch is short, you can use `||'. + In M4sh, the `AS_IF' macro provides an easy way to write these + kinds of conditionals: + + AS_IF([cmp -s file file.new], [], [mv file.new file]) + + This is especially useful in other M4 macros, where the "then" and + "else" branches might be macro arguments. + + Some very old shells did not reset the exit status from an `if' + with no `else': + + $ if (exit 42); then true; fi; echo $? + 42 + + whereas a proper shell should have printed `0'. But this is no + longer a portability problem; any shell that supports functions + gets it correct. However, it explains why some makefiles have + lengthy constructs: + + if test -f "$file"; then + install "$file" "$dest" + else + : + fi + +`printf' + A format string starting with a `-' can cause problems. Bash + interprets it as an option and gives an error. And `--' to mark + the end of options is not good in the NetBSD Almquist shell (e.g., + 0.4.6) which takes that literally as the format string. Putting + the `-' in a `%c' or `%s' is probably easiest: + + printf %s -foo + + Bash 2.03 mishandles an escape sequence that happens to evaluate + to `%': + + $ printf '\045' + bash: printf: `%': missing format character + + Large outputs may cause trouble. On Solaris 2.5.1 through 10, for + example, `/usr/bin/printf' is buggy, so when using `/bin/sh' the + command `printf %010000x 123' normally dumps core. + + Since `printf' is not always a shell builtin, there is a potential + speed penalty for using `printf '%s\n'' as a replacement for an + `echo' that does not interpret `\' or leading `-'. With Solaris + `ksh', it is possible to use `print -r --' for this role instead. + + *Note Limitations of Shell Builtins: echo for a discussion of + portable alternatives to both `printf' and `echo'. + +`pwd' + With modern shells, plain `pwd' outputs a "logical" directory + name, some of whose components may be symbolic links. These + directory names are in contrast to "physical" directory names, + whose components are all directories. + + Posix 1003.1-2001 requires that `pwd' must support the `-L' + ("logical") and `-P' ("physical") options, with `-L' being the + default. However, traditional shells do not support these + options, and their `pwd' command has the `-P' behavior. + + Portable scripts should assume neither option is supported, and + should assume neither behavior is the default. Also, on many hosts + `/bin/pwd' is equivalent to `pwd -P', but Posix does not require + this behavior and portable scripts should not rely on it. + + Typically it's best to use plain `pwd'. On modern hosts this + outputs logical directory names, which have the following + advantages: + + * Logical names are what the user specified. + + * Physical names may not be portable from one installation host + to another due to network file system gymnastics. + + * On modern hosts `pwd -P' may fail due to lack of permissions + to some parent directory, but plain `pwd' cannot fail for this + reason. + + Also please see the discussion of the `cd' command. + +`read' + No options are portable, not even support `-r' (Solaris `/bin/sh' + for example). Tru64/OSF 5.1 `sh' treats `read' as a special + built-in, so it may exit if input is redirected from a + non-existent or unreadable file. + +`set' + With the FreeBSD 6.0 shell, the `set' command (without any + options) does not sort its output. + + The `set' builtin faces the usual problem with arguments starting + with a dash. Modern shells such as Bash or Zsh understand `--' to + specify the end of the options (any argument after `--' is a + parameter, even `-x' for instance), but many traditional shells + (e.g., Solaris 10 `/bin/sh') simply stop option processing as soon + as a non-option argument is found. Therefore, use `dummy' or + simply `x' to end the option processing, and use `shift' to pop it + out: + + set x $my_list; shift + + Avoid `set -', e.g., `set - $my_list'. Posix no longer requires + support for this command, and in traditional shells `set - + $my_list' resets the `-v' and `-x' options, which makes scripts + harder to debug. + + Some nonstandard shells do not recognize more than one option + (e.g., `set -e -x' assigns `-x' to the command line). It is + better to combine them: + + set -ex + + The option `-e' has historically been underspecified, with enough + ambiguities to cause numerous differences across various shell + implementations; see for example this overview + (http://www.in-ulm.de/~mascheck/various/set-e/), or this link + (http://www.austingroupbugs.net/view.php?id=52), documenting a + change to Posix 2008 to match `ksh88' behavior. Note that mixing + `set -e' and shell functions is asking for surprises: + + set -e + doit() + { + rm file + echo one + } + doit || echo two + + According to the recommendation, `one' should always be output + regardless of whether the `rm' failed, because it occurs within + the body of the shell function `doit' invoked on the left side of + `||', where the effects of `set -e' are not enforced. Likewise, + `two' should never be printed, since the failure of `rm' does not + abort the function, such that the status of `doit' is 0. + + The BSD shell has had several problems with the `-e' option. + Older versions of the BSD shell (circa 1990) mishandled `&&', + `||', `if', and `case' when `-e' was in effect, causing the shell + to exit unexpectedly in some cases. This was particularly a + problem with makefiles, and led to circumlocutions like `sh -c + 'test -f file || touch file'', where the seemingly-unnecessary `sh + -c '...'' wrapper works around the bug (*note Failure in Make + Rules::). + + Even relatively-recent versions of the BSD shell (e.g., OpenBSD + 3.4) wrongly exit with `-e' if the last command within a compound + statement fails and is guarded by an `&&' only. For example: + + #! /bin/sh + set -e + foo='' + test -n "$foo" && exit 1 + echo one + if :; then + test -n "$foo" && exit 1 + echo two + test -n "$foo" && exit 1 + fi + echo three + + does not print `three'. One workaround is to change the last + instance of `test -n "$foo" && exit 1' to be `if test -n "$foo"; + then exit 1; fi' instead. Another possibility is to warn BSD + users not to use `sh -e'. + + When `set -e' is in effect, a failed command substitution in + Solaris `/bin/sh' cannot be ignored, even with `||'. + + $ /bin/sh -c 'set -e; foo=`false` || echo foo; echo bar' + $ bash -c 'set -e; foo=`false` || echo foo; echo bar' + foo + bar + + Moreover, a command substitution, successful or not, causes this + shell to exit from a failing outer command even in presence of an + `&&' list: + + $ bash -c 'set -e; false `true` && echo notreached; echo ok' + ok + $ sh -c 'set -e; false `true` && echo notreached; echo ok' + $ + + Portable scripts should not use `set -e' if `trap' is used to + install an exit handler. This is because Tru64/OSF 5.1 `sh' + sometimes enters the trap handler with the exit status of the + command prior to the one that triggered the errexit handler: + + $ sh -ec 'trap '\''echo $?'\'' 0; false' + 0 + $ sh -c 'set -e; trap '\''echo $?'\'' 0; false' + 1 + + Thus, when writing a script in M4sh, rather than trying to rely on + `set -e', it is better to append `|| AS_EXIT' to any statement + where it is desirable to abort on failure. + + Job control is not provided by all shells, so the use of `set -m' + or `set -b' must be done with care. When using `zsh' in native + mode, asynchronous notification (`set -b') is enabled by default, + and using `emulate sh' to switch to Posix mode does not clear this + setting (although asynchronous notification has no impact unless + job monitoring is also enabled). Also, `zsh' 4.3.10 and earlier + have a bug where job control can be manipulated in interactive + shells, but not in subshells or scripts. Furthermore, some + shells, like `pdksh', fail to treat subshells as interactive, even + though the parent shell was. + + $ echo $ZSH_VERSION + 4.3.10 + $ set -m; echo $? + 0 + $ zsh -c 'set -m; echo $?' + set: can't change option: -m + $ (set -m); echo $? + set: can't change option: -m + 1 + $ pdksh -ci 'echo $-; (echo $-)' + cim + c + + Use of `set -n' (typically via `sh -n script') to validate a + script is not foolproof. Modern `ksh93' tries to be helpful by + informing you about better syntax, but switching the script to use + the suggested syntax in order to silence the warnings would render + the script no longer portable to older shells: + + $ ksh -nc '``' + ksh: warning: line 1: `...` obsolete, use $(...) + 0 + + Furthermore, on ancient hosts, such as SunOS 4, `sh -n' could go + into an infinite loop; even with that bug fixed, Solaris 8 + `/bin/sh' takes extremely long to parse large scripts. Autoconf + itself uses `sh -n' within its testsuite to check that correct + scripts were generated, but only after first probing for other + shell features (such as `test -n "${BASH_VERSION+set}"') that + indicate a reasonably fast and working implementation. + +`shift' + Not only is `shift'ing a bad idea when there is nothing left to + shift, but in addition it is not portable: the shell of MIPS + RISC/OS 4.52 refuses to do it. + + Don't use `shift 2' etc.; while it in the SVR1 shell (1983), it is + also absent in many pre-Posix shells. + +`source' + This command is not portable, as Posix does not require it; use + `.' instead. + +`test' + The `test' program is the way to perform many file and string + tests. It is often invoked by the alternate name `[', but using + that name in Autoconf code is asking for trouble since it is an M4 + quote character. + + The `-a', `-o', `(', and `)' operands are not present in all + implementations, and have been marked obsolete by Posix 2008. + This is because there are inherent ambiguities in using them. For + example, `test "$1" -a "$2"' looks like a binary operator to check + whether two strings are both non-empty, but if `$1' is the literal + `!', then some implementations of `test' treat it as a negation of + the unary operator `-a'. + + Thus, portable uses of `test' should never have more than four + arguments, and scripts should use shell constructs like `&&' and + `||' instead. If you combine `&&' and `||' in the same statement, + keep in mind that they have equal precedence, so it is often + better to parenthesize even when this is redundant. For example: + + # Not portable: + test "X$a" = "X$b" -a \ + '(' "X$c" != "X$d" -o "X$e" = "X$f" ')' + + # Portable: + test "X$a" = "X$b" && + { test "X$c" != "X$d" || test "X$e" = "X$f"; } + + `test' does not process options like most other commands do; for + example, it does not recognize the `--' argument as marking the + end of options. + + It is safe to use `!' as a `test' operator. For example, `if test + ! -d foo; ...' is portable even though `if ! test -d foo; ...' is + not. + +`test' (files) + To enable `configure' scripts to support cross-compilation, they + shouldn't do anything that tests features of the build system + instead of the host system. But occasionally you may find it + necessary to check whether some arbitrary file exists. To do so, + use `test -f', `test -r', or `test -x'. Do not use `test -e', + because Solaris 10 `/bin/sh' lacks it. To test for symbolic links + on systems that have them, use `test -h' rather than `test -L'; + either form conforms to Posix 1003.1-2001, but older shells like + Solaris 8 `/bin/sh' support only `-h'. + + For historical reasons, Posix reluctantly allows implementations of + `test -x' that will succeed for the root user, even if no execute + permissions are present. Furthermore, shells do not all agree on + whether Access Control Lists should affect `test -r', `test -w', + and `test -x'; some shells base test results strictly on the + current user id compared to file owner and mode, as if by + `stat(2)'; while other shells base test results on whether the + current user has the given right, even if that right is only + granted by an ACL, as if by `faccessat(2)'. Furthermore, there is + a classic time of check to time of use race between any use of + `test' followed by operating on the just-checked file. Therefore, + it is a good idea to write scripts that actually attempt an + operation, and are prepared for the resulting failure if + permission is denied, rather than trying to avoid an operation + based solely on whether `test' guessed that it might not be + permitted. + +`test' (strings) + Posix says that `test "STRING"' succeeds if STRING is not null, + but this usage is not portable to traditional platforms like + Solaris 10 `/bin/sh', which mishandle strings like `!' and `-n'. + + Posix also says that `test ! "STRING"', `test -n "STRING"' and + `test -z "STRING"' work with any string, but many shells (such as + Solaris, AIX 3.2, UNICOS 10.0.0.6, Digital Unix 4, etc.) get + confused if STRING looks like an operator: + + $ test -n = + test: argument expected + $ test ! -n + test: argument expected + $ test -z ")"; echo $? + 0 + + Similarly, Posix says that both `test "STRING1" = "STRING2"' and + `test "STRING1" != "STRING2"' work for any pairs of strings, but + in practice this is not true for troublesome strings that look + like operators or parentheses, or that begin with `-'. + + It is best to protect such strings with a leading `X', e.g., `test + "XSTRING" != X' rather than `test -n "STRING"' or `test ! + "STRING"'. + + It is common to find variations of the following idiom: + + test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" && + ACTION + + to take an action when a token matches a given pattern. Such + constructs should be avoided by using: + + case $ac_feature in + *[!-a-zA-Z0-9_]*) ACTION;; + esac + + If the pattern is a complicated regular expression that cannot be + expressed as a shell pattern, use something like this instead: + + expr "X$ac_feature" : 'X.*[^-a-zA-Z0-9_]' >/dev/null && + ACTION + + `expr "XFOO" : "XBAR"' is more robust than `echo "XFOO" | grep + "^XBAR"', because it avoids problems when `FOO' contains + backslashes. + +`trap' + It is safe to trap at least the signals 1, 2, 13, and 15. You can + also trap 0, i.e., have the `trap' run when the script ends + (either via an explicit `exit', or the end of the script). The + trap for 0 should be installed outside of a shell function, or AIX + 5.3 `/bin/sh' will invoke the trap at the end of this function. + + Posix says that `trap - 1 2 13 15' resets the traps for the + specified signals to their default values, but many common shells + (e.g., Solaris `/bin/sh') misinterpret this and attempt to execute + a "command" named `-' when the specified conditions arise. Posix + 2008 also added a requirement to support `trap 1 2 13 15' to reset + traps, as this is supported by a larger set of shells, but there + are still shells like `dash' that mistakenly try to execute `1' + instead of resetting the traps. Therefore, there is no portable + workaround, except for `trap - 0', for which `trap '' 0' is a + portable substitute. + + Although Posix is not absolutely clear on this point, it is widely + admitted that when entering the trap `$?' should be set to the exit + status of the last command run before the trap. The ambiguity can + be summarized as: "when the trap is launched by an `exit', what is + the _last_ command run: that before `exit', or `exit' itself?" + + Bash considers `exit' to be the last command, while Zsh and + Solaris `/bin/sh' consider that when the trap is run it is _still_ + in the `exit', hence it is the previous exit status that the trap + receives: + + $ cat trap.sh + trap 'echo $?' 0 + (exit 42); exit 0 + $ zsh trap.sh + 42 + $ bash trap.sh + 0 + + The portable solution is then simple: when you want to `exit 42', + run `(exit 42); exit 42', the first `exit' being used to set the + exit status to 42 for Zsh, and the second to trigger the trap and + pass 42 as exit status for Bash. In M4sh, this is covered by using + `AS_EXIT'. + + The shell in FreeBSD 4.0 has the following bug: `$?' is reset to 0 + by empty lines if the code is inside `trap'. + + $ trap 'false + + echo $?' 0 + $ exit + 0 + + Fortunately, this bug only affects `trap'. + + Several shells fail to execute an exit trap that is defined inside + a subshell, when the last command of that subshell is not a + builtin. A workaround is to use `exit $?' as the shell builtin. + + $ bash -c '(trap "echo hi" 0; /bin/true)' + hi + $ /bin/sh -c '(trap "echo hi" 0; /bin/true)' + $ /bin/sh -c '(trap "echo hi" 0; /bin/true; exit $?)' + hi + + Likewise, older implementations of `bash' failed to preserve `$?' + across an exit trap consisting of a single cleanup command. + + $ bash -c 'trap "/bin/true" 0; exit 2'; echo $? + 2 + $ bash-2.05b -c 'trap "/bin/true" 0; exit 2'; echo $? + 0 + $ bash-2.05b -c 'trap ":; /bin/true" 0; exit 2'; echo $? + 2 + +`true' + Don't worry: as far as we know `true' is portable. Nevertheless, + it's not always a builtin (e.g., Bash 1.x), and the portable shell + community tends to prefer using `:'. This has a funny side + effect: when asked whether `false' is more portable than `true' + Alexandre Oliva answered: + + In a sense, yes, because if it doesn't exist, the shell will + produce an exit status of failure, which is correct for + `false', but not for `true'. + + Remember that even though `:' ignores its arguments, it still takes + time to compute those arguments. It is a good idea to use double + quotes around any arguments to `:' to avoid time spent in field + splitting and file name expansion. + +`unset' + In some nonconforming shells (e.g., Solaris 10 `/bin/ksh' and + `/usr/xpg4/bin/sh', NetBSD 5.99.43 sh, or Bash 2.05a), `unset FOO' + fails when `FOO' is not set. This can interfere with `set -e' + operation. You can use + + FOO=; unset FOO + + if you are not sure that `FOO' is set. + + A few ancient shells lack `unset' entirely. For some variables + such as `PS1', you can use a neutralizing value instead: + + PS1='$ ' + + Usually, shells that do not support `unset' need less effort to + make the environment sane, so for example is not a problem if you + cannot unset `CDPATH' on those shells. However, Bash 2.01 + mishandles `unset MAIL' and `unset MAILPATH' in some cases and + dumps core. So, you should do something like + + ( (unset MAIL) || exit 1) >/dev/null 2>&1 && unset MAIL || : + + *Note Special Shell Variables::, for some neutralizing values. + Also, see *note Limitations of Builtins: export, for the case of + environment variables. + +`wait' + The exit status of `wait' is not always reliable. + + +File: autoconf.info, Node: Limitations of Usual Tools, Prev: Limitations of Builtins, Up: Portable Shell + +11.15 Limitations of Usual Tools +================================ + +The small set of tools you can expect to find on any machine can still +include some limitations you should be aware of. + +`awk' + Don't leave white space before the opening parenthesis in a user + function call. Posix does not allow this and GNU Awk rejects it: + + $ gawk 'function die () { print "Aaaaarg!" } + BEGIN { die () }' + gawk: cmd. line:2: BEGIN { die () } + gawk: cmd. line:2: ^ parse error + $ gawk 'function die () { print "Aaaaarg!" } + BEGIN { die() }' + Aaaaarg! + + Posix says that if a program contains only `BEGIN' actions, and + contains no instances of `getline', then the program merely + executes the actions without reading input. However, traditional + Awk implementations (such as Solaris 10 `awk') read and discard + input in this case. Portable scripts can redirect input from + `/dev/null' to work around the problem. For example: + + awk 'BEGIN {print "hello world"}' </dev/null + + Posix says that in an `END' action, `$NF' (and presumably, `$1') + retain their value from the last record read, if no intervening + `getline' occurred. However, some implementations (such as + Solaris 10 `/usr/bin/awk', `nawk', or Darwin `awk') reset these + variables. A workaround is to use an intermediate variable prior + to the `END' block. For example: + + $ cat end.awk + { tmp = $1 } + END { print "a", $1, $NF, "b", tmp } + $ echo 1 | awk -f end.awk + a b 1 + $ echo 1 | gawk -f end.awk + a 1 1 b 1 + + If you want your program to be deterministic, don't depend on `for' + on arrays: + + $ cat for.awk + END { + arr["foo"] = 1 + arr["bar"] = 1 + for (i in arr) + print i + } + $ gawk -f for.awk </dev/null + foo + bar + $ nawk -f for.awk </dev/null + bar + foo + + Some Awk implementations, such as HP-UX 11.0's native one, + mishandle anchors: + + $ echo xfoo | $AWK '/foo|^bar/ { print }' + $ echo bar | $AWK '/foo|^bar/ { print }' + bar + $ echo xfoo | $AWK '/^bar|foo/ { print }' + xfoo + $ echo bar | $AWK '/^bar|foo/ { print }' + bar + + Either do not depend on such patterns (i.e., use `/^(.*foo|bar)/', + or use a simple test to reject such implementations. + + On `ia64-hp-hpux11.23', Awk mishandles `printf' conversions after + `%u': + + $ awk 'BEGIN { printf "%u %d\n", 0, -1 }' + 0 0 + + AIX version 5.2 has an arbitrary limit of 399 on the length of + regular expressions and literal strings in an Awk program. + + Traditional Awk implementations derived from Unix version 7, such + as Solaris `/bin/awk', have many limitations and do not conform to + Posix. Nowadays `AC_PROG_AWK' (*note Particular Programs::) finds + you an Awk that doesn't have these problems, but if for some + reason you prefer not to use `AC_PROG_AWK' you may need to address + them. For more detailed descriptions, see *note `awk' language + history: (gawk)Language History. + + Traditional Awk does not support multidimensional arrays or + user-defined functions. + + Traditional Awk does not support the `-v' option. You can use + assignments after the program instead, e.g., `$AWK '{print v $1}' + v=x'; however, don't forget that such assignments are not + evaluated until they are encountered (e.g., after any `BEGIN' + action). + + Traditional Awk does not support the keywords `delete' or `do'. + + Traditional Awk does not support the expressions `A?B:C', `!A', + `A^B', or `A^=B'. + + Traditional Awk does not support the predefined `CONVFMT' or + `ENVIRON' variables. + + Traditional Awk supports only the predefined functions `exp', + `index', `int', `length', `log', `split', `sprintf', `sqrt', and + `substr'. + + Traditional Awk `getline' is not at all compatible with Posix; + avoid it. + + Traditional Awk has `for (i in a) ...' but no other uses of the + `in' keyword. For example, it lacks `if (i in a) ...'. + + In code portable to both traditional and modern Awk, `FS' must be a + string containing just one ordinary character, and similarly for + the field-separator argument to `split'. + + Traditional Awk has a limit of 99 fields in a record. Since some + Awk implementations, like Tru64's, split the input even if you + don't refer to any field in the script, to circumvent this + problem, set `FS' to an unusual character and use `split'. + + Traditional Awk has a limit of at most 99 bytes in a number + formatted by `OFMT'; for example, `OFMT="%.300e"; print 0.1;' + typically dumps core. + + The original version of Awk had a limit of at most 99 bytes per + `split' field, 99 bytes per `substr' substring, and 99 bytes per + run of non-special characters in a `printf' format, but these bugs + have been fixed on all practical hosts that we know of. + + HP-UX 11.00 and IRIX 6.5 Awk require that input files have a line + length of at most 3070 bytes. + +`basename' + Not all hosts have a working `basename'. You can use `expr' + instead. + +`cat' + Don't rely on any option. + +`cc' + The command `cc -c foo.c' traditionally produces an object file + named `foo.o'. Most compilers allow `-c' to be combined with `-o' + to specify a different object file name, but Posix does not + require this combination and a few compilers lack support for it. + *Note C Compiler::, for how GNU Make tests for this feature with + `AC_PROG_CC_C_O'. + + When a compilation such as `cc -o foo foo.c' fails, some compilers + (such as CDS on Reliant Unix) leave a `foo.o'. + + HP-UX `cc' doesn't accept `.S' files to preprocess and assemble. + `cc -c foo.S' appears to succeed, but in fact does nothing. + + The default executable, produced by `cc foo.c', can be + + * `a.out' -- usual Posix convention. + + * `b.out' -- i960 compilers (including `gcc'). + + * `a.exe' -- DJGPP port of `gcc'. + + * `a_out.exe' -- GNV `cc' wrapper for DEC C on OpenVMS. + + * `foo.exe' -- various MS-DOS compilers. + + The C compiler's traditional name is `cc', but other names like + `gcc' are common. Posix 1003.1-2001 specifies the name `c99', but + older Posix editions specified `c89' and anyway these standard + names are rarely used in practice. Typically the C compiler is + invoked from makefiles that use `$(CC)', so the value of the `CC' + make variable selects the compiler name. + +`chgrp' +`chown' + It is not portable to change a file's group to a group that the + owner does not belong to. + +`chmod' + Avoid usages like `chmod -w file'; use `chmod a-w file' instead, + for two reasons. First, plain `-w' does not necessarily make the + file unwritable, since it does not affect mode bits that + correspond to bits in the file mode creation mask. Second, Posix + says that the `-w' might be interpreted as an + implementation-specific option, not as a mode; Posix suggests + using `chmod -- -w file' to avoid this confusion, but unfortunately + `--' does not work on some older hosts. + +`cmp' + `cmp' performs a raw data comparison of two files, while `diff' + compares two text files. Therefore, if you might compare DOS + files, even if only checking whether two files are different, use + `diff' to avoid spurious differences due to differences of newline + encoding. + +`cp' + Avoid the `-r' option, since Posix 1003.1-2004 marks it as + obsolescent and its behavior on special files is + implementation-defined. Use `-R' instead. On GNU hosts the two + options are equivalent, but on Solaris hosts (for example) `cp -r' + reads from pipes instead of replicating them. AIX 5.3 `cp -R' may + corrupt its own memory with some directory hierarchies and error + out or dump core: + + mkdir -p 12345678/12345678/12345678/12345678 + touch 12345678/12345678/x + cp -R 12345678 t + cp: 0653-440 12345678/12345678/: name too long. + + Some `cp' implementations (e.g., BSD/OS 4.2) do not allow trailing + slashes at the end of nonexistent destination directories. To + avoid this problem, omit the trailing slashes. For example, use + `cp -R source /tmp/newdir' rather than `cp -R source /tmp/newdir/' + if `/tmp/newdir' does not exist. + + The ancient SunOS 4 `cp' does not support `-f', although its `mv' + does. + + Traditionally, file timestamps had 1-second resolution, and `cp + -p' copied the timestamps exactly. However, many modern file + systems have timestamps with 1-nanosecond resolution. + Unfortunately, some older `cp -p' implementations truncate + timestamps when copying files, which can cause the destination + file to appear to be older than the source. The exact amount of + truncation depends on the resolution of the system calls that `cp' + uses. Traditionally this was `utime', which has 1-second + resolution. Less-ancient `cp' implementations such as GNU Core + Utilities 5.0.91 (2003) use `utimes', which has 1-microsecond + resolution. Modern implementations such as GNU Core Utilities + 6.12 (2008) can set timestamps to the full nanosecond resolution, + using the modern system calls `futimens' and `utimensat' when they + are available. As of 2011, though, many platforms do not yet + fully support these new system calls. + + Bob Proulx notes that `cp -p' always _tries_ to copy ownerships. + But whether it actually does copy ownerships or not is a system + dependent policy decision implemented by the kernel. If the + kernel allows it then it happens. If the kernel does not allow it + then it does not happen. It is not something `cp' itself has + control over. + + In Unix System V any user can chown files to any other user, and + System V also has a non-sticky `/tmp'. That probably derives from + the heritage of System V in a business environment without hostile + users. BSD changed this to be a more secure model where only root + can `chown' files and a sticky `/tmp' is used. That undoubtedly + derives from the heritage of BSD in a campus environment. + + GNU/Linux and Solaris by default follow BSD, but can be configured + to allow a System V style `chown'. On the other hand, HP-UX + follows System V, but can be configured to use the modern security + model and disallow `chown'. Since it is an + administrator-configurable parameter you can't use the name of the + kernel as an indicator of the behavior. + +`date' + Some versions of `date' do not recognize special `%' directives, + and unfortunately, instead of complaining, they just pass them + through, and exit with success: + + $ uname -a + OSF1 medusa.sis.pasteur.fr V5.1 732 alpha + $ date "+%s" + %s + +`diff' + Option `-u' is nonportable. + + Some implementations, such as Tru64's, fail when comparing to + `/dev/null'. Use an empty file instead. + +`dirname' + Not all hosts have a working `dirname', and you should instead use + `AS_DIRNAME' (*note Programming in M4sh::). For example: + + dir=`dirname "$file"` # This is not portable. + dir=`AS_DIRNAME(["$file"])` # This is more portable. + +`egrep' + Posix 1003.1-2001 no longer requires `egrep', but many hosts do + not yet support the Posix replacement `grep -E'. Also, some + traditional implementations do not work on long input lines. To + work around these problems, invoke `AC_PROG_EGREP' and then use + `$EGREP'. + + Portable extended regular expressions should use `\' only to escape + characters in the string `$()*+.?[\^{|'. For example, `\}' is not + portable, even though it typically matches `}'. + + The empty alternative is not portable. Use `?' instead. For + instance with Digital Unix v5.0: + + > printf "foo\n|foo\n" | $EGREP '^(|foo|bar)$' + |foo + > printf "bar\nbar|\n" | $EGREP '^(foo|bar|)$' + bar| + > printf "foo\nfoo|\n|bar\nbar\n" | $EGREP '^(foo||bar)$' + foo + |bar + + `$EGREP' also suffers the limitations of `grep' (*note Limitations + of Usual Tools: grep.). + +`expr' + Not all implementations obey the Posix rule that `--' separates + options from arguments; likewise, not all implementations provide + the extension to Posix that the first argument can be treated as + part of a valid expression rather than an invalid option if it + begins with `-'. When performing arithmetic, use `expr 0 + $var' + if `$var' might be a negative number, to keep `expr' from + interpreting it as an option. + + No `expr' keyword starts with `X', so use `expr X"WORD" : + 'XREGEX'' to keep `expr' from misinterpreting WORD. + + Don't use `length', `substr', `match' and `index'. + +`expr' (`|') + You can use `|'. Although Posix does require that `expr ''' + return the empty string, it does not specify the result when you + `|' together the empty string (or zero) with the empty string. For + example: + + expr '' \| '' + + Posix 1003.2-1992 returns the empty string for this case, but + traditional Unix returns `0' (Solaris is one such example). In + Posix 1003.1-2001, the specification was changed to match + traditional Unix's behavior (which is bizarre, but it's too late + to fix this). Please note that the same problem does arise when + the empty string results from a computation, as in: + + expr bar : foo \| foo : bar + + Avoid this portability problem by avoiding the empty string. + +`expr' (`:') + Portable `expr' regular expressions should use `\' to escape only + characters in the string `$()*.0123456789[\^n{}'. For example, + alternation, `\|', is common but Posix does not require its + support, so it should be avoided in portable scripts. Similarly, + `\+' and `\?' should be avoided. + + Portable `expr' regular expressions should not begin with `^'. + Patterns are automatically anchored so leading `^' is not needed + anyway. + + On the other hand, the behavior of the `$' anchor is not portable + on multi-line strings. Posix is ambiguous whether the anchor + applies to each line, as was done in older versions of the GNU + Core Utilities, or whether it applies only to the end of the + overall string, as in Coreutils 6.0 and most other implementations. + + $ baz='foo + > bar' + $ expr "X$baz" : 'X\(foo\)$' + + $ expr-5.97 "X$baz" : 'X\(foo\)$' + foo + + The Posix standard is ambiguous as to whether `expr 'a' : '\(b\)'' + outputs `0' or the empty string. In practice, it outputs the + empty string on most platforms, but portable scripts should not + assume this. For instance, the QNX 4.25 native `expr' returns `0'. + + One might think that a way to get a uniform behavior would be to + use the empty string as a default value: + + expr a : '\(b\)' \| '' + + Unfortunately this behaves exactly as the original expression; see + the `expr' (`|') entry for more information. + + Some ancient `expr' implementations (e.g., SunOS 4 `expr' and + Solaris 8 `/usr/ucb/expr') have a silly length limit that causes + `expr' to fail if the matched substring is longer than 120 bytes. + In this case, you might want to fall back on `echo|sed' if `expr' + fails. Nowadays this is of practical importance only for the rare + installer who mistakenly puts `/usr/ucb' before `/usr/bin' in + `PATH'. + + On Mac OS X 10.4, `expr' mishandles the pattern `[^-]' in some + cases. For example, the command + expr Xpowerpc-apple-darwin8.1.0 : 'X[^-]*-[^-]*-\(.*\)' + + outputs `apple-darwin8.1.0' rather than the correct `darwin8.1.0'. + This particular case can be worked around by substituting `[^--]' + for `[^-]'. + + Don't leave, there is some more! + + The QNX 4.25 `expr', in addition of preferring `0' to the empty + string, has a funny behavior in its exit status: it's always 1 + when parentheses are used! + + $ val=`expr 'a' : 'a'`; echo "$?: $val" + 0: 1 + $ val=`expr 'a' : 'b'`; echo "$?: $val" + 1: 0 + + $ val=`expr 'a' : '\(a\)'`; echo "?: $val" + 1: a + $ val=`expr 'a' : '\(b\)'`; echo "?: $val" + 1: 0 + + In practice this can be a big problem if you are ready to catch + failures of `expr' programs with some other method (such as using + `sed'), since you may get twice the result. For instance + + $ expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/' + + outputs `a' on most hosts, but `aa' on QNX 4.25. A simple + workaround consists of testing `expr' and using a variable set to + `expr' or to `false' according to the result. + + Tru64 `expr' incorrectly treats the result as a number, if it can + be interpreted that way: + + $ expr 00001 : '.*\(...\)' + 1 + + On HP-UX 11, `expr' only supports a single sub-expression. + + $ expr 'Xfoo' : 'X\(f\(oo\)*\)$' + expr: More than one '\(' was used. + +`fgrep' + Posix 1003.1-2001 no longer requires `fgrep', but many hosts do + not yet support the Posix replacement `grep -F'. Also, some + traditional implementations do not work on long input lines. To + work around these problems, invoke `AC_PROG_FGREP' and then use + `$FGREP'. + + Tru64/OSF 5.1 `fgrep' does not match an empty pattern. + +`find' + The option `-maxdepth' seems to be GNU specific. Tru64 v5.1, + NetBSD 1.5 and Solaris `find' commands do not understand it. + + The replacement of `{}' is guaranteed only if the argument is + exactly _{}_, not if it's only a part of an argument. For + instance on DU, and HP-UX 10.20 and HP-UX 11: + + $ touch foo + $ find . -name foo -exec echo "{}-{}" \; + {}-{} + + while GNU `find' reports `./foo-./foo'. + +`grep' + Portable scripts can rely on the `grep' options `-c', `-l', `-n', + and `-v', but should avoid other options. For example, don't use + `-w', as Posix does not require it and Irix 6.5.16m's `grep' does + not support it. Also, portable scripts should not combine `-c' + with `-l', as Posix does not allow this. + + Some of the options required by Posix are not portable in practice. + Don't use `grep -q' to suppress output, because many `grep' + implementations (e.g., Solaris) do not support `-q'. Don't use + `grep -s' to suppress output either, because Posix says `-s' does + not suppress output, only some error messages; also, the `-s' + option of traditional `grep' behaved like `-q' does in most modern + implementations. Instead, redirect the standard output and + standard error (in case the file doesn't exist) of `grep' to + `/dev/null'. Check the exit status of `grep' to determine whether + it found a match. + + The QNX4 implementation fails to count lines with `grep -c '$'', + but works with `grep -c '^''. Other alternatives for counting + lines are to use `sed -n '$='' or `wc -l'. + + Some traditional `grep' implementations do not work on long input + lines. On AIX the default `grep' silently truncates long lines on + the input before matching. + + Also, many implementations do not support multiple regexps with + `-e': they either reject `-e' entirely (e.g., Solaris) or honor + only the last pattern (e.g., IRIX 6.5 and NeXT). To work around + these problems, invoke `AC_PROG_GREP' and then use `$GREP'. + + Another possible workaround for the multiple `-e' problem is to + separate the patterns by newlines, for example: + + grep 'foo + bar' in.txt + + except that this fails with traditional `grep' implementations and + with OpenBSD 3.8 `grep'. + + Traditional `grep' implementations (e.g., Solaris) do not support + the `-E' or `-F' options. To work around these problems, invoke + `AC_PROG_EGREP' and then use `$EGREP', and similarly for + `AC_PROG_FGREP' and `$FGREP'. Even if you are willing to require + support for Posix `grep', your script should not use both `-E' and + `-F', since Posix does not allow this combination. + + Portable `grep' regular expressions should use `\' only to escape + characters in the string `$()*.0123456789[\^{}'. For example, + alternation, `\|', is common but Posix does not require its + support in basic regular expressions, so it should be avoided in + portable scripts. Solaris and HP-UX `grep' do not support it. + Similarly, the following escape sequences should also be avoided: + `\<', `\>', `\+', `\?', `\`', `\'', `\B', `\b', `\S', `\s', `\W', + and `\w'. + + Posix does not specify the behavior of `grep' on binary files. An + example where this matters is using BSD `grep' to search text that + includes embedded ANSI escape sequences for colored output to + terminals (`\033[m' is the sequence to restore normal output); the + behavior depends on whether input is seekable: + + $ printf 'esc\033[mape\n' > sample + $ grep . sample + Binary file sample matches + $ cat sample | grep . + escape + +`join' + Solaris 8 `join' has bugs when the second operand is standard + input, and when standard input is a pipe. For example, the + following shell script causes Solaris 8 `join' to loop forever: + + cat >file <<'EOF' + 1 x + 2 y + EOF + cat file | join file - + + Use `join - file' instead. + + On NetBSD, `join -a 1 file1 file2' mistakenly behaves like `join + -a 1 -a 2 1 file1 file2', resulting in a usage warning; the + workaround is to use `join -a1 file1 file2' instead. + +`ln' + Don't rely on `ln' having a `-f' option. Symbolic links are not + available on old systems; use `$(LN_S)' as a portable substitute. + + For versions of the DJGPP before 2.04, `ln' emulates symbolic links + to executables by generating a stub that in turn calls the real + program. This feature also works with nonexistent files like in + the Posix spec. So `ln -s file link' generates `link.exe', which + attempts to call `file.exe' if run. But this feature only works + for executables, so `cp -p' is used instead for these systems. + DJGPP versions 2.04 and later have full support for symbolic links. + +`ls' + The portable options are `-acdilrtu'. Current practice is for + `-l' to output both owner and group, even though ancient versions + of `ls' omitted the group. + + On ancient hosts, `ls foo' sent the diagnostic `foo not found' to + standard output if `foo' did not exist. Hence a shell command + like `sources=`ls *.c 2>/dev/null`' did not always work, since it + was equivalent to `sources='*.c not found'' in the absence of `.c' + files. This is no longer a practical problem, since current `ls' + implementations send diagnostics to standard error. + + The behavior of `ls' on a directory that is being concurrently + modified is not always predictable, because of a data race where + cached information returned by `readdir' does not match the current + directory state. In fact, MacOS 10.5 has an intermittent bug where + `readdir', and thus `ls', sometimes lists a file more than once if + other files were added or removed from the directory immediately + prior to the `ls' call. Since `ls' already sorts its output, the + duplicate entries can be avoided by piping the results through + `uniq'. + +`mkdir' + No `mkdir' option is portable to older systems. Instead of `mkdir + -p FILE-NAME', you should use `AS_MKDIR_P(FILE-NAME)' (*note + Programming in M4sh::) or `AC_PROG_MKDIR_P' (*note Particular + Programs::). + + Combining the `-m' and `-p' options, as in `mkdir -m go-w -p DIR', + often leads to trouble. FreeBSD `mkdir' incorrectly attempts to + change the permissions of DIR even if it already exists. HP-UX + 11.23 and IRIX 6.5 `mkdir' often assign the wrong permissions to + any newly-created parents of DIR. + + Posix does not clearly specify whether `mkdir -p foo' should + succeed when `foo' is a symbolic link to an already-existing + directory. The GNU Core Utilities 5.1.0 `mkdir' succeeds, but + Solaris `mkdir' fails. + + Traditional `mkdir -p' implementations suffer from race conditions. + For example, if you invoke `mkdir -p a/b' and `mkdir -p a/c' at + the same time, both processes might detect that `a' is missing, + one might create `a', then the other might try to create `a' and + fail with a `File exists' diagnostic. The GNU Core Utilities + (`fileutils' version 4.1), FreeBSD 5.0, NetBSD 2.0.2, and OpenBSD + 2.4 are known to be race-free when two processes invoke `mkdir -p' + simultaneously, but earlier versions are vulnerable. Solaris + `mkdir' is still vulnerable as of Solaris 10, and other + traditional Unix systems are probably vulnerable too. This + possible race is harmful in parallel builds when several Make + rules call `mkdir -p' to construct directories. You may use + `install-sh -d' as a safe replacement, provided this script is + recent enough; the copy shipped with Autoconf 2.60 and Automake + 1.10 is OK, but copies from older versions are vulnerable. + +`mkfifo' +`mknod' + The GNU Coding Standards state that `mknod' is safe to use on + platforms where it has been tested to exist; but it is generally + portable only for creating named FIFOs, since device numbers are + platform-specific. Autotest uses `mkfifo' to implement parallel + testsuites. Posix states that behavior is unspecified when + opening a named FIFO for both reading and writing; on at least + Cygwin, this results in failure on any attempt to read or write to + that file descriptor. + +`mktemp' + Shell scripts can use temporary files safely with `mktemp', but it + does not exist on all systems. A portable way to create a safe + temporary file name is to create a temporary directory with mode + 700 and use a file inside this directory. Both methods prevent + attackers from gaining control, though `mktemp' is far less likely + to fail gratuitously under attack. + + Here is sample code to create a new temporary directory `$dir' + safely: + + # Create a temporary directory $dir in $TMPDIR (default /tmp). + # Use mktemp if possible; otherwise fall back on mkdir, + # with $RANDOM to make collisions less likely. + : "${TMPDIR:=/tmp}" + { + dir=` + (umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null + ` && + test -d "$dir" + } || { + dir=$TMPDIR/foo$$-$RANDOM + (umask 077 && mkdir "$dir") + } || exit $? + +`mv' + The only portable options are `-f' and `-i'. + + Moving individual files between file systems is portable (it was + in Unix version 6), but it is not always atomic: when doing `mv + new existing', there's a critical section where neither the old + nor the new version of `existing' actually exists. + + On some systems moving files from `/tmp' can sometimes cause + undesirable (but perfectly valid) warnings, even if you created + these files. This is because `/tmp' belongs to a group that + ordinary users are not members of, and files created in `/tmp' + inherit the group of `/tmp'. When the file is copied, `mv' issues + a diagnostic without failing: + + $ touch /tmp/foo + $ mv /tmp/foo . + error-->mv: ./foo: set owner/group (was: 100/0): Operation not permitted + $ echo $? + 0 + $ ls foo + foo + + This annoying behavior conforms to Posix, unfortunately. + + Moving directories across mount points is not portable, use `cp' + and `rm'. + + DOS variants cannot rename or remove open files, and do not + support commands like `mv foo bar >foo', even though this is + perfectly portable among Posix hosts. + +`od' + In Mac OS X 10.3, `od' does not support the standard Posix options + `-A', `-j', `-N', or `-t', or the XSI option `-s'. The only + supported Posix option is `-v', and the only supported XSI options + are those in `-bcdox'. The BSD `hexdump' program can be used + instead. + + This problem no longer exists in Mac OS X 10.4.3. + +`rm' + The `-f' and `-r' options are portable. + + It is not portable to invoke `rm' without options or operands. On + the other hand, Posix now requires `rm -f' to silently succeed + when there are no operands (useful for constructs like `rm -rf + $filelist' without first checking if `$filelist' was empty). But + this was not always portable; at least NetBSD `rm' built before + 2008 would fail with a diagnostic. + + A file might not be removed even if its parent directory is + writable and searchable. Many Posix hosts cannot remove a mount + point, a named stream, a working directory, or a last link to a + file that is being executed. + + DOS variants cannot rename or remove open files, and do not + support commands like `rm foo >foo', even though this is perfectly + portable among Posix hosts. + +`rmdir' + Just as with `rm', some platforms refuse to remove a working + directory. + +`sed' + Patterns should not include the separator (unless escaped), even + as part of a character class. In conformance with Posix, the Cray + `sed' rejects `s/[^/]*$//': use `s%[^/]*$%%'. Even when escaped, + patterns should not include separators that are also used as `sed' + metacharacters. For example, GNU sed 4.0.9 rejects + `s,x\{1\,\},,', while sed 4.1 strips the backslash before the comma + before evaluating the basic regular expression. + + Avoid empty patterns within parentheses (i.e., `\(\)'). Posix does + not require support for empty patterns, and Unicos 9 `sed' rejects + them. + + Unicos 9 `sed' loops endlessly on patterns like `.*\n.*'. + + Sed scripts should not use branch labels longer than 7 characters + and should not contain comments; AIX 5.3 `sed' rejects indented + comments. HP-UX sed has a limit of 99 commands (not counting `:' + commands) and 48 labels, which cannot be circumvented by using + more than one script file. It can execute up to 19 reads with the + `r' command per cycle. Solaris `/usr/ucb/sed' rejects usages that + exceed a limit of about 6000 bytes for the internal representation + of commands. + + Avoid redundant `;', as some `sed' implementations, such as NetBSD + 1.4.2's, incorrectly try to interpret the second `;' as a command: + + $ echo a | sed 's/x/x/;;s/x/x/' + sed: 1: "s/x/x/;;s/x/x/": invalid command code ; + + Some `sed' implementations have a buffer limited to 4000 bytes, + and this limits the size of input lines, output lines, and internal + buffers that can be processed portably. Likewise, not all `sed' + implementations can handle embedded `NUL' or a missing trailing + newline. + + Remember that ranges within a bracket expression of a regular + expression are only well-defined in the `C' (or `POSIX') locale. + Meanwhile, support for character classes like `[[:upper:]]' is not + yet universal, so if you cannot guarantee the setting of `LC_ALL', + it is better to spell out a range `[ABCDEFGHIJKLMNOPQRSTUVWXYZ]' + than to rely on `[A-Z]'. + + Additionally, Posix states that regular expressions are only + well-defined on characters. Unfortunately, there exist platforms + such as MacOS X 10.5 where not all 8-bit byte values are valid + characters, even though that platform has a single-byte `C' + locale. And Posix allows the existence of a multi-byte `C' + locale, although that does not yet appear to be a common + implementation. At any rate, it means that not all bytes will be + matched by the regular expression `.': + + $ printf '\200\n' | LC_ALL=C sed -n /./p | wc -l + 0 + $ printf '\200\n' | LC_ALL=en_US.ISO8859-1 sed -n /./p | wc -l + 1 + + Portable `sed' regular expressions should use `\' only to escape + characters in the string `$()*.0123456789[\^n{}'. For example, + alternation, `\|', is common but Posix does not require its + support, so it should be avoided in portable scripts. Solaris + `sed' does not support alternation; e.g., `sed '/a\|b/d'' deletes + only lines that contain the literal string `a|b'. Similarly, `\+' + and `\?' should be avoided. + + Anchors (`^' and `$') inside groups are not portable. + + Nested parentheses in patterns (e.g., `\(\(a*\)b*)\)') are quite + portable to current hosts, but was not supported by some ancient + `sed' implementations like SVR3. + + Some `sed' implementations, e.g., Solaris, restrict the special + role of the asterisk `*' to one-character regular expressions and + back-references, and the special role of interval expressions + `\{M\}', `\{M,\}', or `\{M,N\}' to one-character regular + expressions. This may lead to unexpected behavior: + + $ echo '1*23*4' | /usr/bin/sed 's/\(.\)*/x/g' + x2x4 + $ echo '1*23*4' | /usr/xpg4/bin/sed 's/\(.\)*/x/g' + x + + The `-e' option is mostly portable. However, its argument cannot + start with `a', `c', or `i', as this runs afoul of a Tru64 5.1 bug. + Also, its argument cannot be empty, as this fails on AIX 5.3. + Some people prefer to use `-e': + + sed -e 'COMMAND-1' \ + -e 'COMMAND-2' + + as opposed to the equivalent: + + sed ' + COMMAND-1 + COMMAND-2 + ' + + The following usage is sometimes equivalent: + + sed 'COMMAND-1;COMMAND-2' + + but Posix says that this use of a semicolon has undefined effect if + COMMAND-1's verb is `{', `a', `b', `c', `i', `r', `t', `w', `:', + or `#', so you should use semicolon only with simple scripts that + do not use these verbs. + + Posix up to the 2008 revision requires the argument of the `-e' + option to be a syntactically complete script. GNU `sed' allows to + pass multiple script fragments, each as argument of a separate + `-e' option, that are then combined, with newlines between the + fragments, and a future Posix revision may allow this as well. + This approach is not portable with script fragments ending in + backslash; for example, the `sed' programs on Solaris 10, HP-UX + 11, and AIX don't allow splitting in this case: + + $ echo a | sed -n -e 'i\ + 0' + 0 + $ echo a | sed -n -e 'i\' -e 0 + Unrecognized command: 0 + + In practice, however, this technique of joining fragments through + `-e' works for multiple `sed' functions within `{' and `}', even + if that is not specified by Posix: + + $ echo a | sed -n -e '/a/{' -e s/a/b/ -e p -e '}' + b + + Commands inside { } brackets are further restricted. Posix 2008 + says that they cannot be preceded by addresses, `!', or `;', and + that each command must be followed immediately by a newline, + without any intervening blanks or semicolons. The closing bracket + must be alone on a line, other than white space preceding or + following it. However, a future version of Posix may standardize + the use of addresses within brackets. + + Contrary to yet another urban legend, you may portably use `&' in + the replacement part of the `s' command to mean "what was + matched". All descendants of Unix version 7 `sed' (at least; we + don't have first hand experience with older `sed' implementations) + have supported it. + + Posix requires that you must not have any white space between `!' + and the following command. It is OK to have blanks between the + address and the `!'