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diff --git a/doc/FAQ.orig b/doc/FAQ.orig deleted file mode 100644 index 1cff3c8e..00000000 --- a/doc/FAQ.orig +++ /dev/null @@ -1,1745 +0,0 @@ -This is the Bash FAQ, version 3.24, for Bash version 2.05b. - -This document contains a set of frequently-asked questions concerning -Bash, the GNU Bourne-Again Shell. Bash is a freely-available command -interpreter with advanced features for both interactive use and shell -programming. - -Another good source of basic information about shells is the collection -of FAQ articles periodically posted to comp.unix.shell. - -Questions and comments concerning this document should be sent to -chet@po.cwru.edu. - -This document is available for anonymous FTP with the URL - -ftp://ftp.cwru.edu/pub/bash/FAQ - -The Bash home page is http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html - ----------- -Contents: - -Section A: The Basics - -A1) What is it? -A2) What's the latest version? -A3) Where can I get it? -A4) On what machines will bash run? -A5) Will bash run on operating systems other than Unix? -A6) How can I build bash with gcc? -A7) How can I make bash my login shell? -A8) I just changed my login shell to bash, and now I can't FTP into my - machine. Why not? -A9) What's the `POSIX 1003.2 standard'? -A10) What is the bash `posix mode'? - -Section B: The latest version - -B1) What's new in version 2.05b? -B2) Are there any user-visible incompatibilities between bash-2.05b and - bash-1.14.7? - -Section C: Differences from other Unix shells - -C1) How does bash differ from sh, the Bourne shell? -C2) How does bash differ from the Korn shell, version ksh88? -C3) Which new features in ksh-93 are not in bash, and which are? - -Section D: Why does bash do some things differently than other Unix shells? - -D1) Why does bash run a different version of `command' than - `which command' says it will? -D2) Why doesn't bash treat brace expansions exactly like csh? -D3) Why doesn't bash have csh variable modifiers? -D4) How can I make my csh aliases work when I convert to bash? -D5) How can I pipe standard output and standard error from one command to - another, like csh does with `|&'? -D6) Now that I've converted from ksh to bash, are there equivalents to - ksh features like autoloaded functions and the `whence' command? - -Section E: Why does bash do certain things the way it does? - -E1) Why is the bash builtin `test' slightly different from /bin/test? -E2) Why does bash sometimes say `Broken pipe'? -E3) When I have terminal escape sequences in my prompt, why does bash - wrap lines at the wrong column? -E4) If I pipe the output of a command into `read variable', why doesn't - the output show up in $variable when the read command finishes? -E5) I have a bunch of shell scripts that use backslash-escaped characters - in arguments to `echo'. Bash doesn't interpret these characters. Why - not, and how can I make it understand them? -E6) Why doesn't a while or for loop get suspended when I type ^Z? -E7) What about empty for loops in Makefiles? -E8) Why does the arithmetic evaluation code complain about `08'? -E9) Why does the pattern matching expression [A-Z]* match files beginning - with every letter except `z'? -E10) Why does `cd //' leave $PWD as `//'? -E11) If I resize my xterm while another program is running, why doesn't bash - notice the change? - -Section F: Things to watch out for on certain Unix versions - -F1) Why can't I use command line editing in my `cmdtool'? -F2) I built bash on Solaris 2. Why do globbing expansions and filename - completion chop off the first few characters of each filename? -F3) Why does bash dump core after I interrupt username completion or - `~user' tilde expansion on a machine running NIS? -F4) I'm running SVR4.2. Why is the line erased every time I type `@'? -F5) Why does bash report syntax errors when my C News scripts use a - redirection before a subshell command? -F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? -F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on - HP/UX 11.x? - -Section G: How can I get bash to do certain common things? - -G1) How can I get bash to read and display eight-bit characters? -G2) How do I write a function `x' to replace builtin command `x', but - still invoke the command from within the function? -G3) How can I find the value of a shell variable whose name is the value - of another shell variable? -G4) How can I make the bash `time' reserved word print timing output that - looks like the output from my system's /usr/bin/time? -G5) How do I get the current directory into my prompt? -G6) How can I rename "*.foo" to "*.bar"? -G7) How can I translate a filename from uppercase to lowercase? -G8) How can I write a filename expansion (globbing) pattern that will match - all files in the current directory except "." and ".."? - -Section H: Where do I go from here? - -H1) How do I report bugs in bash, and where should I look for fixes and - advice? -H2) What kind of bash documentation is there? -H3) What's coming in future versions? -H4) What's on the bash `wish list'? -H5) When will the next release appear? - ----------- -Section A: The Basics - -A1) What is it? - -Bash is a Unix command interpreter (shell). It is an implementation of -the Posix 1003.2 shell standard, and resembles the Korn and System V -shells. - -Bash contains a number of enhancements over those shells, both -for interactive use and shell programming. Features geared -toward interactive use include command line editing, command -history, job control, aliases, and prompt expansion. Programming -features include additional variable expansions, shell -arithmetic, and a number of variables and options to control -shell behavior. - -Bash was originally written by Brian Fox of the Free Software -Foundation. The current developer and maintainer is Chet Ramey -of Case Western Reserve University. - -A2) What's the latest version? - -The latest version is 2.05b, first made available on Wednesday, 17 -July, 2002. - -A3) Where can I get it? - -Bash is the GNU project's shell, and so is available from the -master GNU archive site, ftp.gnu.org, and its mirrors. The -latest version is also available for FTP from ftp.cwru.edu. -The following URLs tell how to get version 2.05b: - -ftp://ftp.gnu.org/pub/gnu/bash/bash-2.05b.tar.gz -ftp://ftp.cwru.edu/pub/bash/bash-2.05b.tar.gz - -Formatted versions of the documentation are available with the URLs: - -ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-2.05b.tar.gz -ftp://ftp.cwru.edu/pub/bash/bash-doc-2.05b.tar.gz - -A4) On what machines will bash run? - -Bash has been ported to nearly every version of UNIX. All you -should have to do to build it on a machine for which a port -exists is to type `configure' and then `make'. The build process -will attempt to discover the version of UNIX you have and tailor -itself accordingly, using a script created by GNU autoconf. - -More information appears in the file `INSTALL' in the distribution. - -The Bash web page (http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html) -explains how to obtain binary versions of bash for most of the major -commercial Unix systems. - -A5) Will bash run on operating systems other than Unix? - -Configuration specifics for Unix-like systems such as QNX and -LynxOS are included in the distribution. Bash-2.05 and later -versions should compile and run on Minix 2.0 (patches were -contributed), but I don't believe anyone has built bash-2.x on -earlier Minix versions yet. - -Bash has been ported to versions of Windows implementing the Win32 -programming interface. This includes Windows 95 and Windows NT. -The port was done by Cygnus Solutions as part of their CYGWIN -project. For more information about the project, look at the URLs - -http://www.cygwin.com/ -http://sourceware.cygnus.com/cygwin - -Cygnus originally ported bash-1.14.7, and that port was part of their -early GNU-Win32 (the original name) releases. Cygnus has also done a -port of bash-2.05 to the CYGWIN environment, and it is available as -part of their current release. - -Bash-2.05b should require no local Cygnus changes to build and run under -CYGWIN. - -The Cygnus port works only on Intel machines. There is a port of bash -(I don't know which version) to the alpha/NT environment available from - -ftp://ftp.gnustep.org//pub/win32/bash-alpha-nt-1.01.tar.gz - -DJ Delorie has a port of bash-2.x which runs under MS-DOS, as part -of the DJGPP project. For more information on the project, see - -http://www.delorie.com/djgpp/ - -I have been told that the original DJGPP port was done by Daisuke Aoyama. - -Mark Elbrecht <snowball3@bigfoot.com> has sent me notice that bash-2.04 -is available for DJGPP