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diff --git a/doc/diffutils.texi b/doc/diffutils.texi new file mode 100644 index 0000000..b478380 --- /dev/null +++ b/doc/diffutils.texi @@ -0,0 +1,4759 @@ +\input texinfo @c -*-texinfo-*- +@comment %**start of header +@setfilename diffutils.info +@include version.texi +@settitle Comparing and Merging Files +@syncodeindex vr cp +@setchapternewpage odd +@comment %**end of header +@copying +This manual is for GNU Diffutils +(version @value{VERSION}, @value{UPDATED}), +and documents the @acronym{GNU} @command{diff}, @command{diff3}, +@command{sdiff}, and @command{cmp} commands for showing the +differences between files and the @acronym{GNU} @command{patch} command for +using their output to update files. + +Copyright @copyright{} 1992-1994, 1998, 2001-2002, 2004, 2006, 2009-2016 Free +Software Foundation, Inc. + +@quotation +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 +``@acronym{GNU} Free Documentation License.'' +@end quotation +@end copying + +@c Debian install-info (up through at least version 1.9.20) uses only the +@c first dircategory. Put this one first, as it is more useful in practice. +@dircategory Individual utilities +@direntry +* cmp: (diffutils)Invoking cmp. Compare 2 files byte by byte. +* diff: (diffutils)Invoking diff. Compare 2 files line by line. +* diff3: (diffutils)Invoking diff3. Compare 3 files line by line. +* patch: (diffutils)Invoking patch. Apply a patch to a file. +* sdiff: (diffutils)Invoking sdiff. Merge 2 files side-by-side. +@end direntry + +@dircategory Text creation and manipulation +@direntry +* Diffutils: (diffutils). Comparing and merging files. +@end direntry + +@titlepage +@title Comparing and Merging Files +@subtitle for Diffutils @value{VERSION} and @code{patch} 2.5.4 +@subtitle @value{UPDATED} +@author David MacKenzie, Paul Eggert, and Richard Stallman +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage + +@shortcontents +@contents + +@ifnottex +@node Top +@top Comparing and Merging Files + +@insertcopying +@end ifnottex + +@menu +* Overview:: Preliminary information. +* Comparison:: What file comparison means. + +* Output Formats:: Formats for two-way difference reports. +* Incomplete Lines:: Lines that lack trailing newlines. +* Comparing Directories:: Comparing files and directories. +* Adjusting Output:: Making @command{diff} output prettier. +* diff Performance:: Making @command{diff} smarter or faster. + +* Comparing Three Files:: Formats for three-way difference reports. +* diff3 Merging:: Merging from a common ancestor. + +* Interactive Merging:: Interactive merging with @command{sdiff}. + +* Merging with patch:: Using @command{patch} to change old files into new ones. +* Making Patches:: Tips for making and using patch distributions. + +* Invoking cmp:: Compare two files byte by byte. +* Invoking diff:: Compare two files line by line. +* Invoking diff3:: Compare three files line by line. +* Invoking patch:: Apply a diff file to an original. +* Invoking sdiff:: Side-by-side merge of file differences. + +* Standards conformance:: Conformance to the @acronym{POSIX} standard. +* Projects:: If you've found a bug or other shortcoming. + +* Copying This Manual:: How to make copies of this manual. +* Translations:: Available translations of this manual. +* Index:: Index. +@end menu + +@node Overview +@unnumbered Overview +@cindex overview of @command{diff} and @command{patch} + +Computer users often find occasion to ask how two files differ. Perhaps +one file is a newer version of the other file. Or maybe the two files +started out as identical copies but were changed by different people. + +You can use the @command{diff} command to show differences between two +files, or each corresponding file in two directories. @command{diff} +outputs differences between files line by line in any of several +formats, selectable by command line options. This set of differences is +often called a @dfn{diff} or @dfn{patch}. For files that are identical, +@command{diff} normally produces no output; for binary (non-text) files, +@command{diff} normally reports only that they are different. + +You can use the @command{cmp} command to show the byte and line numbers +where two files differ. @command{cmp} can also show all the bytes +that differ between the two files, side by side. A way to compare +two files character by character is the Emacs command @kbd{M-x +compare-windows}. @xref{Other Window, , Other Window, emacs, The @acronym{GNU} +Emacs Manual}, for more information on that command. + +You can use the @command{diff3} command to show differences among three +files. When two people have made independent changes to a common +original, @command{diff3} can report the differences between the original +and the two changed versions, and can produce a merged file that +contains both persons' changes together with warnings about conflicts. + +You can use the @command{sdiff} command to merge two files interactively. + +You can use the set of differences produced by @command{diff} to distribute +updates to text files (such as program source code) to other people. +This method is especially useful when the differences are small compared +to the complete files. Given @command{diff} output, you can use the +@command{patch} program to update, or @dfn{patch}, a copy of the file. If you +think of @command{diff} as subtracting one file from another to produce +their difference, you can think of @command{patch} as adding the difference +to one file to reproduce the other. + +This manual first concentrates on making diffs, and later shows how to +use diffs to update files. + +@acronym{GNU} @command{diff} was written by Paul Eggert, Mike Haertel, +David Hayes, Richard Stallman, and Len Tower. Wayne Davison designed and +implemented the unified output format. The basic algorithm is described +by Eugene W. Myers in ``An O(ND) Difference Algorithm and its Variations'', +@cite{Algorithmica} Vol.