. For instance, on Solaris: + + $ echo "foo" | sed -n '/bar/ ! p' + error-->Unrecognized command: /bar/ ! p + $ echo "foo" | sed -n '/bar/! p' + error-->Unrecognized command: /bar/! p + $ echo "foo" | sed -n '/bar/ !p' + foo + + Posix also says that you should not combine `!' and `;'. If you + use `!', it is best to put it on a command that is delimited by + newlines rather than `;'. + + Also note that Posix requires that the `b', `t', `r', and `w' + commands be followed by exactly one space before their argument. + On the other hand, no white space is allowed between `:' and the + subsequent label name. + + If a sed script is specified on the command line and ends in an + `a', `c', or `i' command, the last line of inserted text should be + followed by a newline. Otherwise some `sed' implementations + (e.g., OpenBSD 3.9) do not append a newline to the inserted text. + + Many `sed' implementations (e.g., MacOS X 10.4, OpenBSD 3.9, + Solaris 10 `/usr/ucb/sed') strip leading white space from the text + of `a', `c', and `i' commands. Prepend a backslash to work around + this incompatibility with Posix: + + $ echo flushleft | sed 'a\ + > indented + > ' + flushleft + indented + $ echo foo | sed 'a\ + > \ indented + > ' + flushleft + indented + + Posix requires that with an empty regular expression, the last + non-empty regular expression from either an address specification + or substitution command is applied. However, busybox 1.6.1 + complains when using a substitution command with a replacement + containing a back-reference to an empty regular expression; the + workaround is repeating the regular expression. + + $ echo abc | busybox sed '/a\(b\)c/ s//\1/' + sed: No previous regexp. + $ echo abc | busybox sed '/a\(b\)c/ s/a\(b\)c/\1/' + b + +`sed' (`t') + Some old systems have `sed' that "forget" to reset their `t' flag + when starting a new cycle. For instance on MIPS RISC/OS, and on + IRIX 5.3, if you run the following `sed' script (the line numbers + are not actual part of the texts): + + s/keep me/kept/g # a + t end # b + s/.*/deleted/g # c + :end # d + + on + + delete me # 1 + delete me # 2 + keep me # 3 + delete me # 4 + + you get + + deleted + delete me + kept + deleted + + instead of + + deleted + deleted + kept + deleted + + Why? When processing line 1, (c) matches, therefore sets the `t' + flag, and the output is produced. When processing line 2, the `t' + flag is still set (this is the bug). Command (a) fails to match, + but `sed' is not supposed to clear the `t' flag when a + substitution fails. Command (b) sees that the flag is set, + therefore it clears it, and jumps to (d), hence you get `delete me' + instead of `deleted'. When processing line (3), `t' is clear, (a) + matches, so the flag is set, hence (b) clears the flags and jumps. + Finally, since the flag is clear, line 4 is processed properly. + + There are two things one should remember about `t' in `sed'. + Firstly, always remember that `t' jumps if _some_ substitution + succeeded, not only the immediately preceding substitution. + Therefore, always use a fake `t clear' followed by a `:clear' on + the next line, to reset the `t' flag where needed. + + Secondly, you cannot rely on `sed' to clear the flag at each new + cycle. + + One portable implementation of the script above is: + + t clear + :clear + s/keep me/kept/g + t end + s/.*/deleted/g + :end + +`sleep' + Using `sleep' is generally portable. However, remember that + adding a `sleep' to work around timestamp issues, with a minimum + granularity of one second, doesn't scale well for parallel builds + on modern machines with sub-second process completion. + +`sort' + Remember that sort order is influenced by the current locale. + Inside `configure', the C locale is in effect, but in Makefile + snippets, you may need to specify `LC_ALL=C sort'. + +`tar' + There are multiple file formats for `tar'; if you use Automake, + the macro `AM_INIT_AUTOMAKE' has some options controlling which + level of portability to use. + +`touch' + If you specify the desired timestamp (e.g., with the `-r' option), + older `touch' implementations use the `utime' or `utimes' system + call, which can result in the same kind of timestamp truncation + problems that `cp -p' has. + + On ancient BSD systems, `touch' or any command that results in an + empty file does not update the timestamps, so use a command like + `echo' as a workaround. Also, GNU `touch' 3.16r (and presumably + all before that) fails to work on SunOS 4.1.3 when the empty file + is on an NFS-mounted 4.2 volume. However, these problems are no + longer of practical concern. + +`tr' + Not all versions of `tr' handle all backslash character escapes. + For example, Solaris 10 `/usr/ucb/tr' falls over, even though + Solaris contains more modern `tr' in other locations. Using octal + escapes is more portable for carriage returns, since `\015' is the + same for both ASCII and EBCDIC, and since use of literal carriage + returns in scripts causes a number of other problems. But for + other characters, like newline, using octal escapes ties the + operation to ASCII, so it is better to use literal characters. + + $ { echo moon; echo light; } | /usr/ucb/tr -d '\n' ; echo + moo + light + $ { echo moon; echo light; } | /usr/bin/tr -d '\n' ; echo + moonlight + $ { echo moon; echo light; } | /usr/ucb/tr -d '\012' ; echo + moonlight + $ nl=' + '; { echo moon; echo light; } | /usr/ucb/tr -d "$nl" ; echo + moonlight + + Not all versions of `tr' recognize direct ranges of characters: at + least Solaris `/usr/bin/tr' still fails to do so. But you can use + `/usr/xpg4/bin/tr' instead, or add brackets (which in Posix + transliterate to themselves). + + $ echo "Hazy Fantazy" | LC_ALL=C /usr/bin/tr a-z A-Z + HAZy FAntAZy + $ echo "Hazy Fantazy" | LC_ALL=C /usr/bin/tr '[a-z]' '[A-Z]' + HAZY FANTAZY + $ echo "Hazy Fantazy" | LC_ALL=C /usr/xpg4/bin/tr a-z A-Z + HAZY FANTAZY + + When providing two arguments, be sure the second string is at + least as long as the first. + + $ echo abc | /usr/xpg4/bin/tr bc d + adc + $ echo abc | coreutils/tr bc d + add + + Posix requires `tr' to operate on binary files. But at least + Solaris `/usr/ucb/tr' and `/usr/bin/tr' silently discard `NUL' in + the input prior to doing any translation. When using `tr' to + process a binary file that may contain `NUL' bytes, it is + necessary to use `/usr/xpg4/bin/tr' instead, or `/usr/xpg6/bin/tr' + if that is available. + + $ printf 'a\0b' | /usr/ucb/tr x x | od -An -tx1 + 61 62 + $ printf 'a\0b' | /usr/bin/tr x x | od -An -tx1 + 61 62 + $ printf 'a\0b' | /usr/xpg4/bin/tr x x | od -An -tx1 + 61 00 62 + + Solaris `/usr/ucb/tr' additionally fails to handle `\0' as the + octal escape for `NUL'. + + $ printf 'abc' | /usr/ucb/tr 'bc' '\0d' | od -An -tx1 + 61 62 63 + $ printf 'abc' | /usr/bin/tr 'bc' '\0d' | od -An -tx1 + 61 00 64 + $ printf 'abc' | /usr/xpg4/bin/tr 'bc' '\0d' | od -An -tx1 + 61 00 64 + + + +File: autoconf.info, Node: Portable Make, Next: Portable C and C++, Prev: Portable Shell, Up: Top + +12 Portable Make Programming +**************************** + +Writing portable makefiles is an art. Since a makefile's commands are +executed by the shell, you must consider the shell portability issues +already mentioned. However, other issues are specific to `make' itself. + +* Menu: + +* $< in Ordinary Make Rules:: $< in ordinary rules +* Failure in Make Rules:: Failing portably in rules +* Special Chars in Names:: Special Characters in Macro Names +* Backslash-Newline-Empty:: Empty lines after backslash-newline +* Backslash-Newline Comments:: Spanning comments across line boundaries +* Long Lines in Makefiles:: Line length limitations +* Macros and Submakes:: `make macro=value' and submakes +* The Make Macro MAKEFLAGS:: `$(MAKEFLAGS)' portability issues +* The Make Macro SHELL:: `$(SHELL)' portability issues +* Parallel Make:: Parallel `make' quirks +* Comments in Make Rules:: Other problems with Make comments +* Newlines in Make Rules:: Using literal newlines in rules +* Comments in Make Macros:: Other problems with Make comments in macros +* Trailing whitespace in Make Macros:: Macro substitution problems +* Command-line Macros and whitespace:: Whitespace trimming of values +* obj/ and Make:: Don't name a subdirectory `obj' +* make -k Status:: Exit status of `make -k' +* VPATH and Make:: `VPATH' woes +* Single Suffix Rules:: Single suffix rules and separated dependencies +* Timestamps and Make:: Subsecond timestamp resolution + + +File: autoconf.info, Node: $< in Ordinary Make Rules, Next: Failure in Make Rules, Up: Portable Make + +12.1 `$<' in Ordinary Make Rules +================================ + +Posix says that the `$<' construct in makefiles can be used only in +inference rules and in the `.DEFAULT' rule; its meaning in ordinary +rules is unspecified. Solaris `make' for instance replaces it with the +empty string. OpenBSD (3.0 and later) `make' diagnoses these uses and +errors out. + + +File: autoconf.info, Node: Failure in Make Rules, Next: Special Chars in Names, Prev: $< in Ordinary Make Rules, Up: Portable Make + +12.2 Failure in Make Rules +========================== + +Posix 2008 requires that `make' must invoke each command with the +equivalent of a `sh -e -c' subshell, which causes the subshell to exit +immediately if a subsidiary simple-command fails, although not all +`make' implementations have historically followed this rule. For +example, the command `touch T; rm -f U' may attempt to remove `U' even +if the `touch' fails, although this is not permitted with Posix make. +One way to work around failures in simple commands is to reword them so +that they always succeed, e.g., `touch T || :; rm -f U'. However, even +this approach can run into common bugs in BSD implementations of the +`-e' option of `sh' and `set' (*note Limitations of Shell Builtins: +set.), so if you are worried about porting to buggy BSD shells it may +be simpler to migrate complicated `make' actions into separate scripts. + + +File: autoconf.info, Node: Special Chars in Names, Next: Backslash-Newline-Empty, Prev: Failure in Make Rules, Up: Portable Make + +12.3 Special Characters in Make Macro Names +=========================================== + +Posix limits macro names to nonempty strings containing only ASCII +letters and digits, `.', and `_'. Many `make' implementations allow a +wider variety of characters, but portable makefiles should avoid them. +It is portable to start a name with a special character, e.g., +`$(.FOO)'. + + Some ancient `make' implementations don't support leading +underscores in macro names. An example is NEWS-OS 4.2R. + + $ cat Makefile + _am_include = # + _am_quote = + all:; @echo this is test + $ make + Make: Must be a separator on rules line 2. Stop. + $ cat Makefile2 + am_include = # + am_quote = + all:; @echo this is test + $ make -f Makefile2 + this is test + +However, this problem is no longer of practical concern. + + +File: autoconf.info, Node: Backslash-Newline-Empty, Next: Backslash-Newline Comments, Prev: Special Chars in Names, Up: Portable Make + +12.4 Backslash-Newline Before Empty Lines +========================================= + +A bug in Bash 2.03 can cause problems if a Make rule contains a +backslash-newline followed by line that expands to nothing. For +example, on Solaris 8: + + SHELL = /bin/bash + EMPTY = + foo: + touch foo \ + $(EMPTY) + +executes + + /bin/bash -c 'touch foo \ + ' + +which fails with a syntax error, due to the Bash bug. To avoid this +problem, avoid nullable macros in the last line of a multiline command. + + On some versions of HP-UX, `make' reads multiple newlines following +a backslash, continuing to the next non-empty line. For example, + + FOO = one \ + + BAR = two + + test: + : FOO is "$(FOO)" + : BAR is "$(BAR)" + +shows `FOO' equal to `one BAR = two'. Other implementations sensibly +let a backslash continue only to the immediately following line. + + +File: autoconf.info, Node: Backslash-Newline Comments, Next: Long Lines in Makefiles, Prev: Backslash-Newline-Empty, Up: Portable Make + +12.5 Backslash-Newline in Make Comments +======================================= + +According to Posix, Make comments start with `#' and continue until an +unescaped newline is reached. + + $ cat Makefile + # A = foo \ + bar \ + baz + + all: + @echo ok + $ make # GNU make + ok + +However this is not always the case. Some implementations discard +everything from `#' through the end of the line, ignoring any trailing +backslash. + + $ pmake # BSD make + "Makefile", line 3: Need an operator + Fatal errors encountered -- cannot continue + +Therefore, if you want to comment out a multi-line definition, prefix +each line with `#', not only the first. + + # A = foo \ + # bar \ + # baz + + +File: autoconf.info, Node: Long Lines in Makefiles, Next: Macros and Submakes, Prev: Backslash-Newline Comments, Up: Portable Make + +12.6 Long Lines in Makefiles +============================ + +Tru64 5.1's `make' has been reported to crash when given a makefile +with lines longer than around 20 kB. Earlier versions are reported to +exit with `Line too long' diagnostics. + + +File: autoconf.info, Node: Macros and Submakes, Next: The Make Macro MAKEFLAGS, Prev: Long Lines in Makefiles, Up: Portable Make + +12.7 `make macro=value' and Submakes +==================================== + +A command-line variable definition such as `foo=bar' overrides any +definition of `foo' in a makefile. Some `make' implementations (such +as GNU `make') propagate this override to subsidiary invocations of +`make'. Some other implementations do not pass the substitution along +to submakes. + + $ cat Makefile + foo = foo + one: + @echo $(foo) + $(MAKE) two + two: + @echo $(foo) + $ make foo=bar # GNU make 3.79.1 + bar + make two + make[1]: Entering directory `/home/adl' + bar + make[1]: Leaving directory `/home/adl' + $ pmake foo=bar # BSD make + bar + pmake two + foo + + You have a few possibilities if you do want the `foo=bar' override +to propagate to submakes. One is to use the `-e' option, which causes +all environment variables to have precedence over the makefile macro +definitions, and declare foo as an environment variable: + + $ env foo=bar make -e + + The `-e' option is propagated to submakes automatically, and since +the environment is inherited between `make' invocations, the `foo' +macro is overridden in submakes as expected. + + This syntax (`foo=bar make -e') is portable only when used outside +of a makefile, for instance from a script or from the command line. +When run inside a `make' rule, GNU `make' 3.80 and prior versions +forget to propagate the `-e' option to submakes. + + Moreover, using `-e' could have unexpected side effects if your +environment contains some other macros usually defined by the makefile. +(See also the note about `make -e' and `SHELL' below.) + + If you can foresee all macros that a user might want to override, +then you can propagate them to submakes manually, from your makefile: + + foo = foo + one: + @echo $(foo) + $(MAKE) foo=$(foo) two + two: + @echo $(foo) + + Another way to propagate a variable to submakes in a portable way is +to expand an extra variable in every invocation of `$(MAKE)' within +your makefile: + + foo = foo + one: + @echo $(foo) + $(MAKE) $(SUBMAKEFLAGS) two + two: + @echo $(foo) + + Users must be aware that this technique is in use to take advantage +of it, e.g. with `make foo=bar SUBMAKEFLAGS='foo=bar'', but it allows +any macro to be overridden. Makefiles generated by `automake' use this +technique, expanding `$(AM_MAKEFLAGS)' on the command lines of submakes +(*note Automake: (automake)Subdirectories.). + + +File: autoconf.info, Node: The Make Macro MAKEFLAGS, Next: The Make Macro SHELL, Prev: Macros and Submakes, Up: Portable Make + +12.8 The Make Macro MAKEFLAGS +============================= + +Posix requires `make' to use `MAKEFLAGS' to affect the current and +recursive invocations of make, but allows implementations several +formats for the variable. It is tricky to parse `$MAKEFLAGS' to +determine whether `-s' for silent execution or `-k' for continued +execution are in effect. For example, you cannot assume that the first +space-separated word in `$MAKEFLAGS' contains single-letter options, +since in the Cygwin version of GNU `make' it is either `--unix' or +`--win32' with the second word containing single-letter options. + + $ cat Makefile + all: + @echo MAKEFLAGS = $(MAKEFLAGS) + $ make + MAKEFLAGS = --unix + $ make -k + MAKEFLAGS = --unix -k + + +File: autoconf.info, Node: The Make Macro SHELL, Next: Parallel Make, Prev: The Make Macro MAKEFLAGS, Up: Portable Make + +12.9 The Make Macro `SHELL' +=========================== + +Posix-compliant `make' internally uses the `$(SHELL)' macro to spawn +shell processes and execute Make rules. This is a builtin macro +supplied by `make', but it can be modified by a makefile or by a +command-line argument. + + Not all `make' implementations define this `SHELL' macro. Tru64 +`make' is an example; this implementation always uses `/bin/sh'. So +it's a good idea to always define `SHELL' in your makefiles. If you +use Autoconf, do + + SHELL = @SHELL@ + +If you use Automake, this is done for you. + + Do not force `SHELL = /bin/sh' because that is not correct +everywhere. Remember, `/bin/sh' is not Posix compliant on many +systems, such as FreeBSD 4, NetBSD 3, AIX 3, Solaris 10, or Tru64. +Additionally, DJGPP lacks `/bin/sh', and when its GNU `make' port sees +such a setting it enters a special emulation mode where features like +pipes and redirections are emulated on top of DOS's `command.com'. +Unfortunately this emulation is incomplete; for instance it does not +handle command substitutions. Using `@SHELL@' means that your makefile +will benefit from the same improved shell, such as `bash' or `ksh', +that was discovered during `configure', so that you aren't fighting two +different sets of shell bugs between the two contexts. + + Posix-compliant `make' should never acquire the value of $(SHELL) +from the environment, even when `make -e' is used (otherwise, think +about what would happen to your rules if `SHELL=/bin/tcsh'). + + However not all `make' implementations have this exception. For +instance it's not surprising that Tru64 `make' doesn't protect `SHELL', +since it doesn't use it. + + $ cat Makefile + SHELL = /bin/sh + FOO = foo + all: + @echo $(SHELL) + @echo $(FOO) + $ env SHELL=/bin/tcsh FOO=bar make -e # Tru64 Make + /bin/tcsh + bar + $ env SHELL=/bin/tcsh FOO=bar gmake -e # GNU make + /bin/sh + bar + + Conversely, `make' is not supposed to export any changes to the +macro `SHELL' to child processes. Again, many implementations break +this rule: + + $ cat Makefile + all: + @echo $(SHELL) + @printenv SHELL + $ env SHELL=sh make -e SHELL=/bin/ksh # BSD Make, GNU make 3.80 + /bin/ksh + /bin/ksh + $ env SHELL=sh gmake -e SHELL=/bin/ksh # GNU make 3.81 + /bin/ksh + sh + + +File: autoconf.info, Node: Parallel Make, Next: Comments in Make Rules, Prev: The Make Macro SHELL, Up: Portable Make + +12.10 Parallel Make +=================== + +Support for parallel execution in `make' implementation varies. +Generally, using GNU make is your best bet. + + When NetBSD or FreeBSD `make' are run in parallel mode, they will +reuse the same shell for multiple commands within one recipe. This can +have various unexpected consequences. For example, changes of +directories or variables persist between recipes, so that: + + all: + @var=value; cd /; pwd; echo $$var; echo $$$$ + @pwd; echo $$var; echo $$$$ + +may output the following with `make -j1', at least on NetBSD up to 5.1 +and FreeBSD up to 8.2: + + / + value + 32235 + / + value + 32235 + +while without `-j1', or with `-B', the output looks less surprising: + + / + value + 32238 + /tmp + + 32239 + +Another consequence is that, if one command in a recipe uses `exit 0' +to indicate a successful exit, the shell will be gone and the remaining +commands of this recipe will not be executed. + + The BSD `make' implementations, when run in parallel mode, will also +pass the `Makefile' recipes to the shell through its standard input, +thus making it unusable from the recipes: + + $ cat Makefile + read: + @read line; echo LINE: $$line + $ echo foo | make read + LINE: foo + $ echo foo | make -j1 read # NetBSD 5.1 and FreeBSD 8.2 + LINE: + +Moreover, when FreeBSD `make' (up at least to 8.2) is run in parallel +mode, it implements the `@' and `-' "recipe modifiers" by dynamically +modifying the active shell flags. This behavior has the effects of +potentially clobbering the exit status of recipes silenced with the `@' +modifier if they also unset the `errexit' shell flag, and of mangling +the output in unexpected ways: + + $ cat Makefile + a: + @echo $$-; set +e; false + b: + -echo $$-; false; echo set - + $ make a; echo status: $? + ehBc + *** Error code 1 + status: 1 + $ make -j1 a; echo status: $? + ehB + status: 0 + $ make b + echo $-; echo set - + hBc + set - + $ make -j1 b + echo $-; echo hvB + +You can avoid all these issues by using the `-B' option to enable +compatibility semantics. However, that will effectively also disable +all parallelism as that will cause prerequisites to be updated in the +order they are listed in a rule. + + Some make implementations (among them, FreeBSD `make', NetBSD +`make', and Solaris `dmake'), when invoked with a `-jN' option, connect +the standard output and standard error of all their child processes to +pipes or temporary regular files. This can lead to subtly different +semantics in the behavior of the spawned processes. For example, even +if the `make' standard output is connected to a tty, the recipe command +will not be: + + $ cat Makefile + all: + @test -t 1 && echo "Is a tty" || echo "Is not a tty" + $ make -j 2 # FreeBSD 8.2 make + Is not a tty + $ make -j 2 # NetBSD 5.1 make + --- all --- + Is not a tty + $ dmake -j 2 # Solaris 10 dmake + HOSTNAME --> 1 job + HOSTNAME --> Job output + Is not a tty + +On the other hand: + + $ make -j 2 # GNU make, Heirloom make + Is a tty + +The above examples also show additional status output produced in +parallel mode for targets being updated by Solaris `dmake' and NetBSD +`make' (but _not_ by FreeBSD `make'). + + Furthermore, parallel runs of those `make' implementations will +route standard error from commands that they spawn into their own +standard output, and may remove leading whitespace from output lines. + + +File: autoconf.info, Node: Comments in Make Rules, Next: Newlines in Make Rules, Prev: Parallel Make, Up: Portable Make + +12.11 Comments in Make Rules +============================ + +Never put comments in a rule. + + Some `make' treat anything starting with a tab as a command for the +current rule, even if the tab is immediately followed by a `#'. The +`make' from Tru64 Unix V5.1 is one of them. The following makefile +runs `# foo' through the shell. + + all: + # foo + + As a workaround, you can use the `:' no-op command with a string +argument that gets ignored: + + all: + : "foo" + + Conversely, if you want to use the `#' character in some command, +you can only do so by expanding it inside a rule (*note Comments in +Make Macros::). So for example, if `COMMENT_CHAR' is substituted by +`config.status' as `#', then the following substitutes `@COMMENT_CHAR@' +in a generated header: + + foo.h: foo.h.in + sed -e 's|@''COMMENT_CHAR''@|@COMMENT_CHAR@|g' \ + $(srcdir)/foo.h.in > $@ + + The funny shell quoting avoids a substitution at `config.status' run +time of the left-hand side of the `sed' `s' command. + + +File: autoconf.info, Node: Newlines in Make Rules, Next: Comments in Make Macros, Prev: Comments in Make Rules, Up: Portable Make + +12.12 Newlines in Make Rules +============================ + +In shell scripts, newlines can be used inside string literals. But in +the shell statements of `Makefile' rules, this is not possible: A +newline not preceded by a backslash is a separator between shell +statements. Whereas a newline that is preceded by a backslash becomes +part of the shell statement according to POSIX, but gets replaced, +together with the backslash that precedes it, by a space in GNU `make' +3.80 and older. So, how can a newline be used in a string literal? + + The trick is to set up a shell variable that contains a newline: + + nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit" + + For example, in order to create a multiline `sed' expression that +inserts a blank line after every line of a file, this code can be used: + + nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \ + sed -e "s/\$$/\\$${nl}/" < input > output + + +File: autoconf.info, Node: Comments in Make Macros, Next: Trailing whitespace in Make Macros, Prev: Newlines in Make Rules, Up: Portable Make + +12.13 Comments in Make Macros +============================= + +Avoid putting comments in macro values as far as possible. Posix +specifies that the text starting from the `#' sign until the end of the +line is to be ignored, which has the unfortunate effect of disallowing +them even within quotes. Thus, the following might lead to a syntax +error at compile time: + + CPPFLAGS = "-DCOMMENT_CHAR='#'" + +as `CPPFLAGS' may be expanded to `"-DCOMMENT_CHAR=''. + + Most `make' implementations disregard this and treat single and +double quotes specially here. Also, GNU `make' lets you put `#' into a +macro value by escaping it with a backslash, i.e., `\#'. However, +neither of these usages are portable. *Note Comments in Make Rules::, +for a portable alternative. + + Even without quoting involved, comments can have surprising effects, +because the whitespace before them is part of the variable value: + + foo = bar # trailing comment + print: ; @echo "$(foo)." + +prints `bar .', which is usually not intended, and can expose `make' +bugs as described below. + + +File: autoconf.info, Node: Trailing whitespace in Make Macros, Next: Command-line Macros and whitespace, Prev: Comments in Make Macros, Up: Portable Make + +12.14 Trailing whitespace in Make Macros +======================================== + +GNU `make' 3.80 mistreats trailing whitespace in macro substitutions +and appends another spurious suffix: + + empty = + foo = bar $(empty) + print: ; @echo $(foo:=.test) + +prints `bar.test .test'. + + BSD and Solaris `make' implementations do not honor trailing +whitespace in macro definitions as Posix requires: + + foo = bar # Note the space after "bar". + print: ; @echo $(foo)t + +prints `bart' instead of `bar t'. To work around this, you can use a +helper macro as in the previous example. + + +File: autoconf.info, Node: Command-line Macros and whitespace, Next: obj/ and Make, Prev: Trailing whitespace in Make Macros, Up: Portable Make + +12.15 Command-line Macros and whitespace +======================================== + +Some `make' implementations may strip trailing whitespace off of macros +set on the command line in addition to leading whitespace. Further, +some may strip leading whitespace off of macros set from environment +variables: + + $ echo 'print: ; @echo "x$(foo)x$(bar)x"' | + foo=' f f ' make -f - bar=' b b ' + x f f xb b x # AIX, BSD, GNU make + xf f xb b x # HP-UX, IRIX, Tru64/OSF make + x f f xb bx # Solaris make + + +File: autoconf.info, Node: obj/ and Make, Next: make -k Status, Prev: Command-line Macros and whitespace, Up: Portable Make + +12.16 The `obj/' Subdirectory and Make +====================================== + +Never name one of your subdirectories `obj/' if you don't like +surprises. + + If an `obj/' directory exists, BSD `make' enters it before reading +the makefile. Hence the makefile in the current directory is not read. + + $ cat Makefile + all: + echo Hello + $ cat obj/Makefile + all: + echo World + $ make # GNU make + echo Hello + Hello + $ pmake # BSD make + echo World + World + + +File: autoconf.info, Node: make -k Status, Next: VPATH and Make, Prev: obj/ and Make, Up: Portable Make + +12.17 Exit Status of `make -k' +============================== + +Do not rely on the exit status of `make -k'. Some implementations +reflect whether they encountered an error in their exit status; other +implementations always succeed. + + $ cat Makefile + all: + false + $ make -k; echo exit status: $? # GNU make + false + make: *** [all] Error 1 + exit status: 2 + $ pmake -k; echo exit status: $? # BSD make + false + *** Error code 1 (continuing) + exit status: 0 + + +File: autoconf.info, Node: VPATH and Make, Next: Single Suffix Rules, Prev: make -k Status, Up: Portable Make + +12.18 `VPATH' and Make +====================== + +Posix does not specify the semantics of `VPATH'. Typically, `make' +supports `VPATH', but its implementation is not consistent. + + Autoconf and Automake support makefiles whose usages of `VPATH' are +portable to recent-enough popular implementations of `make', but to +keep the resulting makefiles portable, a package's makefile prototypes +must take the following issues into account. These issues are +complicated and are often poorly understood, and installers who use +`VPATH' should expect to find many bugs in this area. If you use +`VPATH', the simplest way to avoid these portability bugs is to stick +with GNU `make', since it is the most commonly-used `make' among +Autoconf users. + + Here are some known issues with some `VPATH' implementations. + +* Menu: + +* Variables listed in VPATH:: `VPATH' must be literal on ancient hosts +* VPATH and Double-colon:: Problems with `::' on ancient hosts +* $< in Explicit Rules:: `$<' does not work in ordinary rules +* Automatic Rule Rewriting:: `VPATH' goes wild on Solaris +* Tru64 Directory Magic:: `mkdir' goes wild on Tru64 +* Make Target Lookup:: More details about `VPATH' lookup + + +File: autoconf.info, Node: Variables listed in VPATH, Next: VPATH and Double-colon, Up: VPATH and Make + +12.18.1 Variables listed in `VPATH' +----------------------------------- + +Do not set `VPATH' to the value of another variable, for example `VPATH += $(srcdir)', because some ancient versions of `make' do not do +variable substitutions on the value of `VPATH'. For example, use this + + srcdir = @srcdir@ + VPATH = @srcdir@ + +rather than `VPATH = $(srcdir)'. Note that with GNU Automake, there is +no need to set this yourself. + + +File: autoconf.info, Node: VPATH and Double-colon, Next: $< in Explicit Rules, Prev: Variables listed in VPATH, Up: VPATH and Make + +12.18.2 `VPATH' and Double-colon Rules +-------------------------------------- + +With ancient versions of Sun `make', any assignment to `VPATH' causes +`make' to execute only the first set of double-colon rules. However, +this problem is no longer of practical concern. + + +File: autoconf.info, Node: $< in Explicit Rules, Next: Automatic Rule Rewriting, Prev: VPATH and Double-colon, Up: VPATH and Make + +12.18.3 `$<' Not Supported in Explicit Rules +-------------------------------------------- + +Using `$<' in explicit rules is not portable. The prerequisite file +must be named explicitly in the rule. If you want to find the +prerequisite via a `VPATH' search, you have to code the whole thing +manually. *Note Build Directories::. + + +File: autoconf.info, Node: Automatic Rule Rewriting, Next: Tru64 Directory Magic, Prev: $< in Explicit Rules, Up: VPATH and Make + +12.18.4 Automatic Rule Rewriting +-------------------------------- + +Some `make' implementations, such as Solaris and Tru64, search for +prerequisites in `VPATH' and then rewrite each occurrence as a plain +word in the rule. For instance: + + # This isn't portable to GNU make. + VPATH = ../pkg/src + f.c: if.c + cp if.c f.c + +executes `cp ../pkg/src/if.c f.c' if `if.c' is found in `../pkg/src'. + + However, this rule leads to real problems in practice. For example, +if the source directory contains an ordinary file named `test' that is +used in a dependency, Solaris `make' rewrites commands like `if test -r +foo; ...' to `if ../pkg/src/test -r foo; ...', which is typically +undesirable. In fact, `make' is completely unaware of shell syntax +used in the rules, so the VPATH rewrite can potentially apply to _any_ +whitespace-separated word in a rule, including shell variables, +functions, and keywords. + + $ mkdir build + $ cd build + $ cat > Makefile <<'END' + VPATH = .. + all: arg func for echo + func () { for arg in "$$@"; do echo $$arg; done; }; \ + func "hello world" + END + $ touch ../arg ../func ../for ../echo + $ make + ../func () { ../for ../arg in "$@"; do ../echo $arg; done; }; \ + ../func "hello world" + sh: syntax error at line 1: `do' unexpected + *** Error code 2 + +To avoid this problem, portable makefiles should never mention a source +file or dependency whose name is that of a shell keyword like `for' or +`until', a shell command like `cat' or `gcc' or `test', or a shell +function or variable used in the corresponding `Makefile' recipe. + + Because of these problems GNU `make' and many other `make' +implementations do not rewrite commands, so portable makefiles should +search `VPATH' manually. It is tempting to write this: + + # This isn't portable to Solaris make. + VPATH = ../pkg/src + f.c: if.c + cp `test -f if.c || echo $(VPATH)/`if.c f.c + +However, the "prerequisite rewriting" still applies here. So if `if.c' +is in `../pkg/src', Solaris and Tru64 `make' execute + + cp `test -f ../pkg/src/if.c || echo ../pkg/src/`if.c f.c + +which reduces to + + cp if.c f.c + +and thus fails. Oops. + + A simple workaround, and good practice anyway, is to use `$?' and +`$@' when possible: + + VPATH = ../pkg/src + f.c: if.c + cp $? $@ + +but this does not generalize well to commands with multiple +prerequisites. A more general workaround is to rewrite the rule so that +the prerequisite `if.c' never appears as a plain word. For example, +these three rules would be safe, assuming `if.c' is in `../pkg/src' and +the other files are in the working directory: + + VPATH = ../pkg/src + f.c: if.c f1.c + cat `test -f ./if.c || echo $(VPATH)/`if.c f1.c >$@ + g.c: if.c g1.c + cat `test -f 'if.c' || echo $(VPATH)/`if.c g1.c >$@ + h.c: if.c h1.c + cat `test -f "if.c" || echo $(VPATH)/`if.c h1.c >$@ + + Things get worse when your prerequisites are in a macro. + + VPATH = ../pkg/src + HEADERS = f.h g.h h.h + install-HEADERS: $(HEADERS) + for i in $(HEADERS); do \ + $(INSTALL) -m 644 \ + `test -f $$i || echo $(VPATH)/`$$i \ + $(DESTDIR)$(includedir)/$$i; \ + done + + The above `install-HEADERS' rule is not Solaris-proof because `for i +in $(HEADERS);' is expanded to `for i in f.h g.h h.h;' where `f.h' and +`g.h' are plain words and are hence subject to `VPATH' adjustments. + + If the three files are in `../pkg/src', the rule is run as: + + for i in ../pkg/src/f.h ../pkg/src/g.h h.h; do \ + install -m 644 \ + `test -f $i || echo ../pkg/src/`$i \ + /usr/local/include/$i; \ + done + + where the two first `install' calls fail. For instance, consider +the `f.h' installation: + + install -m 644 \ + `test -f ../pkg/src/f.h || \ + echo ../pkg/src/ \ + `../pkg/src/f.h \ + /usr/local/include/../pkg/src/f.h; + +It reduces to: + + install -m 644 \ + ../pkg/src/f.h \ + /usr/local/include/../pkg/src/f.h; + + Note that the manual `VPATH' search did not cause any problems here; +however this command installs `f.h' in an incorrect directory. + + Trying to quote `$(HEADERS)' in some way, as we did for `foo.c' a +few makefiles ago, does not help: + + install-HEADERS: $(HEADERS) + headers='$(HEADERS)'; \ + for i in $$headers; do \ + $(INSTALL) -m 644 \ + `test -f $$i || echo $(VPATH)/`$$i \ + $(DESTDIR)$(includedir)/$$i; \ + done + + Now, `headers='$(HEADERS)'' macro-expands to: + + headers='f.h g.h h.h' + +but `g.h' is still a plain word. (As an aside, the idiom +`headers='$(HEADERS)'; for i in $$headers;' is a good idea if +`$(HEADERS)' can be empty, because some shells diagnose a syntax error +on `for i in;'.) + + One workaround is to strip this unwanted `../pkg/src/' prefix +manually: + + VPATH = ../pkg/src + HEADERS = f.h g.h h.h + install-HEADERS: $(HEADERS) + headers='$(HEADERS)'; \ + for i in $$headers; do \ + i=`expr "$$i" : '$(VPATH)/\(.*\)'`; + $(INSTALL) -m 644 \ + `test -f $$i || echo $(VPATH)/`$$i \ + $(DESTDIR)$(includedir)/$$i; \ + done + + Automake does something similar. However the above hack works only +if the files listed in `HEADERS' are in the current directory or a +subdirectory; they should not be in an enclosing directory. If we had +`HEADERS = ../f.h', the above fragment would fail in a VPATH build with +Tru64 `make'. The reason is that not only does Tru64 `make' rewrite +dependencies, but it also simplifies them. Hence `../f.h' becomes +`../pkg/f.h' instead of `../pkg/src/../f.h'. This obviously defeats +any attempt to strip a leading `../pkg/src/' component. + + The following example makes the behavior of Tru64 `make' more +apparent. + + $ cat Makefile + VPATH = sub + all: ../foo + echo ../foo + $ ls + Makefile foo + $ make + echo foo + foo + +Dependency `../foo' was found in `sub/../foo', but Tru64 `make' +simplified it as `foo'. (Note that the `sub/' directory does not even +exist, this just means that the simplification occurred before the file +was checked for.) + + For the record here is how SunOS 4 `make' behaves on this example. + + $ make + make: Fatal error: Don't know how to make target `../foo' + $ mkdir sub + $ make + echo sub/../foo + sub/../foo + + +File: autoconf.info, Node: Tru64 Directory Magic, Next: Make Target Lookup, Prev: Automatic Rule Rewriting, Up: VPATH and Make + +12.18.5 Tru64 `make' Creates Prerequisite Directories Magically +--------------------------------------------------------------- + +When a prerequisite is a subdirectory of `VPATH', Tru64 `make' creates +it in the current directory. + + $ mkdir -p foo/bar build + $ cd build + $ cat >Makefile <<END + VPATH = .. + all: foo/bar + END + $ make + mkdir foo + mkdir foo/bar + + This can yield unexpected results if a rule uses a manual `VPATH' +search as presented before. + + VPATH = .. + all : foo/bar + command `test -d foo/bar || echo ../`foo/bar + + The above `command' is run on the empty `foo/bar' directory that was +created in the current directory. + + +File: autoconf.info, Node: Make Target Lookup, Prev: Tru64 Directory Magic, Up: VPATH and Make + +12.18.6 Make Target Lookup +-------------------------- + +GNU `make' uses a complex algorithm to decide when it should use files +found via a `VPATH' search. *Note How Directory Searches are +Performed: (make)Search Algorithm. + + If a target needs to be rebuilt, GNU `make' discards the file name +found during the `VPATH' search for this target, and builds the file +locally using the file name given in the makefile. If a target does +not need to be rebuilt, GNU `make' uses the file name found during the +`VPATH' search. + + Other `make' implementations, like NetBSD `make', are easier to +describe: the file name found during the `VPATH' search is used whether +the target needs to be rebuilt or not. Therefore new files are created +locally, but existing files are updated at their `VPATH' location. + + OpenBSD and FreeBSD `make', however, never perform a `VPATH' search +for a dependency that has an explicit rule. This is extremely annoying. + + When attempting a `VPATH' build for an autoconfiscated package +(e.g., `mkdir build && cd build && ../configure'), this means GNU +`make' builds everything locally in the `build' directory, while BSD +`make' builds new files locally and updates existing files in the +source directory. + + $ cat Makefile + VPATH = .. + all: foo.x bar.x + foo.x bar.x: newer.x + @echo Building $@ + $ touch ../bar.x + $ touch ../newer.x + $ make # GNU make + Building foo.x + Building bar.x + $ pmake # NetBSD make + Building foo.x + Building ../bar.x + $ fmake # FreeBSD make, OpenBSD make + Building foo.x + Building bar.x + $ tmake # Tru64 make + Building foo.x + Building bar.x + $ touch ../bar.x + $ make # GNU make + Building foo.x + $ pmake # NetBSD make + Building foo.x + $ fmake # FreeBSD make, OpenBSD make + Building foo.x + Building bar.x + $ tmake # Tru64 make + Building foo.x + Building bar.x + + Note how NetBSD `make' updates `../bar.x' in its VPATH location, and +how FreeBSD, OpenBSD, and Tru64 `make' always update `bar.x', even when +`../bar.x' is up to date. + + Another point worth mentioning is that once GNU `make' has decided +to ignore a `VPATH' file name (e.g., it ignored `../bar.x' in the above +example) it continues to ignore it when the target occurs as a +prerequisite of another rule. + + The following example shows that GNU `make' does not look up `bar.x' +in `VPATH' before performing the `.x.y' rule, because it ignored the +`VPATH' result of `bar.x' while running the `bar.x: newer.x' rule. + + $ cat Makefile + VPATH = .. + all: bar.y + bar.x: newer.x + @echo Building $@ + .SUFFIXES: .x .y + .x.y: + cp $< $@ + $ touch ../bar.x + $ touch ../newer.x + $ make # GNU make + Building bar.x + cp bar.x bar.y + cp: cannot stat `bar.x': No such file or directory + make: *** [bar.y] Error 1 + $ pmake # NetBSD make + Building ../bar.x + cp ../bar.x bar.y + $ rm bar.y + $ fmake # FreeBSD make, OpenBSD make + echo Building bar.x + cp bar.x bar.y + cp: cannot stat `bar.x': No such file or directory + *** Error code 1 + $ tmake # Tru64 make + Building bar.x + cp: bar.x: No such file or directory + *** Exit 1 + + Note that if you drop away the command from the `bar.x: newer.x' +rule, GNU `make' magically starts to work: it knows that `bar.x' hasn't +been updated, therefore it doesn't discard the result from `VPATH' +(`../bar.x') in succeeding uses. Tru64 also works, but FreeBSD and +OpenBSD still don't. + + $ cat Makefile + VPATH = .. + all: bar.y + bar.x: newer.x + .SUFFIXES: .x .y + .x.y: + cp $< $@ + $ touch ../bar.x + $ touch ../newer.x + $ make # GNU make + cp ../bar.x bar.y + $ rm bar.y + $ pmake # NetBSD make + cp ../bar.x bar.y + $ rm bar.y + $ fmake # FreeBSD make, OpenBSD make + cp bar.x bar.y + cp: cannot stat `bar.x': No such file or directory + *** Error code 1 + $ tmake # Tru64 make + cp ../bar.x bar.y + + It seems the sole solution that would please every `make' +implementation is to never rely on `VPATH' searches for targets. In +other words, `VPATH' should be reserved to unbuilt sources. + + +File: autoconf.info, Node: Single Suffix Rules, Next: Timestamps and Make, Prev: VPATH and Make, Up: Portable Make + +12.19 Single Suffix Rules and Separated Dependencies +==================================================== + +A "Single Suffix Rule" is basically a usual suffix (inference) rule +(`.from.to:'), but which _destination_ suffix is empty (`.from:'). + + "Separated dependencies" simply refers to listing the prerequisite +of a target, without defining a rule. Usually one can list on the one +hand side, the rules, and on the other hand side, the dependencies. + + Solaris `make' does not support separated dependencies for targets +defined by single suffix rules: + + $ cat Makefile + .SUFFIXES: .in + foo: foo.in + .in: + cp $< $@ + $ touch foo.in + $ make + $ ls + Makefile foo.in + +while GNU Make does: + + $ gmake + cp foo.in foo + $ ls + Makefile foo foo.in + + Note it works without the `foo: foo.in' dependency. + + $ cat Makefile + .SUFFIXES: .in + .in: + cp $< $@ + $ make foo + cp foo.in foo + +and it works with double suffix inference rules: + + $ cat Makefile + foo.out: foo.in + .SUFFIXES: .in .out + .in.out: + cp $< $@ + $ make + cp foo.in foo.out + + As a result, in such a case, you have to write target rules. + + +File: autoconf.info, Node: Timestamps and Make, Prev: Single Suffix Rules, Up: Portable Make + +12.20 Timestamp Resolution and Make +=================================== + +Traditionally, file timestamps had 1-second resolution, and `make' used +those timestamps to determine whether one file was newer than the +other. However, many modern file systems have timestamps with +1-nanosecond resolution. Some `make' implementations look at the +entire timestamp; others ignore the fractional part, which can lead to +incorrect results. Normally this is not a problem, but in some extreme +cases you may need to use tricks like `sleep 1' to work around +timestamp truncation bugs. + + Commands like `cp -p' and `touch -r' typically do not copy file +timestamps to their full resolutions (*note Limitations of Usual Tools: +touch.). Hence you should be wary of rules like this: + + dest: src + cp -p src dest + + as `dest' often appears to be older than `src' after the timestamp +is truncated, and this can cause `make' to do needless rework the next +time it is invoked. To work around this problem, you can use a +timestamp file, e.g.: + + dest-stamp: src + cp -p src dest + date >dest-stamp + + Apart from timestamp resolution, there are also differences in +handling equal timestamps. HP-UX `make' updates targets if it has the +same time stamp as one of its prerequisites, in violation of Posix +rules. + + This can cause spurious rebuilds for repeated runs of `make'. This +in turn can cause `make' to fail if it tries to rebuild generated files +in a possibly read-only source tree with tools not present on the +end-user machine. Use GNU `make' instead. + + +File: autoconf.info, Node: Portable C and C++, Next: Manual Configuration, Prev: Portable Make, Up: Top + +13 Portable C and C++ Programming +********************************* + +C and C++ programs often use low-level features of the underlying +system, and therefore are often more difficult to make portable to other +platforms. + + Several standards have been developed to help make your programs more +portable. If you write programs with these standards in mind, you can +have greater confidence that your programs work on a wide variety of +systems. *Note Language Standards Supported by GCC: (gcc)Standards, +for a list of C-related standards. Many programs also assume the Posix +standard (http://www.opengroup.org/susv3). + + Some old code is written to be portable to K&R C, which predates any +C standard. K&R C compilers are no longer of practical interest, +though, and the rest of section assumes at least C89, the first C +standard. + + Program portability is a huge topic, and this section can only +briefly introduce common pitfalls. *Note Portability between System +Types: (standards)System Portability, for more information. + +* Menu: + +* Varieties of Unportability:: How to make your programs unportable +* Integer Overflow:: When integers get too large +* Preprocessor Arithmetic:: `#if' expression problems +* Null Pointers:: Properties of null pointers +* Buffer Overruns:: Subscript errors and the like +* Volatile Objects:: `volatile' and signals +* Floating Point Portability:: Portable floating-point arithmetic +* Exiting Portably:: Exiting and the exit status + + +File: autoconf.info, Node: Varieties of Unportability, Next: Integer Overflow, Up: Portable C and C++ + +13.1 Varieties of Unportability +=============================== + +Autoconf tests and ordinary programs often need to test what is allowed +on a system, and therefore they may need to deliberately exceed the +boundaries of what the standards allow, if only to see whether an +optional feature is present. When you write such a program, you should +keep in mind the difference between constraints, unspecified behavior, +and undefined behavior. + + In C, a "constraint" is a rule that the compiler must enforce. An +example constraint is that C programs must not declare a bit-field with +negative width. Tests can therefore reliably assume that programs with +negative-width bit-fields are rejected by a compiler that conforms to +the standard. + + "Unspecified behavior" is valid behavior, where the standard allows +multiple possibilities. For example, the order of evaluation of +function arguments is unspecified. Some unspecified behavior is +"implementation-defined", i.e., documented by the implementation, but +since Autoconf tests cannot read the documentation they cannot +distinguish between implementation-defined and other unspecified +behavior. It is common for Autoconf tests to probe implementations to +determine otherwise-unspecified behavior. + + "Undefined behavior" is invalid behavior, where the standard allows +the implementation to do anything it pleases. For example, +dereferencing a null pointer leads to undefined behavior. If possible, +test programs should avoid undefined behavior, since a program with +undefined behavior might succeed on a test that should fail. + + The above rules apply to programs that are intended to conform to the +standard. However, strictly-conforming programs are quite rare, since +the standards are so limiting. A major goal of Autoconf is to support +programs that use implementation features not described by the standard, +and it is fairly common for test programs to violate the above rules, if +the programs work well enough in practice. + + +File: autoconf.info, Node: Integer Overflow, Next: Preprocessor Arithmetic, Prev: Varieties of Unportability, Up: Portable C and C++ + +13.2 Integer Overflow +===================== + +In practice many portable C programs assume that signed integer +overflow wraps around reliably using two's complement arithmetic. Yet +the C standard says that program behavior is undefined on overflow, and +in a few cases C programs do not work on some modern implementations +because their overflows do not wrap around as their authors expected. +Conversely, in signed integer remainder, the C standard requires +overflow behavior that is commonly not implemented. + +* Menu: + +* Integer Overflow Basics:: Why integer overflow is a problem +* Signed Overflow Examples:: Examples of code assuming wraparound +* Optimization and Wraparound:: Optimizations that break uses of wraparound +* Signed Overflow Advice:: Practical advice for signed overflow issues +* Signed Integer Division:: `INT_MIN / -1' and `INT_MIN % -1' + + +File: autoconf.info, Node: Integer Overflow Basics, Next: Signed Overflow Examples, Up: Integer Overflow + +13.2.1 Basics of Integer Overflow +--------------------------------- + +In languages like C, unsigned integer overflow reliably wraps around; +e.g., `UINT_MAX + 1' yields zero. This is guaranteed by the C standard +and is portable in practice, unless you specify aggressive, nonstandard +optimization options suitable only for special applications. + + In contrast, the C standard says that signed integer overflow leads +to undefined behavior where a program can do anything, including dumping +core or overrunning a buffer. The misbehavior can even precede the +overflow. Such an overflow can occur during addition, subtraction, +multiplication, division, and left shift. + + Despite this requirement of the standard, many C programs and +Autoconf tests assume that signed integer overflow silently wraps +around modulo a power of two, using two's complement arithmetic, so +long as you cast the resulting value to a signed integer type or store +it into a signed integer variable. If you use conservative +optimization flags, such programs are generally portable to the vast +majority of modern platforms, with a few exceptions discussed later. + + For historical reasons the C standard also allows implementations +with ones' complement or signed magnitude arithmetic, but it is safe to +assume two's complement nowadays. + + Also, overflow can occur when converting an out-of-range value to a +signed integer type. Here a standard implementation must define what +happens, but this might include raising an exception. In practice all +known implementations support silent wraparound in this case, so you +need not worry about other possibilities. + + +File: autoconf.info, Node: Signed Overflow Examples, Next: Optimization and Wraparound, Prev: Integer Overflow Basics, Up: Integer Overflow + +13.2.2 Examples of Code Assuming Wraparound Overflow +---------------------------------------------------- + +There has long been a tension between what the C standard requires for +signed integer overflow, and what C programs commonly assume. The +standard allows aggressive optimizations based on assumptions that +overflow never occurs, but many practical C programs rely on overflow +wrapping around. These programs do not conform to the standard, but +they commonly work in practice because compiler writers are +understandably reluctant to implement optimizations