V2. The files are available as: - -ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204b.zip binary -ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204d.zip documentation -ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204s.zip source - -Mark has begun to work with bash-2.05, but I don't know the status. - -Ports of bash-1.12 and bash-2.0 are available for OS/2 from - -ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash_112.zip -ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash-2.0(253).zip - -I haven't looked at either, but the second appears to be a binary-only -distribution. Beware. - -I have received word that Bash (I'm not sure which version, but I -believe that it's at least bash-2.02.1) is the standard shell on -BeOS. - -A6) How can I build bash with gcc? - -Bash configures to use gcc by default if it is available. Read the -file INSTALL in the distribution for more information. - -A7) How can I make bash my login shell? - -Some machines let you use `chsh' to change your login shell. Other -systems use `passwd -s' or `passwd -e'. If one of these works for -you, that's all you need. Note that many systems require the full -pathname to a shell to appear in /etc/shells before you can make it -your login shell. For this, you may need the assistance of your -friendly local system administrator. - -If you cannot do this, you can still use bash as your login shell, but -you need to perform some tricks. The basic idea is to add a command -to your login shell's startup file to replace your login shell with -bash. - -For example, if your login shell is csh or tcsh, and you have installed -bash in /usr/gnu/bin/bash, add the following line to ~/.login: - - if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login - -(the `--login' tells bash that it is a login shell). - -It's not a good idea to put this command into ~/.cshrc, because every -csh you run without the `-f' option, even ones started to run csh scripts, -reads that file. If you must put the command in ~/.cshrc, use something -like - - if ( $?prompt ) exec /usr/gnu/bin/bash --login - -to ensure that bash is exec'd only when the csh is interactive. - -If your login shell is sh or ksh, you have to do two things. - -First, create an empty file in your home directory named `.bash_profile'. -The existence of this file will prevent the exec'd bash from trying to -read ~/.profile, and re-execing itself over and over again. ~/.bash_profile -is the first file bash tries to read initialization commands from when -it is invoked as a login shell. - -Next, add a line similar to the above to ~/.profile: - - [ -f /usr/gnu/bin/bash ] && [ -x /usr/gnu/bin/bash ] && \ - exec /usr/gnu/bin/bash --login - -This will cause login shells to replace themselves with bash running as -a login shell. Once you have this working, you can copy your initialization -code from ~/.profile to ~/.bash_profile. - -I have received word that the recipe supplied above is insufficient for -machines running CDE. CDE has a maze of twisty little startup files, all -slightly different. - -If you cannot change your login shell in the password file to bash, you -will have to (apparently) live with CDE using the shell in the password -file to run its startup scripts. If you have changed your shell to bash, -there is code in the CDE startup files (on Solaris, at least) that attempts -to do the right thing. It is, however, often broken, and may require that -you use the $BASH_ENV trick described below. - -`dtterm' claims to use $SHELL as the default program to start, so if you -can change $SHELL in the CDE startup files, you should be able to use bash -in your terminal windows. - -Setting DTSOURCEPROFILE in ~/.dtprofile will cause the `Xsession' program -to read your login shell's startup files. You may be able to use bash for -the rest of the CDE programs by setting SHELL to bash in ~/.dtprofile as -well, but I have not tried this. - -You can use the above `exec' recipe to start bash when not logging in with -CDE by testing the value of the DT variable: - - if [ -n "$DT" ]; then - [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login - fi - -If CDE starts its shells non-interactively during login, the login shell -startup files (~/.profile, ~/.bash_profile) will not be sourced at login. -To get around this problem, append a line similar to the following to your -~/.dtprofile: - - BASH_ENV=${HOME}/.bash_profile ; export BASH_ENV - -and add the following line to the beginning of ~/.bash_profile: - - unset BASH_ENV - -A8) I just changed my login shell to bash, and now I can't FTP into my - machine. Why not? - -You must add the full pathname to bash to the file /etc/shells. As -noted in the answer to the previous question, many systems require -this before you can make bash your login shell. - -Most versions of ftpd use this file to prohibit `special' users -such as `uucp' and `news' from using FTP. - -A9) What's the `POSIX 1003.2 standard'? - -POSIX is a name originally coined by Richard Stallman for a -family of open system standards based on UNIX. There are a -number of aspects of UNIX under consideration for -standardization, from the basic system services at the system -call and C library level to applications and tools to system -administration and management. Each area of standardization is -assigned to a working group in the 1003 series. - -The POSIX Shell and Utilities standard has been developed by IEEE -Working Group 1003.2 (POSIX.2). It concentrates on the command -interpreter interface and utility programs commonly executed from -the command line or by other programs. An initial version of the -standard has been approved and published by the IEEE, and work is -currently underway to update it. - -Bash is concerned with the aspects of the shell's behavior -defined by POSIX.2. The shell command language has of course -been standardized, including the basic flow control and program -execution constructs, I/O redirection and pipelining, argument -handling, variable expansion, and quoting. - -The `special' builtins, which must be implemented as part of the -shell to provide the desired functionality, are specified as -being part of the shell; examples of these are `eval' and -`export'. Other utilities appear in the sections of POSIX.2 not -devoted to the shell which are commonly (and in some cases must -be) implemented as builtin commands, such as `read' and `test'. -POSIX.2 also specifies aspects of the shell's interactive -behavior as part of the UPE, including job control and command -line editing. Only vi-style line editing commands have been -standardized; emacs editing commands were left out due to -objections. - -The Open Group has made an older version of its Single Unix -Specification (version 2), which is very similar to POSIX.2, -available on the web at - -http://www.opengroup.org/onlinepubs/007908799/ - -The Single Unix Specification, version 3, is available on the web at - -http://www.opengroup.org/onlinepubs/007904975/ - -A10) What is the bash `posix mode'? - -Although bash is an implementation of the POSIX.2 shell -specification, there are areas where the bash default behavior -differs from that spec. The bash `posix mode' changes the bash -behavior in these areas so that it obeys the spec more closely. - -Posix mode is entered by starting bash with the --posix or -'-o posix' option or executing `set -o posix' after bash is running. - -The specific aspects of bash which change when posix mode is -active are listed in the file POSIX in the bash distribution. -They are also listed in a section in the Bash Reference Manual -(from which that file is generated). - -Section B: The latest version - -B1) What's new in version 2.05b? - -The raison d'etre for bash-2.05b is to make a second intermediate -release containing the first of the new features to be available -in bash-3.0 and get feedback on those features before proceeding. -The major new feature is multibyte character support in both Bash -and Readline. - -Bash-2.05b contains the following new features (see the manual page for -complete descriptions and the CHANGES and NEWS files in the bash-2.05b -distribution): - -o support for multibyte characters has been added to both bash and readline - -o the DEBUG trap is now run *before* simple commands, ((...)) commands, - [[...]] conditional commands, and for ((...)) loops - -o the shell now performs arithmetic in the largest integer size the machine - supports (intmax_t) - -o there is a new \D{...} prompt expansion; passes the `...' to strftime(3) - and inserts the result into the expanded prompt - -o there is a new `here-string' redirection operator: <<< word - -o when displaying variables, function attributes and definitions are shown - separately, allowing them to be re-used as input (attempting to re-use - the old output would result in syntax errors). - -o `read' has a new `-u fd' option to read from a specified file descriptor - -o the bash debugger in examples/bashdb has been modified to work with the - new DEBUG trap semantics, the command set has been made more gdb-like, - and the changes to $LINENO make debugging functions work better - -o the expansion of $LINENO inside a shell function is only relative to the - function start if the shell is interactive -- if the shell is running a - script, $LINENO expands to the line number in the script. This is as - POSIX-2001 requires - - -A short feature history dating from Bash-2.0: - -Bash-2.05a introduced the following new features: - -o The `printf' builtin has undergone major work - -o There is a new read-only `shopt' option: login_shell, which is set by - login shells and unset otherwise - -o New `\A' prompt string escape sequence; expanding to time in 24-hour - HH:MM format - -o New `-A group/-g' option to complete and compgen; goes group name - completion - -o New [+-]O invocation option to set and unset `shopt' options at startup - -o ksh-like `ERR' trap - -o `for' loops now allow empty word lists after the `in' reserved word - -o new `hard' and `soft' arguments for the `ulimit' builtin - -o Readline can be configured to place the user at the same point on the line - when retrieving commands from the history list - -o Readline can be configured to skip `hidden' files (filenames with a leading - `.' on Unix) when performing completion - -Bash-2.05 introduced the following new features: - -o This version has once again reverted to using locales and strcoll(3) when - processing pattern matching bracket expressions, as POSIX requires. -o Added a new `--init-file' invocation argument as a synonym for `--rcfile', - per the new GNU coding standards. -o The /dev/tcp and /dev/udp redirections now accept service names as well as - port numbers. -o `complete' and `compgen' now take a `-o value' option, which controls some - of the aspects of that compspec. Valid values are: - - default - perform bash default completion if programmable - completion produces no matches - dirnames - perform directory name completion if programmable - completion produces no matches - filenames - tell readline that the compspec produces filenames, - so it can do things like append slashes to - directory names and suppress trailing spaces -o A new loadable builtin, realpath, which canonicalizes and expands symlinks - in pathname arguments. -o When `set' is called without options, it prints function defintions in a - way that allows them to be reused as input. This affects `declare' and - `declare -p' as well. This only happens when the shell is not in POSIX - mode, since POSIX.2 forbids this behavior. - -Bash-2.04 introduced the following new features: - -o Programmable word completion with the new `complete' and `compgen' builtins; - examples are provided in examples/complete/complete-examples -o `history' has a new `-d' option to delete a history entry -o `bind' has a new `-x' option to bind key sequences to shell commands -o The prompt expansion code has new `\j' and `\l' escape sequences -o The `no_empty_cmd_completion' shell option, if enabled, inhibits - command completion when TAB is typed on an empty line -o `help' has a new `-s' option to print a usage synopsis -o New arithmetic operators: var++, var--, ++var, --var, expr1,expr2 (comma) -o New ksh93-style arithmetic for command: - for ((expr1 ; expr2; expr3 )); do list; done -o `read' has new options: `-t', `-n', `-d', `-s' -o The redirection code handles several filenames specially: /dev/fd/N, - /dev/stdin, /dev/stdout, /dev/stderr -o The redirection code now recognizes /dev/tcp/HOST/PORT and - /dev/udp/HOST/PORT and tries to open a TCP or UDP socket, respectively, - to the specified port on the specified host -o The ${!prefix*} expansion has been implemented -o A new FUNCNAME variable, which expands to the name of a currently-executing - function -o The GROUPS variable is no longer readonly -o A new shopt `xpg_echo' variable, to control the behavior of echo with - respect to backslash-escape sequences at runtime -o The NON_INTERACTIVE_LOGIN_SHELLS #define has returned - -The version of Readline released with Bash-2.04, Readline-4.1, had several -new features as well: - -o Parentheses matching is always compiled into readline, and controllable - with the new `blink-matching-paren' variable -o The history-search-forward and history-search-backward functions now leave - point at the end of the line when the search string is empty, like - reverse-search-history, and forward-search-history -o A new function for applications: rl_on_new_line_with_prompt() -o New variables for applications: rl_already_prompted, and rl_gnu_readline_p - - -Bash-2.03 had very few new features, in keeping with the convention -that odd-numbered releases provide mainly bug fixes. A number of new -features were added to Readline, mostly at the request of the Cygnus -folks. - -A new shopt option, `restricted_shell', so that startup files can test - whether or not the shell was started in restricted mode -Filename generation is now performed on the words between ( and ) in - compound array assignments (this is really a bug fix) -OLDPWD is now auto-exported, as POSIX.2 requires -ENV and BASH_ENV are read-only variables in a restricted shell -Bash may now be linked against an already-installed Readline library, - as long as the Readline library is version 4 or newer -All shells begun with the `--login' option will source the login shell - startup files, even if the shell is not interactive - -There were lots of changes to the version of the Readline library released -along with Bash-2.03. For a complete list of the changes, read the file -CHANGES in the Bash-2.03 distribution. - -Bash-2.02 contained the following new features: - -a new version of malloc (based on the old GNU malloc code in previous - bash versions) that is more page-oriented, more conservative - with memory usage, does not `orphan' large blocks when they - are freed, is usable on 64-bit machines, and has allocation - checking turned on unconditionally -POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.) -POSIX.2-style globbing equivalence classes -POSIX.2-style globbing collating symbols -the ksh [[...]] extended conditional command -the ksh egrep-style extended pattern matching operators -a new `printf' builtin -the ksh-like $(<filename) command substitution, which is equivalent to - $(cat filename) -new tilde prefixes that expand to directories from the directory stack -new `**' arithmetic operator to do exponentiation -case-insensitive globbing (filename expansion) -menu completion a la tcsh -`magic-space' history expansion function like tcsh -the readline inputrc `language' has a new file inclusion directive ($include) - -Bash-2.01 contained only a few new features: - -new `GROUPS' builtin array variable containing the user's group list -new bindable readline commands: history-and-alias-expand-line and - alias-expand-line - -Bash-2.0 contained extensive changes and new features from bash-1.14.7. -Here's a short list: - -new `time' reserved word to time pipelines, shell builtins, and - shell functions -one-dimensional arrays with a new compound assignment statement, - appropriate expansion constructs and modifications to some - of the builtins (read, declare, etc.) to use them -new quoting syntaxes for ANSI-C string expansion and locale-specific - string translation -new expansions to do substring extraction, pattern replacement, and - indirect variable expansion -new builtins: `disown' and `shopt' -new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE, - MACHTYPE, BASH_VERSINFO -special handling of many unused or redundant variables removed - (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec) -dynamic loading of new builtin commands; many loadable examples provided -new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V -history and aliases available in shell scripts -new readline variables: enable-keypad, mark-directories, input-meta, - visible-stats, disable-completion, comment-begin -new readline commands to manipulate the mark and operate on the region -new readline emacs mode commands and bindings for ksh-88 compatibility -updated and extended builtins -new DEBUG trap -expanded (and now documented) restricted shell mode - -implementation stuff: -autoconf-based configuration -nearly all of the bugs reported since version 1.14 have been fixed -most builtins converted to use builtin `getopt' for consistency -most builtins use -p option to display output in a reusable