that would break +many programs, unless perhaps a user specifies aggressive optimization. + + The C Standard says that if a program has signed integer overflow its +behavior is undefined, and the undefined behavior can even precede the +overflow. To take an extreme example: + + if (password == expected_password) + allow_superuser_privileges (); + else if (counter++ == INT_MAX) + abort (); + else + printf ("%d password mismatches\n", counter); + +If the `int' variable `counter' equals `INT_MAX', `counter++' must +overflow and the behavior is undefined, so the C standard allows the +compiler to optimize away the test against `INT_MAX' and the `abort' +call. Worse, if an earlier bug in the program lets the compiler deduce +that `counter == INT_MAX' or that `counter' previously overflowed, the +C standard allows the compiler to optimize away the password test and +generate code that allows superuser privileges unconditionally. + + Despite this requirement by the standard, it has long been common +for C code to assume wraparound arithmetic after signed overflow, and +all known practical C implementations support some C idioms that assume +wraparound signed arithmetic, even if the idioms do not conform +strictly to the standard. If your code looks like the following +examples it will almost surely work with real-world compilers. + + Here is an example derived from the 7th Edition Unix implementation +of `atoi' (1979-01-10): + + char *p; + int f, n; + ... + while (*p >= '0' && *p <= '9') + n = n * 10 + *p++ - '0'; + return (f ? -n : n); + +Even if the input string is in range, on most modern machines this has +signed overflow when computing the most negative integer (the `-n' +overflows) or a value near an extreme integer (the first `+' overflows). + + Here is another example, derived from the 7th Edition implementation +of `rand' (1979-01-10). Here the programmer expects both +multiplication and addition to wrap on overflow: + + static long int randx = 1; + ... + randx = randx * 1103515245 + 12345; + return (randx >> 16) & 077777; + + In the following example, derived from the GNU C Library 2.5 +implementation of `mktime' (2006-09-09), the code assumes wraparound +arithmetic in `+' to detect signed overflow: + + time_t t, t1, t2; + int sec_requested, sec_adjustment; + ... + t1 = t + sec_requested; + t2 = t1 + sec_adjustment; + if (((t1 < t) != (sec_requested < 0)) + | ((t2 < t1) != (sec_adjustment < 0))) + return -1; + + If your code looks like these examples, it is probably safe even +though it does not strictly conform to the C standard. This might lead +one to believe that one can generally assume wraparound on overflow, +but that is not always true, as can be seen in the next section. + + +File: autoconf.info, Node: Optimization and Wraparound, Next: Signed Overflow Advice, Prev: Signed Overflow Examples, Up: Integer Overflow + +13.2.3 Optimizations That Break Wraparound Arithmetic +----------------------------------------------------- + +Compilers sometimes generate code that is incompatible with wraparound +integer arithmetic. A simple example is an algebraic simplification: a +compiler might translate `(i * 2000) / 1000' to `i * 2' because it +assumes that `i * 2000' does not overflow. The translation is not +equivalent to the original when overflow occurs: e.g., in the typical +case of 32-bit signed two's complement wraparound `int', if `i' has +type `int' and value `1073742', the original expression returns +-2147483 but the optimized version returns the mathematically correct +value 2147484. + + More subtly, loop induction optimizations often exploit the undefined +behavior of signed overflow. Consider the following contrived function +`sumc': + + int + sumc (int lo, int hi) + { + int sum = 0; + int i; + for (i = lo; i <= hi; i++) + sum ^= i * 53; + return sum; + } + +To avoid multiplying by 53 each time through the loop, an optimizing +compiler might internally transform `sumc' to the equivalent of the +following: + + int + transformed_sumc (int lo, int hi) + { + int sum = 0; + int hic = hi * 53; + int ic; + for (ic = lo * 53; ic <= hic; ic += 53) + sum ^= ic; + return sum; + } + +This transformation is allowed by the C standard, but it is invalid for +wraparound arithmetic when `INT_MAX / 53 < hi', because then the +overflow in computing expressions like `hi * 53' can cause the +expression `i <= hi' to yield a different value from the transformed +expression `ic <= hic'. + + For this reason, compilers that use loop induction and similar +techniques often do not support reliable wraparound arithmetic when a +loop induction variable like `ic' is involved. Since loop induction +variables are generated by the compiler, and are not visible in the +source code, it is not always trivial to say whether the problem +affects your code. + + Hardly any code actually depends on wraparound arithmetic in cases +like these, so in practice these loop induction optimizations are almost +always useful. However, edge cases in this area can cause problems. +For example: + + int j; + for (j = 1; 0 < j; j *= 2) + test (j); + +Here, the loop attempts to iterate through all powers of 2 that `int' +can represent, but the C standard allows a compiler to optimize away +the comparison and generate an infinite loop, under the argument that +behavior is undefined on overflow. As of this writing this +optimization is not done by any production version of GCC with `-O2', +but it might be performed by other compilers, or by more aggressive GCC +optimization options, and the GCC developers have not decided whether +it will continue to work with GCC and `-O2'. + + +File: autoconf.info, Node: Signed Overflow Advice, Next: Signed Integer Division, Prev: Optimization and Wraparound, Up: Integer Overflow + +13.2.4 Practical Advice for Signed Overflow Issues +-------------------------------------------------- + +Ideally the safest approach is to avoid signed integer overflow +entirely. For example, instead of multiplying two signed integers, you +can convert them to unsigned integers, multiply the unsigned values, +then test whether the result is in signed range. + + Rewriting code in this way will be inconvenient, though, +particularly if the signed values might be negative. Also, it may hurt +performance. Using unsigned arithmetic to check for overflow is +particularly painful to do portably and efficiently when dealing with an +integer type like `uid_t' whose width and signedness vary from platform +to platform. + + Furthermore, many C applications pervasively assume wraparound +behavior and typically it is not easy to find and remove all these +assumptions. Hence it is often useful to maintain nonstandard code +that assumes wraparound on overflow, instead of rewriting the code. +The rest of this section attempts to give practical advice for this +situation. + + If your code wants to detect signed integer overflow in `sum = a + +b', it is generally safe to use an expression like `(sum < a) != (b < +0)'. + + If your code uses a signed loop index, make sure that the index +cannot overflow, along with all signed expressions derived from the +index. Here is a contrived example of problematic code with two +instances of overflow. + + for (i = INT_MAX - 10; i <= INT_MAX; i++) + if (i + 1 < 0) + { + report_overflow (); + break; + } + +Because of the two overflows, a compiler might optimize away or +transform the two comparisons in a way that is incompatible with the +wraparound assumption. + + If your code uses an expression like `(i * 2000) / 1000' and you +actually want the multiplication to wrap around on overflow, use +unsigned arithmetic to do it, e.g., `((int) (i * 2000u)) / 1000'. + + If your code assumes wraparound behavior and you want to insulate it +against any GCC optimizations that would fail to support that behavior, +you should use GCC's `-fwrapv' option, which causes signed overflow to +wrap around reliably (except for division and remainder, as discussed +in the next section). + + If you need to port to platforms where signed integer overflow does +not reliably wrap around (e.g., due to hardware overflow checking, or to +highly aggressive optimizations), you should consider debugging with +GCC's `-ftrapv' option, which causes signed overflow to raise an +exception. + + +File: autoconf.info, Node: Signed Integer Division, Prev: Signed Overflow Advice, Up: Integer Overflow + +13.2.5 Signed Integer Division and Integer Overflow +--------------------------------------------------- + +Overflow in signed integer division is not always harmless: for +example, on CPUs of the i386 family, dividing `INT_MIN' by `-1' yields +a SIGFPE signal which by default terminates the program. Worse, taking +the remainder of these two values typically yields the same signal on +these CPUs, even though the C standard requires `INT_MIN % -1' to yield +zero because the expression does not overflow. + + +File: autoconf.info, Node: Preprocessor Arithmetic, Next: Null Pointers, Prev: Integer Overflow, Up: Portable C and C++ + +13.3 Preprocessor Arithmetic +============================ + +In C99, preprocessor arithmetic, used for `#if' expressions, must be +evaluated as if all signed values are of type `intmax_t' and all +unsigned values of type `uintmax_t'. Many compilers are buggy in this +area, though. For example, as of 2007, Sun C mishandles `#if LLONG_MIN +< 0' on a platform with 32-bit `long int' and 64-bit `long long int'. +Also, some older preprocessors mishandle constants ending in `LL'. To +work around these problems, you can compute the value of expressions +like `LONG_MAX < LLONG_MAX' at `configure'-time rather than at +`#if'-time. + + +File: autoconf.info, Node: Null Pointers, Next: Buffer Overruns, Prev: Preprocessor Arithmetic, Up: Portable C and C++ + +13.4 Properties of Null Pointers +================================ + +Most modern hosts reliably fail when you attempt to dereference a null +pointer. + + On almost all modern hosts, null pointers use an all-bits-zero +internal representation, so you can reliably use `memset' with 0 to set +all the pointers in an array to null values. + + If `p' is a null pointer to an object type, the C expression `p + 0' +always evaluates to `p' on modern hosts, even though the standard says +that it has undefined behavior. + + +File: autoconf.info, Node: Buffer Overruns, Next: Volatile Objects, Prev: Null Pointers, Up: Portable C and C++ + +13.5 Buffer Overruns and Subscript Errors +========================================= + +Buffer overruns and subscript errors are the most common dangerous +errors in C programs. They result in undefined behavior because storing +outside an array typically modifies storage that is used by some other +object, and most modern systems lack runtime checks to catch these +errors. Programs should not rely on buffer overruns being caught. + + There is one exception to the usual rule that a portable program +cannot address outside an array. In C, it is valid to compute the +address just past an object, e.g., `&a[N]' where `a' has `N' elements, +so long as you do not dereference the resulting pointer. But it is not +valid to compute the address just before an object, e.g., `&a[-1]'; nor +is it valid to compute two past the end, e.g., `&a[N+1]'. On most +platforms `&a[-1] < &a[0] && &a[N] < &a[N+1]', but this is not reliable +in general, and it is usually easy enough to avoid the potential +portability problem, e.g., by allocating an extra unused array element +at the start or end. + + Valgrind (http://valgrind.org/) can catch many overruns. GCC users +might also consider using the `-fmudflap' option to catch overruns. + + Buffer overruns are usually caused by off-by-one errors, but there +are more subtle ways to get them. + + Using `int' values to index into an array or compute array sizes +causes problems on typical 64-bit hosts where an array index might be +2^31 or larger. Index values of type `size_t' avoid this problem, but +cannot be negative. Index values of type `ptrdiff_t' are signed, and +are wide enough in practice. + + If you add or multiply two numbers to calculate an array size, e.g., +`malloc (x * sizeof y + z)', havoc ensues if the addition or +multiplication overflows. + + Many implementations of the `alloca' function silently misbehave and +can generate buffer overflows if given sizes that are too large. The +size limits are implementation dependent, but are at least 4000 bytes +on all platforms that we know about. + + The standard functions `asctime', `asctime_r', `ctime', `ctime_r', +and `gets' are prone to buffer overflows, and portable code should not +use them unless the inputs are known to be within certain limits. The +time-related functions can overflow their buffers if given timestamps +out of range (e.g., a year less than -999 or greater than 9999). +Time-related buffer overflows cannot happen with recent-enough versions +of the GNU C library, but are possible with other implementations. The +`gets' function is the worst, since it almost invariably overflows its +buffer when presented with an input line larger than the buffer. + + +File: autoconf.info, Node: Volatile Objects, Next: Floating Point Portability, Prev: Buffer Overruns, Up: Portable C and C++ + +13.6 Volatile Objects +===================== + +The keyword `volatile' is often misunderstood in portable code. Its +use inhibits some memory-access optimizations, but programmers often +wish that it had a different meaning than it actually does. + + `volatile' was designed for code that accesses special objects like +memory-mapped device registers whose contents spontaneously change. +Such code is inherently low-level, and it is difficult to specify +portably what `volatile' means in these cases. The C standard says, +"What constitutes an access to an object that has volatile-qualified +type is implementation-defined," so in theory each implementation is +supposed to fill in the gap by documenting what `volatile' means for +that implementation. In practice, though, this documentation is +usually absent or incomplete. + + One area of confusion is the distinction between objects defined with +volatile types, and volatile lvalues. From the C standard's point of +view, an object defined with a volatile type has externally visible +behavior. You can think of such objects as having little oscilloscope +probes attached to them, so that the user can observe some properties of +accesses to them, just as the user can observe data written to output +files. However, the standard does not make it clear whether users can +observe accesses by volatile lvalues to ordinary objects. For example: + + /* Declare and access a volatile object. + Accesses to X are "visible" to users. */ + static int volatile x; + x = 1; + + /* Access two ordinary objects via a volatile lvalue. + It's not clear whether accesses to *P are "visible". */ + int y; + int *z = malloc (sizeof (int)); + int volatile *p; + p = &y; + *p = 1; + p = z; + *p = 1; + + Programmers often wish that `volatile' meant "Perform the memory +access here and now, without merging several memory accesses, without +changing the memory word size, and without reordering." But the C +standard does not require this. For objects defined with a volatile +type, accesses must be done before the next sequence point; but +otherwise merging, reordering, and word-size change is allowed. Worse, +it is not clear from the standard whether volatile lvalues provide more +guarantees in general than nonvolatile lvalues, if the underlying +objects are ordinary. + + Even when accessing objects defined with a volatile type, the C +standard allows only extremely limited signal handlers: the behavior is +undefined if a signal handler reads any nonlocal object, or writes to +any nonlocal object whose type is not `sig_atomic_t volatile', or calls +any standard library function other than `abort', `signal', and (if C99) +`_Exit'. Hence C compilers need not worry about a signal handler +disturbing ordinary computation, unless the computation accesses a +`sig_atomic_t volatile' lvalue that is not a local variable. (There is +an obscure exception for accesses via a pointer to a volatile +character, since it may point into part of a `sig_atomic_t volatile' +object.) Posix adds to the list of library functions callable from a +portable signal handler, but otherwise is like the C standard in this +area. + + Some C implementations allow memory-access optimizations within each +translation unit, such that actual behavior agrees with the behavior +required by the standard only when calling a function in some other +translation unit, and a signal handler acts like it was called from a +different translation unit. The C standard hints that in these +implementations, objects referred to by signal handlers "would require +explicit specification of `volatile' storage, as well as other +implementation-defined restrictions." But unfortunately even for this +special case these other restrictions are often not documented well. +*Note When is a Volatile Object Accessed?: (gcc)Volatiles, for some +restrictions imposed by GCC. *Note Defining Signal Handlers: +(libc)Defining Handlers, for some restrictions imposed by the GNU C +library. Restrictions differ on other platforms. + + If possible, it is best to use a signal handler that fits within the +limits imposed by the C and Posix standards. + + If this is not practical, you can try the following rules of thumb. +A signal handler should access only volatile lvalues, preferably lvalues +that refer to objects defined with a volatile type, and should not +assume that the accessed objects have an internally consistent state if +they are larger than a machine word. Furthermore, installers should +employ compilers and compiler options that are commonly used for +building operating system kernels, because kernels often need more from +`volatile' than the C Standard requires, and installers who compile an +application in a similar environment can sometimes benefit from the +extra constraints imposed by kernels on compilers. Admittedly we are +handwaving somewhat here, as there are few guarantees in this area; the +rules of thumb may help to fix some bugs but there is a good chance +that they will not fix them all. + + For `volatile', C++ has the same problems that C does. +Multithreaded applications have even more problems with `volatile', but +they are beyond the scope of this section. + + The bottom line is that using `volatile' typically hurts performance +but should not hurt correctness. In some cases its use does help +correctness, but these cases are often so poorly understood that all +too often adding `volatile' to a data structure merely alleviates some +symptoms of a bug while not fixing the bug in general. + + +File: autoconf.info, Node: Floating Point Portability, Next: Exiting Portably, Prev: Volatile Objects, Up: Portable C and C++ + +13.7 Floating Point Portability +=============================== + +Almost all modern systems use IEEE-754 floating point, and it is safe to +assume IEEE-754 in most portable code these days. For more information, +please see David Goldberg's classic paper What Every Computer Scientist +Should Know About Floating-Point Arithmetic +(http://www.validlab.com/goldberg/paper.pdf). + + +File: autoconf.info, Node: Exiting Portably, Prev: Floating Point Portability, Up: Portable C and C++ + +13.8 Exiting Portably +===================== + +A C or C++ program can exit with status N by returning N from the +`main' function. Portable programs are supposed to exit either with +status 0 or `EXIT_SUCCESS' to succeed, or with status `EXIT_FAILURE' to +fail, but in practice it is portable to fail by exiting with status 1, +and test programs that assume Posix can fail by exiting with status +values from 1 through 255. Programs on SunOS 2.0 (1985) through 3.5.2 +(1988) incorrectly exited with zero status when `main' returned +nonzero, but ancient systems like these are no longer of practical +concern. + + A program can also exit with status N by passing N to the `exit' +function, and a program can fail by calling the `abort' function. If a +program is specialized to just some platforms, it can fail by calling +functions specific to those platforms, e.g., `_exit' (Posix) and +`_Exit' (C99). However, like other functions, an exit function should +be declared, typically by including a header. For example, if a C +program calls `exit', it should include `stdlib.h' either directly or +via the default includes (*note Default Includes::). + + A program can fail due to undefined behavior such as dereferencing a +null pointer, but this is not recommended as undefined behavior allows +an implementation to do whatever it pleases and this includes exiting +successfully. + + +File: autoconf.info, Node: Manual Configuration, Next: Site Configuration, Prev: Portable C and C++, Up: Top + +14 Manual Configuration +*********************** + +A few kinds of features can't be guessed automatically by running test +programs. For example, the details of the object-file format, or +special options that need to be passed to the compiler or linker. You +can check for such features using ad-hoc means, such as having +`configure' check the output of the `uname' program, or looking for +libraries that are unique to particular systems. However, Autoconf +provides a uniform method for handling unguessable features. + +* Menu: + +* Specifying Target Triplets:: Specifying target triplets +* Canonicalizing:: Getting the canonical system type +* Using System Type:: What to do with the system type + + +File: autoconf.info, Node: Specifying Target Triplets, Next: Canonicalizing, Up: Manual Configuration + +14.1 Specifying target triplets +=============================== + +Autoconf-generated `configure' scripts can make decisions based on a +canonical name for the system type, or "target triplet", which has the +form: `CPU-VENDOR-OS', where OS can be `SYSTEM' or `KERNEL-SYSTEM' + + `configure' can usually guess the canonical name for the type of +system it's running on. To do so it runs a script called +`config.guess', which infers the name using the `uname' command or +symbols predefined by the C preprocessor. + + Alternately, the user can specify the system type with command line +arguments to `configure' (*note System Type::. Doing so is necessary +when cross-compiling. In the most complex case of cross-compiling, +three system types are involved. The options to specify them are: + +`--build=BUILD-TYPE' + the type of system on which the package is being configured and + compiled. It defaults to the result of running `config.guess'. + Specifying a BUILD-TYPE that differs from HOST-TYPE enables + cross-compilation mode. + +`--host=HOST-TYPE' + the type of system on which the package runs. By default it is the + same as the build machine. Specifying a HOST-TYPE that differs + from BUILD-TYPE, when BUILD-TYPE was also explicitly specified, + enables cross-compilation mode. + +`--target=TARGET-TYPE' + the type of system for which any compiler tools in the package + produce code (rarely needed). By default, it is the same as host. + + If you mean to override the result of `config.guess', use `--build', +not `--host', since the latter enables cross-compilation. For +historical reasons, whenever you specify `--host', be sure to specify +`--build' too; this will be fixed in the future. So, to enter +cross-compilation mode, use a command like this + + ./configure --build=i686-pc-linux-gnu --host=m68k-coff + +Note that if you do not specify `--host', `configure' fails if it can't +run the code generated by the specified compiler. For example, +configuring as follows fails: + + ./configure CC=m68k-coff-gcc + + When cross-compiling, `configure' will warn about any tools +(compilers, linkers, assemblers) whose name is not prefixed with the +host type. This is an aid to users performing cross-compilation. +Continuing the example above, if a cross-compiler named `cc' is used +with a native `pkg-config', then libraries found by `pkg-config' will +likely cause subtle build failures; but using the names `m68k-coff-cc' +and `m68k-coff-pkg-config' avoids any confusion. Avoiding the warning +is as simple as creating the correct symlinks naming the cross tools. + + `configure' recognizes short aliases for many system types; for +example, `decstation' can be used instead of `mips-dec-ultrix4.2'. +`configure' runs a script called `config.sub' to canonicalize system +type aliases. + + This section deliberately omits the description of the obsolete +interface; see *note Hosts and Cross-Compilation::. + + +File: autoconf.info, Node: Canonicalizing, Next: Using System Type, Prev: Specifying Target Triplets, Up: Manual Configuration + +14.2 Getting the Canonical System Type +====================================== + +The following macros make the system type available to `configure' +scripts. + + The variables `build_alias', `host_alias', and `target_alias' are +always exactly the arguments of `--build', `--host', and `--target'; in +particular, they are left empty if the user did not use them, even if +the corresponding `AC_CANONICAL' macro was run. Any configure script +may use these variables anywhere. These are the variables that should +be used when in interaction with the user. + + If you need to recognize some special environments based on their +system type, run the following macros to get canonical system names. +These variables are not set before the macro call. + + If you use these macros, you must distribute `config.guess' and +`config.sub' along with your source code. *Note Output::, for +information about the `AC_CONFIG_AUX_DIR' macro which you can use to +control in which directory `configure' looks for those scripts. + + -- Macro: AC_CANONICAL_BUILD + Compute the canonical build-system type variable, `build', and its + three individual parts `build_cpu', `build_vendor', and `build_os'. + + If `--build' was specified, then `build' is the canonicalization + of `build_alias' by `config.sub', otherwise it is determined by + the shell script `config.guess'. + + -- Macro: AC_CANONICAL_HOST + Compute the canonical host-system type variable, `host', and its + three individual parts `host_cpu', `host_vendor', and `host_os'. + + If `--host' was specified, then `host' is the canonicalization of + `host_alias' by `config.sub', otherwise it defaults to `build'. + + -- Macro: AC_CANONICAL_TARGET + Compute the canonical target-system type variable, `target', and + its three individual parts `target_cpu', `target_vendor', and + `target_os'. + + If `--target' was specified, then `target' is the canonicalization + of `target_alias' by `config.sub', otherwise it defaults to `host'. + + Note that there can be artifacts due to the backward compatibility +code. *Note Hosts and Cross-Compilation::, for more. + + +File: autoconf.info, Node: Using System Type, Prev: Canonicalizing, Up: Manual Configuration + +14.3 Using the System Type +========================== + +In `configure.ac' the system type is generally used by one or more +`case' statements to select system-specifics. Shell wildcards can be +used to match a group of system types. + + For example, an extra assembler code object file could be chosen, +giving access to a CPU cycle counter register. `$(CYCLE_OBJ)' in the +following would be used in a makefile to add the object to a program or +library. + + AS_CASE([$host], + [alpha*-*-*], [CYCLE_OBJ=rpcc.o], + [i?86-*-*], [CYCLE_OBJ=rdtsc.o], + [CYCLE_OBJ=""] + ) + AC_SUBST([CYCLE_OBJ]) + + `AC_CONFIG_LINKS' (*note Configuration Links::) is another good way +to select variant source files, for example optimized code for some +CPUs. The configured CPU type doesn't always indicate exact CPU types, +so some runtime capability checks may be necessary too. + + case $host in + alpha*-*-*) AC_CONFIG_LINKS([dither.c:alpha/dither.c]) ;; + powerpc*-*-*) AC_CONFIG_LINKS([dither.c:powerpc/dither.c]) ;; + *-*-*) AC_CONFIG_LINKS([dither.c:generic/dither.c]) ;; + esac + + The host system type can also be used to find cross-compilation tools +with `AC_CHECK_TOOL' (*note Generic Programs::). + + The above examples all show `$host', since this is where the code is +going to run. Only rarely is it necessary to test `$build' (which is +where the build is being done). + + Whenever you're tempted to use `$host' it's worth considering +whether some sort of probe would be better. New system types come along +periodically or previously missing features are added. Well-written +probes can adapt themselves to such things, but hard-coded lists of +names can't. Here are some guidelines, + + * Availability of libraries and library functions should always be + checked by probing. + + * Variant behavior of system calls is best identified with runtime + tests if possible, but bug workarounds or obscure difficulties + might have to be driven from `$host'. + + * Assembler code is inevitably highly CPU-specific and is best + selected according to `$host_cpu'. + + * Assembler variations like underscore prefix on globals or ELF + versus COFF type directives are however best determined by + probing, perhaps even examining the compiler output. + + `$target' is for use by a package creating a compiler or similar. +For ordinary packages it's meaningless and should not be used. It +indicates what the created compiler should generate code for, if it can +cross-compile. `$target' generally selects various hard-coded CPU and +system conventions, since usually the compiler or tools under +construction themselves determine how the target works. + + +File: autoconf.info, Node: Site Configuration, Next: Running configure Scripts, Prev: Manual Configuration, Up: Top + +15 Site Configuration +********************* + +`configure' scripts support several kinds of local configuration +decisions. There are ways for users to specify where external software +packages are, include or exclude optional features, install programs +under modified names, and set default values for `configure' options. + +* Menu: + +* Help Formatting:: Customizing `configure --help' +* External Software:: Working with other optional software +* Package Options:: Selecting optional features +* Pretty Help Strings:: Formatting help string +* Option Checking:: Controlling checking of `configure' options +* Site Details:: Configuring site details +* Transforming Names:: Changing program names when installing +* Site Defaults:: Giving `configure' local defaults + + +File: autoconf.info, Node: Help Formatting, Next: External Software, Up: Site Configuration + +15.1 Controlling Help Output +============================ + +Users consult `configure --help' to learn of configuration decisions +specific to your package. By default, `configure' breaks this output +into sections for each type of option; within each section, help +strings appear in the order `configure.ac' defines them: + + Optional Features: + ... + --enable-bar include bar + + Optional Packages: + ... + --with-foo use foo + + -- Macro: AC_PRESERVE_HELP_ORDER + Request an alternate `--help' format, in which options of all + types appear together, in the order defined. Call this macro + before any `AC_ARG_ENABLE' or `AC_ARG_WITH'. + + Optional Features and Packages: + ... + --enable-bar include bar + --with-foo use foo + + + +File: autoconf.info, Node: External Software, Next: Package Options, Prev: Help Formatting, Up: Site Configuration + +15.2 Working With External Software +=================================== + +Some packages require, or can optionally use, other software packages +that are already installed. The user can give `configure' command line +options to specify which such external software to use. The options +have one of these forms: + + --with-PACKAGE[=ARG] + --without-PACKAGE + + For example, `--with-gnu-ld' means work with the GNU linker instead +of some other linker. `--with-x' means work with The X Window System. + + The user can give an argument by following the package name with `=' +and the argument. Giving an argument of `no' is for packages that are +used by default; it says to _not_ use the package. An argument that is +neither `yes' nor `no' could include a name or number of a version of +the other package, to specify more precisely which other package this +program is supposed to work with. If no argument is given, it defaults +to `yes'. `--without-PACKAGE' is equivalent to `--with-PACKAGE=no'. + + Normally `configure' scripts complain about `--with-PACKAGE' options +that they do not support. *Note Option Checking::, for details, and +for how to override the defaults. + + For each external software package that may be used, `configure.ac' +should call `AC_ARG_WITH' to detect whether the `configure' user asked +to use it. Whether each package is used or not by default, and which +arguments are valid, is up to you. + + -- Macro: AC_ARG_WITH (PACKAGE, HELP-STRING, [ACTION-IF-GIVEN], + [ACTION-IF-NOT-GIVEN]) + If the user gave `configure' the option `--with-PACKAGE' or + `--without-PACKAGE', run shell commands ACTION-IF-GIVEN. If + neither option was given, run shell commands ACTION-IF-NOT-GIVEN. + The name PACKAGE indicates another software package that this + program should work with. It should consist only of alphanumeric + characters, dashes, plus signs, and dots. + + The option's argument is available to the shell commands + ACTION-IF-GIVEN in the shell variable `withval', which is actually + just the value of the shell variable named `with_PACKAGE', with + any non-alphanumeric characters in PACKAGE changed into `_'. You + may use that variable instead, if you wish. + + The argument HELP-STRING is a description of the option that looks + like this: + --with-readline support fancy command line editing + + HELP-STRING may be more than one line long, if more detail is + needed. Just make sure the columns line up in `configure --help'. + Avoid tabs in the help string. The easiest way to provide the + proper leading whitespace is to format your HELP-STRING with the + macro `AS_HELP_STRING' (*note Pretty Help Strings::). + + The following example shows how to use the `AC_ARG_WITH' macro in + a common situation. You want to let the user decide whether to + enable support for an external library (e.g., the readline + library); if the user specified neither `--with-readline' nor + `--without-readline', you want to enable support for readline only + if the library is available on the system. + + AC_ARG_WITH([readline], + [AS_HELP_STRING([--with-readline], + [support fancy command line editing @<:@default=check@:>@])], + [], + [with_readline=check]) + + LIBREADLINE= + AS_IF([test "x$with_readline" != xno], + [AC_CHECK_LIB([readline], [main], + [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) + AC_DEFINE([HAVE_LIBREADLINE], [1], + [Define if you have libreadline]) + ], + [if test "x$with_readline" != xcheck; then + AC_MSG_FAILURE( + [--with-readline was given, but test for readline failed]) + fi + ], -lncurses)]) + + The next example shows how to use `AC_ARG_WITH' to give the user + the possibility to enable support for the readline library, in + case it is still experimental and not well tested, and is + therefore disabled by default. + + AC_ARG_WITH([readline], + [AS_HELP_STRING([--with-readline], + [enable experimental support for readline])], + [], + [with_readline=no]) + + LIBREADLINE= + AS_IF([test "x$with_readline" != xno], + [AC_CHECK_LIB([readline], [main], + [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) + AC_DEFINE([HAVE_LIBREADLINE], [1], + [Define if you have libreadline]) + ], + [AC_MSG_FAILURE( + [--with-readline was given, but test for readline failed])], + [-lncurses])]) + + The last example shows how to use `AC_ARG_WITH' to give the user + the possibility to disable support for the readline library, given + that it is an important feature and that it should be enabled by + default. + + AC_ARG_WITH([readline], + [AS_HELP_STRING([--without-readline], + [disable support for readline])], + [], + [with_readline=yes]) + + LIBREADLINE= + AS_IF([test "x$with_readline" != xno], + [AC_CHECK_LIB([readline], [main], + [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) + AC_DEFINE([HAVE_LIBREADLINE], [1], + [Define if you have libreadline]) + ], + [AC_MSG_FAILURE( + [readline test failed (--without-readline to disable)])], + [-lncurses])]) + + These three examples can be easily adapted to the case where + `AC_ARG_ENABLE' should be preferred to `AC_ARG_WITH' (see *note + Package Options::). + + +File: autoconf.info, Node: Package Options, Next: Pretty Help Strings, Prev: External Software, Up: Site Configuration + +15.3 Choosing Package Options +============================= + +If a software package has optional compile-time features, the user can +give `configure' command line options to specify whether to compile +them. The options have one of these forms: + + --enable-FEATURE[=ARG] + --disable-FEATURE + + These options allow users to choose which optional features to build +and install. `--enable-FEATURE' options should never make a feature +behave differently or cause one feature to replace another. They +should only cause parts of the program to be built rather than left out. + + The user can give an argument by following the feature name with `=' +and the argument. Giving an argument of `no' requests that the feature +_not_ be made available. A feature with an argument looks like +`--enable-debug=stabs'. If no argument is given, it defaults to `yes'. +`--disable-FEATURE' is equivalent to `--enable-FEATURE=no'. + + Normally `configure' scripts complain about `--enable-PACKAGE' +options that they do not support. *Note Option Checking::, for +details, and for how to override the defaults. + + For each optional feature, `configure.ac' should call +`AC_ARG_ENABLE' to detect whether the `configure' user asked to include +it. Whether each feature is included or not by default, and which +arguments are valid, is up to you. + + -- Macro: AC_ARG_ENABLE (FEATURE, HELP-STRING, [ACTION-IF-GIVEN], + [ACTION-IF-NOT-GIVEN]) + If the user gave `configure' the option `--enable-FEATURE' or + `--disable-FEATURE', run shell commands ACTION-IF-GIVEN. If + neither option was given, run shell commands ACTION-IF-NOT-GIVEN. + The name FEATURE indicates an optional user-level facility. It + should consist only of alphanumeric characters, dashes, plus + signs, and dots. + + The option's argument is available to the shell commands + ACTION-IF-GIVEN in the shell variable `enableval', which is + actually just the value of the shell variable named + `enable_FEATURE', with any non-alphanumeric characters in FEATURE + changed into `_'. You may use that variable instead, if you wish. + The HELP-STRING argument is like that of `AC_ARG_WITH' (*note + External Software::). + + You should format your HELP-STRING with the macro `AS_HELP_STRING' + (*note Pretty Help Strings::). + + See the examples suggested with the definition of `AC_ARG_WITH' + (*note External Software::) to get an idea of possible + applications of `AC_ARG_ENABLE'. + + +File: autoconf.info, Node: Pretty Help Strings, Next: Option Checking, Prev: Package Options, Up: Site Configuration + +15.4 Making Your Help Strings Look Pretty +========================================= + +Properly formatting the `help strings' which are used in `AC_ARG_WITH' +(*note External Software::) and `AC_ARG_ENABLE' (*note Package +Options::) can be challenging. Specifically, you want your own `help +strings' to line up in the appropriate columns of `configure --help' +just like the standard Autoconf `help strings' do. This is the purpose +of the `AS_HELP_STRING' macro. + + -- Macro: AS_HELP_STRING (LEFT-HAND-SIDE, RIGHT-HAND-SIDE + [INDENT-COLUMN = `26'], [WRAP-COLUMN = `79']) + Expands into a help string that looks pretty when the user executes + `configure --help'. It is typically used in `AC_ARG_WITH' (*note + External Software::) or `AC_ARG_ENABLE' (*note Package Options::). + The following example makes this clearer. + + AC_ARG_WITH([foo], + [AS_HELP_STRING([--with-foo], + [use foo (default is no)])], + [use_foo=$withval], + [use_foo=no]) + + Then the last few lines of `configure --help' appear like this: + + --enable and --with options recognized: + --with-foo use foo (default is no) + + Macro expansion is performed on the first argument. However, the + second argument of `AS_HELP_STRING' is treated as a whitespace + separated list of text to be reformatted, and is not subject to + macro expansion. Since it is not expanded, it should not be + double quoted. *Note Autoconf Language::, for a more detailed + explanation. + + The `AS_HELP_STRING' macro is particularly helpful when the + LEFT-HAND-SIDE and/or RIGHT-HAND-SIDE are composed of macro + arguments, as shown in the following example. Be aware that + LEFT-HAND-SIDE may not expand to unbalanced quotes, although + quadrigraphs can be used. + + AC_DEFUN([MY_ARG_WITH], + [AC_ARG_WITH(m4_translit([[$1]], [_], [-]), + [AS_HELP_STRING([--with-m4_translit([$1], [_], [-])], + [use $1 (default is $2)])], + [use_[]$1=$withval], + [use_[]$1=$2])]) + MY_ARG_WITH([a_b], [no]) + Here, the last few lines of `configure --help' will include: + + --enable and --with options recognized: + --with-a-b use a_b (default is no) + + The parameters INDENT-COLUMN and WRAP-COLUMN were introduced in + Autoconf 2.62. Generally, they should not be specified; they exist + for fine-tuning of the wrapping. + AS_HELP_STRING([--option], [description of option]) + => --option description of option + AS_HELP_STRING([--option], [description of option], [15], [30]) + => --option description of + => option + + +File: autoconf.info, Node: Option Checking, Next: Site Details, Prev: Pretty Help Strings, Up: Site Configuration + +15.5 Controlling Checking of `configure' Options +================================================ + +The `configure' script checks its command-line options against a list +of known options, like `--help' or `--config-cache'. An unknown option +ordinarily indicates a mistake by the user and `configure' halts with +an error. However, by default unknown `--with-PACKAGE' and +`--enable-FEATURE' options elicit only a warning, to support +configuring entire source trees. + + Source trees often contain multiple packages with a top-level +`configure' script that uses the `AC_CONFIG_SUBDIRS' macro (*note +Subdirectories::). Because the packages generally support different +`--with-PACKAGE' and `--enable-FEATURE' options, the GNU Coding +Standards say they must accept unrecognized options without halting. +Even a warning message is undesirable here, so `AC_CONFIG_SUBDIRS' +automatically disables the warnings. + + This default behavior may be modified in two ways. First, the +installer can invoke `configure --disable-option-checking' to disable +these warnings, or invoke `configure --enable-option-checking=fatal' +options to turn them into fatal errors, respectively. Second, the +maintainer can use `AC_DISABLE_OPTION_CHECKING'. + + -- Macro: AC_DISABLE_OPTION_CHECKING + By default, disable warnings related to any unrecognized + `--with-PACKAGE' or `--enable-FEATURE' options. This is implied + by `AC_CONFIG_SUBDIRS'. + + The installer can override this behavior by passing + `--enable-option-checking' (enable warnings) or + `--enable-option-checking=fatal' (enable errors) to `configure'. + + +File: autoconf.info, Node: Site Details, Next: Transforming Names, Prev: Option Checking, Up: Site Configuration + +15.6 Configuring Site Details +============================= + +Some software packages require complex site-specific information. Some +examples are host names to use for certain services, company names, and +email addresses to contact. Since some configuration scripts generated +by Metaconfig ask for such information interactively, people sometimes +wonder how to get that information in Autoconf-generated configuration +scripts, which aren't interactive. + + Such site configuration information should be put in a file that is +edited _only by users_, not by programs. The location of the file can +either be based on the `prefix' variable, or be a standard location +such as the user's home directory. It could even be specified by an +environment variable. The programs should examine that file at +runtime, rather than at compile time. Runtime configuration is more +convenient for users and makes the configuration process simpler than +getting the information while configuring. *Note Variables for +Installation Directories: (standards)Directory Variables, for more +information on where to put data files. + + +File: autoconf.info, Node: Transforming Names, Next: Site Defaults, Prev: Site Details, Up: Site Configuration + +15.7 Transforming Program Names When Installing +=============================================== + +Autoconf supports changing the names of programs when installing them. +In order to use these transformations, `configure.ac' must call the +macro `AC_ARG_PROGRAM'. + + -- Macro: AC_ARG_PROGRAM + Place in output variable `program_transform_name' a sequence of + `sed' commands for changing the names of installed programs. + + If any of the options described below are given to `configure', + program names are transformed accordingly. Otherwise, if + `AC_CANONICAL_TARGET' has been called and a `--target' value is + given, the target type followed by a dash is used as a prefix. + Otherwise, no program name transformation is done. + +* Menu: + +* Transformation Options:: `configure' options to transform names +* Transformation Examples:: Sample uses of transforming names +* Transformation Rules:: Makefile uses of transforming names + + +File: autoconf.info, Node: Transformation Options, Next: Transformation Examples, Up: Transforming Names + +15.7.1 Transformation Options +----------------------------- + +You can specify name transformations by giving `configure' these +command line options: + +`--program-prefix=PREFIX' + prepend PREFIX to the names; + +`--program-suffix=SUFFIX' + append SUFFIX to the names; + +`--program-transform-name=EXPRESSION' + perform `sed' substitution EXPRESSION on the names. + + +File: autoconf.info, Node: Transformation Examples, Next: Transformation Rules, Prev: Transformation Options, Up: Transforming Names + +15.7.2 Transformation Examples +------------------------------ + +These transformations are useful with programs that can be part of a +cross-compilation development environment. For example, a +cross-assembler running on a Sun 4 configured with +`--target=i960-vxworks' is normally installed as `i960-vxworks-as', +rather than `as', which could be confused with a native Sun 4 assembler. + + You can force a program name to begin with `g', if you don't want +GNU programs installed on your system to shadow other programs with the +same name. For example, if you configure GNU `diff' with +`--program-prefix=g', then when you run `make install' it is installed +as `/usr/local/bin/gdiff'. + + As a more sophisticated example, you could use + + --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/' + to prepend `g' to most of the program names in a source tree, +excepting those like `gdb' that already have one and those like `less' +and `lesskey' that aren't GNU programs. (That is assuming that you +have a source tree containing those programs that is set up to use this +feature.) + + One way to install multiple versions of some programs simultaneously +is to append a version number to the name of one or both. For example, +if you want to keep Autoconf version 1 around for awhile, you can +configure Autoconf version 2 using `--program-suffix=2' to install the +programs as `/usr/local/bin/autoconf2', `/usr/local/bin/autoheader2', +etc. Nevertheless, pay attention that only the binaries are renamed, +therefore you'd have problems with the library files which might +overlap. + + +File: autoconf.info, Node: Transformation Rules, Prev: Transformation Examples, Up: Transforming Names + +15.7.3 Transformation Rules +--------------------------- + +Here is how to use the variable `program_transform_name' in a +`Makefile.in': + + PROGRAMS = cp ls rm + transform = @program_transform_name@ + install: + for p in $(PROGRAMS); do \ + $(INSTALL_PROGRAM) $$p $(DESTDIR)$(bindir)/`echo $$p | \ + sed '$(transform)'`; \ + done + + uninstall: + for p in $(PROGRAMS); do \ + rm -f $(DESTDIR)$(bindir)/`echo $$p | sed '$(transform)'`; \ + done + + It is guaranteed that `program_transform_name' is never empty, and +that there are no useless separators. Therefore you may safely embed +`program_transform_name' within a sed program using `;': + + transform = @program_transform_name@ + transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/ + + Whether to do the transformations on documentation files (Texinfo or +`man') is a tricky question; there seems to be no perfect answer, due +to the several reasons for name transforming. Documentation is not +usually particular to a specific architecture, and Texinfo files do not +conflict with system documentation. But they might conflict with +earlier versions of the same files, and `man' pages sometimes do +conflict with system documentation. As a compromise, it is probably +best to do name transformations on `man' pages but not on Texinfo +manuals. + + +File: autoconf.info, Node: Site Defaults, Prev: Transforming Names, Up: Site Configuration + +15.8 Setting Site Defaults +========================== + +Autoconf-generated `configure' scripts allow your site to provide +default values for some configuration values. You do this by creating +site- and system-wide initialization files. + + If the environment variable `CONFIG_SITE' is set, `configure' uses +its value as the name of a shell script to read; it is recommended that +this be an absolute file name. Otherwise, it reads the shell script +`PREFIX/share/config.site' if it exists, then `PREFIX/etc/config.site' +if it exists. Thus, settings in machine-specific files override those +in machine-independent ones in case of conflict. + + Site files can be arbitrary shell scripts, but only certain kinds of +code are really appropriate to be in them. Because `configure' reads +any cache file after it has read any site files, a site file can define +a default cache file to be shared between all Autoconf-generated +`configure' scripts run on that system (*note Cache Files::). If you +set a default cache file in a site file, it is a good idea to also set +the output variable `CC' in that site file, because the cache file is +only valid for a particular compiler, but many systems have several +available. + + You can examine or override the value set by a command line option to +`configure' in a site file; options set shell variables that have the +same names as the options, with any dashes turned into underscores. +The exceptions are that `--without-' and `--disable-' options are like +giving the corresponding `--with-' or `--enable-' option and the value +`no'. Thus, `--cache-file=localcache' sets the variable `cache_file' +to the value `localcache'; `--enable-warnings=no' or +`--disable-warnings' sets the variable `enable_warnings' to the value +`no'; `--prefix=/usr' sets the variable `prefix' to the value `/usr'; +etc. + + Site files are also good places to set default values for other +output variables, such as `CFLAGS', if you need to give them non-default +values: anything you would normally do, repetitively, on the command +line. If you use non-default values for PREFIX or EXEC_PREFIX +(wherever you locate the site file), you can set them in the site file +if you specify it with the `CONFIG_SITE' environment variable. + + You can set some cache values in the site file itself. Doing this is +useful if you are cross-compiling, where it is impossible to check +features that require running a test program. You could "prime the +cache" by setting those values correctly for that system in +`PREFIX/etc/config.site'. To find out the names of the cache variables +you need to set, see the documentation of the respective Autoconf +macro. If the variables or their semantics are undocumented, you may +need to look for shell variables with `_cv_' in their names in the +affected `configure' scripts, or in the