form - (for consistency) -grammar tighter and smaller (66 reduce-reduce conflicts gone) -lots of code now smaller and faster -test suite greatly expanded - -B2) Are there any user-visible incompatibilities between bash-2.05b and - bash-1.14.7? - -There are a few incompatibilities between version 1.14.7 and version 2.05b. -They are detailed in the file COMPAT in the bash distribution. That file -is not meant to be all-encompassing; send mail to bash-maintainers@gnu.org -if if you find something that's not mentioned there. - -Section C: Differences from other Unix shells - -C1) How does bash differ from sh, the Bourne shell? - -This is a non-comprehensive list of features that differentiate bash -from the SVR4.2 shell. The bash manual page explains these more -completely. - -Things bash has that sh does not: - long invocation options - [+-]O invocation option - -l invocation option - `!' reserved word to invert pipeline return value - `time' reserved word to time pipelines and shell builtins - the `function' reserved word - the `select' compound command and reserved word - arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done - new $'...' and $"..." quoting - the $(...) form of command substitution - the $(<filename) form of command substitution, equivalent to - $(cat filename) - the ${#param} parameter value length operator - the ${!param} indirect parameter expansion operator - the ${!param*} prefix expansion operator - the ${param:offset[:length]} parameter substring operator - the ${param/pat[/string]} parameter pattern substitution operator - expansions to perform substring removal (${p%[%]w}, ${p#[#]w}) - expansion of positional parameters beyond $9 with ${num} - variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY, - TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS, - LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME, - ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE, - HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS, - PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC, - SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars, - auto_resume - DEBUG trap - ERR trap - variable arrays with new compound assignment syntax - redirections: <>, &>, >|, <<<, [n]<&word-, [n]>&word- - prompt string special char translation and variable expansion - auto-export of variables in initial environment - command search finds functions before builtins - bash return builtin will exit a file sourced with `.' - builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -d/-l/-p/-t. - export -n/-f/-p/name=value, pwd -L/-P, - read -e/-p/-a/-t/-n/-d/-s/-u, - readonly -a/-f/name=value, trap -l, set +o, - set -b/-m/-o option/-h/-p/-B/-C/-H/-P, - unset -f/-v, ulimit -m/-p/-u, - type -a/-p/-t/-f/-P, suspend -f, kill -n, - test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S - bash reads ~/.bashrc for interactive shells, $ENV for non-interactive - bash restricted shell mode is more extensive - bash allows functions and variables with the same name - brace expansion - tilde expansion - arithmetic expansion with $((...)) and `let' builtin - the `[[...]]' extended conditional command - process substitution - aliases and alias/unalias builtins - local variables in functions and `local' builtin - readline and command-line editing with programmable completion - command history and history/fc builtins - csh-like history expansion - other new bash builtins: bind, command, compgen, complete, builtin, - declare/typeset, dirs, enable, fc, help, - history, logout, popd, pushd, disown, shopt, - printf - exported functions - filename generation when using output redirection (command >a*) - POSIX.2-style globbing character classes - POSIX.2-style globbing equivalence classes - POSIX.2-style globbing collating symbols - egrep-like extended pattern matching operators - case-insensitive pattern matching and globbing - variable assignments preceding commands affect only that command, - even for builtins and functions - posix mode - redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr, - /dev/tcp/host/port, /dev/udp/host/port - -Things sh has that bash does not: - uses variable SHACCT to do shell accounting - includes `stop' builtin (bash can use alias stop='kill -s STOP') - `newgrp' builtin - turns on job control if called as `jsh' - $TIMEOUT (like bash $TMOUT) - `^' is a synonym for `|' - new SVR4.2 sh builtins: mldmode, priv - -Implementation differences: - redirection to/from compound commands causes sh to create a subshell - bash does not allow unbalanced quotes; sh silently inserts them at EOF - bash does not mess with signal 11 - sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100 - bash splits only the results of expansions on IFS, using POSIX.2 - field splitting rules; sh splits all words on IFS - sh does not allow MAILCHECK to be unset (?) - sh does not allow traps on SIGALRM or SIGCHLD - bash allows multiple option arguments when invoked (e.g. -x -v); - sh allows only a single option argument (`sh -x -v' attempts - to open a file named `-v', and, on SunOS 4.1.4, dumps core. - On Solaris 2.4 and earlier versions, sh goes into an infinite - loop.) - sh exits a script if any builtin fails; bash exits only if one of - the POSIX.2 `special' builtins fails - -C2) How does bash differ from the Korn shell, version ksh88? - -Things bash has or uses that ksh88 does not: - long invocation options - [-+]O invocation option - -l invocation option - `!' reserved word - arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done - arithmetic in largest machine-supported size (intmax_t) - posix mode and posix conformance - command hashing - tilde expansion for assignment statements that look like $PATH - process substitution with named pipes if /dev/fd is not available - the ${!param} indirect parameter expansion operator - the ${!param*} prefix expansion operator - the ${param:offset[:length]} parameter substring operator - the ${param/pat[/string]} parameter pattern substitution operator - variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL, - TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, - HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND, - IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK, - PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE, - GROUPS, FUNCNAME, histchars, auto_resume - prompt expansion with backslash escapes and command substitution - redirection: &> (stdout and stderr), <<<, [n]<&word-, [n]>&word- - more extensive and extensible editing and programmable completion - builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable, - exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history, - jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd, - read -e/-p/-a/-t/-n/-d/-s, readonly -a/-n/-f/-p, - set -o braceexpand/-o histexpand/-o interactive-comments/ - -o notify/-o physical/-o posix/-o hashall/-o onecmd/ - -h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type, - typeset -a/-F/-p, ulimit -u, umask -S, alias -p, shopt, - disown, printf, complete, compgen - `!' csh-style history expansion - POSIX.2-style globbing character classes - POSIX.2-style globbing equivalence classes - POSIX.2-style globbing collating symbols - egrep-like extended pattern matching operators - case-insensitive pattern matching and globbing - `**' arithmetic operator to do exponentiation - redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr - arrays of unlimited size - TMOUT is default timeout for `read' and `select' - -Things ksh88 has or uses that bash does not: - tracked aliases (alias -t) - variables: ERRNO, FPATH, EDITOR, VISUAL - co-processes (|&, >&p, <&p) - weirdly-scoped functions - typeset +f to list all function names without definitions - text of command history kept in a file, not memory - builtins: alias -x, cd old new, fc -e -, newgrp, print, - read -p/-s/var?prompt, set -A/-o gmacs/ - -o bgnice/-o markdirs/-o nolog/-o trackall/-o viraw/-s, - typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-l/-u/-t, whence - using environment to pass attributes of exported variables - arithmetic evaluation done on arguments to some builtins - reads .profile from $PWD when invoked as login shell - -Implementation differences: - ksh runs last command of a pipeline in parent shell context - bash has brace expansion by default (ksh88 compile-time option) - bash has fixed startup file for all interactive shells; ksh reads $ENV - bash has exported functions - bash command search finds functions before builtins - bash waits for all commands in pipeline to exit before returning status - emacs-mode editing has some slightly different key bindings - -C3) Which new features in ksh-93 are not in bash, and which are? - -New things