Autoconf M4 source code for +those macros; but in that case, their name or semantics may change in a +future Autoconf version. + + The cache file is careful to not override any variables set in the +site files. Similarly, you should not override command-line options in +the site files. Your code should check that variables such as `prefix' +and `cache_file' have their default values (as set near the top of +`configure') before changing them. + + Here is a sample file `/usr/share/local/gnu/share/config.site'. The +command `configure --prefix=/usr/share/local/gnu' would read this file +(if `CONFIG_SITE' is not set to a different file). + + # /usr/share/local/gnu/share/config.site for configure + # + # Change some defaults. + test "$prefix" = NONE && prefix=/usr/share/local/gnu + test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu + test "$sharedstatedir" = '${prefix}/com' && sharedstatedir=/var + test "$localstatedir" = '${prefix}/var' && localstatedir=/var + + # Give Autoconf 2.x generated configure scripts a shared default + # cache file for feature test results, architecture-specific. + if test "$cache_file" = /dev/null; then + cache_file="$prefix/var/config.cache" + # A cache file is only valid for one C compiler. + CC=gcc + fi + + Another use of `config.site' is for priming the directory variables +in a manner consistent with the Filesystem Hierarchy Standard (FHS). +Once the following file is installed at `/usr/share/config.site', a +user can execute simply `./configure --prefix=/usr' to get all the +directories chosen in the locations recommended by FHS. + + # /usr/share/config.site for FHS defaults when installing below /usr, + # and the respective settings were not changed on the command line. + if test "$prefix" = /usr; then + test "$sysconfdir" = '${prefix}/etc' && sysconfdir=/etc + test "$sharedstatedir" = '${prefix}/com' && sharedstatedir=/var + test "$localstatedir" = '${prefix}/var' && localstatedir=/var + fi + + Likewise, on platforms where 64-bit libraries are built by default, +then installed in `/usr/local/lib64' instead of `/usr/local/lib', it is +appropriate to install `/usr/local/share/config.site': + + # /usr/local/share/config.site for platforms that prefer + # the directory /usr/local/lib64 over /usr/local/lib. + test "$libdir" = '${exec_prefix}/lib' && libdir='${exec_prefix}/lib64' + + +File: autoconf.info, Node: Running configure Scripts, Next: config.status Invocation, Prev: Site Configuration, Up: Top + +16 Running `configure' Scripts +****************************** + +Below are instructions on how to configure a package that uses a +`configure' script, suitable for inclusion as an `INSTALL' file in the +package. A plain-text version of `INSTALL' which you may use comes +with Autoconf. + +* Menu: + +* Basic Installation:: Instructions for typical cases +* Compilers and Options:: Selecting compilers and optimization +* Multiple Architectures:: Compiling for multiple architectures at once +* Installation Names:: Installing in different directories +* Optional Features:: Selecting optional features +* Particular Systems:: Particular systems +* System Type:: Specifying the system type +* Sharing Defaults:: Setting site-wide defaults for `configure' +* Defining Variables:: Specifying the compiler etc. +* configure Invocation:: Changing how `configure' runs + + +File: autoconf.info, Node: Basic Installation, Next: Compilers and Options, Up: Running configure Scripts + +16.1 Basic Installation +======================= + +Briefly, the shell commands `./configure; make; make install' should +configure, build, and install this package. The following +more-detailed instructions are generic; see the `README' file for +instructions specific to this package. More recommendations for GNU +packages can be found in *note Makefile Conventions: +(standards)Makefile Conventions. + + The `configure' shell script attempts to guess correct values for +various system-dependent variables used during compilation. It uses +those values to create a `Makefile' in each directory of the package. +It may also create one or more `.h' files containing system-dependent +definitions. Finally, it creates a shell script `config.status' that +you can run in the future to recreate the current configuration, and a +file `config.log' containing compiler output (useful mainly for +debugging `configure'). + + It can also use an optional file (typically called `config.cache' +and enabled with `--cache-file=config.cache' or simply `-C') that saves +the results of its tests to speed up reconfiguring. Caching is +disabled by default to prevent problems with accidental use of stale +cache files. + + If you need to do unusual things to compile the package, please try +to figure out how `configure' could check whether to do them, and mail +diffs or instructions to the address given in the `README' so they can +be considered for the next release. If you are using the cache, and at +some point `config.cache' contains results you don't want to keep, you +may remove or edit it. + + The file `configure.ac' (or `configure.in') is used to create +`configure' by a program called `autoconf'. You need `configure.ac' if +you want to change it or regenerate `configure' using a newer version +of `autoconf'. + + The simplest way to compile this package is: + + 1. `cd' to the directory containing the package's source code and type + `./configure' to configure the package for your system. + + Running `configure' might take a while. While running, it prints + some messages telling which features it is checking for. + + 2. Type `make' to compile the package. + + 3. Optionally, type `make check' to run any self-tests that come with + the package, generally using the just-built uninstalled binaries. + + 4. Type `make install' to install the programs and any data files and + documentation. When installing into a prefix owned by root, it is + recommended that the package be configured and built as a regular + user, and only the `make install' phase executed with root + privileges. + + 5. Optionally, type `make installcheck' to repeat any self-tests, but + this time using the binaries in their final installed location. + This target does not install anything. Running this target as a + regular user, particularly if the prior `make install' required + root privileges, verifies that the installation completed + correctly. + + 6. You can remove the program binaries and object files from the + source code directory by typing `make clean'. To also remove the + files that `configure' created (so you can compile the package for + a different kind of computer), type `make distclean'. There is + also a `make maintainer-clean' target, but that is intended mainly + for the package's developers. If you use it, you may have to get + all sorts of other programs in order to regenerate files that came + with the distribution. + + 7. Often, you can also type `make uninstall' to remove the installed + files again. In practice, not all packages have tested that + uninstallation works correctly, even though it is required by the + GNU Coding Standards. + + 8. Some packages, particularly those that use Automake, provide `make + distcheck', which can by used by developers to test that all other + targets like `make install' and `make uninstall' work correctly. + This target is generally not run by end users. + + +File: autoconf.info, Node: Compilers and Options, Next: Multiple Architectures, Prev: Basic Installation, Up: Running configure Scripts + +16.2 Compilers and Options +========================== + +Some systems require unusual options for compilation or linking that the +`configure' script does not know about. Run `./configure --help' for +details on some of the pertinent environment variables. + + You can give `configure' initial values for configuration parameters +by setting variables in the command line or in the environment. Here +is an example: + + ./configure CC=c99 CFLAGS=-g LIBS=-lposix + + *Note Defining Variables::, for more details. + + +File: autoconf.info, Node: Multiple Architectures, Next: Installation Names, Prev: Compilers and Options, Up: Running configure Scripts + +16.3 Compiling For Multiple Architectures +========================================= + +You can compile the package for more than one kind of computer at the +same time, by placing the object files for each architecture in their +own directory. To do this, you can use GNU `make'. `cd' to the +directory where you want the object files and executables to go and run +the `configure' script. `configure' automatically checks for the +source code in the directory that `configure' is in and in `..'. This +is known as a "VPATH" build. + + With a non-GNU `make', it is safer to compile the package for one +architecture at a time in the source code directory. After you have +installed the package for one architecture, use `make distclean' before +reconfiguring for another architecture. + + On MacOS X 10.5 and later systems, you can create libraries and +executables that work on multiple system types--known as "fat" or +"universal" binaries--by specifying multiple `-arch' options to the +compiler but only a single `-arch' option to the preprocessor. Like +this: + + ./configure CC="gcc -arch i386 -arch x86_64 -arch ppc -arch ppc64" \ + CXX="g++ -arch i386 -arch x86_64 -arch ppc -arch ppc64" \ + CPP="gcc -E" CXXCPP="g++ -E" + + This is not guaranteed to produce working output in all cases, you +may have to build one architecture at a time and combine the results +using the `lipo' tool if you have problems. + + +File: autoconf.info, Node: Installation Names, Next: Optional Features, Prev: Multiple Architectures, Up: Running configure Scripts + +16.4 Installation Names +======================= + +By default, `make install' installs the package's commands under +`/usr/local/bin', include files under `/usr/local/include', etc. You +can specify an installation prefix other than `/usr/local' by giving +`configure' the option `--prefix=PREFIX', where PREFIX must be an +absolute file name. + + You can specify separate installation prefixes for +architecture-specific files and architecture-independent files. If you +pass the option `--exec-prefix=PREFIX' to `configure', the package uses +PREFIX as the prefix for installing programs and libraries. +Documentation and other data files still use the regular prefix. + + In addition, if you use an unusual directory layout you can give +options like `--bindir=DIR' to specify different values for particular +kinds of files. Run `configure --help' for a list of the directories +you can set and what kinds of files go in them. In general, the +default for these options is expressed in terms of `${prefix}', so that +specifying just `--prefix' will affect all of the other directory +specifications that were not explicitly provided. + + The most portable way to affect installation locations is to pass the +correct locations to `configure'; however, many packages provide one or +both of the following shortcuts of passing variable assignments to the +`make install' command line to change installation locations without +having to reconfigure or recompile. + + The first method involves providing an override variable for each +affected directory. For example, `make install +prefix=/alternate/directory' will choose an alternate location for all +directory configuration variables that were expressed in terms of +`${prefix}'. Any directories that were specified during `configure', +but not in terms of `${prefix}', must each be overridden at install +time for the entire installation to be relocated. The approach of +makefile variable overrides for each directory variable is required by +the GNU Coding Standards, and ideally causes no recompilation. +However, some platforms have known limitations with the semantics of +shared libraries that end up requiring recompilation when using this +method, particularly noticeable in packages that use GNU Libtool. + + The second method involves providing the `DESTDIR' variable. For +example, `make install DESTDIR=/alternate/directory' will prepend +`/alternate/directory' before all installation names. The approach of +`DESTDIR' overrides is not required by the GNU Coding Standards, and +does not work on platforms that have drive letters. On the other hand, +it does better at avoiding recompilation issues, and works well even +when some directory options were not specified in terms of `${prefix}' +at `configure' time. + + +File: autoconf.info, Node: Optional Features, Next: Particular Systems, Prev: Installation Names, Up: Running configure Scripts + +16.5 Optional Features +====================== + +If the package supports it, you can cause programs to be installed with +an extra prefix or suffix on their names by giving `configure' the +option `--program-prefix=PREFIX' or `--program-suffix=SUFFIX'. + + Some packages pay attention to `--enable-FEATURE' options to +`configure', where FEATURE indicates an optional part of the package. +They may also pay attention to `--with-PACKAGE' options, where PACKAGE +is something like `gnu-as' or `x' (for the X Window System). The +`README' should mention any `--enable-' and `--with-' options that the +package recognizes. + + For packages that use the X Window System, `configure' can usually +find the X include and library files automatically, but if it doesn't, +you can use the `configure' options `--x-includes=DIR' and +`--x-libraries=DIR' to specify their locations. + + Some packages offer the ability to configure how verbose the +execution of `make' will be. For these packages, running `./configure +--enable-silent-rules' sets the default to minimal output, which can be +overridden with `make V=1'; while running `./configure +--disable-silent-rules' sets the default to verbose, which can be +overridden with `make V=0'. + + +File: autoconf.info, Node: Particular Systems, Next: System Type, Prev: Optional Features, Up: Running configure Scripts + +16.6 Particular systems +======================= + +On HP-UX, the default C compiler is not ANSI C compatible. If GNU CC is +not installed, it is recommended to use the following options in order +to use an ANSI C compiler: + + ./configure CC="cc -Ae -D_XOPEN_SOURCE=500" + +and if that doesn't work, install pre-built binaries of GCC for HP-UX. + + HP-UX `make' updates targets which have the same time stamps as +their prerequisites, which makes it generally unusable when shipped +generated files such as `configure' are involved. Use GNU `make' +instead. + + On OSF/1 a.k.a. Tru64, some versions of the default C compiler cannot +parse its `<wchar.h>' header file. The option `-nodtk' can be used as +a workaround. If GNU CC is not installed, it is therefore recommended +to try + + ./configure CC="cc" + +and if that doesn't work, try + + ./configure CC="cc -nodtk" + + On Solaris, don't put `/usr/ucb' early in your `PATH'. This +directory contains several dysfunctional programs; working variants of +these programs are available in `/usr/bin'. So, if you need `/usr/ucb' +in your `PATH', put it _after_ `/usr/bin'. + + On Haiku, software installed for all users goes in `/boot/common', +not `/usr/local'. It is recommended to use the following options: + + ./configure --prefix=/boot/common + + +File: autoconf.info, Node: System Type, Next: Sharing Defaults, Prev: Particular Systems, Up: Running configure Scripts + +16.7 Specifying the System Type +=============================== + +There may be some features `configure' cannot figure out automatically, +but needs to determine by the type of machine the package will run on. +Usually, assuming the package is built to be run on the _same_ +architectures, `configure' can figure that out, but if it prints a +message saying it cannot guess the machine type, give it the +`--build=TYPE' option. TYPE can either be a short name for the system +type, such as `sun4', or a canonical name which has the form: + + CPU-COMPANY-SYSTEM + +where SYSTEM can have one of these forms: + + OS + KERNEL-OS + + See the file `config.sub' for the possible values of each field. If +`config.sub' isn't included in this package, then this package doesn't +need to know the machine type. + + If you are _building_ compiler tools for cross-compiling, you should +use the option `--target=TYPE' to select the type of system they will +produce code for. + + If you want to _use_ a cross compiler, that generates code for a +platform different from the build platform, you should specify the +"host" platform (i.e., that on which the generated programs will +eventually be run) with `--host=TYPE'. + + +File: autoconf.info, Node: Sharing Defaults, Next: Defining Variables, Prev: System Type, Up: Running configure Scripts + +16.8 Sharing Defaults +===================== + +If you want to set default values for `configure' scripts to share, you +can create a site shell script called `config.site' that gives default +values for variables like `CC', `cache_file', and `prefix'. +`configure' looks for `PREFIX/share/config.site' if it exists, then +`PREFIX/etc/config.site' if it exists. Or, you can set the +`CONFIG_SITE' environment variable to the location of the site script. +A warning: not all `configure' scripts look for a site script. + + +File: autoconf.info, Node: Defining Variables, Next: configure Invocation, Prev: Sharing Defaults, Up: Running configure Scripts + +16.9 Defining Variables +======================= + +Variables not defined in a site shell script can be set in the +environment passed to `configure'. However, some packages may run +configure again during the build, and the customized values of these +variables may be lost. In order to avoid this problem, you should set +them in the `configure' command line, using `VAR=value'. For example: + + ./configure CC=/usr/local2/bin/gcc + +causes the specified `gcc' to be used as the C compiler (unless it is +overridden in the site shell script). + +Unfortunately, this technique does not work for `CONFIG_SHELL' due to +an Autoconf limitation. Until the limitation is lifted, you can use +this workaround: + + CONFIG_SHELL=/bin/bash ./configure CONFIG_SHELL=/bin/bash + + +File: autoconf.info, Node: configure Invocation, Prev: Defining Variables, Up: Running configure Scripts + +16.10 `configure' Invocation +============================ + +`configure' recognizes the following options to control how it operates. + +`--help' +`-h' + Print a summary of all of the options to `configure', and exit. + +`--help=short' +`--help=recursive' + Print a summary of the options unique to this package's + `configure', and exit. The `short' variant lists options used + only in the top level, while the `recursive' variant lists options + also present in any nested packages. + +`--version' +`-V' + Print the version of Autoconf used to generate the `configure' + script, and exit. + +`--cache-file=FILE' + Enable the cache: use and save the results of the tests in FILE, + traditionally `config.cache'. FILE defaults to `/dev/null' to + disable caching. + +`--config-cache' +`-C' + Alias for `--cache-file=config.cache'. + +`--quiet' +`--silent' +`-q' + Do not print messages saying which checks are being made. To + suppress all normal output, redirect it to `/dev/null' (any error + messages will still be shown). + +`--srcdir=DIR' + Look for the package's source code in directory DIR. Usually + `configure' can determine that directory automatically. + +`--prefix=DIR' + Use DIR as the installation prefix. *note Installation Names:: + for more details, including other options available for fine-tuning + the installation locations. + +`--no-create' +`-n' + Run the configure checks, but stop before creating any output + files. + +`configure' also accepts some other, not widely useful, options. Run +`configure --help' for more details. + + +File: autoconf.info, Node: config.status Invocation, Next: Obsolete Constructs, Prev: Running configure Scripts, Up: Top + +17 config.status Invocation +*************************** + +The `configure' script creates a file named `config.status', which +actually configures, "instantiates", the template files. It also +records the configuration options that were specified when the package +was last configured in case reconfiguring is needed. + + Synopsis: + ./config.status [OPTION]... [TAG]... + + It configures each TAG; if none are specified, all the templates are +instantiated. A TAG refers to a file or other tag associated with a +configuration action, as specified by an `AC_CONFIG_ITEMS' macro (*note +Configuration Actions::). The files must be specified without their +dependencies, as in + + ./config.status foobar + +not + + ./config.status foobar:foo.in:bar.in + + The supported options are: + +`--help' +`-h' + Print a summary of the command line options, the list of the + template files, and exit. + +`--version' +`-V' + Print the version number of Autoconf and the configuration + settings, and exit. + +`--config' + Print the configuration settings in reusable way, quoted for the + shell, and exit. For example, for a debugging build that + otherwise reuses the configuration from a different build + directory BUILD-DIR of a package in SRC-DIR, you could use the + following: + + args=`BUILD-DIR/config.status --config` + eval SRC-DIR/configure "$args" CFLAGS=-g --srcdir=SRC-DIR + + Note that it may be necessary to override a `--srcdir' setting + that was saved in the configuration, if the arguments are used in a + different build directory. + +`--silent' +`--quiet' +`-q' + Do not print progress messages. + +`--debug' +`-d' + Don't remove the temporary files. + +`--file=FILE[:TEMPLATE]' + Require that FILE be instantiated as if + `AC_CONFIG_FILES(FILE:TEMPLATE)' was used. Both FILE and TEMPLATE + may be `-' in which case the standard output and/or standard + input, respectively, is used. If a TEMPLATE file name is + relative, it is first looked for in the build tree, and then in + the source tree. *Note Configuration Actions::, for more details. + + This option and the following ones provide one way for separately + distributed packages to share the values computed by `configure'. + Doing so can be useful if some of the packages need a superset of + the features that one of them, perhaps a common library, does. + These options allow a `config.status' file to create files other + than the ones that its `configure.ac' specifies, so it can be used + for a different package, or for extracting a subset of values. + For example, + + echo '@CC@' | ./config.status --file=- + + provides the value of `@CC@' on standard output. + +`--header=FILE[:TEMPLATE]' + Same as `--file' above, but with `AC_CONFIG_HEADERS'. + +`--recheck' + Ask `config.status' to update itself and exit (no instantiation). + This option is useful if you change `configure', so that the + results of some tests might be different from the previous run. + The `--recheck' option reruns `configure' with the same arguments + you used before, plus the `--no-create' option, which prevents + `configure' from running `config.status' and creating `Makefile' + and other files, and the `--no-recursion' option, which prevents + `configure' from running other `configure' scripts in + subdirectories. (This is so other Make rules can run + `config.status' when it changes; *note Automatic Remaking::, for + an example). + + `config.status' checks several optional environment variables that +can alter its behavior: + + -- Variable: CONFIG_SHELL + The shell with which to run `configure'. It must be + Bourne-compatible, and the absolute name of the shell should be + passed. The default is a shell that supports `LINENO' if + available, and `/bin/sh' otherwise. + + -- Variable: CONFIG_STATUS + The file name to use for the shell script that records the + configuration. The default is `./config.status'. This variable is + useful when one package uses parts of another and the `configure' + scripts shouldn't be merged because they are maintained separately. + + You can use `./config.status' in your makefiles. For example, in +the dependencies given above (*note Automatic Remaking::), +`config.status' is run twice when `configure.ac' has changed. If that +bothers you, you can make each run only regenerate the files for that +rule: + config.h: stamp-h + stamp-h: config.h.in config.status + ./config.status config.h + echo > stamp-h + + Makefile: Makefile.in config.status + ./config.status Makefile + + The calling convention of `config.status' has changed; see *note +Obsolete config.status Use::, for details. + + +File: autoconf.info, Node: Obsolete Constructs, Next: Using Autotest, Prev: config.status Invocation, Up: Top + +18 Obsolete Constructs +********************** + +Autoconf changes, and throughout the years some constructs have been +obsoleted. Most of the changes involve the macros, but in some cases +the tools themselves, or even some concepts, are now considered +obsolete. + + You may completely skip this chapter if you are new to Autoconf. Its +intention is mainly to help maintainers updating their packages by +understanding how to move to more modern constructs. + +* Menu: + +* Obsolete config.status Use:: Obsolete convention for `config.status' +* acconfig Header:: Additional entries in `config.h.in' +* autoupdate Invocation:: Automatic update of `configure.ac' +* Obsolete Macros:: Backward compatibility macros +* Autoconf 1:: Tips for upgrading your files +* Autoconf 2.13:: Some fresher tips + + +File: autoconf.info, Node: Obsolete config.status Use, Next: acconfig Header, Up: Obsolete Constructs + +18.1 Obsolete `config.status' Invocation +======================================== + +`config.status' now supports arguments to specify the files to +instantiate; see *note config.status Invocation::, for more details. +Before, environment variables had to be used. + + -- Variable: CONFIG_COMMANDS + The tags of the commands to execute. The default is the arguments + given to `AC_OUTPUT' and `AC_CONFIG_COMMANDS' in `configure.ac'. + + -- Variable: CONFIG_FILES + The files in which to perform `@VARIABLE@' substitutions. The + default is the arguments given to `AC_OUTPUT' and + `AC_CONFIG_FILES' in `configure.ac'. + + -- Variable: CONFIG_HEADERS + The files in which to substitute C `#define' statements. The + default is the arguments given to `AC_CONFIG_HEADERS'; if that + macro was not called, `config.status' ignores this variable. + + -- Variable: CONFIG_LINKS + The symbolic links to establish. The default is the arguments + given to `AC_CONFIG_LINKS'; if that macro was not called, + `config.status' ignores this variable. + + In *note config.status Invocation::, using this old interface, the +example would be: + + config.h: stamp-h + stamp-h: config.h.in config.status + CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \ + CONFIG_HEADERS=config.h ./config.status + echo > stamp-h + + Makefile: Makefile.in config.status + CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \ + CONFIG_FILES=Makefile ./config.status + +(If `configure.ac' does not call `AC_CONFIG_HEADERS', there is no need +to set `CONFIG_HEADERS' in the `make' rules. Equally for +`CONFIG_COMMANDS', etc.) + + +File: autoconf.info, Node: acconfig Header, Next: autoupdate Invocation, Prev: Obsolete config.status Use, Up: Obsolete Constructs + +18.2 `acconfig.h' +================= + +In order to produce `config.h.in', `autoheader' needs to build or to +find templates for each symbol. Modern releases of Autoconf use +`AH_VERBATIM' and `AH_TEMPLATE' (*note Autoheader Macros::), but in +older releases a file, `acconfig.h', contained the list of needed +templates. `autoheader' copied comments and `#define' and `#undef' +statements from `acconfig.h' in the current directory, if present. +This file used to be mandatory if you `AC_DEFINE' any additional +symbols. + + Modern releases of Autoconf also provide `AH_TOP' and `AH_BOTTOM' if +you need to prepend/append some information to `config.h.in'. Ancient +versions of Autoconf had a similar feature: if `./acconfig.h' contains +the string `@TOP@', `autoheader' copies the lines before the line +containing `@TOP@' into the top of the file that it generates. +Similarly, if `./acconfig.h' contains the string `@BOTTOM@', +`autoheader' copies the lines after that line to the end of the file it +generates. Either or both of those strings may be omitted. An even +older alternate way to produce the same effect in ancient versions of +Autoconf is to create the files `FILE.top' (typically `config.h.top') +and/or `FILE.bot' in the current directory. If they exist, +`autoheader' copies them to the beginning and end, respectively, of its +output. + + In former versions of Autoconf, the files used in preparing a +software package for distribution were: + configure.ac --. .------> autoconf* -----> configure + +---+ + [aclocal.m4] --+ `---. + [acsite.m4] ---' | + +--> [autoheader*] -> [config.h.in] + [acconfig.h] ----. | + +-----' + [config.h.top] --+ + [config.h.bot] --' + + Using only the `AH_' macros, `configure.ac' should be +self-contained, and should not depend upon `acconfig.h' etc. + + +File: autoconf.info, Node: autoupdate Invocation, Next: Obsolete Macros, Prev: acconfig Header, Up: Obsolete Constructs + +18.3 Using `autoupdate' to Modernize `configure.ac' +=================================================== + +The `autoupdate' program updates a `configure.ac' file that calls +Autoconf macros by their old names to use the current macro names. In +version 2 of Autoconf, most of the macros were renamed to use a more +uniform and descriptive naming scheme. *Note Macro Names::, for a +description of the new scheme. Although the old names still work +(*note Obsolete Macros::, for a list of the old macros and the +corresponding new names), you can make your `configure.ac' files more +readable and make it easier to use the current Autoconf documentation +if you update them to use the new macro names. + + If given no arguments, `autoupdate' updates `configure.ac', backing +up the original version with the suffix `~' (or the value of the +environment variable `SIMPLE_BACKUP_SUFFIX', if that is set). If you +give `autoupdate' an argument, it reads that file instead of +`configure.ac' and writes the updated file to the standard output. + +`autoupdate' accepts the following options: + +`--help' +`-h' + Print a summary of the command line options and exit. + +`--version' +`-V' + Print the version number of Autoconf and exit. + +`--verbose' +`-v' + Report processing steps. + +`--debug' +`-d' + Don't remove the temporary files. + +`--force' +`-f' + Force the update even if the file has not changed. Disregard the + cache. + +`--include=DIR' +`-I DIR' + Also look for input files in DIR. Multiple invocations accumulate. + Directories are browsed from last to first. + +`--prepend-include=DIR' +`-B DIR' + Prepend directory DIR to the search path. This is used to include + the language-specific files before any third-party macros. + + +File: autoconf.info, Node: Obsolete Macros, Next: Autoconf 1, Prev: autoupdate Invocation, Up: Obsolete Constructs + +18.4 Obsolete Macros +==================== + +Several macros are obsoleted in Autoconf, for various reasons (typically +they failed to quote properly, couldn't be extended for more recent +issues, etc.). They are still supported, but deprecated: their use +should be avoided. + + During the jump from Autoconf version 1 to version 2, most of the +macros were renamed to use a more uniform and descriptive naming scheme, +but their signature did not change. *Note Macro Names::, for a +description of the new naming scheme. Below, if there is just the +mapping from old names to new names for these macros, the reader is +invited to refer to the definition of the new macro for the signature +and the description. + + -- Macro: AC_AIX + This macro is a platform-specific subset of + `AC_USE_SYSTEM_EXTENSIONS' (*note AC_USE_SYSTEM_EXTENSIONS::). + + -- Macro: AC_ALLOCA + Replaced by `AC_FUNC_ALLOCA' (*note AC_FUNC_ALLOCA::). + + -- Macro: AC_ARG_ARRAY + Removed because of limited usefulness. + + -- Macro: AC_C_CROSS + This macro is obsolete; it does nothing. + + -- Macro: AC_C_LONG_DOUBLE + If the C compiler supports a working `long double' type with more + range or precision than the `double' type, define + `HAVE_LONG_DOUBLE'. + + You should use `AC_TYPE_LONG_DOUBLE' or + `AC_TYPE_LONG_DOUBLE_WIDER' instead. *Note Particular Types::. + + -- Macro: AC_CANONICAL_SYSTEM + Determine the system type and set output variables to the names of + the canonical system types. *Note Canonicalizing::, for details + about the variables this macro sets. + + The user is encouraged to use either `AC_CANONICAL_BUILD', or + `AC_CANONICAL_HOST', or `AC_CANONICAL_TARGET', depending on the + needs. Using `AC_CANONICAL_TARGET' is enough to run the two other + macros (*note Canonicalizing::). + + -- Macro: AC_CHAR_UNSIGNED + Replaced by `AC_C_CHAR_UNSIGNED' (*note AC_C_CHAR_UNSIGNED::). + + -- Macro: AC_CHECK_TYPE (TYPE, DEFAULT) + Autoconf, up to 2.13, used to provide this version of + `AC_CHECK_TYPE', deprecated because of its flaws. First, although + it is a member of the `CHECK' clan, it does more than just + checking. Secondly, missing types are defined using `#define', + not `typedef', and this can lead to problems in the case of + pointer types. + + This use of `AC_CHECK_TYPE' is obsolete and discouraged; see *note + Generic Types::, for the description of the current macro. + + If the type TYPE is not defined, define it to be the C (or C++) + builtin type DEFAULT, e.g., `short int' or `unsigned int'. + + This macro is equivalent to: + + AC_CHECK_TYPE([TYPE], [], + [AC_DEFINE_UNQUOTED([TYPE], [DEFAULT], + [Define to `DEFAULT' + if <sys/types.h> does not define.])]) + + In order to keep backward compatibility, the two versions of + `AC_CHECK_TYPE' are implemented, selected using these heuristics: + + 1. If there are three or four arguments, the modern version is + used. + + 2. If the second argument appears to be a C or C++ type, then the + obsolete version is used. This happens if the argument is a + C or C++ _builtin_ type or a C identifier ending in `_t', + optionally followed by one of `[(* ' and then by a string of + zero or more characters taken from the set `[]()* _a-zA-Z0-9'. + + 3. If the second argument is spelled with the alphabet of valid + C and C++ types, the user is warned and the modern version is + used. + + 4. Otherwise, the modern version is used. + + You are encouraged either to use a valid builtin type, or to use + the equivalent modern code (see above), or better yet, to use + `AC_CHECK_TYPES' together with + + #ifndef HAVE_LOFF_T + typedef loff_t off_t; + #endif + + -- Macro: AC_CHECKING (FEATURE-DESCRIPTION) + Same as + + AC_MSG_NOTICE([checking FEATURE-DESCRIPTION...] + + *Note AC_MSG_NOTICE::. + + -- Macro: AC_COMPILE_CHECK (ECHO-TEXT, INCLUDES, FUNCTION-BODY, + ACTION-IF-TRUE, [ACTION-IF-FALSE]) + This is an obsolete version of `AC_TRY_COMPILE' itself replaced by + `AC_COMPILE_IFELSE' (*note Running the Compiler::), with the + addition that it prints `checking for ECHO-TEXT' to the standard + output first, if ECHO-TEXT is non-empty. Use `AC_MSG_CHECKING' + and `AC_MSG_RESULT' instead to print messages (*note Printing + Messages::). + + -- Macro: AC_CONST + Replaced by `AC_C_CONST' (*note AC_C_CONST::). + + -- Macro: AC_CROSS_CHECK + Same as `AC_C_CROSS', which is obsolete too, and does nothing + `:-)'. + + -- Macro: AC_CYGWIN + Check for the Cygwin environment in which case the shell variable + `CYGWIN' is set to `yes'. Don't use this macro, the dignified + means to check the nature of the host is using `AC_CANONICAL_HOST' + (*note Canonicalizing::). As a matter of fact this macro is + defined as: + + AC_REQUIRE([AC_CANONICAL_HOST])[]dnl + case $host_os in + *cygwin* ) CYGWIN=yes;; + * ) CYGWIN=no;; + esac + + Beware that the variable `CYGWIN' has a special meaning when + running Cygwin, and should not be changed. That's yet another + reason not to use this macro. + + -- Macro: AC_DECL_SYS_SIGLIST + Same as: + + AC_CHECK_DECLS([sys_siglist], [], [], + [#include <signal.h> + /* NetBSD declares sys_siglist in unistd.h. */ + #ifdef HAVE_UNISTD_H + # include <unistd.h> + #endif + ]) + + *Note AC_CHECK_DECLS::. + + -- Macro: AC_DECL_YYTEXT + Does nothing, now integrated in `AC_PROG_LEX' (*note + AC_PROG_LEX::). + + -- Macro: AC_DIR_HEADER + Like calling `AC_FUNC_CLOSEDIR_VOID' (*note + AC_FUNC_CLOSEDIR_VOID::) and `AC_HEADER_DIRENT' (*note + AC_HEADER_DIRENT::), but defines a different set of C preprocessor + macros to indicate which header file is found: + + Header Old Symbol New Symbol + `dirent.h' `DIRENT' `HAVE_DIRENT_H' + `sys/ndir.h' `SYSNDIR' `HAVE_SYS_NDIR_H' + `sys/dir.h' `SYSDIR' `HAVE_SYS_DIR_H' + `ndir.h' `NDIR' `HAVE_NDIR_H' + + -- Macro: AC_DYNIX_SEQ + If on DYNIX/ptx, add `-lseq' to output variable `LIBS'. This + macro used to be defined as + + AC_CHECK_LIB([seq], [getmntent], [LIBS="-lseq $LIBS"]) + + now it is just `AC_FUNC_GETMNTENT' (*note AC_FUNC_GETMNTENT::). + + -- Macro: AC_EXEEXT + Defined the output variable `EXEEXT' based on the output of the + compiler, which is now done automatically. Typically set to empty + string if Posix and `.exe' if a DOS variant. + + -- Macro: AC_EMXOS2 + Similar to `AC_CYGWIN' but checks for the EMX environment on OS/2 + and sets `EMXOS2'. Don't use this macro, the dignified means to + check the nature of the host is using `AC_CANONICAL_HOST' (*note + Canonicalizing::). + + -- Macro: AC_ENABLE (FEATURE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN]) + This is an obsolete version of `AC_ARG_ENABLE' that does not + support providing a help string (*note AC_ARG_ENABLE::). + + -- Macro: AC_ERROR + Replaced by `AC_MSG_ERROR' (*note AC_MSG_ERROR::). + + -- Macro: AC_FIND_X + Replaced by `AC_PATH_X' (*note AC_PATH_X::). + + -- Macro: AC_FIND_XTRA + Replaced by `AC_PATH_XTRA' (*note AC_PATH_XTRA::). + + -- Macro: AC_FOREACH + Replaced by `m4_foreach_w' (*note m4_foreach_w::). + + -- Macro: AC_FUNC_CHECK + Replaced by `AC_CHECK_FUNC' (*note AC_CHECK_FUNC::). + + -- Macro: AC_FUNC_SETVBUF_REVERSED + Do nothing. Formerly, this macro checked whether `setvbuf' takes + the buffering type as its second argument and the buffer pointer + as the third, instead of the other way around, and defined + `SETVBUF_REVERSED'. However, the last systems to have the problem + were those based on SVR2, which became obsolete in 1987, and the + macro is no longer needed. + + -- Macro: AC_FUNC_WAIT3 + If `wait3' is found and fills in the contents of its third argument + (a `struct rusage *'), which HP-UX does not do, define + `HAVE_WAIT3'. + + These days portable programs should use `waitpid', not `wait3', as + `wait3' has been removed from Posix. + + -- Macro: AC_GCC_TRADITIONAL + Replaced by `AC_PROG_GCC_TRADITIONAL' (*note + AC_PROG_GCC_TRADITIONAL::). + + -- Macro: AC_GETGROUPS_T + Replaced by `AC_TYPE_GETGROUPS' (*note AC_TYPE_GETGROUPS::). + + -- Macro: AC_GETLOADAVG + Replaced by `AC_FUNC_GETLOADAVG' (*note AC_FUNC_GETLOADAVG::). + + -- Macro: AC_GNU_SOURCE + This macro is a platform-specific subset of + `AC_USE_SYSTEM_EXTENSIONS' (*note AC_USE_SYSTEM_EXTENSIONS::). + + -- Macro: AC_HAVE_FUNCS + Replaced by `AC_CHECK_FUNCS' (*note AC_CHECK_FUNCS::). + + -- Macro: AC_HAVE_HEADERS + Replaced by `AC_CHECK_HEADERS' (*note AC_CHECK_HEADERS::). + + -- Macro: AC_HAVE_LIBRARY (LIBRARY, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND], [OTHER-LIBRARIES]) + This macro is equivalent to calling `AC_CHECK_LIB' with a FUNCTION + argument of `main'. In addition, LIBRARY can be written as any of + `foo', `-lfoo', or `libfoo.a'. In all of those cases, the + compiler is passed `-lfoo'. However, LIBRARY cannot be a shell + variable; it must be a literal name. *Note AC_CHECK_LIB::. + + -- Macro: AC_HAVE_POUNDBANG + Replaced by `AC_SYS_INTERPRETER' (*note AC_SYS_INTERPRETER::). + + -- Macro: AC_HEADER_CHECK + Replaced by `AC_CHECK_HEADER' (*note AC_CHECK_HEADER::). + + -- Macro: AC_HEADER_EGREP + Replaced by `AC_EGREP_HEADER' (*note AC_EGREP_HEADER::). + + -- Macro: AC_HELP_STRING + Replaced by `AS_HELP_STRING' (*note AS_HELP_STRING::). + + -- Macro: AC_INIT (UNIQUE-FILE-IN-SOURCE-DIR) + Formerly `AC_INIT' used to have a single argument, and was + equivalent to: + + AC_INIT + AC_CONFIG_SRCDIR(UNIQUE-FILE-IN-SOURCE-DIR) + See *note AC_INIT:: and *note AC_CONFIG_SRCDIR::. + + -- Macro: AC_INLINE + Replaced by `AC_C_INLINE' (*note AC_C_INLINE::). + + -- Macro: AC_INT_16_BITS + If the C type `int' is 16 bits wide, define `INT_16_BITS'. Use + `AC_CHECK_SIZEOF(int)' instead (*note AC_CHECK_SIZEOF::). + + -- Macro: AC_IRIX_SUN + If on IRIX (Silicon Graphics Unix), add `-lsun' to output `LIBS'. + If you were using it to get `getmntent', use `AC_FUNC_GETMNTENT' + instead. If you used it for the NIS versions of the password and + group functions, use `AC_CHECK_LIB(sun, getpwnam)'. Up to + Autoconf 2.13, it used to be + + AC_CHECK_LIB([sun], [getmntent], [LIBS="-lsun $LIBS"]) + + now it is defined as + + AC_FUNC_GETMNTENT + AC_CHECK_LIB([sun], [getpwnam]) + + See *note AC_FUNC_GETMNTENT:: and *note AC_CHECK_LIB::. + + -- Macro: AC_ISC_POSIX + This macro adds `-lcposix' to output variable `LIBS' if necessary + for Posix facilities. Sun dropped support for the obsolete + INTERACTIVE Systems Corporation Unix on 2006-07-23. New programs + need not use this macro. It is implemented as + `AC_SEARCH_LIBS([strerror], [cposix])' (*note AC_SEARCH_LIBS::). + + -- Macro: AC_LANG_C + Same as `AC_LANG([C])' (*note AC_LANG::). + + -- Macro: AC_LANG_CPLUSPLUS + Same as `AC_LANG([C++])' (*note AC_LANG::). + + -- Macro: AC_LANG_FORTRAN77 + Same as `AC_LANG([Fortran 77])' (*note AC_LANG::). + + -- Macro: AC_LANG_RESTORE + Select the LANGUAGE that is saved on the top of the stack, as set + by `AC_LANG_SAVE', remove it from the stack, and call + `AC_LANG(LANGUAGE)'. *Note Language Choice::, for the preferred + way to change languages. + + -- Macro: AC_LANG_SAVE + Remember the current language (as set by `AC_LANG') on a stack. + The current language does not change. `AC_LANG_PUSH' is preferred + (*note AC_LANG_PUSH::). + + -- Macro: AC_LINK_FILES (SOURCE..., DEST...) + This is an obsolete version of `AC_CONFIG_LINKS' (*note + AC_CONFIG_LINKS::. An updated version of: + + AC_LINK_FILES(config/$machine.h config/$obj_format.h, + host.h object.h) + + is: + + AC_CONFIG_LINKS([host.h:config/$machine.h + object.h:config/$obj_format.h]) + + -- Macro: AC_LN_S + Replaced by `AC_PROG_LN_S' (*note AC_PROG_LN_S::). + + -- Macro: AC_LONG_64_BITS + Define `LONG_64_BITS' if the C type `long int' is 64 bits wide. + Use the generic macro `AC_CHECK_SIZEOF([long int])' instead (*note + AC_CHECK_SIZEOF::). + + -- Macro: AC_LONG_DOUBLE + If the C compiler supports a working `long double' type with more + range or precision than the `double' type, define + `HAVE_LONG_DOUBLE'. + + You should use `AC_TYPE_LONG_DOUBLE' or + `AC_TYPE_LONG_DOUBLE_WIDER' instead. *Note Particular Types::. + + -- Macro: AC_LONG_FILE_NAMES + Replaced by + AC_SYS_LONG_FILE_NAMES + *Note AC_SYS_LONG_FILE_NAMES::. + + -- Macro: AC_MAJOR_HEADER + Replaced by `AC_HEADER_MAJOR' (*note AC_HEADER_MAJOR::). + + -- Macro: AC_MEMORY_H + Used to define `NEED_MEMORY_H' if the `mem' functions were defined + in `memory.h'. Today it is equivalent to + `AC_CHECK_HEADERS([memory.h])' (*note AC_CHECK_HEADERS::). Adjust + your code to depend upon `HAVE_MEMORY_H', not `NEED_MEMORY_H'; see + *note Standard Symbols::. + + -- Macro: AC_MINGW32 + Similar to `AC_CYGWIN' but checks for the MinGW compiler + environment and sets `MINGW32'. Don't use this macro, the + dignified means to check the nature of the host is using + `AC_CANONICAL_HOST' (*note Canonicalizing::). + + -- Macro: AC_MINIX + This macro is a platform-specific subset of + `AC_USE_SYSTEM_EXTENSIONS' (*note AC_USE_SYSTEM_EXTENSIONS::). + + -- Macro: AC_MINUS_C_MINUS_O + Replaced by `AC_PROG_CC_C_O' (*note AC_PROG_CC_C_O::). + + -- Macro: AC_MMAP + Replaced by `AC_FUNC_MMAP' (*note AC_FUNC_MMAP::). + + -- Macro: AC_MODE_T + Replaced by `AC_TYPE_MODE_T' (*note AC_TYPE_MODE_T::). + + -- Macro: AC_OBJEXT + Defined the output variable `OBJEXT' based on the output of the + compiler, after .c files have been excluded. Typically set to `o' + if Posix, `obj' if a DOS variant. Now the compiler checking + macros handle this automatically. + + -- Macro: AC_OBSOLETE (THIS-MACRO-NAME, [SUGGESTION]) + Make M4 print a message to the standard error output warning that + THIS-MACRO-NAME is obsolete, and giving the file and line number + where it was called. THIS-MACRO-NAME should be the name of the + macro that is calling `AC_OBSOLETE'. If SUGGESTION is given, it + is printed at the end of the warning message; for example, it can + be a suggestion for what to use instead of THIS-MACRO-NAME. + + For instance + + AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl + + You are encouraged to use `AU_DEFUN' instead, since it gives better + services to the user (*note AU_DEFUN::). + + -- Macro: AC_OFF_T + Replaced by `AC_TYPE_OFF_T' (*note AC_TYPE_OFF_T::). + + -- Macro: AC_OUTPUT ([FILE]..., [EXTRA-CMDS], [INIT-CMDS]) + The use of `AC_OUTPUT' with arguments is deprecated. This + obsoleted interface is equivalent to: + + AC_CONFIG_FILES(FILE...) + AC_CONFIG_COMMANDS([default], + EXTRA-CMDS, INIT-CMDS) + AC_OUTPUT + + See *note AC_CONFIG_FILES::, *note AC_CONFIG_COMMANDS::, and *note + AC_OUTPUT::. + + -- Macro: AC_OUTPUT_COMMANDS (EXTRA-CMDS, [INIT-CMDS]) + Specify additional shell commands to run at the end of + `config.status', and shell commands to initialize any variables + from `configure'. This macro may be called multiple times. It is + obsolete, replaced by `AC_CONFIG_COMMANDS' (*note + AC_CONFIG_COMMANDS::). + + Here is an unrealistic example: + + fubar=27 + AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.], + [fubar=$fubar]) + AC_OUTPUT_COMMANDS([echo this is another, extra, bit], + [echo init bit]) + + Aside from the fact that `AC_CONFIG_COMMANDS' requires an + additional key, an important difference is that + `AC_OUTPUT_COMMANDS' is quoting its arguments twice, unlike + `AC_CONFIG_COMMANDS'. This means that `AC_CONFIG_COMMANDS' can + safely be given macro calls as arguments: + + AC_CONFIG_COMMANDS(foo, [my_FOO()]) + + Conversely, where one level of quoting was enough for literal + strings with `AC_OUTPUT_COMMANDS', you need two with + `AC_CONFIG_COMMANDS'. The following lines are equivalent: + + AC_OUTPUT_COMMANDS([echo "Square brackets: []"]) + AC_CONFIG_COMMANDS([default], [[echo "Square brackets: []"]]) + + -- Macro: AC_PID_T + Replaced by `AC_TYPE_PID_T' (*note AC_TYPE_PID_T::). + + -- Macro: AC_PREFIX + Replaced by `AC_PREFIX_PROGRAM' (*note AC_PREFIX_PROGRAM::). + + -- Macro: AC_PROGRAMS_CHECK + Replaced by `AC_CHECK_PROGS' (*note AC_CHECK_PROGS::). + + -- Macro: AC_PROGRAMS_PATH + Replaced by `AC_PATH_PROGS' (*note AC_PATH_PROGS::). + + -- Macro: AC_PROGRAM_CHECK + Replaced by `AC_CHECK_PROG' (*note AC_CHECK_PROG::). + + -- Macro: AC_PROGRAM_EGREP + Replaced by `AC_EGREP_CPP' (*note AC_EGREP_CPP::). + + -- Macro: AC_PROGRAM_PATH + Replaced by `AC_PATH_PROG' (*note AC_PATH_PROG::). + + -- Macro: AC_REMOTE_TAPE + Removed because of limited usefulness. + + -- Macro: AC_RESTARTABLE_SYSCALLS + This macro was renamed `AC_SYS_RESTARTABLE_SYSCALLS'. However, + these days portable programs should use `sigaction' with + `SA_RESTART' if they want restartable system calls. They should + not rely on `HAVE_RESTARTABLE_SYSCALLS', since nowadays whether a + system call is restartable is a dynamic issue, not a + configuration-time issue. + + -- Macro: AC_RETSIGTYPE + Replaced by `AC_TYPE_SIGNAL' (*note AC_TYPE_SIGNAL::), which itself + is obsolete when assuming C89 or better. + + -- Macro: AC_RSH + Removed because of limited usefulness. + + -- Macro: AC_SCO_INTL + If on SCO Unix, add `-lintl' to output variable `LIBS'. This + macro used to do this: + + AC_CHECK_LIB([intl], [strftime], [LIBS="-lintl $LIBS"]) + + Now it just calls `AC_FUNC_STRFTIME' instead (*note + AC_FUNC_STRFTIME::). + + -- Macro: AC_SETVBUF_REVERSED + Replaced by + AC_FUNC_SETVBUF_REVERSED + *Note AC_FUNC_SETVBUF_REVERSED::. + + -- Macro: AC_SET_MAKE + Replaced by `AC_PROG_MAKE_SET' (*note AC_PROG_MAKE_SET::). + + -- Macro: AC_SIZEOF_TYPE + Replaced by `AC_CHECK_SIZEOF' (*note AC_CHECK_SIZEOF::). + + -- Macro: AC_SIZE_T + Replaced by `AC_TYPE_SIZE_T' (*note AC_TYPE_SIZE_T::). + + -- Macro: AC_STAT_MACROS_BROKEN + Replaced by `AC_HEADER_STAT' (*note AC_HEADER_STAT::). + + -- Macro: AC_STDC_HEADERS + Replaced by `AC_HEADER_STDC' (*note AC_HEADER_STDC::). + + -- Macro: AC_STRCOLL + Replaced by `AC_FUNC_STRCOLL' (*note AC_FUNC_STRCOLL::). + + -- Macro: AC_STRUCT_ST_BLKSIZE + If `struct stat' contains an `st_blksize' member, define + `HAVE_STRUCT_STAT_ST_BLKSIZE'. The former name, `HAVE_ST_BLKSIZE' + is to be avoided, as its support will cease in the future. This + macro is obsoleted, and should be replaced by + + AC_CHECK_MEMBERS([struct stat.st_blksize]) + *Note AC_CHECK_MEMBERS::. + + -- Macro: AC_STRUCT_ST_RDEV + If `struct stat' contains an `st_rdev' member, define + `HAVE_STRUCT_STAT_ST_RDEV'. The former name for this macro, + `HAVE_ST_RDEV', is to be avoided as it will cease to be supported + in the future. Actually, even the new macro is obsolete and + should be replaced by: + AC_CHECK_MEMBERS([struct stat.st_rdev]) + *Note AC_CHECK_MEMBERS::. + + -- Macro: AC_ST_BLKSIZE + Replaced by `AC_CHECK_MEMBERS' (*note AC_CHECK_MEMBERS::). + + -- Macro: AC_ST_BLOCKS + Replaced by `AC_STRUCT_ST_BLOCKS' (*note AC_STRUCT_ST_BLOCKS::). + + -- Macro: AC_ST_RDEV + Replaced by `AC_CHECK_MEMBERS' (*note AC_CHECK_MEMBERS::). + + -- Macro: AC_SYS_RESTARTABLE_SYSCALLS + If the system automatically restarts a system call that is + interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'. This + macro does not check whether system calls are restarted in + general--it checks whether a signal handler installed with + `signal' (but not `sigaction') causes system calls to be + restarted. It does not check whether system calls can be + restarted when interrupted by signals that have no handler. + + These days portable programs should use `sigaction' with + `SA_RESTART' if they want restartable system calls. They should + not rely on `HAVE_RESTARTABLE_SYSCALLS', since nowadays whether a + system call is restartable is a dynamic issue, not a + configuration-time issue. + + -- Macro: AC_SYS_SIGLIST_DECLARED + This macro was renamed `AC_DECL_SYS_SIGLIST'. However, even that + name is obsolete, as the same functionality is now achieved via + `AC_CHECK_DECLS' (*note AC_CHECK_DECLS::). + + -- Macro: AC_TEST_CPP + This macro was renamed `AC_TRY_CPP', which in turn was replaced by + `AC_PREPROC_IFELSE' (*note AC_PREPROC_IFELSE::). + + -- Macro: AC_TEST_PROGRAM + This macro was renamed `AC_TRY_RUN', which in turn was replaced by + `AC_RUN_IFELSE' (*note AC_RUN_IFELSE::). + + -- Macro: AC_TIMEZONE + Replaced by `AC_STRUCT_TIMEZONE' (*note AC_STRUCT_TIMEZONE::). + + -- Macro: AC_TIME_WITH_SYS_TIME + Replaced by `AC_HEADER_TIME' (*note AC_HEADER_TIME::). + + -- Macro: AC_TRY_COMPILE (INCLUDES, FUNCTION-BODY, [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + Same as: + + AC_COMPILE_IFELSE( + [AC_LANG_PROGRAM([[INCLUDES]], + [[FUNCTION-BODY]])], + [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + + *Note Running the Compiler::. + + This macro double quotes both INCLUDES and FUNCTION-BODY. + + For C and C++, INCLUDES is any `#include' statements needed by the + code in FUNCTION-BODY (INCLUDES is ignored if the currently + selected language is Fortran or Fortran 77). The compiler and + compilation flags are determined by the current language (*note + Language Choice::). + + -- Macro: AC_TRY_CPP (INPUT, [ACTION-IF-TRUE], [ACTION-IF-FALSE]) + Same as: + + AC_PREPROC_IFELSE( + [AC_LANG_SOURCE([[INPUT]])], + [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + + *Note Running the Preprocessor::. + + This macro double quotes the INPUT. + + -- Macro: AC_TRY_LINK (INCLUDES, FUNCTION-BODY, [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + Same as: + + AC_LINK_IFELSE( + [AC_LANG_PROGRAM([[INCLUDES]], + [[FUNCTION-BODY]])], + [ACTION-IF-TRUE], + [ACTION-IF-FALSE]) + + *Note Running the Compiler::. + + This macro double quotes both INCLUDES and FUNCTION-BODY. + + Depending on the current language (*note Language Choice::), + create a test program to see whether a function whose body + consists of FUNCTION-BODY can be compiled and linked. If the file + compiles and links successfully, run shell commands + ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND. + + This macro double quotes both INCLUDES and FUNCTION-BODY. + + For C and C++, INCLUDES is any `#include' statements needed by the + code in FUNCTION-BODY (INCLUDES is ignored if the currently + selected language is Fortran or Fortran 77). The compiler and + compilation flags are determined by the current language (*note + Language Choice::), and in addition `LDFLAGS' and `LIBS' are used + for linking. + + -- Macro: AC_TRY_LINK_FUNC (FUNCTION, [ACTION-IF-FOUND], + [ACTION-IF-NOT-FOUND]) + This macro is equivalent to + AC_LINK_IFELSE([AC_LANG_CALL([], [FUNCTION])], + [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) + *Note AC_LINK_IFELSE::. + + -- Macro: AC_TRY_RUN (PROGRAM, [ACTION-IF-TRUE], [ACTION-IF-FALSE], + [ACTION-IF-CROSS-COMPILING = `AC_MSG_FAILURE']) + Same as: + + AC_RUN_IFELSE( + [AC_LANG_SOURCE([[PROGRAM]])], + [ACTION-IF-TRUE], + [ACTION-IF-FALSE], + [ACTION-IF-CROSS-COMPILING]) + + *Note Runtime::. + + -- Macro: AC_TYPE_SIGNAL + If `signal.h' declares `signal' as returning a pointer to a + function returning `void', define `RETSIGTYPE' to be `void'; + otherwise, define it to be `int'. These days, it is portable to + assume C89, and that signal handlers return `void', without + needing to use this macro or `RETSIGTYPE'. + + When targeting older K&R C, it is possible to define signal + handlers as returning type `RETSIGTYPE', and omit a return + statement: + + RETSIGTYPE + hup_handler () + { + ... + } + + -- Macro: AC_UID_T + Replaced by `AC_TYPE_UID_T' (*note AC_TYPE_UID_T::). + + -- Macro: AC_UNISTD_H + Same as `AC_CHECK_HEADERS([unistd.h])' (*note AC_CHECK_HEADERS::). + + -- Macro: AC_USG + Define `USG' if the BSD string functions are defined in + `strings.h'. You should no longer depend upon `USG', but on + `HAVE_STRING_H'; see *note Standard Symbols::. + + -- Macro: AC_UTIME_NULL + Replaced by `AC_FUNC_UTIME_NULL' (*note AC_FUNC_UTIME_NULL::). + + -- Macro: AC_VALIDATE_CACHED_SYSTEM_TUPLE ([CMD]) + If the cache file is inconsistent with the current host, target and + build system types, it used to execute CMD or print a default + error message. This is now handled by default. + + -- Macro: AC_VERBOSE (RESULT-DESCRIPTION) + Replaced by `AC_MSG_RESULT' (*note AC_MSG_RESULT::). + + -- Macro: AC_VFORK + Replaced by `AC_FUNC_FORK' (*note AC_FUNC_FORK::). + + -- Macro: AC_VPRINTF + Replaced by `AC_FUNC_VPRINTF' (*note AC_FUNC_VPRINTF::). + + -- Macro: AC_WAIT3 + This macro was renamed `AC_FUNC_WAIT3'. However, these days + portable programs should use `waitpid', not `wait3', as `wait3' + has been removed from Posix. + + -- Macro: AC_WARN + Replaced by `AC_MSG_WARN' (*note AC_MSG_WARN::). + + -- Macro: AC_WITH (PACKAGE, ACTION-IF-GIVEN, [ACTION-IF-NOT-GIVEN]) + This is an obsolete version of `AC_ARG_WITH' that does not support + providing a help string (*note AC_ARG_WITH::). + + -- Macro: AC_WORDS_BIGENDIAN + Replaced by `AC_C_BIGENDIAN' (*note AC_C_BIGENDIAN::). + + -- Macro: AC_XENIX_DIR + This macro used to add `-lx' to output variable `LIBS' if on + Xenix. Also, if `dirent.h' is being checked for, added `-ldir' to + `LIBS'. Now it is merely an alias of `AC_HEADER_DIRENT' instead, + plus some code to detect whether running XENIX on which you should + not depend: + + AC_MSG_CHECKING([for Xenix]) + AC_EGREP_CPP([yes], + [#if defined M_XENIX && !defined M_UNIX + yes + #endif], + [AC_MSG_RESULT([yes]); XENIX=yes], + [AC_MSG_RESULT([no]); XENIX=]) + Don't use this macro, the dignified means to check the nature of + the host is using `AC_CANONICAL_HOST' (*note Canonicalizing::). + + -- Macro: AC_YYTEXT_POINTER + This macro was renamed `AC_DECL_YYTEXT', which in turn was + integrated into `AC_PROG_LEX' (*note AC_PROG_LEX::). + + +File: autoconf.info, Node: Autoconf 1, Next: Autoconf 2.13, Prev: Obsolete Macros, Up: Obsolete Constructs + +18.5 Upgrading From Version 1 +============================= + +Autoconf version 2 is mostly backward compatible with version 1. +However, it introduces better ways to do some things, and doesn't +support some of the ugly things in version 1. So, depending on how +sophisticated your `configure.ac' files are, you might have to do some +manual work in order to upgrade to version 2. This chapter points out +some problems to watch for when upgrading. Also, perhaps your +`configure' scripts could benefit from some of the new features in +version 2; the changes are summarized in the file `NEWS' in the +Autoconf distribution. + +* Menu: + +* Changed File Names:: Files you might rename +* Changed Makefiles:: New things to put in `Makefile.in' +* Changed Macros:: Macro calls you might replace +* Changed Results:: Changes in how to check test results +* Changed Macro Writing:: Better ways to write your own macros + + +File: autoconf.info, Node: Changed File Names, Next: Changed Makefiles, Up: Autoconf 1 + +18.5.1 Changed File Names +------------------------- + +If you have an `aclocal.m4' installed with Autoconf (as opposed to in a +particular package's source directory), you must rename it to +`acsite.m4'. *Note autoconf Invocation::. + + If you distribute `install.sh' with your package, rename it to +`install-sh' so `make' builtin rules don't inadvertently create a file +called `install' from it. `AC_PROG_INSTALL' looks for the script under +both names, but it is best to use the new name. + + If you were using `config.h.top', `config.h.bot', or `acconfig.h', +you still can, but you have less clutter if you use the `AH_' macros. +*Note Autoheader Macros::. + + +File: autoconf.info, Node: Changed Makefiles, Next: Changed Macros, Prev: Changed File Names, Up: Autoconf 1 + +18.5.2 Changed Makefiles +------------------------ + +Add `@CFLAGS@', `@CPPFLAGS@', and `@LDFLAGS@' in your `Makefile.in' +files, so they can take advantage of the values of those variables in +the environment when `configure' is run. Doing this isn't necessary, +but it's a convenience for users. + + Also add `@configure_input@' in a comment to each input file for +`AC_OUTPUT', so that the output files contain a comment saying they +were produced by `configure'. Automatically selecting the right +comment syntax for all the kinds of files that people call `AC_OUTPUT' +on became too much work. + + Add `config.log' and `config.cache' to the list of files you remove +in `distclean' targets. + + If you have the following in `Makefile.in': + + prefix = /usr/local + exec_prefix = $(prefix) + +you must change it to: + + prefix = @prefix@ + exec_prefix = @exec_prefix@ + +The old behavior of replacing those variables without `@' characters +around them has been removed. + + +File: autoconf.info, Node: Changed Macros, Next: Changed Results, Prev: Changed Makefiles, Up: Autoconf 1 + +18.5.3 Changed Macros +--------------------- + +Many of the macros were renamed in Autoconf version 2. You can still +use the old names, but the new ones are clearer, and it's easier to find +the documentation for them. *Note Obsolete Macros::, for a table +showing the new names for the old macros. Use the `autoupdate' program +to convert your `configure.ac' to using the new macro names. *Note +autoupdate Invocation::. + + Some macros have been superseded by similar ones that do the job +better, but are not call-compatible. If you get warnings about calling +obsolete macros while running `autoconf', you may safely ignore them, +but your `configure' script generally works better if you follow the +advice that is printed about what to replace the obsolete macros with. +In particular, the mechanism for reporting the results of tests has +changed. If you were using `echo' or `AC_VERBOSE' (perhaps via +`AC_COMPILE_CHECK'), your `configure' script's output looks better if +you switch to `AC_MSG_CHECKING' and `AC_MSG_RESULT'. *Note Printing +Messages::. Those macros work best in conjunction with cache +variables. *Note Caching Results::. + + +File: autoconf.info, Node: Changed Results, Next: Changed Macro Writing, Prev: Changed Macros, Up: Autoconf 1 + +18.5.4 Changed Results +---------------------- + +If you were checking the results of previous tests by examining the +shell variable `DEFS', you need to switch to checking the values of the +cache variables for those tests. `DEFS' no longer exists while +`configure' is running; it is only created when generating output +files. This difference from version 1 is because properly quoting the +contents of that variable turned out to be too cumbersome and +inefficient to do every time `AC_DEFINE' is called. *Note Cache +Variable Names::. + + For example, here is a `configure.ac' fragment written for Autoconf +version 1: + + AC_HAVE_FUNCS(syslog) + case "$DEFS" in + *-DHAVE_SYSLOG*) ;; + *) # syslog is not in the default libraries. See if it's in some other. + saved_LIBS="$LIBS" + for lib in bsd socket inet; do + AC_CHECKING(for syslog in -l$lib) + LIBS="-l$lib $saved_LIBS" + AC_HAVE_FUNCS(syslog) + case "$DEFS" in + *-DHAVE_SYSLOG*) break ;; + *) ;; + esac + LIBS="$saved_LIBS" + done ;; + esac + + Here is a way to write it for version 2: + + AC_CHECK_FUNCS([syslog]) + if test "x$ac_cv_func_syslog" = xno; then + # syslog is not in the default libraries. See if it's in some other. + for lib in bsd socket inet; do + AC_CHECK_LIB([$lib], [syslog], [AC_DEFINE([HAVE_SYSLOG]) + LIBS="-l$lib $LIBS"; break]) + done + fi + + If you were working around bugs in `AC_DEFINE_UNQUOTED' by adding +backslashes before quotes, you need to remove them. It now works +predictably, and does not treat quotes (except back quotes) specially. +*Note Setting Output Variables::. + + All of the Boolean shell variables set by Autoconf macros now use +`yes' for the true value. Most of them use `no' for false, though for +backward compatibility some use the empty string instead. If you were +relying on a shell variable being set to something like 1 or `t' for +true, you need to change your tests. + + +File: autoconf.info, Node: Changed Macro Writing, Prev: Changed Results, Up: Autoconf 1 + +18.5.5 Changed Macro Writing +---------------------------- + +When defining your own macros, you should now use `AC_DEFUN' instead of +`define'. `AC_DEFUN' automatically calls `AC_PROVIDE' and ensures that +macros called via `AC_REQUIRE' do not interrupt other macros, to +prevent nested `checking...' messages on the screen. There's no actual +harm in continuing to use the older way, but it's less convenient and +attractive. *Note Macro Definitions::. + + You probably looked at the macros that came with Autoconf as a guide +for how to do things. It would be a good idea to take a look at the new +versions of them, as the style is somewhat improved and they take +advantage of some new features. + + If you were doing tricky things with undocumented Autoconf internals +(macros, variables, diversions), check whether you need to change +anything to account for changes that have been made. Perhaps you can +even use an officially supported technique in version 2 instead of +kludging. Or perhaps not. + + To speed up your locally written feature tests, add caching to them. +See whether any of your tests are of general enough usefulness to +encapsulate them into macros that you can share. + + +File: autoconf.info, Node: Autoconf 2.13, Prev: Autoconf 1, Up: Obsolete Constructs + +18.6 Upgrading From Version 2.13 +================================ + +The introduction of the previous section (*note Autoconf 1::) perfectly +suits this section... + + Autoconf version 2.50 is mostly backward compatible with version + 2.13. However, it introduces better ways to do some things, and + doesn't support some of the ugly things in version 2.13. So, + depending on how sophisticated your `configure.ac' files are, you + might have to do some manual work in order to upgrade to version + 2.50. This chapter points out some problems to watch for when + upgrading. Also, perhaps your `configure' scripts could benefit + from some of the new features in version 2.50; the changes are + summarized in the file `NEWS' in the Autoconf distribution. + +* Menu: + +* Changed Quotation:: Broken code which used to work +* New Macros:: Interaction with foreign macros +* Hosts and Cross-Compilation:: Bugward compatibility kludges +* AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token +* AC_ACT_IFELSE vs AC_TRY_ACT:: A more generic scheme for testing sources + + +File: autoconf.info, Node: Changed Quotation, Next: New Macros, Up: Autoconf 2.13 + +18.6.1 Changed Quotation +------------------------ + +The most important changes are invisible to you: the implementation of +most macros have completely changed. This allowed more factorization of +the code, better error messages, a higher uniformity of the user's +interface etc. Unfortunately, as a side effect, some construct which +used to (miraculously) work might break starting with Autoconf 2.50. +The most common culprit is bad quotation. + + For instance, in the following example, the message is not properly +quoted: + + AC_INIT + AC_CHECK_HEADERS(foo.h, , + AC_MSG_ERROR(cannot find foo.h, bailing out)) + AC_OUTPUT + +Autoconf 2.13 simply ignores it: + + $ autoconf-2.13; ./configure --silent + creating cache ./config.cache + configure: error: cannot find foo.h + $ + +while Autoconf 2.50 produces a broken `configure': + + $ autoconf-2.50; ./configure --silent + configure: error: cannot find foo.h + ./configure: exit: bad non-numeric arg `bailing' + ./configure: exit: bad non-numeric arg `bailing' + $ + + The message needs to be quoted, and the `AC_MSG_ERROR' invocation +too! + + AC_INIT([Example], [1.0], [bug-example@example.org]) + AC_CHECK_HEADERS([foo.h], [], + [AC_MSG_ERROR([cannot find foo.h, bailing out])]) + AC_OUTPUT + + Many many (and many more) Autoconf macros were lacking proper +quotation, including no less than... `AC_DEFUN' itself! + + $ cat configure.in + AC_DEFUN([AC_PROG_INSTALL], + [# My own much better version + ]) + AC_INIT + AC_PROG_INSTALL + AC_OUTPUT + $ autoconf-2.13 + autoconf: Undefined macros: + ***BUG in Autoconf--please report*** AC_FD_MSG + ***BUG in Autoconf--please report*** AC_EPI + configure.in:1:AC_DEFUN([AC_PROG_INSTALL], + configure.in:5:AC_PROG_INSTALL + $ autoconf-2.50 + $ + + +File: autoconf.info, Node: New Macros, Next: Hosts and Cross-Compilation, Prev: Changed Quotation, Up: Autoconf 2.13 + +18.6.2 New Macros +----------------- + +While Autoconf was relatively dormant in the late 1990s, Automake +provided Autoconf-like macros for a while. Starting with Autoconf 2.50 +in 2001, Autoconf provided versions of these macros, integrated in the +`AC_' namespace, instead of `AM_'. But in order to ease the upgrading +via `autoupdate', bindings to such `AM_' macros are provided. + + Unfortunately older versions of Automake (e.g., Automake 1.4) did +not quote the names of these macros. Therefore, when `m4' finds +something like `AC_DEFUN(AM_TYPE_PTRDIFF_T, ...)' in `aclocal.m4', +`AM_TYPE_PTRDIFF_T' is expanded, replaced with its Autoconf definition. + + Fortunately Autoconf catches pre-`AC_INIT' expansions, and +complains, in its own words: + + $ cat configure.ac + AC_INIT([Example], [1.0], [bug-example@example.org]) + AM_TYPE_PTRDIFF_T + $ aclocal-1.4 + $ autoconf + aclocal.m4:17: error: m4_defn: undefined macro: _m4_divert_diversion + aclocal.m4:17: the top level + autom4te: m4 failed with exit status: 1 + $ + + Modern versions of Automake no longer define most of these macros, +and properly quote the names of the remaining macros. If you must use +an old Automake, do not depend upon macros from Automake as it is +simply not its job to provide macros (but the one it requires itself): + + $ cat configure.ac + AC_INIT([Example], [1.0], [bug-example@example.org]) + AM_TYPE_PTRDIFF_T + $ rm aclocal.m4 + $ autoupdate + autoupdate: `configure.ac' is updated + $ cat configure.ac + AC_INIT([Example], [1.0], [bug-example@example.org]) + AC_CHECK_TYPES([ptrdiff_t]) + $ aclocal-1.4 + $ autoconf + $ + + +File: autoconf.info, Node: Hosts and Cross-Compilation, Next: AC_LIBOBJ vs LIBOBJS, Prev: New Macros, Up: Autoconf 2.13 + +18.6.3 Hosts and Cross-Compilation +---------------------------------- + +Based on the experience of compiler writers, and after long public +debates, many aspects of the cross-compilation chain have changed: + + - the relationship between the build, host, and target architecture + types, + + - the command line interface for specifying them to `configure', + + - the variables defined in `configure', + + - the enabling of cross-compilation mode. + + + The relationship between build, host, and target have been cleaned +up: the chain of default is now simply: target defaults to host, host to +build, and build to the result of `config.guess'. Nevertheless, in +order to ease the transition from 2.13 to 2.50, the following +transition scheme is implemented. _Do not rely on it_, as it will be +completely disabled in a couple of releases (we cannot keep it, as it +proves to cause more problems than it cures). + + They all default to the result of running `config.guess', unless you +specify either `--build' or `--host'. In this case, the default +becomes the system type you specified. If you specify both, and +they're different, `configure' enters cross compilation mode, so it +doesn't run any tests that require execution. + + Hint: if you mean to override the result of `config.guess', prefer +`--build' over `--host'. + + + For backward compatibility, `configure' accepts a system type as an +option by itself. Such an option overrides the defaults for build, +host, and target system types. The following configure statement +configures a cross toolchain that runs on NetBSD/alpha but generates +code for GNU Hurd/sparc, which is also the build platform. + + ./configure --host=alpha-netbsd sparc-gnu + + + In Autoconf 2.13 and before, the variables `build', `host', and +`target' had a different semantics before and after the invocation of +`AC_CANONICAL_BUILD' etc. Now, the argument of `--build' is strictly +copied into `build_alias', and is left empty otherwise. After the +`AC_CANONICAL_BUILD', `build' is set to the canonicalized build type. +To ease the transition, before, its contents is the same as that of +`build_alias'. Do _not_ rely on this broken feature. + + For consistency with the backward compatibility scheme exposed above, +when `--host' is specified but `--build' isn't, the build system is +assumed to be the same as `--host', and `build_alias' is set to that +value. Eventually, this historically incorrect behavior will go away. + + + The former scheme to enable cross-compilation proved to cause more +harm than good, in particular, it used to be triggered too easily, +leaving regular end users puzzled in front of cryptic error messages. +`configure' could even enter cross-compilation mode only because the +compiler was not functional. This is mainly because `configure' used +to try to detect cross-compilation, instead of waiting for an explicit +flag from the user. + + Now, `configure' enters cross-compilation mode if and only if +`--host' is passed. + + That's the short documentation. To ease the transition between 2.13 +and its successors, a more complicated scheme is implemented. _Do not +rely on the following_, as it will be removed in the near future. + + If you specify `--host', but not `--build', when `configure' +performs the first compiler test it tries to run an executable produced +by the compiler. If the execution fails, it enters cross-compilation +mode. This is fragile. Moreover, by the time the compiler test is +performed, it may be too late to modify the build-system type: other +tests may have already been performed. Therefore, whenever you specify +`--host', be sure to specify `--build' too. + + ./configure --build=i686-pc-linux-gnu --host=m68k-coff + +enters cross-compilation mode. The former interface, which consisted +in setting the compiler to a cross-compiler without informing +`configure' is obsolete. For instance, `configure' fails if it can't +run the code generated by the specified compiler if you configure as +follows: + + ./configure CC=m68k-coff-gcc + + +File: autoconf.info, Node: AC_LIBOBJ vs LIBOBJS, Next: AC_ACT_IFELSE vs AC_TRY_ACT, Prev: Hosts and Cross-Compilation, Up: Autoconf 2.13 + +18.6.4 `AC_LIBOBJ' vs. `LIBOBJS' +-------------------------------- + +Up to Autoconf 2.13, the replacement of functions was triggered via the +variable `LIBOBJS'. Since Autoconf 2.50, the macro `AC_LIBOBJ' should +be used instead (*note Generic Functions::). Starting at Autoconf +2.53, the use of `LIBOBJS' is an error. + + This change is mandated by the unification of the GNU Build System +components. In particular, the various fragile techniques used to parse +a `configure.ac' are all replaced with the use of traces. As a +consequence, any action must be traceable, which obsoletes critical +variable assignments. Fortunately, `LIBOBJS' was the only problem, and +it can even be handled gracefully (read, "without your having to change +something"). + + There were two typical uses of `LIBOBJS': asking for a replacement +function, and adjusting `LIBOBJS' for Automake and/or Libtool. + + + As for function replacement, the fix is immediate: use `AC_LIBOBJ'. +For instance: + + LIBOBJS="$LIBOBJS fnmatch.o" + LIBOBJS="$LIBOBJS malloc.$ac_objext" + +should be replaced with: + + AC_LIBOBJ([fnmatch]) + AC_LIBOBJ([malloc]) + + + When used with Automake 1.10 or newer, a suitable value for +`LIBOBJDIR' is set so that the `LIBOBJS' and `LTLIBOBJS' can be +referenced from any `Makefile.am'. Even without Automake, arranging +for `LIBOBJDIR' to be set correctly enables referencing `LIBOBJS' and +`LTLIBOBJS' in another directory. The `LIBOBJDIR' feature is +experimental. + + +File: autoconf.info, Node: AC_ACT_IFELSE vs AC_TRY_ACT, Prev: AC_LIBOBJ vs LIBOBJS, Up: Autoconf 2.13 + +18.6.5 `AC_ACT_IFELSE' vs. `AC_TRY_ACT' +--------------------------------------- + +Since Autoconf 2.50, internal codes uses `AC_PREPROC_IFELSE', +`AC_COMPILE_IFELSE', `AC_LINK_IFELSE', and `AC_RUN_IFELSE' on one hand +and `AC_LANG_SOURCE', and `AC_LANG_PROGRAM' on the other hand instead +of the deprecated `AC_TRY_CPP', `AC_TRY_COMPILE', `AC_TRY_LINK', and +`AC_TRY_RUN'. The motivations where: + - a more consistent interface: `AC_TRY_COMPILE' etc. were double + quoting their arguments; + + - the combinatoric explosion is solved by decomposing on the one + hand the generation of sources, and on the other hand executing + the program; + + - this scheme helps supporting more languages than plain C and C++. + + In addition to the change of syntax, the philosophy has changed too: +while emphasis was put on speed at the expense of accuracy, today's +Autoconf promotes accuracy of the testing framework at, ahem..., the +expense of speed. + + As a perfect example of what is _not_ to be done, here is how to +find out whether a header file contains a particular declaration, such +as a typedef, a structure, a structure member, or a function. Use +`AC_EGREP_HEADER' instead of running `grep' directly on the header +file; on some systems the symbol might be defined in another header +file that the file you are checking includes. + + As a (bad) example, here is how you should not check for C +preprocessor symbols, either defined by header files or predefined by +the C preprocessor: using `AC_EGREP_CPP': + + AC_EGREP_CPP(yes, + [#ifdef _AIX + yes + #endif + ], is_aix=yes, is_aix=no) + + The above example, properly written would (i) use `AC_LANG_PROGRAM', +and (ii) run the compiler: + + AC_COMPILE_IFELSE([AC_LANG_PROGRAM( + [[#ifndef _AIX + error: This isn't AIX! + #endif + ]])], + [is_aix=yes], + [is_aix=no]) + + +File: autoconf.info, Node: Using Autotest, Next: FAQ, Prev: Obsolete Constructs, Up: Top + +19 Generating Test Suites with Autotest +*************************************** + + *N.B.: This section describes a feature which is still + stabilizing. Although we believe that Autotest is useful as-is, this + documentation describes an interface which might change in the future: + do not depend upon Autotest without subscribing to the Autoconf mailing + lists.* + + It is paradoxical that portable projects depend on nonportable tools +to run their test suite. Autoconf by itself is the paragon of this +problem: although it aims at perfectly portability, up to 2.13 its test +suite was using DejaGNU, a rich and complex testing framework, but +which is far from being standard on Posix systems. Worse yet, it was +likely to be missing on the most fragile platforms, the very platforms +that are most likely to torture Autoconf and exhibit deficiencies. + + To circumvent this problem, many package maintainers have developed +their own testing framework, based on simple shell scripts whose sole +outputs are exit status values describing whether the test succeeded. +Most of these tests share common patterns, and this can result in lots +of duplicated code and tedious maintenance. + + Following exactly the same reasoning that yielded to the inception of +Autoconf, Autotest provides a test suite generation framework, based on +M4 macros building a portable shell script. The suite itself is +equipped with automatic logging and tracing facilities which greatly +diminish the interaction with bug reporters, and simple timing reports. + + Autoconf itself has been using Autotest for years, and we do attest +that it has considerably improved the strength of the test suite and the +quality of bug reports. Other projects are known to use some generation +of Autotest, such as Bison, Free Recode, Free Wdiff, GNU Tar, each of +them with different needs, and this usage has validated Autotest as a +general testing framework. + + Nonetheless, compared to DejaGNU, Autotest is inadequate for +interactive tool testing, which is probably its main limitation. + +* Menu: + +* Using an Autotest Test Suite:: Autotest and the user +* Writing Testsuites:: Autotest macros +* testsuite Invocation:: Running `testsuite' scripts +* Making testsuite Scripts:: Using autom4te to create `testsuite' + + +File: autoconf.info, Node: Using an Autotest Test Suite, Next: Writing Testsuites, Up: Using Autotest + +19.1 Using an Autotest Test Suite +================================= + +* Menu: + +* testsuite Scripts:: The concepts of Autotest +* Autotest Logs:: Their contents + + +File: autoconf.info, Node: testsuite Scripts, Next: Autotest Logs, Up: Using an Autotest Test Suite + +19.1.1 `testsuite' Scripts +-------------------------- + +Generating testing or validation suites using Autotest is rather easy. +The whole validation suite is held in a file to be processed through +`autom4te', itself using GNU M4 under the hood, to produce a +stand-alone Bourne shell script which then gets distributed. Neither +`autom4te' nor GNU M4 are needed at the installer's end. + + Each test of the validation suite should be part of some test group. +A "test group" is a sequence of interwoven tests that ought to be +executed together, usually because one test in the group creates data +files that a later test in the same group needs to read. Complex test +groups make later debugging more tedious. It is much better to keep +only a few tests per test group. Ideally there is only one test per +test group. + + For all but the simplest packages, some file such as `testsuite.at' +does not fully hold all test sources, as these are often easier to +maintain in separate files. Each of these separate files holds a single +test group, or a sequence of test groups all addressing some common +functionality in the package. In such cases, `testsuite.at' merely +initializes the validation suite, and sometimes does elementary health +checking, before listing include statements for all other test files. +The special file `package.m4', containing the identification of the +package, is automatically included if found. + + A convenient alternative consists in moving all the global issues +(local Autotest macros, elementary health checking, and `AT_INIT' +invocation) into the file `local.at', and making `testsuite.at' be a +simple list of `m4_include's of sub test suites. In such case, +generating the whole test suite or pieces of it is only a matter of +choosing the `autom4te' command line arguments. + + The validation scripts that Autotest produces are by convention +called `testsuite'. When run, `testsuite' executes each test group in +turn, producing only one summary line per test to say if that +particular test succeeded or failed. At end of all tests, summarizing +counters get printed. One debugging directory is left for each test +group which failed, if any: such directories are named +`testsuite.dir/NN', where NN is the sequence number of the test group, +and they include: + + * a debugging script named `run' which reruns the test in "debug + mode" (*note testsuite Invocation::). The automatic generation of + debugging scripts has the purpose of easing the chase for bugs. + + * all the files created with `AT_DATA' + + * all the Erlang source code files created with `AT_CHECK_EUNIT' + + * a log of the run, named `testsuite.log' + + In the ideal situation, none of the tests fail, and consequently no +debugging directory is left behind for validation. + + It often happens in practice that individual tests in the validation +suite need to get information coming out of the configuration process. +Some of this information, common for all validation suites, is provided +through the file `atconfig', automatically created by +`AC_CONFIG_TESTDIR'. For configuration information which your testing +environment specifically needs, you might prepare an optional file +named `atlocal.in', instantiated by `AC_CONFIG_FILES'. The +configuration process produces `atconfig' and `atlocal' out of these +two input files, and these two produced files are automatically read by +the `testsuite' script. + + Here is a diagram showing the relationship between files. + +Files used in preparing a software package for distribution: + + [package.m4] -->. + \ + subfile-1.at ->. [local.at] ---->+ + ... \ \ + subfile-i.at ---->-- testsuite.at -->-- autom4te* -->testsuite + ... / + subfile-n.at ->' + +Files used in configuring a software package: + + .--> atconfig + / + [atlocal.in] --> config.status* --< + \ + `--> [atlocal] + +Files created during test suite execution: + + atconfig -->. .--> testsuite.log + \ / + >-- testsuite* --< + / \ + [atlocal] ->' `--> [testsuite.dir] + + +File: autoconf.info, Node: Autotest Logs, Prev: testsuite Scripts, Up: Using an Autotest Test Suite + +19.1.2 Autotest Logs +-------------------- + +When run, the test suite creates a log file named after itself, e.g., a +test suite named `testsuite' creates `testsuite.log'. It contains a +lot of information, usually more than maintainers actually need, but +therefore most of the time it contains all that is needed: + +command line arguments + A bad but unfortunately widespread habit consists of setting + environment variables before the command, such as in + `CC=my-home-grown-cc ./testsuite'. The test suite does not know + this change, hence (i) it cannot report it to you, and (ii) it + cannot preserve the value of `CC' for subsequent runs. Autoconf + faced exactly the same problem, and solved it by asking users to + pass the variable definitions as command line arguments. Autotest + requires this rule, too, but has no means to enforce it; the log + then contains a trace of the variables that were changed by the + user. + +`ChangeLog' excerpts + The topmost lines of all the `ChangeLog' files found in the source + hierarchy. This is especially useful when bugs are reported + against development versions of the package, since the version + string does not provide sufficient information to know the exact + state of the sources the user compiled. Of course, this relies on + the use of a `ChangeLog'. + +build machine + Running a test suite in a cross-compile environment is not an easy + task, since it would mean having the test suite run on a machine + BUILD, while running programs on a machine HOST. It is much + simpler to run both the test suite and the programs on HOST, but + then, from the point of view of the test suite, there remains a + single environment, HOST = BUILD. The log contains relevant + information on the state of the BUILD machine, including some + important environment variables. + +tested programs + The absolute file name and answers to `--version' of the tested + programs (see *note Writing Testsuites::, `AT_TESTED'). + +configuration log + The contents of `config.log', as created by `configure', are + appended. It contains the configuration flags and a detailed + report on the configuration itself. + + +File: autoconf.info, Node: Writing Testsuites, Next: testsuite Invocation, Prev: Using an Autotest Test Suite, Up: Using Autotest + +19.2 Writing `testsuite.at' +=========================== + +The `testsuite.at' is a Bourne shell script making use of special +Autotest M4 macros. It often contains a call to `AT_INIT' near its +beginning followed by one call to `m4_include' per source file for +tests. Each such included file, or the remainder of `testsuite.at' if +include files are not used, contain a sequence of test groups. Each +test group begins with a call to `AT_SETUP', then an arbitrary number +of shell commands or calls to `AT_CHECK', and then completes with a +call to `AT_CLEANUP'. Multiple test groups can be categorized by a +call to `AT_BANNER'. + + All of the public Autotest macros have all-uppercase names in the +namespace `^AT_' to prevent them from accidentally conflicting with +other text; Autoconf also reserves the namespace `^_AT_' for internal +macros. All shell variables used in the testsuite for internal +purposes have mostly-lowercase names starting with `at_'. Autotest +also uses here-document delimiters in the namespace `^_AT[A-Z]', and +makes use of the file system namespace `^at-'. + + Since Autoconf is built on top of M4sugar (*note Programming in +M4sugar::) and M4sh (*note Programming in M4sh::), you must also be +aware of those namespaces (`^_?\(m4\|AS\)_'). In general, you _should +not use_ the namespace of a package that does not own the macro or +shell code you are writing. + + -- Macro: AT_INIT ([NAME]) + Initialize Autotest. Giving a NAME to the test suite is + encouraged if your package includes several test suites. Before + this macro is called, `AT_PACKAGE_STRING' and + `AT_PACKAGE_BUGREPORT' must be defined, which are used to display + information about the testsuite to the user. Typically, these + macros are provided by a file `package.m4' built by `make' (*note + Making testsuite Scripts::), in order to inherit the package name, + version, and bug reporting address from `configure.ac'. + + -- Macro: AT_COPYRIGHT (COPYRIGHT-NOTICE) + State that, in addition to the Free Software Foundation's + copyright on the Autotest macros, parts of your test suite are + covered by COPYRIGHT-NOTICE. + + The COPYRIGHT-NOTICE shows up in both the head of `testsuite' and + in `testsuite --version'. + + -- Macro: AT_ARG_OPTION (OPTIONS, HELP-TEXT, [ACTION-IF-GIVEN], + [ACTION-IF-NOT-GIVEN]) + Accept options from the space-separated list OPTIONS, a list that + has leading dashes removed from the options. Long options will be + prefixed with `--', single-character options with `-'. The first + word in this list is the primary OPTION, any others are assumed to + be short-hand aliases. The variable associated with it is + `at_arg_OPTION', with any dashes in OPTION replaced with + underscores. + + If the user passes `--OPTION' to the `testsuite', the variable + will be set to `:'. If the user does not pass the option, or + passes `--no-OPTION', then the variable will be set to `false'. + + ACTION-IF-GIVEN is run each time the option is encountered; here, + the variable `at_optarg' will be set to `:' or `false' as + appropriate. `at_optarg' is actually just a copy of + `at_arg_OPTION'. + + ACTION-IF-NOT-GIVEN will be run once after option parsing is + complete and if no option from OPTIONS was used. + + HELP-TEXT is added to the end of the list of options shown in + `testsuite --help' (*note AS_HELP_STRING::). + + It is recommended that you use a package-specific prefix to OPTIONS + names in order to avoid clashes with future Autotest built-in + options. + + -- Macro: AT_ARG_OPTION_ARG (OPTIONS, HELP-TEXT, [ACTION-IF-GIVEN], + [ACTION-IF-NOT-GIVEN]) + Accept options with arguments from the space-separated list + OPTIONS, a list that has leading dashes removed from the options. + Long options will be prefixed with `--', single-character options + with `-'. The first word in this list is the primary OPTION, any + others are assumed to be short-hand aliases. The variable + associated with it is `at_arg_OPTION', with any dashes in OPTION + replaced with underscores. + + If the user passes `--OPTION=ARG' or `--OPTION ARG' to the + `testsuite', the variable will be set to `ARG'. + + ACTION-IF-GIVEN is run each time the option is encountered; here, + the variable `at_optarg' will be set to `ARG'. `at_optarg' is + actually just a copy of `at_arg_OPTION'. + + ACTION-IF-NOT-GIVEN will be run once after option parsing is + complete and if no option from OPTIONS was used. + + HELP-TEXT is added to the end of the list of options shown in + `testsuite --help' (*note AS_HELP_STRING::). + + It is recommended that you use a package-specific prefix to OPTIONS + names in order to avoid clashes with future Autotest built-in + options. + + -- Macro: AT_COLOR_TESTS + Enable colored test results by default when the output is + connected to a terminal. + + -- Macro: AT_TESTED (EXECUTABLES) + Log the file name and answer to `--version' of each program in + space-separated list EXECUTABLES. Several invocations register + new executables, in other words, don't fear registering one program + several times. + + Autotest test suites rely on `PATH' to find the tested program. + This avoids the need to generate absolute names of the various + tools, and makes it possible to test installed programs. + Therefore, knowing which programs are being exercised is crucial + to understanding problems in the test suite itself, or its + occasional misuses. It is a good idea to also subscribe foreign + programs you depend upon, to avoid incompatible diagnostics. + + + -- Macro: AT_BANNER (TEST-CATEGORY-NAME) + This macro identifies the start of a category of related test + groups. When the resulting `testsuite' is invoked with more than + one test group to run, its output will include a banner containing + TEST-CATEGORY-NAME prior to any tests run from that category. The + banner should be no more than about 40 or 50 characters. A blank + banner indicates uncategorized tests; an empty line will be + inserted after tests from an earlier category, effectively ending + that category. + + -- Macro: AT_SETUP (TEST-GROUP-NAME) + This macro starts a group of related tests, all to be executed in + the same subshell. It accepts a single argument, which holds a + few words (no more than about 30 or 40 characters) quickly + describing the purpose of the test group being started. + TEST-GROUP-NAME must not expand to unbalanced quotes, although + quadrigraphs can be used. + + -- Macro: AT_KEYWORDS (KEYWORDS) + Associate the space-separated list of KEYWORDS to the enclosing + test group. This makes it possible to run "slices" of the test + suite. For instance, if some of your test groups exercise some + `foo' feature, then using `AT_KEYWORDS(foo)' lets you run + `./testsuite -k foo' to run exclusively these test groups. The + TEST-GROUP-NAME of the test group is automatically recorded to + `AT_KEYWORDS'. + + Several invocations within a test group accumulate new keywords. + In other words, don't fear registering the same keyword several + times in a test group. + + -- Macro: AT_CAPTURE_FILE (FILE) + If the current test group fails, log the contents of FILE. + Several identical calls within one test group have no additional + effect. + + -- Macro: AT_FAIL_IF (SHELL-CONDITION) + Make the test group fail and skip the rest of its execution, if + SHELL-CONDITION is true. SHELL-CONDITION is a shell expression + such as a `test' command. Tests before `AT_FAIL_IF' will be + executed and may still cause the test group to be skipped. You + can instantiate this macro many times from within the same test + group. + + You should use this macro only for very simple failure conditions. + If the SHELL-CONDITION could emit any kind of output you should + instead use `AT_CHECK' like + AT_CHECK([if SHELL-CONDITION; then exit 99; fi]) + so that such output is properly recorded in the `testsuite.log' + file. + + -- Macro: AT_SKIP_IF (SHELL-CONDITION) + Determine whether the test should be skipped because it requires + features that are unsupported on the machine under test. + SHELL-CONDITION is a shell expression such as a `test' command. + Tests before `AT_SKIP_IF' will be executed and may still cause the + test group to fail. You can instantiate this macro many times + from within the same test group. + + You should use this macro only for very simple skip conditions. + If the SHELL-CONDITION could emit any kind of output you should + instead use `AT_CHECK' like + AT_CHECK([if SHELL-CONDITION; then exit 77; fi]) + so that such output is properly recorded in the `testsuite.log' + file. + + -- Macro: AT_XFAIL_IF (SHELL-CONDITION) + Determine whether the test is expected to fail because it is a + known bug (for unsupported features, you should skip the test). + SHELL-CONDITION is a shell expression such as a `test' command; + you can instantiate this macro many times from within the same + test group, and one of the conditions is enough to turn the test + into an expected failure. + + -- Macro: AT_CLEANUP + End the current test group. + + + -- Macro: AT_DATA (FILE, CONTENTS) + Initialize an input data FILE with given CONTENTS. Of course, the + CONTENTS have to be properly quoted between square brackets to + protect against included commas or spurious M4 expansion. + CONTENTS must be empty or end with a newline. FILE must be a + single shell word that expands into a single file name. + + -- Macro: AT_CHECK (COMMANDS, [STATUS = `0'], [STDOUT], [STDERR], + [RUN-IF-FAIL], [RUN-IF-PASS]) + -- Macro: AT_CHECK_UNQUOTED (COMMANDS, [STATUS = `0'], [STDOUT], + [STDERR], [RUN-IF-FAIL], [RUN-IF-PASS]) + Execute a test by performing given shell COMMANDS in a subshell. + COMMANDS is output as-is, so shell expansions are honored. These + commands should normally exit with STATUS, while producing expected + STDOUT and STDERR contents. If COMMANDS exit with unexpected + status 77, then the rest of the test group is skipped. If + COMMANDS exit with unexpected status 99, then the test group is + immediately failed. Otherwise, if this test fails, run shell + commands RUN-IF-FAIL or, if this test passes, run shell commands + RUN-IF-PASS, both inside the current shell execution environment. + At the beginning of RUN-IF-FAIL and RUN-IF-PASS, the status of + COMMANDS is available in the `at_status' shell variable. + + This macro must be invoked in between `AT_SETUP' and `AT_CLEANUP'. + + If STATUS is the literal `ignore', then the corresponding exit + status is not checked, except for the special cases of 77 (skip) + and 99 (hard failure). The existence of hard failures allows one + to mark a test as an expected failure with `AT_XFAIL_IF' because a + feature has not yet been implemented, but to still distinguish + between gracefully handling the missing feature and dumping core. + A hard failure also inhibits post-test actions in RUN-IF-FAIL. + + If the value of the STDOUT or STDERR parameter is one of the + literals in the following table, then the test treats the output + according to the rules of that literal. Otherwise, the value of + the parameter is treated as text that must exactly match the + output given by COMMANDS on standard output and standard error + (including an empty parameter for no output); any differences are + captured in the testsuite log and the test is failed (unless an + unexpected exit status of 77 skipped the test instead). The + difference between `AT_CHECK' and `AT_CHECK_UNQUOTED' is that only + the latter performs shell variable expansion (`$'), command + substitution (``'), and backslash escaping (`\') on comparison + text given in the STDOUT and STDERR arguments; if the text + includes a trailing newline, this would be the same as if it were + specified via an unquoted here-document. (However, there is no + difference in the interpretation of COMMANDS). + + `ignore' + The content of the output is ignored, but still captured in + the test group log (if the testsuite is run with option `-v', + the test group log is displayed as the test is run; if the + test group later fails, the test group log is also copied + into the overall testsuite log). This action is valid for + both STDOUT and STDERR. + + `ignore-nolog' + The content of the output is ignored, and nothing is captured + in the log files. If COMMANDS are likely to produce binary + output (including long lines) or large amounts of output, + then logging the output can make it harder to locate details + related to subsequent tests within the group, and could + potentially corrupt terminal display of a user running + `testsuite -v'. + + `stdout' + For the STDOUT parameter, capture the content of standard + output to both the file `stdout' and the test group log. + Subsequent commands in the test group can then post-process + the file. This action is often used when it is desired to + use `grep' to look for a substring in the output, or when the + output must be post-processed to normalize error messages + into a common form. + + `stderr' + Like `stdout', except that it only works for the STDERR + parameter, and the standard error capture file will be named + `stderr'. + + `stdout-nolog' + `stderr-nolog' + Like `stdout' or `stderr', except that the captured output is + not duplicated into the test group log. This action is + particularly useful for an intermediate check that produces + large amounts of data, which will be followed by another + check that filters down to the relevant data, as it makes it + easier to locate details in the log. + + `expout' + For the STDOUT parameter, compare standard output contents + with the previously created file `expout', and list any + differences in the testsuite log. + + `experr' + Like `expout', except that it only works for the STDERR + parameter, and the standard error contents are compared with + `experr'. + + -- Macro: AT_CHECK_EUNIT (MODULE, TEST-SPEC, [ERLFLAGS], + [RUN-IF-FAIL], [RUN-IF-PASS]) + Initialize and execute an Erlang module named MODULE that performs + tests following the TEST-SPEC EUnit test specification. TEST-SPEC + must be a valid EUnit test specification, as defined in the EUnit + Reference Manual (http://erlang.org/doc/apps/eunit/index.html). + ERLFLAGS are optional command-line options passed to the Erlang + interpreter to execute the test Erlang module. Typically, + ERLFLAGS defines at least the paths to directories containing the + compiled Erlang modules under test, as `-pa path1 path2 ...'. + + For example, the unit tests associated with Erlang module `testme', + which compiled code is in subdirectory `src', can be performed + with: + + AT_CHECK_EUNIT([testme_testsuite], [{module, testme}], + [-pa "${abs_top_builddir}/src"]) + + This macro must be invoked in between `AT_SETUP' and `AT_CLEANUP'. + + Variables `ERL', `ERLC', and (optionally) `ERLCFLAGS' must be + defined as the path of the Erlang interpreter, the path of the + Erlang compiler, and the command-line flags to pass to the + compiler, respectively. Those variables should be configured in + `configure.ac' using the `AC_ERLANG_PATH_ERL' and + `AC_ERLANG_PATH_ERLC' macros, and the configured values of those + variables are automatically defined in the testsuite. If `ERL' or + `ERLC' is not defined, the test group is skipped. + + If the EUnit library cannot be found, i.e. if module `eunit' cannot + be loaded, the test group is skipped. Otherwise, if TEST-SPEC is + an invalid EUnit test specification, the test group fails. + Otherwise, if the EUnit test passes, shell commands RUN-IF-PASS + are executed or, if the EUnit test fails, shell commands + RUN-IF-FAIL are executed and the test group fails. + + Only the generated test Erlang module is automatically compiled and + executed. If TEST-SPEC involves testing other Erlang modules, + e.g. module `testme' in the example above, those modules must be + already compiled. + + If the testsuite is run in verbose mode, with option `--verbose', + EUnit is also run in verbose mode to output more details about + individual unit tests. + + +File: autoconf.info, Node: testsuite Invocation, Next: Making testsuite Scripts, Prev: Writing Testsuites, Up: Using Autotest + +19.3 Running `testsuite' Scripts +================================ + +Autotest test suites support the following options: + +`--help' +`-h' + Display the list of options and exit successfully. + +`--version' +`-V' + Display the version of the test suite and exit successfully. + +`--directory=DIR' +`-C DIR' + Change the current directory to DIR before creating any files. + Useful for running the testsuite in a subdirectory from a top-level + Makefile. + +`--jobs[=N]' +`-j[N]' + Run N tests in parallel, if possible. If N is not given, run all + given tests in parallel. Note that there should be no space + before the argument to `-j', as `-j NUMBER' denotes the separate + arguments `-j' and `NUMBER', see below. + + In parallel mode, the standard input device of the testsuite + script is not available to commands inside a test group. + Furthermore, banner lines are not printed, and the summary line + for each test group is output after the test group completes. + Summary lines may appear unordered. If verbose and trace output + are enabled (see below), they may appear intermixed from + concurrently running tests. + + Parallel mode requires the `mkfifo' command to work, and will be + silently disabled otherwise. + +`--clean' +`-c' + Remove all the files the test suite might have created and exit. + Meant for `clean' Make targets. + +`--list' +`-l' + List all the tests (or only the selection), including their + possible keywords. + + + By default all tests are performed (or described with `--list') +silently in the default environment, but the environment, set of tests, +and verbosity level can be tuned: + +`VARIABLE=VALUE' + Set the environment VARIABLE to VALUE. Use this rather than + `FOO=foo ./testsuite' as debugging scripts would then run in a + different environment. + + The variable `AUTOTEST_PATH' specifies the testing path to prepend + to `PATH'. Relative directory names (not starting with `/') are + considered to be relative to the top level of the package being + built. All directories are made absolute, first starting from the + top level _build_ tree, then from the _source_ tree. For instance + `./testsuite AUTOTEST_PATH=tests:bin' for a `/src/foo-1.0' source + package built in `/tmp/foo' results in + `/tmp/foo/tests:/tmp/foo/bin' and then + `/src/foo-1.0/tests:/src/foo-1.0/bin' being prepended to `PATH'. + +`NUMBER' +`NUMBER-NUMBER' +`NUMBER-' +`-NUMBER' + Add the corresponding test groups, with obvious semantics, to the + selection. + +`--keywords=KEYWORDS' +`-k KEYWORDS' + Add to the selection the test groups with title or keywords + (arguments to `AT_SETUP' or `AT_KEYWORDS') that match _all_ + keywords of the comma separated list KEYWORDS, case-insensitively. + Use `!' immediately before the keyword to invert the selection for + this keyword. By default, the keywords match whole words; enclose + them in `.*' to also match parts of words. + + For example, running + + ./testsuite -k 'autoupdate,.*FUNC.