in ksh-93 not in bash-2.05b: - associative arrays - floating point arithmetic and variables - math library functions - ${!name[sub]} name of subscript for associative array - `.' is allowed in variable names to create a hierarchical namespace - more extensive compound assignment syntax - discipline functions - `sleep' and `getconf' builtins (bash has loadable versions) - typeset -n and `nameref' variables - KEYBD trap - variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version, - .sh.name, .sh.subscript, .sh.value, .sh.match, HISTEDIT - backreferences in pattern matching (\N) - `&' operator in pattern lists for matching - print -f (bash uses printf) - `fc' has been renamed to `hist' - `.' can execute shell functions - exit statuses between 0 and 255 - set -o pipefail - `+=' variable assignment operator - FPATH and PATH mixing - getopts -a - -I invocation option - DEBUG trap now executed before each simple command, instead of after - printf %H, %P, %T, %Z modifiers, output base for %d - lexical scoping for local variables in `ksh' functions - no scoping for local variables in `POSIX' functions - -New things in ksh-93 present in bash-2.05b: - [n]<&word- and [n]>&word- redirections (combination dup and close) - for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command - ?:, ++, --, `expr1 , expr2' arithmetic operators - expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]}, - ${!param*} - compound array assignment - the `!' reserved word - loadable builtins -- but ksh uses `builtin' while bash uses `enable' - `command', `builtin', `disown' builtins - new $'...' and $"..." quoting - FIGNORE (but bash uses GLOBIGNORE), HISTCMD - set -o notify/-C - changes to kill builtin - read -A (bash uses read -a) - read -t/-d - trap -p - exec -c/-a - `.' restores the positional parameters when it completes - POSIX.2 `test' - umask -S - unalias -a - command and arithmetic substitution performed on PS1, PS4, and ENV - command name completion - ENV processed only for interactive shells - -Section D: Why does bash do some things differently than other Unix shells? - -D1) Why does bash run a different version of `command' than - `which command' says it will? - -On many systems, `which' is actually a csh script that assumes -you're running csh. In tcsh, `which' and its cousin `where' -are builtins. On other Unix systems, `which' is a perl script -that uses the PATH environment variable. - -The csh script version reads the csh startup files from your -home directory and uses those to determine which `command' will -be invoked. Since bash doesn't use any of those startup files, -there's a good chance that your bash environment differs from -your csh environment. The bash `type' builtin does everything -`which' does, and will report correct results for the running -shell. If you're really wedded to the name `which', try adding -the following function definition to your .bashrc: - - which() - { - builtin type "$@" - } - -If you're moving from tcsh and would like to bring `where' along -as well, use this function: - - where() - { - builtin type -a "$@" - } - -D2) Why doesn't bash treat brace expansions exactly like csh? - -The only difference between bash and csh brace expansion is that -bash requires a brace expression to contain at least one unquoted -comma if it is to be expanded. Any brace-surrounded word not -containing an unquoted comma is left unchanged by the brace -expansion code. This affords the greatest degree of sh -compatibility. - -Bash, ksh, zsh, and pd-ksh all implement brace expansion this way. - -D3) Why doesn't bash have csh variable modifiers? - -Posix has specified a more powerful, albeit somewhat more cryptic, -mechanism cribbed from ksh, and bash implements it. - -${parameter%word} - Remove smallest suffix pattern. The WORD is expanded to produce - a pattern. It then expands to the value of PARAMETER, with the - smallest portion of the suffix matched by the pattern deleted. - - x=file.c - echo ${x%.c}.o - -->file.o - -${parameter%%word} - - Remove largest suffix pattern. The WORD is expanded to produce - a pattern. It then expands to the value of PARAMETER, with the - largest portion of the suffix matched by the pattern deleted. - - x=posix/src/std - echo ${x%%/*} - -->posix - -${parameter#word} - Remove smallest prefix pattern. The WORD is expanded to produce - a pattern. It then expands to the value of PARAMETER, with the - smallest portion of the prefix matched by the pattern deleted. - - x=$HOME/src/cmd - echo ${x#$HOME} - -->/src/cmd - -${parameter##word} - Remove largest prefix pattern. The WORD is expanded to produce - a pattern. It then expands to the value of PARAMETER, with the - largest portion of the prefix matched by the pattern deleted. - - x=/one/two/three - echo ${x##*/} - -->three - - -Given - a=/a/b/c/d - b=b.xxx - - csh bash result - --- ---- ------ - $a:h ${a%/*} /a/b/c - $a:t ${a##*/} d - $b:r ${b%.*} b - $b:e ${b##*.} xxx - - -D4) How can I make my csh aliases work when I convert to bash? - -Bash uses a different syntax to support aliases than csh does. -The details can be found in the documentation. We have provided -a shell script which does most of the work of conversion for you; -this script can be found in ./examples/misc/aliasconv.sh. Here is -how you use it: - -Start csh in the normal way for you. (e.g., `csh') - -Pipe the output of `alias' through `aliasconv.sh', saving the -results into `bash_aliases': - - alias | bash aliasconv.sh >bash_aliases - -Edit `bash_aliases', carefully reading through any created -functions. You will need to change the names of some csh specific -variables to the bash equivalents. The script converts $cwd to -$PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt -to $PS1. You may also have to add quotes to avoid unwanted -expansion. - -For example, the csh alias: - - alias cd 'cd \!*; echo $cwd' - -is converted to the bash function: - - cd () { command cd "$@"; echo $PWD ; } - -The only thing that needs to be done is to quote $PWD: - - cd () { command cd "$@"; echo "$PWD" ; } - -Merge the edited file into your ~/.bashrc. - -There is an additional, more ambitious, script in -examples/misc/cshtobash that attempts to convert your entire csh -environment to its bash equivalent. This script can be run as -simply `cshtobash' to convert your normal interactive -environment, or as `cshtobash ~/.login' to convert your login -environment. - -D5) How can I pipe standard output and standard error from one command to - another, like csh does with `|&'? - -Use - command 2>&1 | command2 - -The key is to remember that piping is performed before redirection, so -file descriptor 1 points to the pipe when it is duplicated onto file -descriptor 2. - -D6) Now that I've converted from ksh to bash, are there equivalents to - ksh features like autoloaded functions and the `whence' command? - -There are features in ksh-88 and ksh-93 that do not have direct bash -equivalents. Most, however, can be emulated with very little trouble. - -ksh-88 feature Bash equivalent --------------- --------------- -compiled-in aliases set up aliases in .bashrc; some ksh aliases are - bash builtins (hash, history, type) -coprocesses named pipe pairs (one for read, one for write) -typeset +f declare -F -cd, print, whence function substitutes in examples/functions/kshenv -autoloaded functions examples/functions/autoload is the same as typeset -fu -read var?prompt read -p prompt var - -ksh-93 feature Bash equivalent --------------- --------------- -sleep, getconf Bash has loadable versions in examples/loadables -${.sh.version} $BASH_VERSION -print -f printf -hist alias hist=fc -$HISTEDIT $FCEDIT - -Section E: How can I get bash to do certain things, and why does bash do - things the way it does? - -E1) Why is the bash builtin `test' slightly different from /bin/test? - -The specific example used here is [ ! x -o x ], which is false. - -Bash's builtin `test' implements the Posix.2 spec, which can be -summarized as follows (the wording is due to David Korn): - -Here is the set of rules for processing test arguments. - - 0 Args: False - 1 Arg: True iff argument is not null. - 2 Args: If first arg is !, True iff second argument is null. - If first argument is unary, then true if unary test is true - Otherwise error. - 3 Args: If second argument is a binary operator, do binary test of $1 $3 - If first argument is !, negate two argument test of $2 $3 - If first argument is `(' and third argument is `)', do the - one-argument test of the second argument. - Otherwise error. - 4 Args: If first argument is !, negate three argument test of $2 $3 $4. - Otherwise unspecified - 5 or more Args: unspecified. (Historical shells would use their - current algorithm). - -The