*' + + selects all tests tagged `autoupdate' _and_ with tags containing + `FUNC' (as in `AC_CHECK_FUNC', `AC_FUNC_ALLOCA', etc.), while + + ./testsuite -k '!autoupdate' -k '.*FUNC.*' + + selects all tests not tagged `autoupdate' _or_ with tags + containing `FUNC'. + +`--errexit' +`-e' + If any test fails, immediately abort testing. This implies + `--debug': post test group clean up, and top-level logging are + inhibited. This option is meant for the full test suite, it is + not really useful for generated debugging scripts. If the + testsuite is run in parallel mode using `--jobs', then + concurrently running tests will finish before exiting. + +`--verbose' +`-v' + Force more verbosity in the detailed output of what is being done. + This is the default for debugging scripts. + +`--color' +`--color[=never|auto|always]' + Enable colored test results. Without an argument, or with + `always', test results will be colored. With `never', color mode + is turned off. Otherwise, if either the macro `AT_COLOR_TESTS' is + used by the testsuite author, or the argument `auto' is given, + then test results are colored if standard output is connected to a + terminal. + +`--debug' +`-d' + Do not remove the files after a test group was performed--but they + are still removed _before_, therefore using this option is sane + when running several test groups. Create debugging scripts. Do + not overwrite the top-level log (in order to preserve a supposedly + existing full log file). This is the default for debugging + scripts, but it can also be useful to debug the testsuite itself. + +`--recheck' + Add to the selection all test groups that failed or passed + unexpectedly during the last non-debugging test run. + +`--trace' +`-x' + Trigger shell tracing of the test groups. + + Besides these options accepted by every Autotest testsuite, the +testsuite author might have added package-specific options via the +`AT_ARG_OPTION' and `AT_ARG_OPTION_ARG' macros (*note Writing +Testsuites::); refer to `testsuite --help' and the package +documentation for details. + + +File: autoconf.info, Node: Making testsuite Scripts, Prev: testsuite Invocation, Up: Using Autotest + +19.4 Making `testsuite' Scripts +=============================== + +For putting Autotest into movement, you need some configuration and +makefile machinery. We recommend, at least if your package uses deep or +shallow hierarchies, that you use `tests/' as the name of the directory +holding all your tests and their makefile. Here is a check list of +things to do. + + - Make sure to create the file `package.m4', which defines the + identity of the package. It must define `AT_PACKAGE_STRING', the + full signature of the package, and `AT_PACKAGE_BUGREPORT', the + address to which bug reports should be sent. For sake of + completeness, we suggest that you also define `AT_PACKAGE_NAME', + `AT_PACKAGE_TARNAME', `AT_PACKAGE_VERSION', and `AT_PACKAGE_URL'. + *Note Initializing configure::, for a description of these + variables. Be sure to distribute `package.m4' and to put it into + the source hierarchy: the test suite ought to be shipped! See + below for an example `Makefile' excerpt. + + - Invoke `AC_CONFIG_TESTDIR'. + + -- Macro: AC_CONFIG_TESTDIR (DIRECTORY, [TEST-PATH = `directory']) + An Autotest test suite is to be configured in DIRECTORY. This + macro causes `DIRECTORY/atconfig' to be created by + `config.status' and sets the default `AUTOTEST_PATH' to + TEST-PATH (*note testsuite Invocation::). + + - Still within `configure.ac', as appropriate, ensure that some + `AC_CONFIG_FILES' command includes substitution for + `tests/atlocal'. + + - The appropriate `Makefile' should be modified so the validation in + your package is triggered by `make check'. An example is provided + below. + + With Automake, here is a minimal example for inclusion in +`tests/Makefile.am', in order to link `make check' with a validation +suite. + + # The `:;' works around a Bash 3.2 bug when the output is not writable. + $(srcdir)/package.m4: $(top_srcdir)/configure.ac + :;{ \ + echo '# Signature of the current package.' && \ + echo 'm4_define([AT_PACKAGE_NAME],' && \ + echo ' [$(PACKAGE_NAME)])' && \ + echo 'm4_define([AT_PACKAGE_TARNAME],' && \ + echo ' [$(PACKAGE_TARNAME)])' && \ + echo 'm4_define([AT_PACKAGE_VERSION],' && \ + echo ' [$(PACKAGE_VERSION)])' && \ + echo 'm4_define([AT_PACKAGE_STRING],' && \ + echo ' [$(PACKAGE_STRING)])' && \ + echo 'm4_define([AT_PACKAGE_BUGREPORT],' && \ + echo ' [$(PACKAGE_BUGREPORT)])'; \ + echo 'm4_define([AT_PACKAGE_URL],' && \ + echo ' [$(PACKAGE_URL)])'; \ + } >'$(srcdir)/package.m4' + + EXTRA_DIST = testsuite.at $(srcdir)/package.m4 $(TESTSUITE) atlocal.in + TESTSUITE = $(srcdir)/testsuite + + check-local: atconfig atlocal $(TESTSUITE) + $(SHELL) '$(TESTSUITE)' $(TESTSUITEFLAGS) + + installcheck-local: atconfig atlocal $(TESTSUITE) + $(SHELL) '$(TESTSUITE)' AUTOTEST_PATH='$(bindir)' \ + $(TESTSUITEFLAGS) + + clean-local: + test ! -f '$(TESTSUITE)' || \ + $(SHELL) '$(TESTSUITE)' --clean + + AUTOM4TE = $(SHELL) $(srcdir)/build-aux/missing --run autom4te + AUTOTEST = $(AUTOM4TE) --language=autotest + $(TESTSUITE): $(srcdir)/testsuite.at $(srcdir)/package.m4 + $(AUTOTEST) -I '$(srcdir)' -o $@.tmp $@.at + mv $@.tmp $@ + + Note that the built testsuite is distributed; this is necessary +because users might not have Autoconf installed, and thus would not be +able to rebuild it. Likewise, the use of `missing' provides the user +with a nicer error message if they modify a source file to the +testsuite, and accidentally trigger the rebuild rules. + + You might want to list explicitly the dependencies, i.e., the list of +the files `testsuite.at' includes. + + If you don't use Automake, you should include the above example in +`tests/Makefile.in', along with additional lines inspired from the +following: + + subdir = tests + PACKAGE_NAME = @PACKAGE_NAME@ + PACKAGE_TARNAME = @PACKAGE_TARNAME@ + PACKAGE_VERSION = @PACKAGE_VERSION@ + PACKAGE_STRING = @PACKAGE_STRING@ + PACKAGE_BUGREPORT = @PACKAGE_BUGREPORT@ + PACKAGE_URL = @PACKAGE_URL@ + + atconfig: $(top_builddir)/config.status + cd $(top_builddir) && \ + $(SHELL) ./config.status $(subdir)/$@ + + atlocal: $(srcdir)/atlocal.in $(top_builddir)/config.status + cd $(top_builddir) && \ + $(SHELL) ./config.status $(subdir)/$@ + +and manage to have `$(EXTRA_DIST)' distributed. You will also want to +distribute the file `build-aux/missing' from the Automake project; a +copy of this file resides in the Autoconf source tree. + + With all this in place, and if you have not initialized +`TESTSUITEFLAGS' within your makefile, you can fine-tune test suite +execution with this variable, for example: + + make check TESTSUITEFLAGS='-v -d -x 75 -k AC_PROG_CC CFLAGS=-g' + + +File: autoconf.info, Node: FAQ, Next: History, Prev: Using Autotest, Up: Top + +20 Frequent Autoconf Questions, with answers +******************************************** + +Several questions about Autoconf come up occasionally. Here some of +them are addressed. + +* Menu: + +* Distributing:: Distributing `configure' scripts +* Why GNU M4:: Why not use the standard M4? +* Bootstrapping:: Autoconf and GNU M4 require each other? +* Why Not Imake:: Why GNU uses `configure' instead of Imake +* Defining Directories:: Passing `datadir' to program +* Autom4te Cache:: What is it? Can I remove it? +* Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree +* Expanded Before Required:: Expanded Before Required +* Debugging:: Debugging `configure' scripts + + +File: autoconf.info, Node: Distributing, Next: Why GNU M4, Up: FAQ + +20.1 Distributing `configure' Scripts +===================================== + + What are the restrictions on distributing `configure' + scripts that Autoconf generates? How does that affect my + programs that use them? + + There are no restrictions on how the configuration scripts that +Autoconf produces may be distributed or used. In Autoconf version 1, +they were covered by the GNU General Public License. We still encourage +software authors to distribute their work under terms like those of the +GPL, but doing so is not required to use Autoconf. + + Of the other files that might be used with `configure', +`config.h.in' is under whatever copyright you use for your +`configure.ac'. `config.sub' and `config.guess' have an exception to +the GPL when they are used with an Autoconf-generated `configure' +script, which permits you to distribute them under the same terms as +the rest of your package. `install-sh' is from the X Consortium and is +not copyrighted. + + +File: autoconf.info, Node: Why GNU M4, Next: Bootstrapping, Prev: Distributing, Up: FAQ + +20.2 Why Require GNU M4? +======================== + + Why does Autoconf require GNU M4? + + Many M4 implementations have hard-coded limitations on the size and +number of macros that Autoconf exceeds. They also lack several builtin +macros that it would be difficult to get along without in a +sophisticated application like Autoconf, including: + + m4_builtin + m4_indir + m4_bpatsubst + __file__ + __line__ + + Autoconf requires version 1.4.6 or later of GNU M4. + + Since only software maintainers need to use Autoconf, and since GNU +M4 is simple to configure and install, it seems reasonable to require +GNU M4 to be installed also. Many maintainers of GNU and other free +software already have most of the GNU utilities installed, since they +prefer them. + + +File: autoconf.info, Node: Bootstrapping, Next: Why Not Imake, Prev: Why GNU M4, Up: FAQ + +20.3 How Can I Bootstrap? +========================= + + If Autoconf requires GNU M4 and GNU M4 has an Autoconf + `configure' script, how do I bootstrap? It seems like a chicken + and egg problem! + + This is a misunderstanding. Although GNU M4 does come with a +`configure' script produced by Autoconf, Autoconf is not required in +order to run the script and install GNU M4. Autoconf is only required +if you want to change the M4 `configure' script, which few people have +to do (mainly its maintainer). + + +File: autoconf.info, Node: Why Not Imake, Next: Defining Directories, Prev: Bootstrapping, Up: FAQ + +20.4 Why Not Imake? +=================== + + Why not use Imake instead of `configure' scripts? + + Several people have written addressing this question, so adaptations +of their explanations are included here. + + The following answer is based on one written by Richard Pixley: + + Autoconf generated scripts frequently work on machines that it has + never been set up to handle before. That is, it does a good job of + inferring a configuration for a new system. Imake cannot do this. + + Imake uses a common database of host specific data. For X11, this + makes sense because the distribution is made as a collection of + tools, by one central authority who has control over the database. + + GNU tools are not released this way. Each GNU tool has a + maintainer; these maintainers are scattered across the world. + Using a common database would be a maintenance nightmare. + Autoconf may appear to be this kind of database, but in fact it is + not. Instead of listing host dependencies, it lists program + requirements. + + If you view the GNU suite as a collection of native tools, then the + problems are similar. But the GNU development tools can be + configured as cross tools in almost any host+target permutation. + All of these configurations can be installed concurrently. They + can even be configured to share host independent files across + hosts. Imake doesn't address these issues. + + Imake templates are a form of standardization. The GNU coding + standards address the same issues without necessarily imposing the + same restrictions. + + Here is some further explanation, written by Per Bothner: + + One of the advantages of Imake is that it is easy to generate large + makefiles using the `#include' and macro mechanisms of `cpp'. + However, `cpp' is not programmable: it has limited conditional + facilities, and no looping. And `cpp' cannot inspect its + environment. + + All of these problems are solved by using `sh' instead of `cpp'. + The shell is fully programmable, has macro substitution, can + execute (or source) other shell scripts, and can inspect its + environment. + + Paul Eggert elaborates more: + + With Autoconf, installers need not assume that Imake itself is + already installed and working well. This may not seem like much + of an advantage to people who are accustomed to Imake. But on + many hosts Imake is not installed or the default installation is + not working well, and requiring Imake to install a package hinders + the acceptance of that package on those hosts. For example, the + Imake template and configuration files might not be installed + properly on a host, or the Imake build procedure might wrongly + assume that all source files are in one big directory tree, or the + Imake configuration might assume one compiler whereas the package + or the installer needs to use another, or there might be a version + mismatch between the Imake expected by the package and the Imake + supported by the host. These problems are much rarer with + Autoconf, where each package comes with its own independent + configuration processor. + + Also, Imake often suffers from unexpected interactions between + `make' and the installer's C preprocessor. The fundamental problem + here is that the C preprocessor was designed to preprocess C + programs, not makefiles. This is much less of a problem with + Autoconf, which uses the general-purpose preprocessor M4, and + where the package's author (rather than the installer) does the + preprocessing in a standard way. + + Finally, Mark Eichin notes: + + Imake isn't all that extensible, either. In order to add new + features to Imake, you need to provide your own project template, + and duplicate most of the features of the existing one. This + means that for a sophisticated project, using the vendor-provided + Imake templates fails to provide any leverage--since they don't + cover anything that your own project needs (unless it is an X11 + program). + + On the other side, though: + + The one advantage that Imake has over `configure': `Imakefile' + files tend to be much shorter (likewise, less redundant) than + `Makefile.in' files. There is a fix to this, however--at least + for the Kerberos V5 tree, we've modified things to call in common + `post.in' and `pre.in' makefile fragments for the entire tree. + This means that a lot of common things don't have to be + duplicated, even though they normally are in `configure' setups. + + +File: autoconf.info, Node: Defining Directories, Next: Autom4te Cache, Prev: Why Not Imake, Up: FAQ + +20.5 How Do I `#define' Installation Directories? +================================================= + + My program needs library files, installed in `datadir' and + similar. If I use + AC_DEFINE_UNQUOTED([DATADIR], [$datadir], + [Define to the read-only architecture-independent + data directory.]) + + I get + #define DATADIR "${prefix}/share" + +As already explained, this behavior is on purpose, mandated by the GNU +Coding Standards, see *note Installation Directory Variables::. There +are several means to achieve a similar goal: + + - Do not use `AC_DEFINE' but use your makefile to pass the actual + value of `datadir' via compilation flags. *Note Installation + Directory Variables::, for the details. + + - This solution can be simplified when compiling a program: you may + either extend the `CPPFLAGS': + + CPPFLAGS = -DDATADIR='"$(datadir)"' @CPPFLAGS@ + + If you are using Automake, you should use `AM_CPPFLAGS' instead: + + AM_CPPFLAGS = -DDATADIR='"$(datadir)"' + + Alternatively, create a dedicated header file: + + DISTCLEANFILES = myprog-paths.h + myprog-paths.h: Makefile + echo '#define DATADIR "$(datadir)"' >$@ + + The gnulib module `configmake' provides such a header with all the + standard directory variables defined, *note configmake: + (gnulib)configmake. + + - Use `AC_DEFINE' but have `configure' compute the literal value of + `datadir' and others. Many people have wrapped macros to automate + this task; for an example, see the macro `AC_DEFINE_DIR' from the + Autoconf Macro Archive + (http://www.gnu.org/software/autoconf-archive/). + + This solution does not conform to the GNU Coding Standards. + + - Note that all the previous solutions hard wire the absolute name of + these directories in the executables, which is not a good + property. You may try to compute the names relative to `prefix', + and try to find `prefix' at runtime, this way your package is + relocatable. + + +File: autoconf.info, Node: Autom4te Cache, Next: Present But Cannot Be Compiled, Prev: Defining Directories, Up: FAQ + +20.6 What is `autom4te.cache'? +============================== + + What is this directory `autom4te.cache'? Can I safely remove it? + + In the GNU Build System, `configure.ac' plays a central role and is +read by many tools: `autoconf' to create `configure', `autoheader' to +create `config.h.in', `automake' to create `Makefile.in', `autoscan' to +check the completeness of `configure.ac', `autoreconf' to check the GNU +Build System components that are used. To "read `configure.ac'" +actually means to compile it with M4, which can be a long process for +complex `configure.ac'. + + This is why all these tools, instead of running directly M4, invoke +`autom4te' (*note autom4te Invocation::) which, while answering to a +specific demand, stores additional information in `autom4te.cache' for +future runs. For instance, if you run `autoconf', behind the scenes, +`autom4te' also stores information for the other tools, so that when +you invoke `autoheader' or `automake' etc., reprocessing `configure.ac' +is not needed. The speed up is frequently 30%, and is increasing with +the size of `configure.ac'. + + But it is and remains being simply a cache: you can safely remove it. + + + Can I permanently get rid of it? + + The creation of this cache can be disabled from `~/.autom4te.cfg', +see *note Customizing autom4te::, for more details. You should be +aware that disabling the cache slows down the Autoconf test suite by +40%. The more GNU Build System components are used, the more the cache +is useful; for instance running `autoreconf -f' on the Core Utilities +is twice slower without the cache _although `--force' implies that the +cache is not fully exploited_, and eight times slower than without +`--force'. + + +File: autoconf.info, Node: Present But Cannot Be Compiled, Next: Expanded Before Required, Prev: Autom4te Cache, Up: FAQ + +20.7 Header Present But Cannot Be Compiled +========================================== + +The most important guideline to bear in mind when checking for features +is to mimic as much as possible the intended use. Unfortunately, old +versions of `AC_CHECK_HEADER' and `AC_CHECK_HEADERS' failed to follow +this idea, and called the preprocessor, instead of the compiler, to +check for headers. As a result, incompatibilities between headers went +unnoticed during configuration, and maintainers finally had to deal +with this issue elsewhere. + + The transition began with Autoconf 2.56. As of Autoconf 2.64 both +checks are performed, and `configure' complains loudly if the compiler +and the preprocessor do not agree. However, only the compiler result +is considered. + + Consider the following example: + + $ cat number.h + typedef int number; + $ cat pi.h + const number pi = 3; + $ cat configure.ac + AC_INIT([Example], [1.0], [bug-example@example.org]) + AC_CHECK_HEADERS([pi.h]) + $ autoconf -Wall + $ ./configure + checking for gcc... gcc + checking for C compiler default output file name... a.out + checking whether the C compiler works... yes + checking whether we are cross compiling... no + checking for suffix of executables... + checking for suffix of object files... o + checking whether we are using the GNU C compiler... yes + checking whether gcc accepts -g... yes + checking for gcc option to accept ISO C89... none needed + checking how to run the C preprocessor... gcc -E + checking for grep that handles long lines and -e... grep + checking for egrep... grep -E + checking for ANSI C header files... yes + checking for sys/types.h... yes + checking for sys/stat.h... yes + checking for stdlib.h... yes + checking for string.h... yes + checking for memory.h... yes + checking for strings.h... yes + checking for inttypes.h... yes + checking for stdint.h... yes + checking for unistd.h... yes + checking pi.h usability... no + checking pi.h presence... yes + configure: WARNING: pi.h: present but cannot be compiled + configure: WARNING: pi.h: check for missing prerequisite headers? + configure: WARNING: pi.h: see the Autoconf documentation + configure: WARNING: pi.h: section "Present But Cannot Be Compiled" + configure: WARNING: pi.h: proceeding with the compiler's result + configure: WARNING: ## -------------------------------------- ## + configure: WARNING: ## Report this to bug-example@example.org ## + configure: WARNING: ## -------------------------------------- ## + checking for pi.h... yes + +The proper way the handle this case is using the fourth argument (*note +Generic Headers::): + + $ cat configure.ac + AC_INIT([Example], [1.0], [bug-example@example.org]) + AC_CHECK_HEADERS([number.h pi.h], [], [], + [[#ifdef HAVE_NUMBER_H + # include <number.h> + #endif + ]]) + $ autoconf -Wall + $ ./configure + checking for gcc... gcc + checking for C compiler default output... a.out + checking whether the C compiler works... yes + checking whether we are cross compiling... no + checking for suffix of executables... + checking for suffix of object files... o + checking whether we are using the GNU C compiler... yes + checking whether gcc accepts -g... yes + checking for gcc option to accept ANSI C... none needed + checking for number.h... yes + checking for pi.h... yes + + See *note Particular Headers::, for a list of headers with their +prerequisites. + + +File: autoconf.info, Node: Expanded Before Required, Next: Debugging, Prev: Present But Cannot Be Compiled, Up: FAQ + +20.8 Expanded Before Required +============================= + +Older versions of Autoconf silently built files with incorrect ordering +between dependent macros if an outer macro first expanded, then later +indirectly required, an inner macro. Starting with Autoconf 2.64, this +situation no longer generates out-of-order code, but results in +duplicate output and a syntax warning: + + $ cat configure.ac + =>AC_DEFUN([TESTA], [[echo in A + =>if test -n "$SEEN_A" ; then echo duplicate ; fi + =>SEEN_A=:]]) + =>AC_DEFUN([TESTB], [AC_REQUIRE([TESTA])[echo in B + =>if test -z "$SEEN_A" ; then echo bug ; fi]]) + =>AC_DEFUN([TESTC], [AC_REQUIRE([TESTB])[echo in C]]) + =>AC_DEFUN([OUTER], [[echo in OUTER] + =>TESTA + =>TESTC]) + =>AC_INIT + =>OUTER + =>AC_OUTPUT + $ autoconf + =>configure.ac:11: warning: AC_REQUIRE: + => `TESTA' was expanded before it was required + =>configure.ac:4: TESTB is expanded from... + =>configure.ac:6: TESTC is expanded from... + =>configure.ac:7: OUTER is expanded from... + =>configure.ac:11: the top level + +To avoid this warning, decide what purpose the macro in question serves. +If it only needs to be expanded once (for example, if it provides +initialization text used by later macros), then the simplest fix is to +change the macro to be declared with `AC_DEFUN_ONCE' (*note One-Shot +Macros::), although this only works in Autoconf 2.64 and newer. A more +portable fix is to change all instances of direct calls to instead go +through `AC_REQUIRE' (*note Prerequisite Macros::). If, instead, the +macro is parameterized by arguments or by the current definition of +other macros in the m4 environment, then the macro should always be +directly expanded instead of required. + + For another case study, consider this example trimmed down from an +actual package. Originally, the package contained shell code and +multiple macro invocations at the top level of `configure.ac': + + AC_DEFUN([FOO], [AC_COMPILE_IFELSE([...])]) + foobar= + AC_PROG_CC + FOO + +but that was getting complex, so the author wanted to offload some of +the text into a new macro in another file included via `aclocal.m4'. +The nai"ve approach merely wraps the text in a new macro: + + AC_DEFUN([FOO], [AC_COMPILE_IFELSE([...])]) + AC_DEFUN([BAR], [ + foobar= + AC_PROG_CC + FOO + ]) + BAR + +With older versions of Autoconf, the setting of `foobar=' occurs before +the single compiler check, as the author intended. But with Autoconf +2.64, this issues the "expanded before it was required" warning for +`AC_PROG_CC', and outputs two copies of the compiler check, one before +`foobar=', and one after. To understand why this is happening, +remember that the use of `AC_COMPILE_IFELSE' includes a call to +`AC_REQUIRE([AC_PROG_CC])' under the hood. According to the documented +semantics of `AC_REQUIRE', this means that `AC_PROG_CC' _must_ occur +before the body of the outermost `AC_DEFUN', which in this case is +`BAR', thus preceding the use of `foobar='. The older versions of +Autoconf were broken with regards to the rules of `AC_REQUIRE', which +explains why the code changed from one over to two copies of +`AC_PROG_CC' when upgrading autoconf. In other words, the author was +unknowingly relying on a bug exploit to get the desired results, and +that exploit broke once the bug was fixed. + + So, what recourse does the author have, to restore their intended +semantics of setting `foobar=' prior to a single compiler check, +regardless of whether Autoconf 2.63 or 2.64 is used? One idea is to +remember that only `AC_DEFUN' is impacted by `AC_REQUIRE'; there is +always the possibility of using the lower-level `m4_define': + + AC_DEFUN([FOO], [AC_COMPILE_IFELSE([...])]) + m4_define([BAR], [ + foobar= + AC_PROG_CC + FOO + ]) + BAR + +This works great if everything is in the same file. However, it does +not help in the case where the author wants to have `aclocal' find the +definition of `BAR' from its own file, since `aclocal' requires the use +of `AC_DEFUN'. In this case, a better fix is to recognize that if +`BAR' also uses `AC_REQUIRE', then there will no longer be direct +expansion prior to a subsequent require. Then, by creating yet another +helper macro, the author can once again guarantee a single invocation of +`AC_PROG_CC', which will still occur after `foobar='. The author can +also use `AC_BEFORE' to make sure no other macro appearing before `BAR' +has triggered an unwanted expansion of `AC_PROG_CC'. + + AC_DEFUN([FOO], [AC_COMPILE_IFELSE([...])]) + AC_DEFUN([BEFORE_CC], [ + foobar= + ]) + AC_DEFUN([BAR], [ + AC_BEFORE([$0], [AC_PROG_CC])dnl + AC_REQUIRE([BEFORE_CC])dnl + AC_REQUIRE([AC_PROG_CC])dnl + FOO + ]) + BAR + + +File: autoconf.info, Node: Debugging, Prev: Expanded Before Required, Up: FAQ + +20.9 Debugging `configure' scripts +================================== + +While in general, `configure' scripts generated by Autoconf strive to +be fairly portable to various systems, compilers, shells, and other +tools, it may still be necessary to debug a failing test, broken script +or makefile, or fix or override an incomplete, faulty, or erroneous +test, especially during macro development. Failures can occur at all +levels, in M4 syntax or semantics, shell script issues, or due to bugs +in the test or the tools invoked by `configure'. Together with the +rather arcane error message that `m4' and `make' may produce when their +input contains syntax errors, this can make debugging rather painful. + + Nevertheless, here is a list of hints and strategies that may help: + + * When `autoconf' fails, common causes for error include: + + * mismatched or unbalanced parentheses or braces (*note + Balancing Parentheses::), + + * under- or overquoted macro arguments (*note Autoconf + Language::, *note Quoting and Parameters::, *note Quotation + and Nested Macros::), + + * spaces between macro name and opening parenthesis (*note + Autoconf Language::). + + Typically, it helps to go back to the last working version of the + input and compare the differences for each of these errors. + Another possibility is to sprinkle pairs of `m4_traceon' and + `m4_traceoff' judiciously in the code, either without a parameter + or listing some macro names and watch `m4' expand its input + verbosely (*note Debugging via autom4te::). + + * Sometimes `autoconf' succeeds but the generated `configure' script + has invalid shell syntax. You can detect this case by running + `bash -n configure' or `sh -n configure'. If this command fails, + the same tips apply, as if `autoconf' had failed. + + * Debugging `configure' script execution may be done by sprinkling + pairs of `set -x' and `set +x' into the shell script before and + after the region that contains a bug. Running the whole script + with `SHELL -vx ./configure 2>&1 | tee LOG-FILE' with a decent + SHELL may work, but produces lots of output. Here, it can help to + search for markers like `checking for' a particular test in the + LOG-FILE. + + * Alternatively, you might use a shell with debugging capabilities + like bashdb (http://bashdb.sourceforge.net/). + + * When `configure' tests produce invalid results for your system, it + may be necessary to override them: + + * For programs, tools or libraries variables, preprocessor, + compiler, or linker flags, it is often sufficient to override + them at `make' run time with some care (*note Macros and + Submakes::). Since this normally won't cause `configure' to + be run again with these changed settings, it may fail if the + changed variable would have caused different test results + from `configure', so this may work only for simple + differences. + + * Most tests which produce their result in a substituted + variable allow to override the test by setting the variable + on the `configure' command line (*note Compilers and + Options::, *note Defining Variables::, *note Particular + Systems::). + + * Many tests store their result in a cache variable (*note + Caching Results::). This lets you override them either on the + `configure' command line as above, or through a primed cache + or site file (*note Cache Files::, *note Site Defaults::). + The name of a cache variable is documented with a test macro + or may be inferred from *note Cache Variable Names::; the + precise semantics of undocumented variables are often + internal details, subject to change. + + * Alternatively, `configure' may produce invalid results because of + uncaught programming errors, in your package or in an upstream + library package. For example, when `AC_CHECK_LIB' fails to find a + library with a specified function, always check `config.log'. This + will reveal the exact error that produced the failing result: the + library linked by `AC_CHECK_LIB' probably has a fatal bug. + + Conversely, as macro author, you can make it easier for users of your +macro: + + * by minimizing dependencies between tests and between test results + as far as possible, + + * by using `make' variables to factorize and allow override of + settings at `make' run time, + + * by honoring the GNU Coding Standards and not overriding flags + reserved for the user except temporarily during `configure' tests, + + * by not requiring users of your macro to use the cache variables. + Instead, expose the result of the test via RUN-IF-TRUE and + RUN-IF-FALSE parameters. If the result is not a boolean, then + provide it through documented shell variables. + + +File: autoconf.info, Node: History, Next: GNU Free Documentation License, Prev: FAQ, Up: Top + +21 History of Autoconf +********************** + +_This chapter was written by the original author, David MacKenzie._ + + You may be wondering, Why was Autoconf originally written? How did +it get into its present form? (Why does it look like gorilla spit?) If +you're not wondering, then this chapter contains no information useful +to you, and you might as well skip it. If you _are_ wondering, then +let there be light... + +* Menu: + +* Genesis:: Prehistory and naming of `configure' +* Exodus:: The plagues of M4 and Perl +* Leviticus:: The priestly code of portability arrives +* Numbers:: Growth and contributors +* Deuteronomy:: Approaching the promises of easy configuration + + +File: autoconf.info, Node: Genesis, Next: Exodus, Up: History + +21.1 Genesis +============ + +In June 1991 I was maintaining many of the GNU utilities for the Free +Software Foundation. As they were ported to more platforms and more +programs were added, the number of `-D' options that users had to +select in the makefile (around 20) became burdensome. Especially for +me--I had to test each new release on a bunch of different systems. So +I wrote a little shell script to guess some of the correct settings for +the fileutils package, and released it as part of fileutils 2.0. That +`configure' script worked well enough that the next month I adapted it +(by hand) to create similar `configure' scripts for several other GNU +utilities packages. Brian Berliner also adapted one of my scripts for +his CVS revision control system. + + Later that summer, I learned that Richard Stallman and Richard Pixley +were developing similar scripts to use in the GNU compiler tools; so I +adapted my `configure' scripts to support their evolving interface: +using the file name `Makefile.in' as the templates; adding `+srcdir', +the first option (of many); and creating `config.status' files. + + +File: autoconf.info, Node: Exodus, Next: Leviticus, Prev: Genesis, Up: History + +21.2 Exodus +=========== + +As I got feedback from users, I incorporated many improvements, using +Emacs to search and replace, cut and paste, similar changes in each of +the scripts. As I adapted more GNU utilities packages to use +`configure' scripts, updating them all by hand became impractical. +Rich Murphey, the maintainer of the GNU graphics utilities, sent me +mail saying that the `configure' scripts were great, and asking if I +had a tool for generating them that I could send him. No, I thought, +but I should! So I started to work out how to generate them. And the +journey from the slavery of hand-written `configure' scripts to the +abundance and ease of Autoconf began. + + Cygnus `configure', which was being developed at around that time, +is table driven; it is meant to deal mainly with a discrete number of +system types with a small number of mainly unguessable features (such as +details of the object file format). The automatic configuration system +that Brian Fox had developed for Bash takes a similar approach. For +general use, it seems to me a hopeless cause to try to maintain an +up-to-date database of which features each variant of each operating +system has. It's easier and more reliable to check for most features on +the fly--especially on hybrid systems that people have hacked on +locally or that have patches from vendors installed. + + I considered using an architecture similar to that of Cygnus +`configure', where there is a single `configure' script that reads +pieces of `configure.in' when run. But I didn't want to have to +distribute all of the feature tests with every package, so I settled on +having a different `configure' made from each `configure.in' by a +preprocessor. That approach also offered more control and flexibility. + + I looked briefly into using the Metaconfig package, by Larry Wall, +Harlan Stenn, and Raphael Manfredi, but I decided not to for several +reasons. The `Configure' scripts it produces are interactive, which I +find quite inconvenient; I didn't like the ways it checked for some +features (such as library functions); I didn't know that it was still +being maintained, and the `Configure' scripts I had seen didn't work on +many modern systems (such as System V R4 and NeXT); it wasn't flexible +in what it could do in response to a feature's presence or absence; I +found it confusing to learn; and it was too big and complex for my +needs (I didn't realize then how much Autoconf would eventually have to +grow). + + I considered using Perl to generate my style of `configure' scripts, +but decided that M4 was better suited to the job of simple textual +substitutions: it gets in the way less, because output is implicit. +Plus, everyone already has it. (Initially I didn't rely on the GNU +extensions to M4.) Also, some of my friends at the University of +Maryland had recently been putting M4 front ends on several programs, +including `tvtwm', and I was interested in trying out a new language. + + +File: autoconf.info, Node: Leviticus, Next: Numbers, Prev: Exodus, Up: History + +21.3 Leviticus +============== + +Since my `configure' scripts determine the system's capabilities +automatically, with no interactive user intervention, I decided to call +the program that generates them Autoconfig. But with a version number +tacked on, that name would be too long for old Unix file systems, so I +shortened it to Autoconf. + + In the fall of 1991 I called together a group of fellow questers +after the Holy Grail of portability (er, that is, alpha testers) to +give me feedback as I encapsulated pieces of my handwritten scripts in +M4 macros and continued to add features and improve the techniques used +in the checks. Prominent among the testers were Franc,ois Pinard, who +came up with the idea of making an Autoconf shell script to run M4 and +check for unresolved macro calls; Richard Pixley, who suggested running +the compiler instead of searching the file system to find include files +and symbols, for more accurate results; Karl Berry, who got Autoconf to +configure TeX and added the macro index to the documentation; and Ian +Lance Taylor, who added support for creating a C header file as an +alternative to putting `-D' options in a makefile, so he could use +Autoconf for his UUCP package. The alpha testers cheerfully adjusted +their files again and again as the names and calling conventions of the +Autoconf macros changed from release to release. They all contributed +many specific checks, great ideas, and bug fixes. + + +File: autoconf.info, Node: Numbers, Next: Deuteronomy, Prev: Leviticus, Up: History + +21.4 Numbers +============ + +In July 1992, after months of alpha testing, I released Autoconf 1.0, +and converted many GNU packages to use it. I was surprised by how +positive the reaction to it was. More people started using it than I +could keep track of, including people working on software that wasn't +part of the GNU Project (such as TCL, FSP, and Kerberos V5). Autoconf +continued to improve rapidly, as many people using the `configure' +scripts reported problems they encountered. + + Autoconf turned out to be a good torture test for M4 implementations. +Unix M4 started to dump core because of the length of the macros that +Autoconf defined, and several bugs showed up in GNU M4 as well. +Eventually, we realized that we needed to use some features that only +GNU M4 has. 4.3BSD M4, in particular, has an impoverished set of +builtin macros; the System V version is better, but still doesn't +provide everything we need. + + More development occurred as people put Autoconf under more stresses +(and to uses I hadn't anticipated). Karl Berry added checks for X11. +david zuhn contributed C++ support. Franc,ois Pinard made it diagnose +invalid arguments. Jim Blandy bravely coerced it into configuring GNU +Emacs, laying the groundwork for several later improvements. Roland +McGrath got it to configure the GNU C Library, wrote the `autoheader' +script to automate the creation of C header file templates, and added a +`--verbose' option to `configure'. Noah Friedman added the +`--autoconf-dir' option and `AC_MACRODIR' environment variable. (He +also coined the term "autoconfiscate" to mean "adapt a software package +to use Autoconf".) Roland and Noah improved the quoting protection in +`AC_DEFINE' and fixed many bugs, especially when I got sick of dealing +with portability problems from February through June, 1993. + + +File: autoconf.info, Node: Deuteronomy, Prev: Numbers, Up: History + +21.5 Deuteronomy +================ + +A long wish list for major features had accumulated, and the effect of +several years of patching by various people had left some residual +cruft. In April 1994, while working for Cygnus Support, I began a major +revision of Autoconf. I added most of the features of the Cygnus +`configure' that Autoconf had lacked, largely by adapting the relevant +parts of Cygnus `configure' with the help of david zuhn and Ken +Raeburn. These features include support for using `config.sub', +`config.guess', `--host', and `--target'; making links to files; and +running `configure' scripts in subdirectories. Adding these features +enabled Ken to convert GNU `as', and Rob Savoye to convert DejaGNU, to +using Autoconf. + + I added more features in response to other peoples' requests. Many +people had asked for `configure' scripts to share the results of the +checks between runs, because (particularly when configuring a large +source tree, like Cygnus does) they were frustratingly slow. Mike +Haertel suggested adding site-specific initialization scripts. People +distributing software that had to unpack on MS-DOS asked for a way to +override the `.in' extension on the file names, which produced file +names like `config.h.in' containing two dots. Jim Avera did an +extensive examination of the problems with quoting in `AC_DEFINE' and +`AC_SUBST'; his insights led to significant improvements. Richard +Stallman asked that compiler output be sent to `config.log' instead of +`/dev/null', to help people debug the Emacs `configure' script. + + I made some other changes because of my dissatisfaction with the +quality of the program. I made the messages showing results of the +checks less ambiguous, always printing a result. I regularized the +names of the macros and cleaned up coding style inconsistencies. I +added some auxiliary utilities that I had developed to help convert +source code packages to use Autoconf. With the help of Franc,ois +Pinard, I made the macros not interrupt each others' messages. (That +feature revealed some performance bottlenecks in GNU M4, which he +hastily corrected!) I reorganized the documentation around problems +people want to solve. And I began a test suite, because experience had +shown that Autoconf has a pronounced tendency to regress when we change +it. + + Again, several alpha testers gave invaluable feedback, especially +Franc,ois Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn, +and Mark Eichin. + + Finally, version 2.0 was ready. And there was much rejoicing. (And +I have free time again. I think. Yeah, right.) + + +File: autoconf.info, Node: GNU Free Documentation License, Next: Indices, Prev: History, Up: Top + +Appendix A GNU Free Documentation License +***************************************** + + Version 1.3, 3 November 2008 + + Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. + `http://fsf.org/' + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + 0. PREAMBLE + + The purpose of this License is to make a manual, textbook, or other + functional and useful document "free" in the sense of freedom: to + assure everyone the effective freedom to copy and redistribute it, + with or without modifying it, either commercially or + noncommercially. Secondarily, this License preserves for the + author and publisher a way to get credit for their work, while not + being considered responsible for modifications made by others. + + This License is a kind of "copyleft", which means that derivative + works of the document must themselves be free in the same sense. + It complements the GNU General Public License, which is a copyleft + license designed for free software. + + We have designed this License in order to use it for manuals for + free software, because free software needs free documentation: a + free program should come with manuals providing the same freedoms + that the software does. But this License is not limited to + software manuals; it can be used for any textual work, regardless + of subject matter or whether it is published as a printed book. + We recommend this License principally for works whose purpose is + instruction or reference. + + 1. APPLICABILITY AND DEFINITIONS + + This License applies to any manual or other work, in any medium, + that contains a notice placed by the copyright holder saying it + can be distributed under the terms of this License. Such a notice + grants a world-wide, royalty-free license, unlimited in duration, + to use that work under the conditions stated herein. The + "Document", below, refers to any such manual or work. Any member + of the public is a licensee, and is addressed as "you". You + accept the license if you copy, modify or distribute the work in a + way requiring permission under copyright law. + + A "Modified Version" of the Document means any work containing the + Document or a portion of it, either copied verbatim, or with + modifications and/or translated into another language. + + A "Secondary Section" is a named appendix or a front-matter section + of the Document that deals exclusively with the relationship of the + publishers or authors of the Document to the Document's overall + subject (or to related matters) and contains nothing that could + fall directly within that overall subject. (Thus, if the Document + is in part a textbook of mathematics, a Secondary Section may not + explain any mathematics.) The relationship could be a matter of + historical connection with the subject or with related matters, or + of legal, commercial, philosophical, ethical or political position + regarding them. + + The "Invariant Sections" are certain Secondary Sections whose + titles are designated, as being those of Invariant Sections, in + the notice that says that the Document is released under this + License. If a section does not fit the above definition of + Secondary then it is not allowed to be designated as Invariant. + The Document may contain zero Invariant Sections. If the Document + does not identify any Invariant Sections then there are none. + + The "Cover Texts" are certain short passages of text that are + listed, as Front-Cover Texts or Back-Cover Texts, in the notice + that says that the Document is released under this License. A + Front-Cover Text may be at most 5 words, and a Back-Cover Text may + be at most 25 words. + + A "Transparent" copy of the Document means a machine-readable copy, + represented in a format whose specification is available to the + general public, that is suitable for revising the document + straightforwardly with generic text editors or (for images + composed of pixels) generic paint programs or (for drawings) some + widely available drawing editor, and that is suitable for input to + text formatters or for automatic translation to a variety of + formats suitable for input to text formatters. A copy made in an + otherwise Transparent file format whose markup, or absence of + markup, has been arranged to thwart or discourage subsequent + modification by readers is not Transparent. An image format is + not Transparent if used for any substantial amount of text. A + copy that is not "Transparent" is called "Opaque". + + Examples of suitable formats for Transparent copies include plain + ASCII without markup, Texinfo input format, LaTeX input format, + SGML or XML using a publicly available DTD, and + standard-conforming simple HTML, PostScript or PDF designed for + human modification. Examples of transparent image formats include + PNG, XCF and JPG. Opaque formats include proprietary formats that + can be read and edited only by proprietary word processors, SGML or + XML for which the DTD and/or processing tools are not generally + available, and the machine-generated HTML, PostScript or PDF + produced by some word processors for output purposes only. + + The "Title Page" means, for a printed book, the title page itself, + plus such following pages as are needed to hold, legibly, the + material this License requires to appear in the title page. For + works in formats which do not have any title page as such, "Title + Page" means the text near the most prominent appearance of the + work's title, preceding the beginning of the body of the text. + + The "publisher" means any person or entity that distributes copies + of the Document to the public. + + A section "Entitled XYZ" means a named subunit of the Document + whose title either is precisely XYZ or contains XYZ in parentheses + following text that translates XYZ in another language. (Here XYZ + stands for a specific section name mentioned below, such as + "Acknowledgements", "Dedications", "Endorsements", or "History".) + To "Preserve the Title" of such a section when you modify the + Document means that it remains a section "Entitled XYZ" according + to this definition. + + The Document may include Warranty Disclaimers next to the notice + which states that this License applies to the Document. These + Warranty Disclaimers are considered to be included by reference in + this License, but only as regards disclaiming warranties: any other + implication that these Warranty Disclaimers may have is void and + has no effect on the meaning of this License. + + 2. VERBATIM COPYING + + You may copy and distribute the Document in any medium, either + commercially or noncommercially, provided that this License, the + copyright notices, and the license notice saying this License + applies to the Document are reproduced in all copies, and that you + add no other conditions whatsoever to those of this License. You + may not use technical measures to obstruct or control the reading + or further copying of the copies you make or distribute. However, + you may accept compensation in exchange for copies. If you + distribute a large enough number of copies you must also follow + the conditions in section 3. + + You may also lend copies, under the same conditions stated above, + and you may publicly display copies. + + 3. COPYING IN QUANTITY + + If you publish printed copies (or copies in media that commonly + have printed covers) of the Document, numbering more than 100, and + the Document's license notice requires Cover Texts, you must + enclose the copies in covers that carry, clearly and legibly, all + these Cover Texts: Front-Cover Texts on the front cover, and + Back-Cover Texts on the back cover. Both covers must also clearly + and legibly identify you as the publisher of these copies. The + front cover must present the full title with all words of the + title equally prominent and visible. You may add other material + on the covers in addition. Copying with changes limited to the + covers, as long as they preserve the title of the Document and + satisfy these conditions, can be treated as verbatim copying in + other respects. + + If the required texts for either cover are too voluminous to fit + legibly, you should put the first ones listed (as many as fit + reasonably) on the actual cover, and continue the rest onto + adjacent pages. + + If you publish or distribute Opaque copies of the Document + numbering more than 100, you must either include a + machine-readable Transparent copy along with each Opaque copy, or + state in or with each Opaque copy a computer-network location from + which the general network-using public has access to download + using public-standard network protocols a complete Transparent + copy of the Document, free of added material. If you use the + latter option, you must take reasonably prudent steps, when you + begin distribution of Opaque copies in quantity, to ensure that + this Transparent copy will remain thus accessible at the stated + location until at least one year after the last time you + distribute an Opaque copy (directly or through your agents or + retailers) of that edition to the public. + + It is requested, but not required, that you contact the authors of + the Document well before redistributing any large number of + copies, to give them a chance to provide you with an updated + version of the Document. + + 4. MODIFICATIONS + + You may copy and distribute a Modified Version of the Document + under the conditions of sections 2 and 3 above, provided that you + release the Modified Version under