operators -a and -o are considered binary operators for the purpose -of the 3 Arg case. - -As you can see, the test becomes (not (x or x)), which is false. - -E2) Why does bash sometimes say `Broken pipe'? - -If a sequence of commands appears in a pipeline, and one of the -reading commands finishes before the writer has finished, the -writer receives a SIGPIPE signal. Many other shells special-case -SIGPIPE as an exit status in the pipeline and do not report it. -For example, in: - - ps -aux | head - -`head' can finish before `ps' writes all of its output, and ps -will try to write on a pipe without a reader. In that case, bash -will print `Broken pipe' to stderr when ps is killed by a -SIGPIPE. - -You can build a version of bash that will not report SIGPIPE errors -by uncommenting the definition of DONT_REPORT_SIGPIPE in the file -config-top.h. - -E3) When I have terminal escape sequences in my prompt, why does bash - wrap lines at the wrong column? - -Readline, the line editing library that bash uses, does not know -that the terminal escape sequences do not take up space on the -screen. The redisplay code assumes, unless told otherwise, that -each character in the prompt is a `printable' character that -takes up one character position on the screen. - -You can use the bash prompt expansion facility (see the PROMPTING -section in the manual page) to tell readline that sequences of -characters in the prompt strings take up no screen space. - -Use the \[ escape to begin a sequence of non-printing characters, -and the \] escape to signal the end of such a sequence. - -E4) If I pipe the output of a command into `read variable', why doesn't - the output show up in $variable when the read command finishes? - -This has to do with the parent-child relationship between Unix -processes. It affects all commands run in pipelines, not just -simple calls to `read'. For example, piping a command's output -into a `while' loop that repeatedly calls `read' will result in -the same behavior. - -Each element of a pipeline runs in a separate process, a child of -the shell running the pipeline. A subprocess cannot affect its -parent's environment. When the `read' command sets the variable -to the input, that variable is set only in the subshell, not the -parent shell. When the subshell exits, the value of the variable -is lost. - -Many pipelines that end with `read variable' can be converted -into command substitutions, which will capture the output of -a specified command. The output can then be assigned to a -variable: - - grep ^gnu /usr/lib/news/active | wc -l | read ngroup - -can be converted into - - ngroup=$(grep ^gnu /usr/lib/news/active | wc -l) - -This does not, unfortunately, work to split the text among -multiple variables, as read does when given multiple variable -arguments. If you need to do this, you can either use the -command substitution above to read the output into a variable -and chop up the variable using the bash pattern removal -expansion operators or use some variant of the following -approach. - -Say /usr/local/bin/ipaddr is the following shell script: - -#! /bin/sh -host `hostname` | awk '/address/ {print $NF}' - -Instead of using - - /usr/local/bin/ipaddr | read A B C D - -to break the local machine's IP address into separate octets, use - - OIFS="$IFS" - IFS=. - set -- $(/usr/local/bin/ipaddr) - IFS="$OIFS" - A="$1" B="$2" C="$3" D="$4" - -Beware, however, that this will change the shell's positional -parameters. If you need them, you should save them before doing -this. - -This is the general approach -- in most cases you will not need to -set $IFS to a different value. - -Some other user-supplied alternatives include: - -read A B C D << HERE - $(IFS=.; echo $(/usr/local/bin/ipaddr)) -HERE - -and, where process substitution is available, - -read A B C D < <(IFS=.; echo $(/usr/local/bin/ipaddr)) - -E5) I have a bunch of shell scripts that use backslash-escaped characters - in arguments to `echo'. Bash doesn't interpret these characters. Why - not, and how can I make it understand them? - -This is the behavior of echo on most Unix System V machines. - -The bash builtin `echo' is modeled after the 9th Edition -Research Unix version of `echo'. It does not interpret -backslash-escaped characters in its argument strings by default; -it requires the use of the -e option to enable the -interpretation. The System V echo provides no way to disable the -special characters; the bash echo has a -E option to disable -them. - -There is a configuration option that will make bash behave like -the System V echo and interpret things like `\t' by default. Run -configure with the --enable-xpg-echo-default option to turn this -on. Be aware that this will cause some of the tests run when you -type `make tests' to fail. - -There is a shell option, `xpg_echo', settable with `shopt', that will -change the behavior of echo at runtime. Enabling this option turns -on expansion of backslash-escape sequences. - -E6) Why doesn't a while or for loop get suspended when I type ^Z? - -This is a consequence of how job control works on Unix. The only -thing that can be suspended is the process group. This is a single -command or pipeline of commands that the shell forks and executes. - -When you run a while or for loop, the only thing that the shell forks -and executes are any commands in the while loop test and commands in -the loop bodies. These, therefore, are the only things that can be -suspended when you type ^Z. - -If you want to be able to stop the entire loop, you need to put it -within parentheses, which will force the loop into a subshell that -may be stopped (and subsequently restarted) as a single unit. - -E7) What about empty for loops in Makefiles? - -It's fairly common to see constructs like this in automatically-generated -Makefiles: - -SUBDIRS = @SUBDIRS@ - - ... - -subdirs-clean: - for d in ${SUBDIRS}; do \ - ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ - done - -When SUBDIRS is empty, this results in a command like this being passed to -bash: - - for d in ; do - ( cd $d && ${MAKE} ${MFLAGS} clean ) - done - -In versions of bash before bash-2.05a, this was a syntax error. If the -reserved word `in' was present, a word must follow it before the semicolon -or newline. The language in the manual page referring to the list of words -being empty referred to the list after it is expanded. These versions of -bash required that there be at least one word following the `in' when the -construct was parsed. - -The idiomatic Makefile solution is something like: - -SUBDIRS = @SUBDIRS@ - -subdirs-clean: - subdirs=$SUBDIRS ; for d in $$subdirs; do \ - ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ - done - -The latest drafts of the updated POSIX standard have changed this: the -word list is no longer required. Bash versions 2.05a and later accept -the new syntax. - -E8) Why does the arithmetic evaluation code complain about `08'? - -The bash arithmetic evaluation code (used for `let', $(()), (()), and in -other places), interprets a leading `0' in numeric constants as denoting -an octal number, and a leading `0x' as denoting hexadecimal. This is -in accordance with the POSIX.2 spec, section 2.9.2.1, which states that -arithmetic constants should be handled as signed long integers as defined -by the ANSI/ISO C standard. - -The POSIX.2 interpretation committee has confirmed this: - -http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-173.html - -E9) Why does the pattern matching expression [A-Z]* match files beginning - with every letter except `z'? - -Bash-2.03, Bash-2.05 and later versions honor the current locale setting -when processing ranges within pattern matching bracket expressions ([A-Z]). -This is what POSIX.2 and SUSv3/XPG6 specify. - -The behavior of the matcher in bash-2.05 and later versions depends on the -current LC_COLLATE setting. Setting this variable to `C' or `POSIX' will -result in the traditional behavior ([A-Z] matches all uppercase ASCII -characters). Many other locales, including the en_US locale (the default -on many US versions of Linux) collate the upper and lower case letters like -this: - - AaBb...Zz - -which means that [A-Z] matches every letter except `z'. Others collate like - - aAbBcC...zZ - -which means that [A-Z] matches every letter except `a'. - -The portable way to specify upper case letters is [:upper:] instead of -A-Z; lower case may be specified as [:lower:] instead of a-z. - -Look at the manual pages for setlocale(3), strcoll(3), and, if it is -present, locale(1). If you have locale(1), you can use it to find -your current locale information even if you do not have any of the -LC_ variables set. - -My advice is to put - - export LC_COLLATE=C - -into /etc/profile and inspect any shell scripts run from cron for -constructs like [A-Z]. This will prevent things like - - rm [A-Z]* - -from removing every file in the current directory except those beginning -with `z' and still allow individual users to change the collation order. -Users may put the above command into their own profiles as well, of course. - -E10) Why does `cd //' leave $PWD as `//'? - -POSIX.2, in its description of `cd', says that *three* or more leading -slashes may be replaced with a single slash when canonicalizing the -current working directory. - -This is, I presume, for historical compatibility. Certain versions of -Unix, and early network file systems, used paths of the form -//hostname/path to access `path' on server `hostname'. - -E11) If I resize my xterm while another program is running, why doesn't bash - notice the change? - -This is another issue that deals with job control. - -The kernel maintains a notion of a current terminal process group. Members -of this process group (processes whose process group ID is equal to the -current terminal process group ID) receive terminal-generated signals like -SIGWINCH. (For more details, see the JOB CONTROL section of the bash -man page.) - -If a terminal is resized, the kernel sends SIGWINCH to each member of -the terminal's current process group (the `foreground' process group). - -When bash is running with job control enabled, each pipeline (which may be -a single command) is run in its own process group, different from bash's -process group. This foreground process group receives the SIGWINCH; bash -does not. Bash has no way of knowing that the terminal has been resized. - -There is a `checkwinsize' option, settable with the `shopt' builtin, that -will cause bash to check the window size and adjust its idea of the -terminal's dimensions each time a process stops or exits and returns control -of the terminal to bash. Enable it with `shopt -s checkwinsize'. - -Section F: Things to watch out for on certain Unix versions - -F1) Why can't I use command line editing in my `cmdtool'? - -The problem is `cmdtool' and bash fighting over the input. When -scrolling is enabled in a cmdtool window, cmdtool puts the tty in -`raw mode' to permit command-line editing using the mouse for -applications that cannot do it themselves. As a result, bash and -cmdtool each try to read keyboard input immediately, with neither -getting enough of it to be useful. - -This mode also causes cmdtool to not implement many of the -terminal functions and control sequences appearing in the -`sun-cmd' termcap entry. For a more complete explanation, see -that file examples/suncmd.termcap in the bash distribution. - -`xterm' is a better choice, and gets along with bash much more -smoothly. - -If you must use cmdtool, you can use the termcap description in -examples/suncmd.termcap. Set the TERMCAP variable to the terminal -description contained in that file, i.e. - -TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:' - -Then export TERMCAP and start a new cmdtool window from that shell. -The bash command-line editing should behave better in the new -cmdtool. If this works, you can put the assignment to TERMCAP -in your bashrc file. - -F2) I built bash on Solaris 2. Why do globbing expansions and filename - completion chop off the first few characters of each filename? - -This is the consequence of building bash on SunOS 5 and linking -with the libraries in /usr/ucblib, but using the definitions -and structures from files in /usr/include. - -The actual conflict is between the dirent structure in -/usr/include/dirent.h and the struct returned by the version of -`readdir' in libucb.a (a 4.3-BSD style `struct direct'). - -Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH -when configuring and building bash. This will ensure that you -use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you -link with libc before libucb. - -If you have installed the Sun C compiler, you may also need to -put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before -/usr/ucb. - -F3) Why does bash dump core after I interrupt username completion or - `~user' tilde expansion on a machine running NIS? - -This is a famous and long-standing bug in the SunOS YP (sorry, NIS) -client library, which is part of libc. - -The YP library code keeps static state -- a pointer into the data -returned from the server. When YP initializes itself (setpwent), -it looks at this pointer and calls free on it if it's non-null. -So far, so good. - -If one of the YP functions is interrupted during getpwent (the -exact function is interpretwithsave()), and returns NULL, the -pointer is freed without being reset to NULL, and the function -returns. The next time getpwent is called, it sees that this -pointer is non-null, calls free, and the bash free() blows up -because it's being asked to free freed memory. - -The traditional Unix mallocs allow memory to be freed multiple -times; that's probably why this has never been fixed. You can -run configure with the `--without-gnu-malloc' option to use -the C library malloc and avoid the problem. - -F4) I'm running SVR4.2. Why is the line erased every time I type `@'? - -The `@' character is the default `line kill' character in most -versions of System V, including SVR4.2. You can change this -character to whatever you want using `stty'. For example, to -change the line kill character to control-u, type - - stty kill ^U - -where the `^' and `U' can be two separate characters. - -F5) Why does bash report syntax errors when my C News scripts use a - redirection before a subshell command? - -The actual command in question is something like - - < file ( command ) - -According to the grammar given in the POSIX.2 standard, this construct -is, in fact, a syntax error. Redirections may only precede `simple -commands'. A subshell construct such as the above is one of the shell's -`compound commands'. A redirection may only follow a compound command. - -This affects the mechanical transformation of commands that use `cat' -to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on -comp.unix.shell). While most commands of the form - - cat file | command - -can be converted to `< file command', shell control structures such as -loops and subshells require `command < file'. - -The file CWRU/sh-redir-hack in the bash-2.05a distribution is an -(unofficial) patch to parse.y that will modify the grammar to -support this construct. It will not apply with `patch'; you must -modify parse.y by hand. Note that if you apply this, you must -recompile with -DREDIRECTION_HACK. This introduces a large -number of reduce/reduce conflicts into the shell grammar. - -F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? - -The short answer is that Red Hat screwed up. - -The long answer is that they shipped an /etc/inputrc that only works -for emacs mode editing, and then screwed all the vi users by setting -INPUTRC to /etc/inputrc in /etc/profile. - -The short fix is to do one of the following: remove or rename -/etc/inputrc, set INPUTRC=~/.inputrc in ~/.bashrc (or .bash_profile, -but make sure you export it if you do), remove the assignment to -INPUTRC from /etc/profile, add - - set keymap emacs - -to the beginning of /etc/inputrc, or bracket the key bindings in -/etc/inputrc with these lines - - $if mode=emacs - [...] - $endif - -F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on - HP/UX 11.x? - -HP/UX's support for long double is imperfect at best. - -GCC will support it without problems, but the HP C library functions -like strtold(3) and printf(3) don't actually work with long doubles. -HP implemented a `long_double' type as a 4-element array of 32-bit -ints, and that is what the library functions use. The ANSI C -`long double' type is a 128-bit floating point scalar. - -The easiest fix, until HP fixes things up, is to edit the generated -config.h and #undef the HAVE_LONG_DOUBLE line. After doing that, -the compilation should complete successfully. - -Section G: How can I get bash to do certain common things? - -G1) How can I get bash to read and display eight-bit characters? - -This is a process requiring several steps. - -First, you must ensure that the `physical' data path is a full eight -bits. For xterms, for example, the `vt100' resources `eightBitInput' -and `eightBitOutput' should be set to `true'. - -Once you have set up an eight-bit path, you must tell the kernel and -tty driver to leave the eighth bit of characters alone when processing -keyboard input. Use `stty' to do this: - - stty cs8 -istrip -parenb - -For old BSD-style systems, you can use - - stty pass8 - -You may also need - - stty even odd - -Finally, you need to tell readline that you will be