precisely this License, with + the Modified Version filling the role of the Document, thus + licensing distribution and modification of the Modified Version to + whoever possesses a copy of it. In addition, you must do these + things in the Modified Version: + + A. Use in the Title Page (and on the covers, if any) a title + distinct from that of the Document, and from those of + previous versions (which should, if there were any, be listed + in the History section of the Document). You may use the + same title as a previous version if the original publisher of + that version gives permission. + + B. List on the Title Page, as authors, one or more persons or + entities responsible for authorship of the modifications in + the Modified Version, together with at least five of the + principal authors of the Document (all of its principal + authors, if it has fewer than five), unless they release you + from this requirement. + + C. State on the Title page the name of the publisher of the + Modified Version, as the publisher. + + D. Preserve all the copyright notices of the Document. + + E. Add an appropriate copyright notice for your modifications + adjacent to the other copyright notices. + + F. Include, immediately after the copyright notices, a license + notice giving the public permission to use the Modified + Version under the terms of this License, in the form shown in + the Addendum below. + + G. Preserve in that license notice the full lists of Invariant + Sections and required Cover Texts given in the Document's + license notice. + + H. Include an unaltered copy of this License. + + I. Preserve the section Entitled "History", Preserve its Title, + and add to it an item stating at least the title, year, new + authors, and publisher of the Modified Version as given on + the Title Page. If there is no section Entitled "History" in + the Document, create one stating the title, year, authors, + and publisher of the Document as given on its Title Page, + then add an item describing the Modified Version as stated in + the previous sentence. + + J. Preserve the network location, if any, given in the Document + for public access to a Transparent copy of the Document, and + likewise the network locations given in the Document for + previous versions it was based on. These may be placed in + the "History" section. You may omit a network location for a + work that was published at least four years before the + Document itself, or if the original publisher of the version + it refers to gives permission. + + K. For any section Entitled "Acknowledgements" or "Dedications", + Preserve the Title of the section, and preserve in the + section all the substance and tone of each of the contributor + acknowledgements and/or dedications given therein. + + L. Preserve all the Invariant Sections of the Document, + unaltered in their text and in their titles. Section numbers + or the equivalent are not considered part of the section + titles. + + M. Delete any section Entitled "Endorsements". Such a section + may not be included in the Modified Version. + + N. Do not retitle any existing section to be Entitled + "Endorsements" or to conflict in title with any Invariant + Section. + + O. Preserve any Warranty Disclaimers. + + If the Modified Version includes new front-matter sections or + appendices that qualify as Secondary Sections and contain no + material copied from the Document, you may at your option + designate some or all of these sections as invariant. To do this, + add their titles to the list of Invariant Sections in the Modified + Version's license notice. These titles must be distinct from any + other section titles. + + You may add a section Entitled "Endorsements", provided it contains + nothing but endorsements of your Modified Version by various + parties--for example, statements of peer review or that the text + has been approved by an organization as the authoritative + definition of a standard. + + You may add a passage of up to five words as a Front-Cover Text, + and a passage of up to 25 words as a Back-Cover Text, to the end + of the list of Cover Texts in the Modified Version. Only one + passage of Front-Cover Text and one of Back-Cover Text may be + added by (or through arrangements made by) any one entity. If the + Document already includes a cover text for the same cover, + previously added by you or by arrangement made by the same entity + you are acting on behalf of, you may not add another; but you may + replace the old one, on explicit permission from the previous + publisher that added the old one. + + The author(s) and publisher(s) of the Document do not by this + License give permission to use their names for publicity for or to + assert or imply endorsement of any Modified Version. + + 5. COMBINING DOCUMENTS + + You may combine the Document with other documents released under + this License, under the terms defined in section 4 above for + modified versions, provided that you include in the combination + all of the Invariant Sections of all of the original documents, + unmodified, and list them all as Invariant Sections of your + combined work in its license notice, and that you preserve all + their Warranty Disclaimers. + + The combined work need only contain one copy of this License, and + multiple identical Invariant Sections may be replaced with a single + copy. If there are multiple Invariant Sections with the same name + but different contents, make the title of each such section unique + by adding at the end of it, in parentheses, the name of the + original author or publisher of that section if known, or else a + unique number. Make the same adjustment to the section titles in + the list of Invariant Sections in the license notice of the + combined work. + + In the combination, you must combine any sections Entitled + "History" in the various original documents, forming one section + Entitled "History"; likewise combine any sections Entitled + "Acknowledgements", and any sections Entitled "Dedications". You + must delete all sections Entitled "Endorsements." + + 6. COLLECTIONS OF DOCUMENTS + + You may make a collection consisting of the Document and other + documents released under this License, and replace the individual + copies of this License in the various documents with a single copy + that is included in the collection, provided that you follow the + rules of this License for verbatim copying of each of the + documents in all other respects. + + You may extract a single document from such a collection, and + distribute it individually under this License, provided you insert + a copy of this License into the extracted document, and follow + this License in all other respects regarding verbatim copying of + that document. + + 7. AGGREGATION WITH INDEPENDENT WORKS + + A compilation of the Document or its derivatives with other + separate and independent documents or works, in or on a volume of + a storage or distribution medium, is called an "aggregate" if the + copyright resulting from the compilation is not used to limit the + legal rights of the compilation's users beyond what the individual + works permit. When the Document is included in an aggregate, this + License does not apply to the other works in the aggregate which + are not themselves derivative works of the Document. + + If the Cover Text requirement of section 3 is applicable to these + copies of the Document, then if the Document is less than one half + of the entire aggregate, the Document's Cover Texts may be placed + on covers that bracket the Document within the aggregate, or the + electronic equivalent of covers if the Document is in electronic + form. Otherwise they must appear on printed covers that bracket + the whole aggregate. + + 8. TRANSLATION + + Translation is considered a kind of modification, so you may + distribute translations of the Document under the terms of section + 4. Replacing Invariant Sections with translations requires special + permission from their copyright holders, but you may include + translations of some or all Invariant Sections in addition to the + original versions of these Invariant Sections. You may include a + translation of this License, and all the license notices in the + Document, and any Warranty Disclaimers, provided that you also + include the original English version of this License and the + original versions of those notices and disclaimers. In case of a + disagreement between the translation and the original version of + this License or a notice or disclaimer, the original version will + prevail. + + If a section in the Document is Entitled "Acknowledgements", + "Dedications", or "History", the requirement (section 4) to + Preserve its Title (section 1) will typically require changing the + actual title. + + 9. TERMINATION + + You may not copy, modify, sublicense, or distribute the Document + except as expressly provided under this License. Any attempt + otherwise to copy, modify, sublicense, or distribute it is void, + and will automatically terminate your rights under this License. + + However, if you cease all violation of this License, then your + license from a particular copyright holder is reinstated (a) + provisionally, unless and until the copyright holder explicitly + and finally terminates your license, and (b) permanently, if the + copyright holder fails to notify you of the violation by some + reasonable means prior to 60 days after the cessation. + + Moreover, your license from a particular copyright holder is + reinstated permanently if the copyright holder notifies you of the + violation by some reasonable means, this is the first time you have + received notice of violation of this License (for any work) from + that copyright holder, and you cure the violation prior to 30 days + after your receipt of the notice. + + Termination of your rights under this section does not terminate + the licenses of parties who have received copies or rights from + you under this License. If your rights have been terminated and + not permanently reinstated, receipt of a copy of some or all of + the same material does not give you any rights to use it. + + 10. FUTURE REVISIONS OF THIS LICENSE + + The Free Software Foundation may publish new, revised versions of + the GNU Free Documentation License from time to time. Such new + versions will be similar in spirit to the present version, but may + differ in detail to address new problems or concerns. See + `http://www.gnu.org/copyleft/'. + + Each version of the License is given a distinguishing version + number. If the Document specifies that a particular numbered + version of this License "or any later version" applies to it, you + have the option of following the terms and conditions either of + that specified version or of any later version that has been + published (not as a draft) by the Free Software Foundation. If + the Document does not specify a version number of this License, + you may choose any version ever published (not as a draft) by the + Free Software Foundation. If the Document specifies that a proxy + can decide which future versions of this License can be used, that + proxy's public statement of acceptance of a version permanently + authorizes you to choose that version for the Document. + + 11. RELICENSING + + "Massive Multiauthor Collaboration Site" (or "MMC Site") means any + World Wide Web server that publishes copyrightable works and also + provides prominent facilities for anybody to edit those works. A + public wiki that anybody can edit is an example of such a server. + A "Massive Multiauthor Collaboration" (or "MMC") contained in the + site means any set of copyrightable works thus published on the MMC + site. + + "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 + license published by Creative Commons Corporation, a not-for-profit + corporation with a principal place of business in San Francisco, + California, as well as future copyleft versions of that license + published by that same organization. + + "Incorporate" means to publish or republish a Document, in whole or + in part, as part of another Document. + + An MMC is "eligible for relicensing" if it is licensed under this + License, and if all works that were first published under this + License somewhere other than this MMC, and subsequently + incorporated in whole or in part into the MMC, (1) had no cover + texts or invariant sections, and (2) were thus incorporated prior + to November 1, 2008. + + The operator of an MMC Site may republish an MMC contained in the + site under CC-BY-SA on the same site at any time before August 1, + 2009, provided the MMC is eligible for relicensing. + + +ADDENDUM: How to use this License for your documents +==================================================== + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.3 + or any later version published by the Free Software Foundation; + with no Invariant Sections, no Front-Cover Texts, and no Back-Cover + Texts. A copy of the license is included in the section entitled ``GNU + Free Documentation License''. + + If you have Invariant Sections, Front-Cover Texts and Back-Cover +Texts, replace the "with...Texts." line with this: + + with the Invariant Sections being LIST THEIR TITLES, with + the Front-Cover Texts being LIST, and with the Back-Cover Texts + being LIST. + + If you have Invariant Sections without Cover Texts, or some other +combination of the three, merge those two alternatives to suit the +situation. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, to +permit their use in free software. + + +File: autoconf.info, Node: Indices, Prev: GNU Free Documentation License, Up: Top + +Appendix B Indices +****************** + +* Menu: + +* Environment Variable Index:: Index of environment variables used +* Output Variable Index:: Index of variables set in output files +* Preprocessor Symbol Index:: Index of C preprocessor symbols defined +* Cache Variable Index:: Index of documented cache variables +* Autoconf Macro Index:: Index of Autoconf macros +* M4 Macro Index:: Index of M4, M4sugar, and M4sh macros +* Autotest Macro Index:: Index of Autotest macros +* Program & Function Index:: Index of those with portability problems +* Concept Index:: General index + + +File: autoconf.info, Node: Environment Variable Index, Next: Output Variable Index, Up: Indices + +B.1 Environment Variable Index +============================== + +This is an alphabetical list of the environment variables that might +influence Autoconf checks. + + +* Menu: + +* _: Special Shell Variables. + (line 36) +* BIN_SH: Special Shell Variables. + (line 40) +* CC: C Compiler. (line 61) +* CDPATH: Special Shell Variables. + (line 44) +* CFLAGS <1>: C Compiler. (line 61) +* CFLAGS: Preset Output Variables. + (line 23) +* CLICOLOR_FORCE: Special Shell Variables. + (line 67) +* CONFIG_COMMANDS: Obsolete config.status Use. + (line 11) +* CONFIG_FILES: Obsolete config.status Use. + (line 15) +* CONFIG_HEADERS: Obsolete config.status Use. + (line 20) +* CONFIG_LINKS: Obsolete config.status Use. + (line 25) +* CONFIG_SHELL: config.status Invocation. + (line 102) +* CONFIG_SITE: Site Defaults. (line 10) +* CONFIG_STATUS: config.status Invocation. + (line 108) +* CPP: C Compiler. (line 113) +* CPPFLAGS: Preset Output Variables. + (line 72) +* CXX: C++ Compiler. (line 7) +* CXXCPP: C++ Compiler. (line 35) +* CXXFLAGS <1>: C++ Compiler. (line 7) +* CXXFLAGS: Preset Output Variables. + (line 94) +* CYGWIN: Obsolete Macros. (line 124) +* DUALCASE: Special Shell Variables. + (line 74) +* ENV: Special Shell Variables. + (line 84) +* ERL: Erlang Compiler and Interpreter. + (line 29) +* ERLC: Erlang Compiler and Interpreter. + (line 10) +* ERLCFLAGS <1>: Erlang Compiler and Interpreter. + (line 10) +* ERLCFLAGS: Preset Output Variables. + (line 120) +* F77: Fortran Compiler. (line 19) +* FC: Fortran Compiler. (line 44) +* FCFLAGS <1>: Fortran Compiler. (line 44) +* FCFLAGS: Preset Output Variables. + (line 126) +* FFLAGS <1>: Fortran Compiler. (line 19) +* FFLAGS: Preset Output Variables. + (line 133) +* FPATH: Special Shell Variables. + (line 101) +* GOFLAGS: Preset Output Variables. + (line 170) +* GREP_OPTIONS: Special Shell Variables. + (line 108) +* IFS: Special Shell Variables. + (line 116) +* LANG: Special Shell Variables. + (line 160) +* LANGUAGE: Special Shell Variables. + (line 167) +* LC_ADDRESS: Special Shell Variables. + (line 177) +* LC_ALL <1>: Special Shell Variables. + (line 160) +* LC_ALL: Initialization Macros. + (line 14) +* LC_COLLATE: Special Shell Variables. + (line 160) +* LC_CTYPE: Special Shell Variables. + (line 160) +* LC_IDENTIFICATION: Special Shell Variables. + (line 177) +* LC_MEASUREMENT: Special Shell Variables. + (line 177) +* LC_MESSAGES: Special Shell Variables. + (line 160) +* LC_MONETARY: Special Shell Variables. + (line 160) +* LC_NAME: Special Shell Variables. + (line 177) +* LC_NUMERIC: Special Shell Variables. + (line 160) +* LC_PAPER: Special Shell Variables. + (line 177) +* LC_TELEPHONE: Special Shell Variables. + (line 177) +* LC_TIME: Special Shell Variables. + (line 160) +* LDFLAGS: Preset Output Variables. + (line 140) +* LIBS: Preset Output Variables. + (line 154) +* LINENO <1>: Special Shell Variables. + (line 182) +* LINENO: Initialization Macros. + (line 67) +* M4: autom4te Invocation. (line 10) +* MAIL: Special Shell Variables. + (line 84) +* MAILPATH: Special Shell Variables. + (line 84) +* NULLCMD: Special Shell Variables. + (line 311) +* OBJC: Objective C Compiler. + (line 7) +* OBJCFLAGS <1>: Objective C Compiler. + (line 7) +* OBJCFLAGS: Preset Output Variables. + (line 162) +* OBJCPP: Objective C Compiler. + (line 26) +* OBJCXX: Objective C++ Compiler. + (line 7) +* OBJCXXCPP: Objective C++ Compiler. + (line 27) +* OBJCXXFLAGS <1>: Objective C++ Compiler. + (line 7) +* OBJCXXFLAGS: Preset Output Variables. + (line 166) +* options: Special Shell Variables. + (line 318) +* PATH_SEPARATOR: Special Shell Variables. + (line 322) +* POSIXLY_CORRECT: Special Shell Variables. + (line 331) +* PS1: Special Shell Variables. + (line 84) +* PS2: Special Shell Variables. + (line 84) +* PS4: Special Shell Variables. + (line 84) +* PWD: Special Shell Variables. + (line 346) +* RANDOM: Special Shell Variables. + (line 355) +* SHELL: Initialization Macros. + (line 14) +* SIMPLE_BACKUP_SUFFIX: autoupdate Invocation. + (line 16) +* status: Special Shell Variables. + (line 363) +* TMPDIR: Initialization Macros. + (line 77) +* WARNINGS <1>: autom4te Invocation. (line 58) +* WARNINGS <2>: autoheader Invocation. + (line 83) +* WARNINGS <3>: autoreconf Invocation. + (line 97) +* WARNINGS: autoconf Invocation. (line 62) +* XMKMF: System Services. (line 10) +* YACC: Particular Programs. (line 200) +* YFLAGS: Particular Programs. (line 200) + + +File: autoconf.info, Node: Output Variable Index, Next: Preprocessor Symbol Index, Prev: Environment Variable Index, Up: Indices + +B.2 Output Variable Index +========================= + +This is an alphabetical list of the variables that Autoconf can +substitute into files that it creates, typically one or more makefiles. +*Note Setting Output Variables::, for more information on how this is +done. + + +* Menu: + +* abs_builddir: Preset Output Variables. + (line 177) +* abs_srcdir: Preset Output Variables. + (line 199) +* abs_top_builddir: Preset Output Variables. + (line 192) +* abs_top_srcdir: Preset Output Variables. + (line 206) +* ac_empty: Fortran Compiler. (line 465) +* ALLOCA: Particular Functions. + (line 10) +* AWK: Particular Programs. (line 10) +* bindir: Installation Directory Variables. + (line 15) +* build: Canonicalizing. (line 26) +* build_alias: Canonicalizing. (line 9) +* build_cpu: Canonicalizing. (line 26) +* build_os: Canonicalizing. (line 26) +* build_vendor: Canonicalizing. (line 26) +* builddir: Preset Output Variables. + (line 174) +* CC <1>: System Services. (line 49) +* CC: C Compiler. (line 61) +* CFLAGS <1>: C Compiler. (line 61) +* CFLAGS: Preset Output Variables. + (line 23) +* configure_input: Preset Output Variables. + (line 58) +* CPP: C Compiler. (line 113) +* CPPFLAGS: Preset Output Variables. + (line 72) +* cross_compiling: Runtime. (line 71) +* CXX: C++ Compiler. (line 7) +* CXXCPP: C++ Compiler. (line 35) +* CXXFLAGS <1>: C++ Compiler. (line 7) +* CXXFLAGS: Preset Output Variables. + (line 94) +* datadir: Installation Directory Variables. + (line 18) +* datarootdir: Installation Directory Variables. + (line 22) +* DEFS: Preset Output Variables. + (line 98) +* docdir: Installation Directory Variables. + (line 26) +* dvidir: Installation Directory Variables. + (line 30) +* ECHO_C: Preset Output Variables. + (line 108) +* ECHO_N: Preset Output Variables. + (line 108) +* ECHO_T: Preset Output Variables. + (line 108) +* EGREP: Particular Programs. (line 29) +* ERL <1>: Running the Compiler. + (line 30) +* ERL <2>: Language Choice. (line 40) +* ERL: Erlang Compiler and Interpreter. + (line 29) +* ERLANG_ERTS_VER: Erlang Libraries. (line 12) +* ERLANG_INSTALL_LIB_DIR <1>: Erlang Libraries. (line 86) +* ERLANG_INSTALL_LIB_DIR: Installation Directory Variables. + (line 201) +* ERLANG_INSTALL_LIB_DIR_LIBRARY <1>: Erlang Libraries. (line 93) +* ERLANG_INSTALL_LIB_DIR_LIBRARY: Installation Directory Variables. + (line 206) +* ERLANG_LIB_DIR: Erlang Libraries. (line 28) +* ERLANG_LIB_DIR_LIBRARY: Erlang Libraries. (line 36) +* ERLANG_LIB_VER_LIBRARY: Erlang Libraries. (line 36) +* ERLANG_ROOT_DIR: Erlang Libraries. (line 22) +* ERLC <1>: Language Choice. (line 40) +* ERLC: Erlang Compiler and Interpreter. + (line 10) +* ERLCFLAGS <1>: Language Choice. (line 40) +* ERLCFLAGS <2>: Erlang Compiler and Interpreter. + (line 10) +* ERLCFLAGS: Preset Output Variables. + (line 120) +* exec_prefix: Installation Directory Variables. + (line 33) +* EXEEXT <1>: Obsolete Macros. (line 178) +* EXEEXT: Compilers and Preprocessors. + (line 6) +* F77: Fortran Compiler. (line 19) +* FC: Fortran Compiler. (line 44) +* FC_MODEXT: Fortran Compiler. (line 438) +* FC_MODINC: Fortran Compiler. (line 465) +* FC_MODOUT: Fortran Compiler. (line 501) +* FCFLAGS <1>: Fortran Compiler. (line 44) +* FCFLAGS: Preset Output Variables. + (line 126) +* FCLIBS: Fortran Compiler. (line 92) +* FFLAGS <1>: Fortran Compiler. (line 19) +* FFLAGS: Preset Output Variables. + (line 133) +* FGREP: Particular Programs. (line 36) +* FLIBS: Fortran Compiler. (line 92) +* GETGROUPS_LIBS: Particular Functions. + (line 155) +* GETLOADAVG_LIBS: Particular Functions. + (line 161) +* GOFLAGS: Preset Output Variables. + (line 170) +* GREP: Particular Programs. (line 20) +* host: Canonicalizing. (line 34) +* host_alias: Canonicalizing. (line 9) +* host_cpu: Canonicalizing. (line 34) +* host_os: Canonicalizing. (line 34) +* host_vendor: Canonicalizing. (line 34) +* htmldir: Installation Directory Variables. + (line 40) +* includedir: Installation Directory Variables. + (line 43) +* infodir: Installation Directory Variables. + (line 46) +* INSTALL: Particular Programs. (line 43) +* INSTALL_DATA: Particular Programs. (line 43) +* INSTALL_PROGRAM: Particular Programs. (line 43) +* INSTALL_SCRIPT: Particular Programs. (line 43) +* KMEM_GROUP: Particular Functions. + (line 161) +* LDFLAGS: Preset Output Variables. + (line 140) +* LEX: Particular Programs. (line 114) +* LEX_OUTPUT_ROOT: Particular Programs. (line 114) +* LEXLIB: Particular Programs. (line 114) +* libdir: Installation Directory Variables. + (line 49) +* libexecdir: Installation Directory Variables. + (line 52) +* LIBOBJDIR: AC_LIBOBJ vs LIBOBJS. + (line 35) +* LIBOBJS <1>: Particular Structures. + (line 26) +* LIBOBJS <2>: Generic Functions. (line 56) +* LIBOBJS: Particular Functions. + (line 161) +* LIBS <1>: Obsolete Macros. (line 295) +* LIBS: Preset Output Variables. + (line 154) +* LN_S: Particular Programs. (line 168) +* localedir: Installation Directory Variables. + (line 55) +* localstatedir: Installation Directory Variables. + (line 60) +* mandir: Installation Directory Variables. + (line 63) +* MKDIR_P: Particular Programs. (line 80) +* NEED_SETGID: Particular Functions. + (line 161) +* OBJC: Objective C Compiler. + (line 7) +* OBJCFLAGS <1>: Objective C Compiler. + (line 7) +* OBJCFLAGS: Preset Output Variables. + (line 162) +* OBJCPP: Objective C Compiler. + (line 26) +* OBJCXX: Objective C++ Compiler. + (line 7) +* OBJCXXCPP: Objective C++ Compiler. + (line 27) +* OBJCXXFLAGS <1>: Objective C++ Compiler. + (line 7) +* OBJCXXFLAGS: Preset Output Variables. + (line 166) +* OBJEXT <1>: Obsolete Macros. (line 384) +* OBJEXT: Compilers and Preprocessors. + (line 11) +* oldincludedir: Installation Directory Variables. + (line 66) +* OPENMP_CFLAGS: Generic Compiler Characteristics. + (line 64) +* OPENMP_CXXFLAGS: Generic Compiler Characteristics. + (line 64) +* OPENMP_FCFLAGS: Generic Compiler Characteristics. + (line 64) +* OPENMP_FFLAGS: Generic Compiler Characteristics. + (line 64) +* PACKAGE_BUGREPORT: Initializing configure. + (line 57) +* PACKAGE_NAME: Initializing configure. + (line 45) +* PACKAGE_STRING: Initializing configure. + (line 54) +* PACKAGE_TARNAME: Initializing configure. + (line 48) +* PACKAGE_URL: Initializing configure. + (line 61) +* PACKAGE_VERSION: Initializing configure. + (line 51) +* pdfdir: Installation Directory Variables. + (line 69) +* POW_LIB: Particular Functions. + (line 408) +* prefix: Installation Directory Variables. + (line 72) +* program_transform_name: Transforming Names. (line 11) +* psdir: Installation Directory Variables. + (line 77) +* RANLIB: Particular Programs. (line 187) +* sbindir: Installation Directory Variables. + (line 80) +* SED: Particular Programs. (line 191) +* SET_MAKE: Output. (line 45) +* sharedstatedir: Installation Directory Variables. + (line 84) +* srcdir: Preset Output Variables. + (line 195) +* subdirs: Subdirectories. (line 12) +* sysconfdir: Installation Directory Variables. + (line 88) +* target: Canonicalizing. (line 41) +* target_alias: Canonicalizing. (line 9) +* target_cpu: Canonicalizing. (line 41) +* target_os: Canonicalizing. (line 41) +* target_vendor: Canonicalizing. (line 41) +* tmp: Initialization Macros. + (line 77) +* top_build_prefix: Preset Output Variables. + (line 184) +* top_builddir: Preset Output Variables. + (line 180) +* top_srcdir: Preset Output Variables. + (line 202) +* X_CFLAGS: System Services. (line 30) +* X_EXTRA_LIBS: System Services. (line 30) +* X_LIBS: System Services. (line 30) +* X_PRE_LIBS: System Services. (line 30) +* YACC: Particular Programs. (line 200) + + +File: autoconf.info, Node: Preprocessor Symbol Index, Next: Cache Variable Index, Prev: Output Variable Index, Up: Indices + +B.3 Preprocessor Symbol Index +============================= + +This is an alphabetical list of the C preprocessor symbols that the +Autoconf macros define. To work with Autoconf, C source code needs to +use these names in `#if' or `#ifdef' directives. + + +* Menu: + +* __CHAR_UNSIGNED__: C Compiler. (line 291) +* __EXTENSIONS__: Posix Variants. (line 10) +* __PROTOTYPES: C Compiler. (line 351) +* _ALL_SOURCE <1>: Obsolete Macros. (line 20) +* _ALL_SOURCE: Posix Variants. (line 10) +* _FILE_OFFSET_BITS: System Services. (line 49) +* _GNU_SOURCE <1>: Obsolete Macros. (line 234) +* _GNU_SOURCE: Posix Variants. (line 10) +* _LARGE_FILES: System Services. (line 49) +* _LARGEFILE_SOURCE: Particular Functions. + (line 147) +* _MINIX <1>: Obsolete Macros. (line 371) +* _MINIX: Posix Variants. (line 10) +* _OPENMP: Generic Compiler Characteristics. + (line 64) +* _POSIX_1_SOURCE <1>: Obsolete Macros. (line 371) +* _POSIX_1_SOURCE: Posix Variants. (line 10) +* _POSIX_PTHREAD_SEMANTICS: Posix Variants. (line 10) +* _POSIX_SOURCE <1>: Obsolete Macros. (line 371) +* _POSIX_SOURCE: Posix Variants. (line 10) +* _POSIX_VERSION: Particular Headers. (line 228) +* _TANDEM_SOURCE: Posix Variants. (line 10) +* ALIGNOF_TYPE: Generic Compiler Characteristics. + (line 30) +* C_ALLOCA: Particular Functions. + (line 10) +* C_GETLOADAVG: Particular Functions. + (line 161) +* CLOSEDIR_VOID: Particular Functions. + (line 69) +* const: C Compiler. (line 217) +* CXX_NO_MINUS_C_MINUS_O: C++ Compiler. (line 48) +* DGUX: Particular Functions. + (line 161) +* DIRENT: Obsolete Macros. (line 158) +* F77_DUMMY_MAIN: Fortran Compiler. (line 130) +* F77_FUNC: Fortran Compiler. (line 202) +* F77_FUNC_: Fortran Compiler. (line 202) +* F77_MAIN: Fortran Compiler. (line 176) +* F77_NO_MINUS_C_MINUS_O: Fortran Compiler. (line 76) +* FC_DUMMY_MAIN: Fortran Compiler. (line 130) +* FC_FUNC: Fortran Compiler. (line 202) +* FC_FUNC_: Fortran Compiler. (line 202) +* FC_MAIN: Fortran Compiler. (line 176) +* FC_NO_MINUS_C_MINUS_O: Fortran Compiler. (line 76) +* FLEXIBLE_ARRAY_MEMBER: C Compiler. (line 315) +* GETGROUPS_T: Particular Types. (line 14) +* GETLOADAVG_PRIVILEGED: Particular Functions. + (line 161) +* GETPGRP_VOID: Particular Functions. + (line 205) +* gid_t: Particular Types. (line 126) +* GWINSZ_IN_SYS_IOCTL: Particular Headers. (line 270) +* HAVE__BOOL: Particular Headers. (line 10) +* HAVE_AGGREGATE_MEMBER: Generic Structures. (line 29) +* HAVE_ALLOCA_H: Particular Functions. + (line 10) +* HAVE_C_BACKSLASH_A: C Compiler. (line 176) +* HAVE_C_VARARRAYS: C Compiler. (line 339) +* HAVE_CHOWN: Particular Functions. + (line 63) +* HAVE_CONFIG_H: Configuration Headers. + (line 33) +* HAVE_DECL_STRERROR_R: Particular Functions. + (line 388) +* HAVE_DECL_SYMBOL: Generic Declarations. + (line 34) +* HAVE_DECL_TZNAME: Particular Structures. + (line 43) +* HAVE_DIRENT_H: Particular Headers. (line 25) +* HAVE_DOPRNT: Particular Functions. + (line 443) +* HAVE_FSEEKO: Particular Functions. + (line 147) +* HAVE_FUNCTION: Generic Functions. (line 27) +* HAVE_GETGROUPS: Particular Functions. + (line 155) +* HAVE_GETMNTENT: Particular Functions. + (line 195) +* HAVE_HEADER: Generic Headers. (line 46) +* HAVE_INT16_T: Particular Types. (line 40) +* HAVE_INT32_T: Particular Types. (line 43) +* HAVE_INT64_T: Particular Types. (line 46) +* HAVE_INT8_T: Particular Types. (line 21) +* HAVE_INTMAX_T: Particular Types. (line 49) +* HAVE_INTPTR_T: Particular Types. (line 54) +* HAVE_LONG_DOUBLE <1>: Obsolete Macros. (line 33) +* HAVE_LONG_DOUBLE: Particular Types. (line 59) +* HAVE_LONG_DOUBLE_WIDER: Particular Types. (line 70) +* HAVE_LONG_FILE_NAMES: System Services. (line 71) +* HAVE_LONG_LONG_INT: Particular Types. (line 78) +* HAVE_LSTAT_EMPTY_STRING_BUG: Particular Functions. + (line 363) +* HAVE_MALLOC: Particular Functions. + (line 247) +* HAVE_MBRTOWC: Particular Functions. + (line 279) +* HAVE_MMAP: Particular Functions. + (line 311) +* HAVE_NDIR_H: Particular Headers. (line 25) +* HAVE_NLIST_H: Particular Functions. + (line 161) +* HAVE_OBSTACK: Particular Functions. + (line 319) +* HAVE_REALLOC: Particular Functions. + (line 326) +* HAVE_RESOLV_H: Particular Headers. (line 73) +* HAVE_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 548) +* HAVE_ST_BLKSIZE: Obsolete Macros. (line 521) +* HAVE_ST_BLOCKS: Particular Structures. + (line 26) +* HAVE_ST_RDEV: Obsolete Macros. (line 530) +* HAVE_STAT_EMPTY_STRING_BUG: Particular Functions. + (line 363) +* HAVE_STDBOOL_H: Particular Headers. (line 101) +* HAVE_STRCOLL: Particular Functions. + (line 379) +* HAVE_STRERROR_R: Particular Functions. + (line 388) +* HAVE_STRFTIME: Particular Functions. + (line 401) +* HAVE_STRINGIZE: C Compiler. (line 305) +* HAVE_STRNLEN: Particular Functions. + (line 426) +* HAVE_STRTOLD: Particular Functions. + (line 420) +* HAVE_STRUCT_DIRENT_D_INO: Particular Structures. + (line 9) +* HAVE_STRUCT_DIRENT_D_TYPE: Particular Structures. + (line 21) +* HAVE_STRUCT_STAT_ST_BLKSIZE: Obsolete Macros. (line 521) +* HAVE_STRUCT_STAT_ST_BLOCKS: Particular Structures. + (line 26) +* HAVE_STRUCT_STAT_ST_RDEV: Obsolete Macros. (line 530) +* HAVE_STRUCT_TM_TM_ZONE: Particular Structures. + (line 43) +* HAVE_SYS_DIR_H: Particular Headers. (line 25) +* HAVE_SYS_NDIR_H: Particular Headers. (line 25) +* HAVE_SYS_WAIT_H: Particular Headers. (line 204) +* HAVE_TM_ZONE: Particular Structures. + (line 43) +* HAVE_TYPE: Generic Types. (line 28) +* HAVE_TYPEOF: C Compiler. (line 345) +* HAVE_TZNAME: Particular Structures. + (line 43) +* HAVE_UINT16_T: Particular Types. (line 138) +* HAVE_UINT32_T: Particular Types. (line 141) +* HAVE_UINT64_T: Particular Types. (line 144) +* HAVE_UINT8_T: Particular Types. (line 132) +* HAVE_UINTMAX_T: Particular Types. (line 147) +* HAVE_UINTPTR_T: Particular Types. (line 152) +* HAVE_UNSIGNED_LONG_LONG_INT: Particular Types. (line 157) +* HAVE_UTIME_NULL: Particular Functions. + (line 433) +* HAVE_VFORK_H: Particular Functions. + (line 120) +* HAVE_VPRINTF: Particular Functions. + (line 443) +* HAVE_WAIT3: Obsolete Macros. (line 216) +* HAVE_WORKING_FORK: Particular Functions. + (line 120) +* HAVE_WORKING_VFORK: Particular Functions. + (line 120) +* inline: C Compiler. (line 286) +* int16_t: Particular Types. (line 40) +* int32_t: Particular Types. (line 43) +* int64_t: Particular Types. (line 46) +* int8_t: Particular Types. (line 21) +* INT_16_BITS: Obsolete Macros. (line 275) +* intmax_t: Particular Types. (line 49) +* intptr_t: Particular Types. (line 54) +* LONG_64_BITS: Obsolete Macros. (line 337) +* LSTAT_FOLLOWS_SLASHED_SYMLINK: Particular Functions. + (line 228) +* MAJOR_IN_MKDEV: Particular Headers. (line 68) +* MAJOR_IN_SYSMACROS: Particular Headers. (line 68) +* malloc: Particular Functions. + (line 247) +* mbstate_t: Particular Types. (line 88) +* mode_t: Particular Types. (line 96) +* NDEBUG: Particular Headers. (line 20) +* NDIR: Obsolete Macros. (line 158) +* NEED_MEMORY_H: Obsolete Macros. (line 358) +* NEED_SETGID: Particular Functions. + (line 161) +* NLIST_NAME_UNION: Particular Functions. + (line 161) +* NO_MINUS_C_MINUS_O: C Compiler. (line 102) +* off_t: Particular Types. (line 102) +* PACKAGE_BUGREPORT: Initializing configure. + (line 57) +* PACKAGE_NAME: Initializing configure. + (line 45) +* PACKAGE_STRING: Initializing configure. + (line 54) +* PACKAGE_TARNAME: Initializing configure. + (line 48) +* PACKAGE_URL: Initializing configure. + (line 61) +* PACKAGE_VERSION: Initializing configure. + (line 51) +* PARAMS: C Compiler. (line 351) +* pid_t: Particular Types. (line 108) +* PROTOTYPES: C Compiler. (line 351) +* realloc: Particular Functions. + (line 326) +* restrict: C Compiler. (line 247) +* RETSIGTYPE: Obsolete Macros. (line 662) +* SELECT_TYPE_ARG1: Particular Functions. + (line 337) +* SELECT_TYPE_ARG234: Particular Functions. + (line 337) +* SELECT_TYPE_ARG5: Particular Functions. + (line 337) +* SETPGRP_VOID: Particular Functions. + (line 348) +* SETVBUF_REVERSED: Obsolete Macros. (line 208) +* size_t: Particular Types. (line 114) +* SIZEOF_TYPE-OR-EXPR: Generic Compiler Characteristics. + (line 8) +* ssize_t: Particular Types. (line 120) +* STAT_MACROS_BROKEN: Particular Headers. (line 92) +* STDC_HEADERS: Particular Headers. (line 135) +* STRERROR_R_CHAR_P: Particular Functions. + (line 388) +* SVR4: Particular Functions. + (line 161) +* SYS_SIGLIST_DECLARED: Obsolete Macros. (line 141) +* SYSDIR: Obsolete Macros. (line 158) +* SYSNDIR: Obsolete Macros. (line 158) +* TIME_WITH_SYS_TIME: Particular Headers. (line 244) +* TM_IN_SYS_TIME: Particular Structures. + (line 35) +* typeof: C Compiler. (line 345) +* uid_t: Particular Types. (line 126) +* uint16_t: Particular Types. (line 138) +* uint32_t: Particular Types. (line 141) +* uint64_t: Particular Types. (line 144) +* uint8_t: Particular Types. (line 132) +* uintmax_t: Particular Types. (line 147) +* uintptr_t: Particular Types. (line 152) +* UMAX: Particular Functions. + (line 161) +* UMAX4_3: Particular Functions. + (line 161) +* USG: Obsolete Macros. (line 685) +* VARIABLE: Defining Symbols. (line 32) +* vfork: Particular Functions. + (line 120) +* volatile: C Compiler. (line 265) +* WORDS_BIGENDIAN: C Compiler. (line 184) +* X_DISPLAY_MISSING: System Services. (line 30) +* YYTEXT_POINTER: Particular Programs. (line 114) + + +File: autoconf.info, Node: Cache Variable Index, Next: Autoconf Macro Index, Prev: Preprocessor Symbol Index, Up: Indices + +B.4 Cache Variable Index +======================== + +This is an alphabetical list of documented cache variables used by +macros defined in Autoconf. Autoconf macros may use additional cache +variables internally. + + +* Menu: + +* ac_cv_alignof_TYPE-OR-EXPR: Generic Compiler Characteristics. + (line 30) +* ac_cv_c_const: C Compiler. (line 217) +* ac_cv_c_int16_t: Particular Types. (line 40) +* ac_cv_c_int32_t: Particular Types. (line 43) +* ac_cv_c_int64_t: Particular Types. (line 46) +* ac_cv_c_int8_t: Particular Types. (line 21) +* ac_cv_c_restrict: C Compiler. (line 247) +* ac_cv_c_uint16_t: Particular Types. (line 138) +* ac_cv_c_uint32_t: Particular Types. (line 141) +* ac_cv_c_uint64_t: Particular Types. (line 144) +* ac_cv_c_uint8_t: Particular Types. (line 132) +* ac_cv_f77_compiler_gnu: Fortran Compiler. (line 19) +* ac_cv_f77_dummy_main: Fortran Compiler. (line 130) +* ac_cv_f77_implicit_none: Fortran Compiler. (line 427) +* ac_cv_f77_libs: Fortran Compiler. (line 92) +* ac_cv_f77_main: Fortran Compiler. (line 176) +* ac_cv_f77_mangling: Fortran Compiler. (line 202) +* ac_cv_fc_check_bounds: Fortran Compiler. (line 413) +* ac_cv_fc_compiler_gnu: Fortran Compiler. (line 44) +* ac_cv_fc_dummy_main: Fortran Compiler. (line 130) +* ac_cv_fc_fixedform: Fortran Compiler. (line 375) +* ac_cv_fc_freeform: Fortran Compiler. (line 351) +* ac_cv_fc_implicit_none: Fortran Compiler. (line 427) +* ac_cv_fc_libs: Fortran Compiler. (line 92) +* ac_cv_fc_line_length: Fortran Compiler. (line 396) +* ac_cv_fc_main: Fortran Compiler. (line 176) +* ac_cv_fc_mangling: Fortran Compiler. (line 202) +* ac_cv_fc_module_ext: Fortran Compiler. (line 438) +* ac_cv_fc_module_flag: Fortran Compiler. (line 465) +* ac_cv_fc_module_output_flag: Fortran Compiler. (line 501) +* ac_cv_fc_pp_define: Fortran Compiler. (line 336) +* ac_cv_fc_pp_srcext_EXT: Fortran Compiler. (line 279) +* ac_cv_fc_srcext_EXT: Fortran Compiler. (line 279) +* ac_cv_file_FILE: Files. (line 13) +* ac_cv_func_chown_works: Particular Functions. + (line 63) +* ac_cv_func_closedir_void: Particular Functions. + (line 69) +* ac_cv_func_fnmatch_gnu: Particular Functions. + (line 109) +* ac_cv_func_fnmatch_works: Particular Functions. + (line 94) +* ac_cv_func_FUNCTION: Generic Functions. (line 15) +* ac_cv_func_getgroups_works: Particular Functions. + (line 155) +* ac_cv_func_getpgrp_void: Particular Functions. + (line 205) +* ac_cv_func_lstat_dereferences_slashed_symlink: Particular Functions. + (line 228) +* ac_cv_func_lstat_empty_string_bug: Particular Functions. + (line 363) +* ac_cv_func_malloc_0_nonnull: Particular Functions. + (line 247) +* ac_cv_func_mbrtowc: Particular Functions. + (line 279) +* ac_cv_func_memcmp_working: Particular Functions. + (line 286) +* ac_cv_func_mmap_fixed_mapped: Particular Functions. + (line 311) +* ac_cv_func_obstack: Particular Functions. + (line 319) +* ac_cv_func_pow: Particular Functions. + (line 408) +* ac_cv_func_realloc_0_nonnull: Particular Functions. + (line 326) +* ac_cv_func_setpgrp_void: Particular Functions. + (line 348) +* ac_cv_func_stat_empty_string_bug: Particular Functions. + (line 363) +* ac_cv_func_strcoll_works: Particular Functions. + (line 379) +* ac_cv_func_strerror_r_char_p: Particular Functions. + (line 388) +* ac_cv_func_strnlen_working: Particular Functions. + (line 426) +* ac_cv_func_strtod: Particular Functions. + (line 408) +* ac_cv_func_strtold: Particular Functions. + (line 420) +* ac_cv_func_utime_null: Particular Functions. + (line 433) +* ac_cv_func_working_mktime: Particular Functions. + (line 299) +* ac_cv_have_decl_SYMBOL: Generic Declarations. + (line 11) +* ac_cv_header_HEADER-FILE: Generic Headers. (line 13) +* ac_cv_header_stdbool_h: Particular Headers. (line 10) +* ac_cv_header_stdc: Particular Headers. (line 135) +* ac_cv_header_sys_wait_h: Particular Headers. (line 204) +* ac_cv_header_time: Particular Headers. (line 244) +* ac_cv_lib_error_at_line: Particular Functions. + (line 84) +* ac_cv_lib_LIBRARY_FUNCTION: Libraries. (line 11) +* ac_cv_member_AGGREGATE_MEMBER: Generic Structures. (line 11) +* ac_cv_member_struct_stat_st_blocks: Particular Structures. + (line 26) +* ac_cv_path_install: Particular Programs. (line 43) +* ac_cv_path_mkdir: Particular Programs. (line 80) +* ac_cv_path_SED: Particular Programs. (line 191) +* ac_cv_path_VARIABLE: Generic Programs. (line 108) +* ac_cv_prog_AWK: Particular Programs. (line 10) +* ac_cv_prog_c_openmp: Generic Compiler Characteristics. + (line 64) +* ac_cv_prog_cc_c89: C Compiler. (line 61) +* ac_cv_prog_cc_c99: C Compiler. (line 161) +* ac_cv_prog_cc_COMPILER_c_o: C Compiler. (line 102) +* ac_cv_prog_cc_stdc: C Compiler. (line 137) +* ac_cv_prog_cxx_openmp: Generic Compiler Characteristics. + (line 64) +* ac_cv_prog_EGREP: Particular Programs. (line 29) +* ac_cv_prog_f77_c_o: Fortran Compiler. (line 76) +* ac_cv_prog_f77_g: Fortran Compiler. (line 19) +* ac_cv_prog_f77_openmp: Generic Compiler Characteristics. + (line 64) +* ac_cv_prog_f77_v: Fortran Compiler. (line 92) +* ac_cv_prog_fc_c_o: Fortran Compiler. (line 76) +* ac_cv_prog_fc_g: Fortran Compiler. (line 44) +* ac_cv_prog_fc_openmp: Generic Compiler Characteristics. + (line 64) +* ac_cv_prog_fc_v: Fortran Compiler. (line 92) +* ac_cv_prog_FGREP: Particular Programs. (line 36) +* ac_cv_prog_GREP: Particular Programs. (line 20) +* ac_cv_prog_LEX: Particular Programs. (line 114) +* ac_cv_prog_VARIABLE: Generic Programs. (line 24) +* ac_cv_prog_YACC: Particular Programs. (line 200) +* ac_cv_search_FUNCTION: Libraries. (line 52) +* ac_cv_search_getmntent: Particular Functions. + (line 195) +* ac_cv_sizeof_TYPE-OR-EXPR: Generic Compiler Characteristics. + (line 8) +* ac_cv_sys_posix_termios: System Services. (line 75) +* ac_cv_type_getgroups: Particular Types. (line 14) +* ac_cv_type_long_double: Particular Types. (line 59) +* ac_cv_type_long_double_wider: Particular Types. (line 70) +* ac_cv_type_long_long_int: Particular Types. (line 78) +* ac_cv_type_mbstate_t: Particular Types. (line 88) +* ac_cv_type_mode_t: Particular Types. (line 96) +* ac_cv_type_off_t: Particular Types. (line 102) +* ac_cv_type_pid_t: Particular Types. (line 108) +* ac_cv_type_size_t: Particular Types. (line 114) +* ac_cv_type_ssize_t: Particular Types. (line 120) +* ac_cv_type_TYPE: Generic Types. (line 11) +* ac_cv_type_uid_t: Particular Types. (line 126) +* ac_cv_type_unsigned_long_long_int: Particular Types. (line 157) + + +File: autoconf.info, Node: Autoconf Macro Index, Next: M4 Macro Index, Prev: Cache Variable Index, Up: Indices + +B.5 Autoconf Macro Index +======================== + +This is an alphabetical list of the Autoconf macros. + + +* Menu: + +* AC_ACT_IFELSE: AC_ACT_IFELSE vs AC_TRY_ACT. + (line 6) +* AC_AIX: Obsolete Macros. (line 20) +* AC_ALLOCA: Obsolete Macros. (line 24) +* AC_ARG_ARRAY: Obsolete Macros. (line 27) +* AC_ARG_ENABLE: Package Options. (line 35) +* AC_ARG_PROGRAM: Transforming Names. (line 11) +* AC_ARG_VAR: Setting Output Variables. + (line 79) +* AC_ARG_WITH: External Software. (line 36) +* AC_AUTOCONF_VERSION: Versioning. (line 21) +* AC_BEFORE: Suggested Ordering. (line 28) +* AC_C_BACKSLASH_A: C Compiler. (line 176) +* AC_C_BIGENDIAN: C Compiler. (line 184) +* AC_C_CHAR_UNSIGNED: C Compiler. (line 291) +* AC_C_CONST: C Compiler. (line 217) +* AC_C_CROSS: Obsolete Macros. (line 30) +* AC_C_FLEXIBLE_ARRAY_MEMBER: C Compiler. (line 315) +* AC_C_INLINE: C Compiler. (line 286) +* AC_C_LONG_DOUBLE: Obsolete Macros. (line 33) +* AC_C_PROTOTYPES: C Compiler. (line 351) +* AC_C_RESTRICT: C Compiler. (line 247) +* AC_C_STRINGIZE: C Compiler. (line 305) +* AC_C_TYPEOF: C Compiler. (line 345) +* AC_C_VARARRAYS: C Compiler. (line 339) +* AC_C_VOLATILE: C Compiler. (line 265) +* AC_CACHE_CHECK: Caching Results. (line 30) +* AC_CACHE_LOAD: Cache Checkpointing. (line 13) +* AC_CACHE_SAVE: Cache Checkpointing. (line 17) +* AC_CACHE_VAL: Caching Results. (line 16) +* AC_CANONICAL_BUILD: Canonicalizing. (line 26) +* AC_CANONICAL_HOST: Canonicalizing. (line 34) +* AC_CANONICAL_SYSTEM: Obsolete Macros. (line 41) +* AC_CANONICAL_TARGET: Canonicalizing. (line 41) +* AC_CHAR_UNSIGNED: Obsolete Macros. (line 51) +* AC_CHECK_ALIGNOF: Generic Compiler Characteristics. + (line 30) +* AC_CHECK_DECL: Generic Declarations. + (line 11) +* AC_CHECK_DECLS: Generic Declarations. + (line 34) +* AC_CHECK_DECLS_ONCE: Generic Declarations. + (line 79) +* AC_CHECK_FILE: Files. (line 13) +* AC_CHECK_FILES: Files. (line 21) +* AC_CHECK_FUNC: Generic Functions. (line 15) +* AC_CHECK_FUNCS: Generic Functions. (line 27) +* AC_CHECK_FUNCS_ONCE: Generic Functions. (line 38) +* AC_CHECK_HEADER: Generic Headers. (line 13) +* AC_CHECK_HEADER_STDBOOL: Particular Headers. (line 10) +* AC_CHECK_HEADERS: Generic Headers. (line 46) +* AC_CHECK_HEADERS_ONCE: Generic Headers. (line 87) +* AC_CHECK_LIB: Libraries. (line 11) +* AC_CHECK_MEMBER: Generic Structures. (line 11) +* AC_CHECK_MEMBERS: Generic Structures. (line 29) +* AC_CHECK_PROG: Generic Programs. (line 24) +* AC_CHECK_PROGS: Generic Programs. (line 36) +* AC_CHECK_SIZEOF: Generic Compiler Characteristics. + (line 8) +* AC_CHECK_TARGET_TOOL: Generic Programs. (line 48) +* AC_CHECK_TARGET_TOOLS: Generic Programs. (line 79) +* AC_CHECK_TOOL: Generic Programs. (line 64) +* AC_CHECK_TOOLS: Generic Programs. (line 92) +* AC_CHECK_TYPE <1>: Obsolete Macros. (line 54) +* AC_CHECK_TYPE: Generic Types. (line 11) +* AC_CHECK_TYPES: Generic Types. (line 28) +* AC_CHECKING: Obsolete Macros. (line 101) +* AC_COMPILE_CHECK: Obsolete Macros. (line 109) +* AC_COMPILE_IFELSE: Running the Compiler. + (line 13) +* AC_COMPUTE_INT: Generic Compiler Characteristics. + (line 42) +* AC_CONFIG_AUX_DIR: Input. (line 20) +* AC_CONFIG_COMMANDS: Configuration Commands. + (line 13) +* AC_CONFIG_COMMANDS_POST: Configuration Commands. + (line 41) +* AC_CONFIG_COMMANDS_PRE: Configuration Commands. + (line 35) +* AC_CONFIG_FILES: Configuration Files. (line 9) +* AC_CONFIG_HEADERS: Configuration Headers. + (line 33) +* AC_CONFIG_ITEMS: Configuration Actions. + (line 12) +* AC_CONFIG_LIBOBJ_DIR: Generic Functions. (line 97) +* AC_CONFIG_LINKS: Configuration Links. (line 12) +* AC_CONFIG_MACRO_DIR: Input. (line 48) +* AC_CONFIG_SRCDIR: Input. (line 7) +* AC_CONFIG_SUBDIRS: Subdirectories. (line 12) +* AC_CONFIG_TESTDIR: Making testsuite Scripts. + (line 26) +* AC_CONST: Obsolete Macros. (line 117) +* AC_COPYRIGHT: Notices. (line 10) +* AC_CROSS_CHECK: Obsolete Macros. (line 120) +* AC_CYGWIN: Obsolete Macros. (line 124) +* AC_DATAROOTDIR_CHECKED: Changed Directory Variables. + (line 58) +* AC_DECL_SYS_SIGLIST: Obsolete Macros. (line 141) +* AC_DECL_YYTEXT: Obsolete Macros. (line 154) +* AC_DEFINE: Defining Symbols. (line 32) +* AC_DEFINE_UNQUOTED: Defining Symbols. (line 74) +* AC_DEFUN: Macro Definitions. (line 7) +* AC_DEFUN_ONCE: One-Shot Macros. (line 14) +* AC_DIAGNOSE: Reporting Messages. (line 18) +* AC_DIR_HEADER: Obsolete Macros. (line 158) +* AC_DISABLE_OPTION_CHECKING: Option Checking. (line 28) +* AC_DYNIX_SEQ: Obsolete Macros. (line 170) +* AC_EGREP_CPP: Running the Preprocessor. + (line 74) +* AC_EGREP_HEADER: Running the Preprocessor. + (line 67) +* AC_EMXOS2: Obsolete Macros. (line 183) +* AC_ENABLE: Obsolete Macros. (line 189) +* AC_ERLANG_CHECK_LIB: Erlang Libraries. (line 36) +* AC_ERLANG_NEED_ERL: Erlang Compiler and Interpreter. + (line 41) +* AC_ERLANG_NEED_ERLC: Erlang Compiler and Interpreter. + (line 24) +* AC_ERLANG_PATH_ERL: Erlang Compiler and Interpreter. + (line 29) +* AC_ERLANG_PATH_ERLC: Erlang Compiler and Interpreter. + (line 10) +* AC_ERLANG_SUBST_ERTS_VER: Erlang Libraries. (line 12) +* AC_ERLANG_SUBST_INSTALL_LIB_DIR <1>: Erlang Libraries. (line 86) +* AC_ERLANG_SUBST_INSTALL_LIB_DIR: Installation Directory Variables. + (line 201) +* AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR <1>: Erlang Libraries. (line 93) +* AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR: Installation Directory Variables. + (line 206) +* AC_ERLANG_SUBST_LIB_DIR: Erlang Libraries. (line 28) +* AC_ERLANG_SUBST_ROOT_DIR: Erlang Libraries. (line 22) +* AC_ERROR: Obsolete Macros. (line 193) +* AC_EXEEXT: Obsolete Macros. (line 178) +* AC_F77_DUMMY_MAIN: Fortran Compiler. (line 130) +* AC_F77_FUNC: Fortran Compiler. (line 266) +* AC_F77_IMPLICIT_NONE: Fortran Compiler. (line 427) +* AC_F77_LIBRARY_LDFLAGS: Fortran Compiler. (line 92) +* AC_F77_MAIN: Fortran Compiler. (line 176) +* AC_F77_WRAPPERS: Fortran Compiler. (line 202) +* AC_FATAL: Reporting Messages. (line 34) +* AC_FC_CHECK_BOUNDS: Fortran Compiler. (line 413) +* AC_FC_DUMMY_MAIN: Fortran Compiler. (line 130) +* AC_FC_FIXEDFORM: Fortran Compiler. (line 375) +* AC_FC_FREEFORM: Fortran Compiler. (line 351) +* AC_FC_FUNC: Fortran Compiler. (line 266) +* AC_FC_IMPLICIT_NONE: Fortran Compiler. (line 427) +* AC_FC_LIBRARY_LDFLAGS: Fortran Compiler. (line 92) +* AC_FC_LINE_LENGTH: Fortran Compiler. (line 396) +* AC_FC_MAIN: Fortran Compiler. (line 176) +* AC_FC_MODULE_EXTENSION: Fortran Compiler. (line 438) +* AC_FC_MODULE_FLAG: Fortran Compiler. (line 465) +* AC_FC_MODULE_OUTPUT_FLAG: Fortran Compiler. (line 501) +* AC_FC_PP_DEFINE: Fortran Compiler. (line 336) +* AC_FC_PP_SRCEXT: Fortran Compiler. (line 279) +* AC_FC_SRCEXT: Fortran Compiler. (line 279) +* AC_FC_WRAPPERS: Fortran Compiler. (line 202) +* AC_FIND_X: Obsolete Macros. (line 196) +* AC_FIND_XTRA: Obsolete Macros. (line 199) +* AC_FOREACH: Obsolete Macros. (line 202) +* AC_FUNC_ALLOCA: Particular Functions. + (line 10) +* AC_FUNC_CHECK: Obsolete Macros. (line 205) +* AC_FUNC_CHOWN: Particular Functions. + (line 63) +* AC_FUNC_CLOSEDIR_VOID: Particular Functions. + (line 69) +* AC_FUNC_ERROR_AT_LINE: Particular Functions. + (line 84) +* AC_FUNC_FNMATCH: Particular Functions. + (line 94) +* AC_FUNC_FNMATCH_GNU: Particular Functions. + (line 109) +* AC_FUNC_FORK: Particular Functions. + (line 120) +* AC_FUNC_FSEEKO: Particular Functions. + (line 147) +* AC_FUNC_GETGROUPS: Particular Functions. + (line 155) +* AC_FUNC_GETLOADAVG: Particular Functions. + (line 161) +* AC_FUNC_GETMNTENT: Particular Functions. + (line 195) +* AC_FUNC_GETPGRP: Particular Functions. + (line 205) +* AC_FUNC_LSTAT: Particular Functions. + (line 363) +* AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK: Particular Functions. + (line 228) +* AC_FUNC_MALLOC: Particular Functions. + (line 247) +* AC_FUNC_MBRTOWC: Particular Functions. + (line 279) +* AC_FUNC_MEMCMP: Particular Functions. + (line 286) +* AC_FUNC_MKTIME: Particular Functions. + (line 299) +* AC_FUNC_MMAP: Particular Functions. + (line 311) +* AC_FUNC_OBSTACK: Particular Functions. + (line 319) +* AC_FUNC_REALLOC: Particular Functions. + (line 326) +* AC_FUNC_SELECT_ARGTYPES: Particular Functions. + (line 337) +* AC_FUNC_SETPGRP: Particular Functions. + (line 348) +* AC_FUNC_SETVBUF_REVERSED: Obsolete Macros. (line 208) +* AC_FUNC_STAT: Particular Functions. + (line 363) +* AC_FUNC_STRCOLL: Particular Functions. + (line 379) +* AC_FUNC_STRERROR_R: Particular Functions. + (line 388) +* AC_FUNC_STRFTIME: Particular Functions. + (line 401) +* AC_FUNC_STRNLEN: Particular Functions. + (line 426) +* AC_FUNC_STRTOD: Particular Functions. + (line 408) +* AC_FUNC_STRTOLD: Particular Functions. + (line 420) +* AC_FUNC_UTIME_NULL: Particular Functions. + (line 433) +* AC_FUNC_VPRINTF: Particular Functions. + (line 443) +* AC_FUNC_WAIT3: Obsolete Macros. (line 216) +* AC_GCC_TRADITIONAL: Obsolete Macros. (line 224) +* AC_GETGROUPS_T: Obsolete Macros. (line 228) +* AC_GETLOADAVG: Obsolete Macros. (line 231) +* AC_GNU_SOURCE: Obsolete Macros. (line 234) +* AC_HAVE_FUNCS: Obsolete Macros. (line 238) +* AC_HAVE_HEADERS: Obsolete Macros. (line 241) +* AC_HAVE_LIBRARY: Obsolete Macros. (line 245) +* AC_HAVE_POUNDBANG: Obsolete Macros. (line 252) +* AC_HEADER_ASSERT: Particular Headers. (line 20) +* AC_HEADER_CHECK: Obsolete Macros. (line 255) +* AC_HEADER_DIRENT: Particular Headers. (line 25) +* AC_HEADER_EGREP: Obsolete Macros. (line 258) +* AC_HEADER_MAJOR: Particular Headers. (line 68) +* AC_HEADER_RESOLV: Particular Headers. (line 73) +* AC_HEADER_STAT: Particular Headers. (line 92) +* AC_HEADER_STDBOOL: Particular Headers. (line 101) +* AC_HEADER_STDC: Particular Headers. (line 135) +* AC_HEADER_SYS_WAIT: Particular Headers. (line 204) +* AC_HEADER_TIME: Particular Headers. (line 244) +* AC_HEADER_TIOCGWINSZ: Particular Headers. (line 270) +* AC_HELP_STRING: Obsolete Macros. (line 261) +* AC_INCLUDES_DEFAULT: Default Includes. (line 29) +* AC_INIT <1>: Obsolete Macros. (line 264) +* AC_INIT: Initializing configure. + (line 14) +* AC_INLINE: Obsolete Macros. (line 272) +* AC_INT_16_BITS: Obsolete Macros. (line 275) +* AC_IRIX_SUN: Obsolete Macros. (line 279) +* AC_ISC_POSIX: Obsolete Macros. (line 295) +* AC_LANG: Language Choice. (line 14) +* AC_LANG_ASSERT: Language Choice. (line 79) +* AC_LANG_C: Obsolete Macros. (line 302) +* AC_LANG_CALL: Generating Sources. (line 142) +* AC_LANG_CONFTEST: Generating Sources. (line 12) +* AC_LANG_CPLUSPLUS: Obsolete Macros. (line 305) +* AC_LANG_DEFINES_PROVIDED: Generating Sources. (line 31) +* AC_LANG_FORTRAN77: Obsolete Macros. (line 308) +* AC_LANG_FUNC_LINK_TRY: Generating Sources. (line 154) +* AC_LANG_POP: Language Choice. (line 66) +* AC_LANG_PROGRAM: Generating Sources. (line 78) +* AC_LANG_PUSH: Language Choice. (line 61) +* AC_LANG_RESTORE: Obsolete Macros. (line 311) +* AC_LANG_SAVE: Obsolete Macros. (line 317) +* AC_LANG_SOURCE: Generating Sources. (line 40) +* AC_LANG_WERROR: Generic Compiler Characteristics. + (line 54) +* AC_LIBOBJ: Generic Functions. (line 56) +* AC_LIBSOURCE: Generic Functions. (line 65) +* AC_LIBSOURCES: Generic Functions. (line 89) +* AC_LINK_FILES: Obsolete Macros. (line 322) +* AC_LINK_IFELSE: Running the Linker. (line 24) +* AC_LN_S: Obsolete Macros. (line 334) +* AC_LONG_64_BITS: Obsolete Macros. (line 337) +* AC_LONG_DOUBLE: Obsolete Macros. (line 342) +* AC_LONG_FILE_NAMES: Obsolete Macros. (line 350) +* AC_MAJOR_HEADER: Obsolete Macros. (line 355) +* AC_MEMORY_H: Obsolete Macros. (line 358) +* AC_MINGW32: Obsolete Macros. (line 365) +* AC_MINIX: Obsolete Macros. (line 371) +* AC_MINUS_C_MINUS_O: Obsolete Macros. (line 375) +* AC_MMAP: Obsolete Macros. (line 378) +* AC_MODE_T: Obsolete Macros. (line 381) +* AC_MSG_CHECKING: Printing Messages. (line 24) +* AC_MSG_ERROR: Printing Messages. (line 56) +* AC_MSG_FAILURE: Printing Messages. (line 66) +* AC_MSG_NOTICE: Printing Messages. (line 46) +* AC_MSG_RESULT: Printing Messages. (line 35) +* AC_MSG_WARN: Printing Messages. (line 72) +* AC_OBJEXT: Obsolete Macros. (line 384) +* AC_OBSOLETE: Obsolete Macros. (line 390) +* AC_OFF_T: Obsolete Macros. (line 405) +* AC_OPENMP: Generic Compiler Characteristics. + (line 64) +* AC_OUTPUT <1>: Obsolete Macros. (line 408) +* AC_OUTPUT: Output. (line 13) +* AC_OUTPUT_COMMANDS: Obsolete Macros. (line 420) +* AC_PACKAGE_BUGREPORT: Initializing configure. + (line 57) +* AC_PACKAGE_NAME: Initializing configure. + (line 45) +* AC_PACKAGE_STRING: Initializing configure. + (line 54) +* AC_PACKAGE_TARNAME: Initializing configure. + (line 48) +* AC_PACKAGE_URL: Initializing configure. + (line 61) +* AC_PACKAGE_VERSION: Initializing configure. + (line 51) +* AC_PATH_PROG: Generic Programs. (line 108) +* AC_PATH_PROGS: Generic Programs. (line 115) +* AC_PATH_PROGS_FEATURE_CHECK: Generic Programs. (line 123) +* AC_PATH_TARGET_TOOL: Generic Programs. (line 159) +* AC_PATH_TOOL: Generic Programs. (line 164) +* AC_PATH_X: System Services. (line 10) +* AC_PATH_XTRA: System Services. (line 30) +* AC_PID_T: Obsolete Macros. (line 450) +* AC_PREFIX: Obsolete Macros. (line 453) +* AC_PREFIX_DEFAULT: Default Prefix. (line 16) +* AC_PREFIX_PROGRAM: Default Prefix. (line 25) +* AC_PREPROC_IFELSE: Running the Preprocessor. + (line 20) +* AC_PREREQ: Versioning. (line 11) +* AC_PRESERVE_HELP_ORDER: Help Formatting. (line 20) +* AC_PROG_AWK: Particular Programs. (line 10) +* AC_PROG_CC: C Compiler. (line 61) +* AC_PROG_CC_C89: C Compiler. (line 147) +* AC_PROG_CC_C99: C Compiler. (line 161) +* AC_PROG_CC_C_O: C Compiler. (line 102) +* AC_PROG_CC_STDC: C Compiler. (line 137) +* AC_PROG_CPP: C Compiler. (line 113) +* AC_PROG_CPP_WERROR: C Compiler. (line 126) +* AC_PROG_CXX: C++ Compiler. (line 7) +* AC_PROG_CXX_C_O: C++ Compiler. (line 48) +* AC_PROG_CXXCPP: C++ Compiler. (line 35) +* AC_PROG_EGREP: Particular Programs. (line 29) +* AC_PROG_F77: Fortran Compiler. (line 19) +* AC_PROG_F77_C_O: Fortran Compiler. (line 76) +* AC_PROG_FC: Fortran Compiler. (line 44) +* AC_PROG_FC_C_O: Fortran Compiler. (line 76) +* AC_PROG_FGREP: Particular Programs. (line 36) +* AC_PROG_GCC_TRADITIONAL: C Compiler. (line 361) +* AC_PROG_GREP: Particular Programs. (line 20) +* AC_PROG_INSTALL: Particular Programs. (line 43) +* AC_PROG_LEX: Particular Programs. (line 114) +* AC_PROG_LN_S: Particular Programs. (line 168) +* AC_PROG_MAKE_SET: Output. (line 45) +* AC_PROG_MKDIR_P: Particular Programs. (line 80) +* AC_PROG_OBJC: Objective C Compiler. + (line 7) +* AC_PROG_OBJCPP: Objective C Compiler. + (line 26) +* AC_PROG_OBJCXX: Objective C++ Compiler. + (line 7) +* AC_PROG_OBJCXXCPP: Objective C++ Compiler. + (line 27) +* AC_PROG_RANLIB: Particular Programs. (line 187) +* AC_PROG_SED: Particular Programs. (line 191) +* AC_PROG_YACC: Particular Programs. (line 200) +* AC_PROGRAM_CHECK: Obsolete Macros. (line 462) +* AC_PROGRAM_EGREP: Obsolete Macros. (line 465) +* AC_PROGRAM_PATH: Obsolete Macros. (line 468) +* AC_PROGRAMS_CHECK: Obsolete Macros. (line 456) +* AC_PROGRAMS_PATH: Obsolete Macros. (line 459) +* AC_REMOTE_TAPE: Obsolete Macros. (line 471) +* AC_REPLACE_FNMATCH: Particular Functions. + (line 452) +* AC_REPLACE_FUNCS: Generic Functions. (line 117) +* AC_REQUIRE: Prerequisite Macros. (line 17) +* AC_REQUIRE_AUX_FILE: Input. (line 37) +* AC_REQUIRE_CPP: Language Choice. (line 94) +* AC_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 474) +* AC_RETSIGTYPE: Obsolete Macros. (line 482) +* AC_REVISION: Notices. (line 18) +* AC_RSH: Obsolete Macros. (line 486) +* AC_RUN_IFELSE: Runtime. (line 20) +* AC_SCO_INTL: Obsolete Macros. (line 489) +* AC_SEARCH_LIBS: Libraries. (line 52) +* AC_SET_MAKE: Obsolete Macros. (line 503) +* AC_SETVBUF_REVERSED: Obsolete Macros. (line 498) +* AC_SIZE_T: Obsolete Macros. (line 509) +* AC_SIZEOF_TYPE: Obsolete Macros. (line 506) +* AC_ST_BLKSIZE: Obsolete Macros. (line 539) +* AC_ST_BLOCKS: Obsolete Macros. (line 542) +* AC_ST_RDEV: Obsolete Macros. (line 545) +* AC_STAT_MACROS_BROKEN: Obsolete Macros. (line 512) +* AC_STDC_HEADERS: Obsolete Macros. (line 515) +* AC_STRCOLL: Obsolete Macros. (line 518) +* AC_STRUCT_DIRENT_D_INO: Particular Structures. + (line 9) +* AC_STRUCT_DIRENT_D_TYPE: Particular Structures. + (line 21) +* AC_STRUCT_ST_BLKSIZE: Obsolete Macros. (line 521) +* AC_STRUCT_ST_BLOCKS: Particular Structures. + (line 26) +* AC_STRUCT_ST_RDEV: Obsolete Macros. (line 530) +* AC_STRUCT_TIMEZONE: Particular Structures. + (line 43) +* AC_STRUCT_TM: Particular Structures. + (line 35) +* AC_SUBST: Setting Output Variables. + (line 13) +* AC_SUBST_FILE: Setting Output Variables. + (line 38) +* AC_SYS_INTERPRETER: System Services. (line 42) +* AC_SYS_LARGEFILE: System Services. (line 49) +* AC_SYS_LONG_FILE_NAMES: System Services. (line 71) +* AC_SYS_POSIX_TERMIOS: System Services. (line 75) +* AC_SYS_RESTARTABLE_SYSCALLS: Obsolete Macros. (line 548) +* AC_SYS_SIGLIST_DECLARED: Obsolete Macros. (line 563) +* AC_TEST_CPP: Obsolete Macros. (line 568) +* AC_TEST_PROGRAM: Obsolete Macros. (line 572) +* AC_TIME_WITH_SYS_TIME: Obsolete Macros. (line 579) +* AC_TIMEZONE: Obsolete Macros. (line 576) +* AC_TRY_ACT: AC_ACT_IFELSE vs AC_TRY_ACT. + (line 6) +* AC_TRY_COMPILE: Obsolete Macros. (line 583) +* AC_TRY_CPP: Obsolete Macros. (line 602) +* AC_TRY_LINK: Obsolete Macros. (line 615) +* AC_TRY_LINK_FUNC: Obsolete Macros. (line 644) +* AC_TRY_RUN: Obsolete Macros. (line 651) +* AC_TYPE_GETGROUPS: Particular Types. (line 14) +* AC_TYPE_INT16_T: Particular Types. (line 40) +* AC_TYPE_INT32_T: Particular Types. (line 43) +* AC_TYPE_INT64_T: Particular Types. (line 46) +* AC_TYPE_INT8_T: Particular Types. (line 21) +* AC_TYPE_INTMAX_T: Particular Types. (line 49) +* AC_TYPE_INTPTR_T: Particular Types. (line 54) +* AC_TYPE_LONG_DOUBLE: Particular Types. (line 59) +* AC_TYPE_LONG_DOUBLE_WIDER: Particular Types. (line 70) +* AC_TYPE_LONG_LONG_INT: Particular Types. (line 78) +* AC_TYPE_MBSTATE_T: Particular Types. (line 88) +* AC_TYPE_MODE_T: Particular Types. (line 96) +* AC_TYPE_OFF_T: Particular Types. (line 102) +* AC_TYPE_PID_T: Particular Types. (line 108) +* AC_TYPE_SIGNAL: Obsolete Macros. (line 662) +* AC_TYPE_SIZE_T: Particular Types. (line 114) +* AC_TYPE_SSIZE_T: Particular Types. (line 120) +* AC_TYPE_UID_T: Particular Types. (line 126) +* AC_TYPE_UINT16_T: Particular Types. (line 138) +* AC_TYPE_UINT32_T: Particular Types. (line 141) +* AC_TYPE_UINT64_T: Particular Types. (line 144) +* AC_TYPE_UINT8_T: Particular Types. (line 132) +* AC_TYPE_UINTMAX_T: Particular Types. (line 147) +* AC_TYPE_UINTPTR_T: Particular Types. (line 152) +* AC_TYPE_UNSIGNED_LONG_LONG_INT: Particular Types. (line 157) +* AC_UID_T: Obsolete Macros. (line 679) +* AC_UNISTD_H: Obsolete Macros. (line 682) +* AC_USE_SYSTEM_EXTENSIONS: Posix Variants. (line 10) +* AC_USG: Obsolete Macros. (line 685) +* AC_UTIME_NULL: Obsolete Macros. (line 690) +* AC_VALIDATE_CACHED_SYSTEM_TUPLE: Obsolete Macros. (line 693) +* AC_VERBOSE: Obsolete Macros. (line 698) +* AC_VFORK: Obsolete Macros. (line 701) +* AC_VPRINTF: Obsolete Macros. (line 704) +* AC_WAIT3: Obsolete Macros. (line 707) +* AC_WARN: Obsolete Macros. (line 712) +* AC_WARNING: Reporting Messages. (line 26) +* AC_WITH: Obsolete Macros. (line 715) +* AC_WORDS_BIGENDIAN: Obsolete Macros. (line 719) +* AC_XENIX_DIR: Obsolete Macros. (line 722) +* AC_YYTEXT_POINTER: Obsolete Macros. (line 739) +* AH_BOTTOM: Autoheader Macros. (line 50) +* AH_HEADER: Configuration Headers. + (line 54) +* AH_TEMPLATE: Autoheader Macros. (line 19) +* AH_TOP: Autoheader Macros. (line 47) +* AH_VERBATIM: Autoheader Macros. (line 40) +* AU_ALIAS: Obsoleting Macros. (line 34) +* AU_DEFUN: Obsoleting Macros. (line 18) + + +File: autoconf.info, Node: M4 Macro Index, Next: Autotest Macro Index, Prev: Autoconf Macro Index, Up: Indices + +B.6 M4 Macro Index +================== + +This is an alphabetical list of the M4, M4sugar, and M4sh macros. + + +* Menu: + +* __file__: Redefined M4 Macros. (line 65) +* __line__: Redefined M4 Macros. (line 65) +* __oline__: Redefined M4 Macros. (line 69) +* AS_BOURNE_COMPATIBLE: Initialization Macros. + (line 7) +* AS_BOX: Common Shell Constructs. + (line 10) +* AS_CASE: Common Shell Constructs. + (line 19) +* AS_DIRNAME: Common Shell Constructs. + (line 26) +* AS_ECHO: Common Shell Constructs. + (line 34) +* AS_ECHO_N: Common Shell Constructs. + (line 42) +* AS_ESCAPE: Common Shell Constructs. + (line 50) +* AS_EXECUTABLE_P: Common Shell Constructs. + (line 90) +* AS_EXIT: Common Shell Constructs. + (line 95) +* AS_HELP_STRING: Pretty Help Strings. (line 15) +* AS_IF: Common Shell Constructs. + (line 101) +* AS_INIT: Initialization Macros. + (line 14) +* AS_INIT_GENERATED: Initialization Macros. + (line 26) +* AS_LINENO_PREPARE: Initialization Macros. + (line 67) +* AS_LITERAL_IF: Polymorphic Variables. + (line 21) +* AS_LITERAL_WORD_IF: Polymorphic Variables. + (line 21) +* AS_ME_PREPARE: Initialization Macros. + (line 72) +* AS_MESSAGE_FD: File Descriptor Macros. + (line 17) +* AS_MESSAGE_LOG_FD: File Descriptor Macros. + (line 29) +* AS_MKDIR_P: Common Shell Constructs. + (line 115) +* AS_ORIGINAL_STDIN_FD: File Descriptor Macros. + (line 39) +* AS_SET_CATFILE: Common Shell Constructs. + (line 155) +* AS_SET_STATUS: Common Shell Constructs. + (line 127) +* AS_SHELL_SANITIZE: Initialization Macros. + (line 101) +* AS_TMPDIR: Initialization Macros. + (line 77) +* AS_TR_CPP: Common Shell Constructs. + (line 135) +* AS_TR_SH: Common Shell Constructs. + (line 144) +* AS_UNSET: Common Shell Constructs. + (line 159) +* AS_VAR_APPEND: Polymorphic Variables. + (line 63) +* AS_VAR_ARITH: Polymorphic Variables. + (line 85) +* AS_VAR_COPY: Polymorphic Variables. + (line 103) +* AS_VAR_IF: Polymorphic Variables. + (line 122) +* AS_VAR_POPDEF: Polymorphic Variables. + (line 131) +* AS_VAR_PUSHDEF: Polymorphic Variables. + (line 131) +* AS_VAR_SET: Polymorphic Variables. + (line 173) +* AS_VAR_SET_IF: Polymorphic Variables. + (line 183) +* AS_VAR_TEST_SET: Polymorphic Variables. + (line 188) +* AS_VERSION_COMPARE: Common Shell Constructs. + (line 165) +* dnl: Redefined M4 Macros. (line 76) +* m4_append: Text processing Macros. + (line 16) +* m4_append_uniq: Text processing Macros. + (line 16) +* m4_append_uniq_w: Text processing Macros. + (line 69) +* m4_apply: Evaluation Macros. (line 10) +* m4_argn: Looping constructs. (line 29) +* m4_assert: Diagnostic Macros. (line 11) +* m4_bmatch: Conditional constructs. + (line 11) +* m4_bpatsubst: Redefined M4 Macros. (line 79) +* m4_bpatsubsts: Conditional constructs. + (line 18) +* m4_bregexp: Redefined M4 Macros. (line 84) +* m4_builtin: Redefined M4 Macros. (line 6) +* m4_car: Looping constructs. (line 35) +* m4_case: Conditional constructs. + (line 33) +* m4_cdr: Looping constructs. (line 41) +* m4_changecom: Redefined M4 Macros. (line 6) +* m4_changequote: Redefined M4 Macros. (line 6) +* m4_chomp: Text processing Macros. + (line 80) +* m4_chomp_all: Text processing Macros. + (line 80) +* m4_cleardivert: Diversion support. (line 125) +* m4_cmp: Number processing Macros. + (line 11) +* m4_combine: Text processing Macros. + (line 88) +* m4_cond: Conditional constructs. + (line 42) +* m4_copy: Redefined M4 Macros. (line 92) +* m4_copy_force: Redefined M4 Macros. (line 92) +* m4_count: Evaluation Macros. (line 26) +* m4_curry: Evaluation Macros. (line 30) +* m4_debugfile: Redefined M4 Macros. (line 6) +* m4_debugmode: Redefined M4 Macros. (line 6) +* m4_decr: Redefined M4 Macros. (line 6) +* m4_default: Conditional constructs. + (line 73) +* m4_default_nblank: Conditional constructs. + (line 73) +* m4_default_nblank_quoted: Conditional constructs. + (line 73) +* m4_default_quoted: Conditional constructs. + (line 73) +* m4_define: Redefined M4 Macros. (line 6) +* m4_define_default: Conditional constructs. + (line 122) +* m4_defn: Redefined M4 Macros. (line 111) +* m4_divert: Redefined M4 Macros. (line 119) +* m4_divert_once: Diversion support. (line 128) +* m4_divert_pop: Diversion support. (line 133) +* m4_divert_push: Diversion support. (line 139) +* m4_divert_text: Diversion support. (line 145) +* m4_divnum: Redefined M4 Macros. (line 6) +* m4_do: Evaluation Macros. (line 45) +* m4_dquote: Evaluation Macros. (line 65) +* m4_dquote_elt: Evaluation Macros. (line 70) +* m4_dumpdef: Redefined M4 Macros. (line 131) +* m4_dumpdefs: Redefined M4 Macros. (line 131) +* m4_echo: Evaluation Macros. (line 75) +* m4_errprint: Redefined M4 Macros. (line 6) +* m4_errprintn: Diagnostic Macros. (line 16) +* m4_escape: Text processing Macros. + (line 108) +* m4_esyscmd: Redefined M4 Macros. (line 6) +* m4_esyscmd_s: Redefined M4 Macros. (line 148) +* m4_eval: Redefined M4 Macros. (line 6) +* m4_exit: Redefined M4 Macros. (line 154) +* m4_expand: Evaluation Macros. (line 79) +* m4_fatal: Diagnostic Macros. (line 20) +* m4_flatten: Text processing Macros. + (line 113) +* m4_for: Looping constructs. (line 59) +* m4_foreach: Looping constructs. (line 69) +* m4_foreach_w: Looping constructs. (line 83) +* m4_format: Redefined M4 Macros. (line 6) +* m4_if: Redefined M4 Macros. (line 160) +* m4_ifblank: Conditional constructs. + (line 127) +* m4_ifdef: Redefined M4 Macros. (line 6) +* m4_ifnblank: Conditional constructs. + (line 127) +* m4_ifndef: Conditional constructs. + (line 135) +* m4_ifset: Conditional constructs. + (line 139) +* m4_ifval: Conditional constructs. + (line 145) +* m4_ifvaln: Conditional constructs. + (line 150) +* m4_ignore: Evaluation Macros. (line 129) +* m4_include: Redefined M4 Macros. (line 167) +* m4_incr: Redefined M4 Macros. (line 6) +* m4_index: Redefined M4 Macros. (line 6) +* m4_indir: Redefined M4 Macros. (line 6) +* m4_init: Diversion support. (line 171) +* m4_join: Text processing Macros. + (line 119) +* m4_joinall: Text processing Macros. + (line 119) +* m4_len: Redefined M4 Macros. (line 6) +* m4_list_cmp: Number processing Macros. + (line 16) +* m4_location: Diagnostic Macros. (line 24) +* m4_make_list: Evaluation Macros. (line 142) +* m4_maketemp: Redefined M4 Macros. (line 171) +* m4_map: Looping constructs. (line 93) +* m4_map_args: Looping constructs. (line 130) +* m4_map_args_pair: Looping constructs. (line 166) +* m4_map_args_sep: Looping constructs. (line 178) +* m4_map_args_w: Looping constructs. (line 189) +* m4_map_sep: Looping constructs. (line 93) +* m4_mapall: Looping constructs. (line 93) +* m4_mapall_sep: Looping constructs. (line 93) +* m4_max: Number processing Macros. + (line 38) +* m4_min: Number processing Macros. + (line 42) +* m4_mkstemp: Redefined M4 Macros. (line 171) +* m4_n: Conditional constructs. + (line 154) +* m4_newline: Text processing Macros. + (line 134) +* m4_normalize: Text processing Macros. + (line 140) +* m4_pattern_allow: Forbidden Patterns. (line 30) +* m4_pattern_forbid: Forbidden Patterns. (line 17) +* m4_popdef: Redefined M4 Macros. (line 182) +* m4_pushdef: Redefined M4 Macros. (line 6) +* m4_quote: Evaluation Macros. (line 161) +* m4_re_escape: Text processing Macros. + (line 148) +* m4_rename: Redefined M4 Macros. (line 92) +* m4_rename_force: Redefined M4 Macros. (line 92) +* m4_reverse: Evaluation Macros. (line 167) +* m4_set_add: Set manipulation Macros. + (line 19) +* m4_set_add_all: Set manipulation Macros. + (line 25) +* m4_set_contains: Set manipulation Macros. + (line 29) +* m4_set_contents: Set manipulation Macros. + (line 49) +* m4_set_delete: Set manipulation Macros. + (line 79) +* m4_set_difference: Set manipulation Macros. + (line 86) +* m4_set_dump: Set manipulation Macros. + (line 49) +* m4_set_empty: Set manipulation Macros. + (line 109) +* m4_set_foreach: Set manipulation Macros. + (line 115) +* m4_set_intersection: Set manipulation Macros. + (line 86) +* m4_set_list: Set manipulation Macros. + (line 136) +* m4_set_listc: Set manipulation Macros. + (line 136) +* m4_set_map: Set manipulation Macros. + (line 171) +* m4_set_map_sep: Set manipulation Macros. + (line 184) +* m4_set_remove: Set manipulation Macros. + (line 195) +* m4_set_size: Set manipulation Macros. + (line 206) +* m4_set_union: Set manipulation Macros. + (line 86) +* m4_shift: Redefined M4 Macros. (line 6) +* m4_shift2: Looping constructs. (line 199) +* m4_shift3: Looping constructs. (line 199) +* m4_shiftn: Looping constructs. (line 199) +* m4_sign: Number processing Macros. + (line 46) +* m4_sinclude: Redefined M4 Macros. (line 167) +* m4_split: Text processing Macros. + (line 152) +* m4_stack_foreach: Looping constructs. (line 208) +* m4_stack_foreach_lifo: Looping constructs. (line 208) +* m4_stack_foreach_sep: Looping constructs. (line 230) +* m4_stack_foreach_sep_lifo: Looping constructs. (line 230) +* m4_strip: Text processing Macros. + (line 158) +* m4_substr: Redefined M4 Macros. (line 6) +* m4_syscmd: Redefined M4 Macros. (line 6) +* m4_sysval: Redefined M4 Macros. (line 6) +* m4_text_box: Text processing Macros. + (line 167) +* m4_text_wrap: Text processing Macros. + (line 182) +* m4_tolower: Text processing Macros. + (line 213) +* m4_toupper: Text processing Macros. + (line 213) +* m4_traceoff: Redefined M4 Macros. (line 6) +* m4_traceon: Redefined M4 Macros. (line 6) +* m4_translit: Redefined M4 Macros. (line 6) +* m4_undefine: Redefined M4 Macros. (line 186) +* m4_undivert: Redefined M4 Macros. (line 194) +* m4_unquote: Evaluation Macros. (line 176) +* m4_version_compare: Number processing Macros. + (line 50) +* m4_version_prereq: Number processing Macros. + (line 90) +* m4_warn: Diagnostic Macros. (line 28) +* m4_wrap: Redefined M4 Macros. (line 204) +* m4_wrap_lifo: Redefined M4 Macros. (line 204) + + +File: autoconf.info, Node: Autotest Macro Index, Next: Program & Function Index, Prev: M4 Macro Index, Up: Indices + +B.7 Autotest Macro Index +======================== + +This is an alphabetical list of the Autotest macros. + + +* Menu: + +* AT_ARG_OPTION: Writing Testsuites. (line 50) +* AT_ARG_OPTION_ARG: Writing Testsuites. (line 79) +* AT_BANNER: Writing Testsuites. (line 124) +* AT_CAPTURE_FILE: Writing Testsuites. (line 155) +* AT_CHECK: Writing Testsuites. (line 212) +* AT_CHECK_EUNIT: Writing Testsuites. (line 302) +* AT_CHECK_UNQUOTED: Writing Testsuites. (line 212) +* AT_CLEANUP: Writing Testsuites. (line 198) +* AT_COLOR_TESTS: Writing Testsuites. (line 105) +* AT_COPYRIGHT: Writing Testsuites. (line 41) +* AT_DATA: Writing Testsuites. (line 202) +* AT_FAIL_IF: Writing Testsuites. (line 160) +* AT_INIT: Writing Testsuites. (line 31) +* AT_KEYWORDS: Writing Testsuites. (line 142) +* AT_PACKAGE_BUGREPORT: Making testsuite Scripts. + (line 12) +* AT_PACKAGE_NAME: Making testsuite Scripts. + (line 12) +* AT_PACKAGE_STRING: Making testsuite Scripts. + (line 12) +* AT_PACKAGE_TARNAME: Making testsuite Scripts. + (line 12) +* AT_PACKAGE_URL: Making testsuite Scripts. + (line 12) +* AT_PACKAGE_VERSION: Making testsuite Scripts. + (line 12) +* AT_SETUP: Writing Testsuites. (line 134) +* AT_SKIP_IF: Writing Testsuites. (line 175) +* AT_TESTED: Writing Testsuites. (line 109) +* AT_XFAIL_IF: Writing Testsuites. (line 190) + + +File: autoconf.info, Node: Program & Function Index, Next: Concept Index, Prev: Autotest Macro Index, Up: Indices + +B.8 Program and Function Index +============================== + +This is an alphabetical list of the programs and functions whose +portability is discussed in this document. + + +* Menu: + +* !: Limitations of Builtins. + (line 41) +* .: Limitations of Builtins. + (line 17) +* /usr/bin/ksh on Solaris: Shellology. (line 63) +* /usr/dt/bin/dtksh on Solaris: Shellology. (line 66) +* /usr/xpg4/bin/sh on Solaris: Shellology. (line 64) +* alloca: Particular Functions. + (line 10) +* alloca.h: Particular Functions. + (line 10) +* assert.h: Particular Headers. (line 20) +* awk: Limitations of Usual Tools. + (line 10) +* basename: Limitations of Usual Tools. + (line 142) +* break: Limitations of Builtins. + (line 107) +* case: Limitations of Builtins. + (line 110) +* cat: Limitations of Usual Tools. + (line 146) +* cc: Limitations of Usual Tools. + (line 149) +* cd: Limitations of Builtins. + (line 203) +* chgrp: Limitations of Usual Tools. + (line 183) +* chmod: Limitations of Usual Tools. + (line 187) +* chown <1>: Limitations of Usual Tools. + (line 183) +* chown: Particular Functions. + (line 63) +* closedir: Particular Functions. + (line 69) +* cmp: Limitations of Usual Tools. + (line 197) +* cp: Limitations of Usual Tools. + (line 204) +* ctype.h: Particular Headers. (line 135) +* date: Limitations of Usual Tools. + (line 264) +* diff: Limitations of Usual Tools. + (line 274) +* dirent.h: Particular Headers. (line 25) +* dirname: Limitations of Usual Tools. + (line 280) +* echo: Limitations of Builtins. + (line 233) +* egrep: Limitations of Usual Tools. + (line 287) +* error_at_line: Particular Functions. + (line 84) +* eval: Limitations of Builtins. + (line 270) +* exec: Limitations of Builtins. + (line 315) +* exit <1>: Limitations of Builtins. + (line 355) +* exit: Function Portability. + (line 17) +* export: Limitations of Builtins. + (line 380) +* expr: Limitations of Usual Tools. + (line 312) +* expr (|): Limitations of Usual Tools. + (line 326) +* false: Limitations of Builtins. + (line 428) +* fgrep: Limitations of Usual Tools. + (line 435) +* find: Limitations of Usual Tools. + (line 444) +* float.h: Particular Headers. (line 135) +* fnmatch: Particular Functions. + (line 94) +* fnmatch.h: Particular Functions. + (line 452) +* for: Limitations of Builtins. + (line 432) +* fork: Particular Functions. + (line 120) +* free: Function Portability. + (line 27) +* fseeko: Particular Functions. + (line 147) +* ftello: Particular Functions. + (line 147) +* getgroups: Particular Functions. + (line 155) +* getloadavg: Particular Functions. + (line 161) +* getmntent: Particular Functions. + (line 195) +* getpgid: Particular Functions. + (line 205) +* getpgrp: Particular Functions. + (line 205) +* grep: Limitations of Usual Tools. + (line 458) +* if: Limitations of Builtins. + (line 477) +* inttypes.h <1>: Particular Types. (line 6) +* inttypes.h: Header Portability. (line 20) +* isinf: Function Portability. + (line 32) +* isnan: Function Portability. + (line 32) +* join: Limitations of Usual Tools. + (line 526) +* ksh: Shellology. (line 57) +* ksh88: Shellology. (line 57) +* ksh93: Shellology. (line 57) +* linux/irda.h: Header Portability. (line 27) +* linux/random.h: Header Portability. (line 30) +* ln: Limitations of Usual Tools. + (line 543) +* ls: Limitations of Usual Tools. + (line 555) +* lstat: Particular Functions. + (line 228) +* make: Portable Make. (line 6) +* malloc <1>: Particular Functions. + (line 247) +* malloc: Function Portability. + (line 82) +* mbrtowc: Particular Functions. + (line 279) +* memcmp: Particular Functions. + (line 286) +* mkdir: Limitations of Usual Tools. + (line 577) +* mkfifo: Limitations of Usual Tools. + (line 611) +* mknod: Limitations of Usual Tools. + (line 611) +* mktemp: Limitations of Usual Tools. + (line 621) +* mktime: Particular Functions. + (line 299) +* mmap: Particular Functions. + (line 311) +* mv: Limitations of Usual Tools. + (line 646) +* ndir.h: Particular Headers. (line 25) +* net/if.h: Header Portability. (line 33) +* netinet/if_ether.h: Header Portability. (line 53) +* nlist.h: Particular Functions. + (line 178) +* od: Limitations of Usual Tools. + (line 678) +* pdksh: Shellology. (line 77) +* printf: Limitations of Builtins. + (line 516) +* putenv: Function Portability. + (line 89) +* pwd: Limitations of Builtins. + (line 543) +* read: Limitations of Builtins. + (line 574) +* realloc <1>: Particular Functions. + (line 326) +* realloc: Function Portability. + (line 105) +* resolv.h: Particular Headers. (line 73) +* rm: Limitations of Usual Tools. + (line 687) +* rmdir: Limitations of Usual Tools. + (line 706) +* sed: Limitations of Usual Tools. + (line 710) +* sed (t): Limitations of Usual Tools. + (line 905) +* select: Particular Functions. + (line 337) +* set: Limitations of Builtins. + (line 580) +* setpgrp: Particular Functions. + (line 348) +* setvbuf: Obsolete Macros. (line 208) +* shift: Limitations of Builtins. + (line 732) +* sigaction: Function Portability. + (line 110) +* signal: Function Portability. + (line 110) +* signal.h: Obsolete Macros. (line 662) +* sleep: Limitations of Usual Tools. + (line 965) +* snprintf: Function Portability. + (line 124) +* sort: Limitations of Usual Tools. + (line 971) +* source: Limitations of Builtins. + (line 740) +* sprintf: Function Portability. + (line 135) +* sscanf: Function Portability. + (line 141) +* stat: Particular Functions. + (line 363) +* stdarg.h: Particular Headers. (line 135) +* stdbool.h: Particular Headers. (line 10) +* stdint.h <1>: Particular Types. (line 6) +* stdint.h: Header Portability. (line 20) +* stdlib.h <1>: Particular Types. (line 6) +* stdlib.h <2>: Particular Headers. (line 135) +* stdlib.h: Header Portability. (line 76) +* strcoll: Particular Functions. + (line 379) +* strerror_r <1>: Particular Functions. + (line 388) +* strerror_r: Function Portability. + (line 149) +* strftime: Particular Functions. + (line 401) +* string.h: Particular Headers. (line 135) +* strings.h: Particular Headers. (line 154) +* strnlen <1>: Particular Functions. + (line 426) +* strnlen: Function Portability. + (line 155) +* strtod: Particular Functions. + (line 408) +* strtold: Particular Functions. + (line 420) +* sys/dir.h: Particular Headers. (line 25) +* sys/ioctl.h: Particular Headers. (line 270) +* sys/mkdev.h: Particular Headers. (line 68) +* sys/mount.h: Header Portability. (line 79) +* sys/ndir.h: Particular Headers. (line 25) +* sys/ptem.h: Header Portability. (line 83) +* sys/socket.h: Header Portability. (line 86) +* sys/stat.h: Particular Headers. (line 92) +* sys/sysmacros.h: Particular Headers. (line 68) +* sys/time.h <1>: Particular Structures. + (line 35) +* sys/time.h: Particular Headers. (line 244) +* sys/types.h: Particular Types. (line 6) +* sys/ucred.h: Header Portability. (line 89) +* sys/wait.h: Particular Headers. (line 204) +* sysconf: Function Portability. + (line 170) +* tar: Limitations of Usual Tools. + (line 976) +* termios.h: Particular Headers. (line 270) +* test: Limitations of Builtins. + (line 744) +* time.h <1>: Particular Structures. + (line 35) +* time.h: Particular Headers. (line 244) +* touch: Limitations of Usual Tools. + (line 981) +* tr: Limitations of Usual Tools. + (line 994) +* trap: Limitations of Builtins. + (line 856) +* true: Limitations of Builtins. + (line 930) +* unistd.h: Particular Headers. (line 228) +* unlink: Function Portability. + (line 174) +* unset: Limitations of Builtins. + (line 946) +* unsetenv: Function Portability. + (line 180) +* utime: Particular Functions. + (line 433) +* va_copy: Function Portability. + (line 185) +* va_list: Function Portability. + (line 192) +* vfork: Particular Functions. + (line 120) +* vfork.h: Particular Functions. + (line 120) +* vprintf: Particular Functions. + (line 443) +* vsnprintf: Function Portability. + (line 124) +* vsprintf <1>: Particular Functions. + (line 443) +* vsprintf: Function Portability. + (line 135) +* wait: Limitations of Builtins. + (line 973) +* wait3: Obsolete Macros. (line 216) +* wchar.h: Particular Types. (line 88) +* X11/extensions/scrnsaver.h: Header Portability. (line 92) +* {...}: Limitations of Builtins. + (line 74) + + +File: autoconf.info, Node: Concept Index, Prev: Program & Function Index, Up: Indices + +B.9 Concept Index +================= + +This is an alphabetical list of the files, tools, and concepts +introduced in this document. + + +* Menu: + +* "$@": Shell Substitutions. (line 70) +* $((EXPRESSION)): Shell Substitutions. (line 456) +* $(COMMANDS): Shell Substitutions. (line 423) +* $<, explicit rules, and VPATH: $< in Explicit Rules. + (line 6) +* ${#VAR}: Shell Substitutions. (line 369) +* ${VAR##WORD}: Shell Substitutions. (line 369) +* ${VAR#WORD}: Shell Substitutions. (line 369) +* ${VAR%%WORD}: Shell Substitutions. (line 369) +* ${VAR%WORD}: Shell Substitutions. (line 369) +* ${VAR+VALUE}: Shell Substitutions. (line 148) +* ${VAR-VALUE}: Shell Substitutions. (line 140) +* ${VAR=EXPANDED-VALUE}: Shell Substitutions. (line 319) +* ${VAR=LITERAL}: Shell Substitutions. (line 295) +* ${VAR=VALUE}: Shell Substitutions. (line 215) +* 64-bit libraries: Site Defaults. (line 97) +* @&t@: Quadrigraphs. (line 6) +* @S|@: Quadrigraphs. (line 6) +* ^ quoting: Shell Substitutions. (line 496) +* _m4_divert_diversion: New Macros. (line 6) +* `COMMANDS`: Shell Substitutions. (line 377) +* abs_builddir: Preset Output Variables. + (line 177) +* abs_srcdir: Preset Output Variables. + (line 199) +* abs_top_builddir: Preset Output Variables. + (line 192) +* abs_top_srcdir: Preset Output Variables. + (line 206) +* absolute file names, detect: File System Conventions. + (line 52) +* ac_objext: Generic Functions. (line 59) +* ac_path_VARIABLE: Generic Programs. (line 123) +* ac_path_VARIABLE_found: Generic Programs. (line 123) +* ac_srcdir: Configuration Actions. + (line 85) +* ac_top_build_prefix: Configuration Actions. + (line 80) +* ac_top_srcdir: Configuration Actions. + (line 76) +* acconfig.h: acconfig Header. (line 6) +* aclocal.m4: Making configure Scripts. + (line 6) +* Ash: Shellology. (line 16) +* at_arg_OPTION: Writing Testsuites. (line 50) +* at_optarg: Writing Testsuites. (line 62) +* at_optarg_OPTION: Writing Testsuites. (line 62) +* at_status: Writing Testsuites. (line 212) +* autoconf: autoconf Invocation. (line 6) +* Autoconf upgrading <1>: Autoconf 2.13. (line 6) +* Autoconf upgrading: Autoconf 1. (line 6) +* Autoconf version: Versioning. (line 6) +* autoheader: autoheader Invocation. + (line 6) +* Autoheader macros: Autoheader Macros. (line 6) +* autom4te debugging tips: Debugging via autom4te. + (line 6) +* Autom4te Library: autom4te Invocation. (line 225) +* autom4te.cache: autom4te Invocation. (line 130) +* autom4te.cfg: autom4te Invocation. (line 258) +* Automake: Automake. (line 19) +* Automatic remaking: Automatic Remaking. (line 6) +* automatic rule rewriting and VPATH: Automatic Rule Rewriting. + (line 6) +* autopoint: autoreconf Invocation. + (line 30) +* autoreconf: autoreconf Invocation. + (line 6) +* autoscan: autoscan Invocation. (line 6) +* Autotest: Using Autotest. (line 6) +* AUTOTEST_PATH: testsuite Invocation. + (line 60) +* autoupdate: autoupdate Invocation. + (line 6) +* Back trace <1>: autom4te Invocation. (line 86) +* Back trace: autoconf Invocation. (line 86) +* balancing parentheses: Balancing Parentheses. + (line 6) +* Bash: Shellology. (line 43) +* Bash 2.05 and later: Shellology. (line 49) +* bindir: Installation Directory Variables. + (line 15) +* Bootstrap: Bootstrapping. (line 6) +* BSD make and obj/: obj/ and Make. (line 6) +* buffer overruns: Buffer Overruns. (line 6) +* Build directories: Build Directories. (line 6) +* builddir: Preset Output Variables. + (line 174) +* C function portability: Function Portability. + (line 6) +* C types: Types. (line 6) +* Cache: Caching Results. (line 6) +* Cache variable: Cache Variable Names. + (line 6) +* Cache, enabling: configure Invocation. + (line 25) +* Canonical system type: Canonicalizing. (line 6) +* carriage return, deleting: Limitations of Usual Tools. + (line 994) +* CFLAGS: Preset Output Variables. + (line 23) +* changequote: Changequote is Evil. (line 6) +* Coding style: Coding Style. (line 6) +* Command Substitution: Shell Substitutions. (line 377) +* command-line, macros set on: Command-line Macros and whitespace. + (line 6) +* Commands for configuration: Configuration Commands. + (line 6) +* Comments in Makefile macros: Comments in Make Macros. + (line 6) +* Comments in Makefile rules: Comments in Make Rules. + (line 6) +* Common autoconf behavior: Common Behavior. (line 6) +* Compilers: Compilers and Preprocessors. + (line 6) +* composing variable names: Polymorphic Variables. + (line 131) +* config.h: Configuration Headers. + (line 6) +* config.h.bot: acconfig Header. (line 6) +* config.h.in: Header Templates. (line 6) +* config.h.top: acconfig Header. (line 6) +* config.site: Site Defaults. (line 6) +* config.status: config.status Invocation. + (line 6) +* config.sub: Specifying Target Triplets. + (line 59) +* CONFIG_COMMANDS: Obsolete config.status Use. + (line 11) +* CONFIG_FILES: Obsolete config.status Use. + (line 15) +* CONFIG_HEADERS: Obsolete config.status Use. + (line 20) +* CONFIG_LINKS: Obsolete config.status Use. + (line 25) +* CONFIG_SHELL: config.status Invocation. + (line 102) +* CONFIG_STATUS: config.status Invocation. + (line 108) +* Configuration actions: Configuration Actions. + (line 6) +* Configuration commands: Configuration Commands. + (line 6) +* Configuration file creation: Configuration Files. (line 6) +* Configuration Header: Configuration Headers. + (line 6) +* Configuration Header Template: Header Templates. (line 6) +* Configuration links: Configuration Links. (line 6) +* configure <1>: Running configure Scripts. + (line 6) +* configure: Making configure Scripts. + (line 6) +* Configure subdirectories: Subdirectories. (line 6) +* configure.ac: Making configure Scripts. + (line 27) +* configure.in: Making configure Scripts. + (line 27) +* configure_input: Preset Output Variables. + (line 58) +* Copyright Notice <1>: Writing Testsuites. (line 41) +* Copyright Notice: Notices. (line 10) +* CPPFLAGS: Preset Output Variables. + (line 72) +* Creating configuration files: Configuration Files. (line 6) +* Creating temporary files: Limitations of Usual Tools. + (line 621) +* Cross compilation: Hosts and Cross-Compilation. + (line 6) +* CXXFLAGS: Preset Output Variables. + (line 94) +* Darwin: Systemology. (line 23) +* Data structure, set: Set manipulation Macros. + (line 6) +* datadir: Installation Directory Variables. + (line 18) +* datarootdir <1>: Changed Directory Variables. + (line 6) +* datarootdir: Installation Directory Variables. + (line 22) +* debugging tips: Debugging via autom4te. + (line 6) +* Declaration, checking: Declarations. (line 6) +* Default includes: Default Includes. (line 6) +* DEFS: Preset Output Variables. + (line 98) +* deleting carriage return: Limitations of Usual Tools. + (line 994) +* Dependencies between macros: Dependencies Between Macros. + (line 6) +* Descriptors: File Descriptors. (line 6) +* descriptors: File Descriptor Macros. + (line 6) +* Directories, build: Build Directories. (line 6) +* Directories, installation: Installation Directory Variables. + (line 6) +* division, integer: Signed Integer Division. + (line 6) +* dnl <1>: Coding Style. (line 42) +* dnl: Macro Definitions. (line 51) +* docdir: Installation Directory Variables. + (line 26) +* double-colon rules and VPATH: VPATH and Double-colon. + (line 6) +* dvidir: Installation Directory Variables. + (line 30) +* ECHO_C: Preset Output Variables. + (line 106) +* ECHO_N: Preset Output Variables. + (line 107) +* ECHO_T: Preset Output Variables. + (line 108) +* Endianness: C Compiler. (line 184) +* environment, macros set from: Command-line Macros and whitespace. + (line 6) +* Erlang: Erlang Compiler and Interpreter. + (line 6) +* Erlang, Library, checking: Erlang Libraries. (line 6) +* ERLANG_INSTALL_LIB_DIR: Installation Directory Variables. + (line 201) +* ERLANG_INSTALL_LIB_DIR_: Installation Directory Variables. + (line 206) +* ERLCFLAGS: Preset Output Variables. + (line 120) +* exec_prefix: Installation Directory Variables. + (line 33) +* exiting portably: Exiting Portably. (line 6) +* expanded before required: Expanded Before Required. + (line 6) +* explicit rules, $<, and VPATH: $< in Explicit Rules. + (line 6) +* External software: External Software. (line 6) +* F77: Fortran Compiler. (line 6) +* FCFLAGS: Preset Output Variables. + (line 126) +* FFLAGS: Preset Output Variables. + (line 133) +* FHS: Site Defaults. (line 83) +* File descriptors: File Descriptors. (line 6) +* file descriptors: File Descriptor Macros. + (line 6) +* File system conventions: File System Conventions. + (line 6) +* File, checking: Files. (line 6) +* Filesystem Hierarchy Standard: Site Defaults. (line 83) +* floating point: Floating Point Portability. + (line 6) +* Forbidden patterns: Forbidden Patterns. (line 6) +* Fortran: Fortran Compiler. (line 6) +* Function, checking: Particular Functions. + (line 6) +* Gettext: autoreconf Invocation. + (line 30) +* GNU build system: The GNU Build System. + (line 6) +* Gnulib: Gnulib. (line 11) +* Go: Go Compiler. (line 6) +* GOFLAGS: Preset Output Variables. + (line 170) +* Header portability: Header Portability. (line 6) +* Header templates: Header Templates. (line 6) +* Header, checking: Header Files. (line 6) +* Help strings: Pretty Help Strings. (line 6) +* Here-documents: Here-Documents. (line 6) +* History of autoconf: History. (line 6) +* htmldir: Installation Directory Variables. + (line 40) +* ifnames: ifnames Invocation. (line 6) +* Imake: Why Not Imake. (line 6) +* includedir: Installation Directory Variables. + (line 43) +* Includes, default: Default Includes. (line 6) +* indirection, variable name: Polymorphic Variables. + (line 6) +* infodir: Installation Directory Variables. + (line 46) +* input: File Descriptor Macros. + (line 6) +* Install prefix: Default Prefix. (line 6) +* Installation directories: Installation Directory Variables. + (line 6) +* Instantiation: Output. (line 13) +* integer overflow <1>: Signed Overflow Advice. + (line 6) +* integer overflow <2>: Signed Overflow Examples. + (line 6) +* integer overflow <3>: Integer Overflow Basics. + (line 6) +* integer overflow: Integer Overflow. (line 6) +* Introduction: Introduction. (line 6) +* invoking the shell: Invoking the Shell. (line 6) +* Korn shell: Shellology. (line 57) +* Ksh: Shellology. (line 57) +* Language: Language Choice. (line 6) +* Large file support: System Services. (line 49) +* LDFLAGS: Preset Output Variables. + (line 140) +* LFS: System Services. (line 49) +* lib64: Site Defaults. (line 97) +* libdir: Installation Directory Variables. + (line 49) +* libexecdir: Installation Directory Variables. + (line 52) +* Library, checking: Libraries. (line 6) +* LIBS: Preset Output Variables. + (line 154) +* Libtool: Libtool. (line 14) +* License: Distributing. (line 6) +* Limitations of make: Portable Make. (line 6) +* Limitations of shell builtins: Limitations of Builtins. + (line 6) +* Limitations of usual tools: Limitations of Usual Tools. + (line 6) +* Links: Configuration Links. (line 12) +* Links for configuration: Configuration Links. (line 6) +* Listing directories: Limitations of Usual Tools. + (line 555) +* localedir: Installation Directory Variables. + (line 55) +* localstatedir: Installation Directory Variables. + (line 60) +* loop induction: Optimization and Wraparound. + (line 6) +* low-level output: File Descriptor Macros. + (line 6) +* M4: Programming in M4. (line 6) +* M4 quotation: M4 Quotation. (line 6) +* M4sugar: Programming in M4sugar. + (line 6) +* m4sugar debugging tips: Debugging via autom4te. + (line 6) +* Macro invocation stack <1>: autom4te Invocation. (line 86) +* Macro invocation stack: autoconf Invocation. (line 86) +* Macros, called once: One-Shot Macros. (line 6) +* Macros, obsoleting: Obsoleting Macros. (line 6) +* Macros, ordering: Suggested Ordering. (line 6) +* Macros, prerequisites: Prerequisite Macros. (line 6) +* make -k: make -k Status. (line 6) +* make and MAKEFLAGS: The Make Macro MAKEFLAGS. + (line 6) +* make and SHELL: The Make Macro SHELL. + (line 6) +* Makefile macros and comments: Comments in Make Macros. + (line 6) +* Makefile macros and whitespace: Trailing whitespace in Make Macros. + (line 6) +* Makefile rules and comments: Comments in Make Rules. + (line 6) +* Makefile rules and newlines: Newlines in Make Rules. + (line 6) +* Makefile substitutions: Makefile Substitutions. + (line 6) +* MAKEFLAGS and make: The Make Macro MAKEFLAGS. + (line 6) +* Making directories: Limitations of Usual Tools. + (line 577) +* mandir: Installation Directory Variables. + (line 63) +* Messages, from autoconf: Reporting Messages. (line 6) +* Messages, from configure: Printing Messages. (line 6) +* Messages, from M4sugar: Diagnostic Macros. (line 6) +* Moving open files: Limitations of Usual Tools. + (line 646) +* newline, deleting: Limitations of Usual Tools. + (line 994) +* Newlines in Makefile rules: Newlines in Make Rules. + (line 6) +* Notices in configure: Notices. (line 6) +* null pointers: Null Pointers. (line 6) +* obj/, subdirectory: obj/ and Make. (line 6) +* OBJCFLAGS: Preset Output Variables. + (line 162) +* OBJCXXFLAGS: Preset Output Variables. + (line 166) +* Obsolete constructs: Obsolete Constructs. (line 6) +* Obsoleting macros: Obsoleting Macros. (line 6) +* obstack: Particular Functions. + (line 319) +* oldincludedir: Installation Directory Variables. + (line 66) +* One-shot macros: One-Shot Macros. (line 6) +* Options, Package: Option Checking. (line 6) +* Options, package: Package Options. (line 6) +* Ordering macros: Suggested Ordering. (line 6) +* Output variables <1>: Setting Output Variables. + (line 6) +* Output variables: Preset Output Variables. + (line 6) +* Output variables, special characters in: Special Chars in Variables. + (line 6) +* output, low-level: File Descriptor Macros. + (line 6) +* Outputting files: Output. (line 6) +* overflow, signed integer <1>: Signed Overflow Advice. + (line 6) +* overflow, signed integer <2>: Signed Overflow Examples. + (line 6) +* overflow, signed integer <3>: Integer Overflow Basics. + (line 6) +* overflow, signed integer: Integer Overflow. (line 6) +* Package options: Package Options. (line 6) +* package.m4: Making testsuite Scripts. + (line 12) +* Parallel make: Parallel Make. (line 6) +* parentheses, balancing: Balancing Parentheses. + (line 6) +* Patterns, forbidden: Forbidden Patterns. (line 6) +* pdfdir: Installation Directory Variables. + (line 69) +* polymorphic variable name: Polymorphic Variables. + (line 6) +* portability: Varieties of Unportability. + (line 6) +* Portability of C functions: Function Portability. + (line 6) +* Portability of headers: Header Portability. (line 6) +* Portable C and C++ programming: Portable C and C++. (line 6) +* Portable shell programming: Portable Shell. (line 6) +* positional parameters: Shell Substitutions. (line 121) +* Posix termios headers: System Services. (line 75) +* Precious Variable: Setting Output Variables. + (line 65) +* prefix: Installation Directory Variables. + (line 72) +* Prefix for install: Default Prefix. (line 6) +* preprocessor arithmetic: Preprocessor Arithmetic. + (line 6) +* Preprocessors: Compilers and Preprocessors. + (line 6) +* prerequisite directories and VPATH: Tru64 Directory Magic. + (line 6) +* Prerequisite macros: Prerequisite Macros. (line 6) +* Program names, transforming: Transforming Names. (line 6) +* Programs, checking: Alternative Programs. + (line 6) +* psdir: Installation Directory Variables. + (line 77) +* QNX 4.25: Systemology. (line 37) +* quadrigraphs: Quadrigraphs. (line 6) +* quotation <1>: M4 Quotation. (line 6) +* quotation: Autoconf Language. (line 6) +* Remaking automatically: Automatic Remaking. (line 6) +* Revision: Notices. (line 18) +* Rule, Single Suffix Inference: Single Suffix Rules. (line 6) +* sbindir: Installation Directory Variables. + (line 80) +* Separated Dependencies: Single Suffix Rules. (line 9) +* set -b: Limitations of Builtins. + (line 689) +* set -e: Limitations of Builtins. + (line 605) +* set -m: Limitations of Builtins. + (line 689) +* set -n: Limitations of Builtins. + (line 713) +* Set manipulation: Set manipulation Macros. + (line 6) +* sharedstatedir: Installation Directory Variables. + (line 84) +* SHELL and make: The Make Macro SHELL. + (line 6) +* Shell assignments: Assignments. (line 6) +* Shell builtins: Limitations of Builtins. + (line 6) +* Shell file descriptors: File Descriptors. (line 6) +* Shell Functions: Shell Functions. (line 6) +* Shell here-documents: Here-Documents. (line 6) +* shell invocation: Invoking the Shell. (line 6) +* Shell parentheses: Parentheses. (line 6) +* Shell pattern matching: Shell Pattern Matching. + (line 6) +* Shell slashes: Slashes. (line 6) +* Shell substitutions: Shell Substitutions. (line 6) +* Shell variables: Special Shell Variables. + (line 6) +* Shellology: Shellology. (line 6) +* Signal handling in the shell: Signal Handling. (line 6) +* Signals, shells and: Signal Handling. (line 6) +* signed integer overflow <1>: Signed Overflow Advice. + (line 6) +* signed integer overflow <2>: Signed Overflow Examples. + (line 6) +* signed integer overflow <3>: Integer Overflow Basics. + (line 6) +* signed integer overflow: Integer Overflow. (line 6) +* Single Suffix Inference Rule: Single Suffix Rules. (line 6) +* Site defaults: Site Defaults. (line 6) +* Site details: Site Details. (line 6) +* Special shell variables: Special Shell Variables. + (line 6) +* srcdir <1>: Preset Output Variables. + (line 195) +* srcdir: Configuration Actions. + (line 71) +* standard input: File Descriptor Macros. + (line 6) +* Standard symbols: Standard Symbols. (line 6) +* Structure, checking: Structures. (line 6) +* Subdirectory configure: Subdirectories. (line 6) +* Substitutions in makefiles: Makefile Substitutions. + (line 6) +* Symbolic links: Limitations of Usual Tools. + (line 543) +* sysconfdir: Installation Directory Variables. + (line 88) +* System type <1>: Canonicalizing. (line 6) +* System type: Specifying Target Triplets. + (line 6) +* Systemology: Systemology. (line 6) +* Target triplet: Specifying Target Triplets. + (line 6) +* termios Posix headers: System Services. (line 75) +* test group: testsuite Scripts. (line 12) +* testsuite <1>: testsuite Invocation. + (line 6) +* testsuite: testsuite Scripts. (line 6) +* timestamp resolution <1>: Timestamps and Make. (line 6) +* timestamp resolution: Limitations of Usual Tools. + (line 226) +* tmp: Configuration Actions. + (line 89) +* top_build_prefix: Preset Output Variables. + (line 184) +* top_builddir: Preset Output Variables. + (line 180) +* top_srcdir: Preset Output Variables. + (line 202) +* Transforming program names: Transforming Names. (line 6) +* Tru64: Systemology. (line 44) +* Types: Types. (line 6) +* unbalanced parentheses, managing: Balancing Parentheses. + (line 6) +* undefined macro: New Macros. (line 6) +* Unix version 7: Systemology. (line 49) +* Unordered set manipulation: Set manipulation Macros. + (line 6) +* Upgrading autoconf <1>: Autoconf 2.13. (line 6) +* Upgrading autoconf: Autoconf 1. (line 6) +* V7: Systemology. (line 49) +* variable name indirection: Polymorphic Variables. + (line 6) +* variable names, composing: Polymorphic Variables. + (line 131) +* Variable, Precious: Setting Output Variables. + (line 65) +* variables and VPATH: Variables listed in VPATH. + (line 6) +* Version: Versioning. (line 11) +* version, Autoconf: Versioning. (line 6) +* volatile objects: Volatile Objects. (line 6) +* VPATH: VPATH and Make. (line 6) +* VPATH and automatic rule rewriting: Automatic Rule Rewriting. + (line 6) +* VPATH and double-colon rules: VPATH and Double-colon. + (line 6) +* VPATH and prerequisite directories: Tru64 Directory Magic. + (line 6) +* VPATH and variables: Variables listed in VPATH. + (line 6) +* VPATH, explicit rules, and $<: $< in Explicit Rules. + (line 6) +* VPATH, resolving target pathnames: Make Target Lookup. (line 6) +* whitespace in command-line macros: Command-line Macros and whitespace. + (line 6) +* whitespace in Makefile macros: Trailing whitespace in Make Macros. + (line 6) +* wraparound arithmetic <1>: Signed Overflow Advice. + (line 6) +* wraparound arithmetic <2>: Signed Overflow Examples. + (line 6) +* wraparound arithmetic <3>: Integer Overflow Basics. + (line 6) +* wraparound arithmetic: Integer Overflow. (line 6) +* X Window System: System Services. (line 10) +* Zsh: Shellology. (line 87) + + + +Tag Table: +Node: Top1954 +Node: Introduction21371 +Node: The GNU Build System27935 +Node: Automake28914 +Node: Gnulib30863 +Node: Libtool32172 +Node: Pointers33594 +Ref: Pointers-Footnote-134895 +Node: Making configure Scripts35055 +Node: Writing Autoconf Input38404 +Node: Shell Script Compiler39867 +Node: Autoconf Language42228 +Node: Autoconf Input Layout49397 +Node: autoscan Invocation50805 +Node: ifnames Invocation53361 +Node: autoconf Invocation54561 +Node: autoreconf Invocation59846 +Node: Setup64607 +Node: Initializing configure65929 +Ref: AC_INIT66434 +Node: Versioning69318 +Node: Notices71179 +Node: Input72354 +Ref: AC_CONFIG_SRCDIR72495 +Node: Output75442 +Ref: AC_OUTPUT75877 +Ref: AC_PROG_MAKE_SET77495 +Node: Configuration Actions77920 +Node: Configuration Files83208 +Ref: AC_CONFIG_FILES83469 +Node: Makefile Substitutions84688 +Node: Preset Output Variables86431 +Node: Installation Directory Variables95945 +Node: Changed Directory Variables103793 +Node: 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AC_FUNC_CLOSEDIR_VOID172306 +Ref: AC_FUNC_FORK174296 +Ref: AC_FUNC_GETLOADAVG176338 +Ref: AC_FUNC_GETMNTENT177903 +Ref: AC_FUNC_MMAP182145 +Ref: AC_FUNC_STRCOLL185000 +Ref: AC_FUNC_STRFTIME185975 +Ref: AC_FUNC_UTIME_NULL187257 +Ref: AC_FUNC_VPRINTF187605 +Node: Generic Functions188821 +Ref: AC_CHECK_FUNC189347 +Ref: AC_CHECK_FUNCS189976 +Node: Header Files194602 +Node: Header Portability195235 +Node: Particular Headers198330 +Ref: AC_HEADER_DIRENT199369 +Ref: AC_HEADER_MAJOR200899 +Ref: AC_HEADER_STAT201683 +Ref: AC_HEADER_STDC203189 +Ref: AC_HEADER_TIME207928 +Node: Generic Headers209315 +Ref: AC_CHECK_HEADER209715 +Ref: AC_CHECK_HEADERS211588 +Node: Declarations214153 +Node: Particular Declarations214749 +Node: Generic Declarations214973 +Ref: AC_CHECK_DECLS216358 +Node: Structures218884 +Node: Particular Structures219499 +Ref: AC_STRUCT_ST_BLOCKS220568 +Ref: AC_STRUCT_TIMEZONE221264 +Node: Generic Structures221593 +Ref: AC_CHECK_MEMBERS222584 +Node: Types223417 +Node: Particular 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