inputting and -displaying eight-bit characters. You use readline variables to do -this. These variables can be set in your .inputrc or using the bash -`bind' builtin. Here's an example using `bind': - - bash$ bind 'set convert-meta off' - bash$ bind 'set meta-flag on' - bash$ bind 'set output-meta on' - -The `set' commands between the single quotes may also be placed -in ~/.inputrc. - -G2) How do I write a function `x' to replace builtin command `x', but - still invoke the command from within the function? - -This is why the `command' and `builtin' builtins exist. The -`command' builtin executes the command supplied as its first -argument, skipping over any function defined with that name. The -`builtin' builtin executes the builtin command given as its first -argument directly. - -For example, to write a function to replace `cd' that writes the -hostname and current directory to an xterm title bar, use -something like the following: - - cd() - { - builtin cd "$@" && xtitle "$HOST: $PWD" - } - -This could also be written using `command' instead of `builtin'; -the version above is marginally more efficient. - -G3) How can I find the value of a shell variable whose name is the value - of another shell variable? - -Versions of Bash newer than Bash-2.0 support this directly. You can use - - ${!var} - -For example, the following sequence of commands will echo `z': - - var1=var2 - var2=z - echo ${!var1} - -For sh compatibility, use the `eval' builtin. The important -thing to remember is that `eval' expands the arguments you give -it again, so you need to quote the parts of the arguments that -you want `eval' to act on. - -For example, this expression prints the value of the last positional -parameter: - - eval echo \"\$\{$#\}\" - -The expansion of the quoted portions of this expression will be -deferred until `eval' runs, while the `$#' will be expanded -before `eval' is executed. In versions of bash later than bash-2.0, - - echo ${!#} - -does the same thing. - -This is not the same thing as ksh93 `nameref' variables, though the syntax -is similar. I may add namerefs in a future bash version. - -G4) How can I make the bash `time' reserved word print timing output that - looks like the output from my system's /usr/bin/time? - -The bash command timing code looks for a variable `TIMEFORMAT' and -uses its value as a format string to decide how to display the -timing statistics. - -The value of TIMEFORMAT is a string with `%' escapes expanded in a -fashion similar in spirit to printf(3). The manual page explains -the meanings of the escape sequences in the format string. - -If TIMEFORMAT is not set, bash acts as if the following assignment had -been performed: - - TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS' - -The POSIX.2 default time format (used by `time -p command') is - - TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S' - -The BSD /usr/bin/time format can be emulated with: - - TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys' - -The System V /usr/bin/time format can be emulated with: - - TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S' - -The ksh format can be emulated with: - - TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS' - -G5) How do I get the current directory into my prompt? - -Bash provides a number of backslash-escape sequences which are expanded -when the prompt string (PS1 or PS2) is displayed. The full list is in -the manual page. - -The \w expansion gives the full pathname of the current directory, with -a tilde (`~') substituted for the current value of $HOME. The \W -expansion gives the basename of the current directory. To put the full -pathname of the current directory into the path without any tilde -subsitution, use $PWD. Here are some examples: - - PS1='\w$ ' # current directory with tilde - PS1='\W$ ' # basename of current directory - PS1='$PWD$ ' # full pathname of current directory - -The single quotes are important in the final example to prevent $PWD from -being expanded when the assignment to PS1 is performed. - -G6) How can I rename "*.foo" to "*.bar"? - -Use the pattern removal functionality described in D3. The following `for' -loop will do the trick: - - for f in *.foo; do - mv $f ${f%foo}bar - done - -G7) How can I translate a filename from uppercase to lowercase? - -The script examples/functions/lowercase, originally written by John DuBois, -will do the trick. The converse is left as an exercise. - -G8) How can I write a filename expansion (globbing) pattern that will match - all files in the current directory except "." and ".."? - -You must have set the `extglob' shell option using `shopt -s extglob' to use -this: - - echo .!(.|) * - -A solution that works without extended globbing is given in the Unix Shell -FAQ, posted periodically to comp.unix.shell. - -Section H: Where do I go from here? - -H1) How do I report bugs in bash, and where should I look for fixes and - advice? - -Use the `bashbug' script to report bugs. It is built and -installed at the same time as bash. It provides a standard -template for reporting a problem and automatically includes -information about your configuration and build environment. - -`bashbug' sends its reports to bug-bash@gnu.org, which -is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug. - -Bug fixes, answers to questions, and announcements of new releases -are all posted to gnu.bash.bug. Discussions concerning bash features -and problems also take place there. - -To reach the bash maintainers directly, send mail to -bash-maintainers@gnu.org. - -H2) What kind of bash documentation is there? - -First, look in the doc directory in the bash distribution. It should -contain at least the following files: - -bash.1 an extensive, thorough Unix-style manual page -builtins.1 a manual page covering just bash builtin commands -bashref.texi a reference manual in GNU tex`info format -bashref.info an info version of the reference manual -FAQ this file -article.ms text of an article written for The Linux Journal -readline.3 a man page describing readline - -Postscript, HTML, and ASCII files created from the above source are -available in the documentation distribution. - -There is additional documentation available for anonymous FTP from host -ftp.cwru.edu in the `pub/bash' directory. - -Cameron Newham and Bill Rosenblatt have written a book on bash, published -by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn -Shell book. The title is ``Learning the Bash Shell'', and the ISBN number -is 1-56592-147-X. Look for it in fine bookstores near you. This book -covers bash-1.14, but has an appendix describing some of the new features -in bash-2.0. - -A second edition of this book is available, published in January, 1998. -The ISBN number is 1-56592-347-2. Look for it in the same fine bookstores -or on the web. - -The GNU Bash Reference Manual has been published as a printed book by -Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Feb 2003). It covers -bash-2.0 and is available from most online bookstores (see -http://www.network-theory.co.uk/bash/manual/ for details). The publisher -will donate $1 to the Free Software Foundation for each copy sold. - -H3) What's coming in future versions? - -These are features I hope to include in a future version of bash. - -a better bash debugger (a minimally-tested version is included with bash-2.05b) -associative arrays -co-processes, but with a new-style syntax that looks like function declaration - -H4) What's on the bash `wish list' for future versions? - -These are features that may or may not appear in a future version of bash. - -breaking some of the shell functionality into embeddable libraries -a module system like zsh's, using dynamic loading like builtins -better internationalization using GNU `gettext' -date-stamped command history -a bash programmer's guide with a chapter on creating loadable builtins -a better loadable interface to perl with access to the shell builtins and - variables (contributions gratefully accepted) -ksh93-like `nameref' variables -ksh93-like `+=' variable assignment operator -ksh93-like `xx.yy' variables (including some of the .sh.* variables) and - associated disipline functions -Some of the new ksh93 pattern matching operators, like backreferencing - -H5) When will the next release appear? - -The next version will appear sometime in 2002. Never make predictions. - - -This document is Copyright 1995-2003 by Chester Ramey. - -Permission is hereby granted, without written agreement and -without license or royalty fees, to use, copy, and distribute -this document for any purpose, provided that the above copyright -notice appears in all copies of this document and that the -contents of this document remain unaltered. |