@: 1, 1986, pp.@: 251--266, +@url{http://dx.doi.org/10.1007/BF01840446}; and in ``A File +Comparison Program'', Webb Miller and Eugene W. Myers, +@cite{Software---Practice and Experience} Vol.@: 15, 1985, +pp.@: 1025--1040, +@url{http://dx.doi.org/10.1002/spe.4380151102}. +@c From: "Gene Myers" <gene@cs.arizona.edu> +@c They are about the same basic algorithm; the Algorithmica +@c paper gives a rigorous treatment and the sub-algorithm for +@c delivering scripts and should be the primary reference, but +@c both should be mentioned. +The algorithm was independently discovered as described by Esko Ukkonen in +``Algorithms for Approximate String Matching'', +@cite{Information and Control} Vol.@: 64, 1985, pp.@: 100--118, +@url{http://dx.doi.org/10.1016/S0019-9958(85)80046-2}. +@c From: "Gene Myers" <gene@cs.arizona.edu> +@c Date: Wed, 29 Sep 1993 08:27:55 MST +@c Ukkonen should be given credit for also discovering the algorithm used +@c in GNU diff. +Related algorithms are surveyed by Alfred V. Aho in +section 6.3 of ``Algorithms for Finding Patterns in Strings'', +@cite{Handbook of Theoretical Computer Science} (Jan Van Leeuwen, +ed.), Vol.@: A, @cite{Algorithms and Complexity}, Elsevier/MIT Press, +1990, pp.@: 255--300. + +@acronym{GNU} @command{diff3} was written by Randy Smith. @acronym{GNU} +@command{sdiff} was written by Thomas Lord. @acronym{GNU} @command{cmp} +was written by Torbj@"orn Granlund and David MacKenzie. + +@acronym{GNU} @command{patch} was written mainly by Larry Wall and Paul Eggert; +several @acronym{GNU} enhancements were contributed by Wayne Davison and +David MacKenzie. Parts of this manual are adapted from a manual page +written by Larry Wall, with his permission. + +@node Comparison +@chapter What Comparison Means +@cindex introduction + +There are several ways to think about the differences between two files. +One way to think of the differences is as a series of lines that were +deleted from, inserted in, or changed in one file to produce the other +file. @command{diff} compares two files line by line, finds groups of +lines that differ, and reports each group of differing lines. It can +report the differing lines in several formats, which have different +purposes. + +@acronym{GNU} @command{diff} can show whether files are different +without detailing the differences. It also provides ways to suppress +certain kinds of differences that are not important to you. Most +commonly, such differences are changes in the amount of white space +between words or lines. @command{diff} also provides ways to suppress +differences in alphabetic case or in lines that match a regular +expression that you provide. These options can accumulate; for +example, you can ignore changes in both white space and alphabetic +case. + +Another way to think of the differences between two files is as a +sequence of pairs of bytes that can be either identical or +different. @command{cmp} reports the differences between two files +byte by byte, instead of line by line. As a result, it is often +more useful than @command{diff} for comparing binary files. For text +files, @command{cmp} is useful mainly when you want to know only whether +two files are identical, or whether one file is a prefix of the other. + +To illustrate the effect that considering changes byte by byte +can have compared with considering them line by line, think of what +happens if a single newline character is added to the beginning of a +file. If that file is then compared with an otherwise identical file +that lacks the newline at the beginning, @command{diff} will report that a +blank line has been added to the file, while @command{cmp} will report that +almost every byte of the two files differs. + +@command{diff3} normally compares three input files line by line, finds +groups of lines that differ, and reports each group of differing lines. +Its output is designed to make it easy to inspect two different sets of +changes to the same file. + +These commands compare input files without necessarily reading them. +For example, if @command{diff} is asked simply to report whether two +files differ, and it discovers that the files have different sizes, it +need not read them to do its job. + +@menu +* Hunks:: Groups of differing lines. +* White Space:: Suppressing differences in white space. +* Blank Lines:: Suppressing differences whose lines are all blank. +* Specified Lines:: Suppressing differences whose lines all match a pattern. +* Case Folding:: Suppressing differences in alphabetic case. +* Brief:: Summarizing which files are different. +* Binary:: Comparing binary files or forcing text comparisons. +@end menu + +@node Hunks +@section Hunks +@cindex hunks + +When comparing two files, @command{diff} finds sequences of lines common to +both files, interspersed with groups of differing lines called +@dfn{hunks}. Comparing two identical files yields one sequence of +common lines and no hunks, because no lines differ. Comparing two +entirely different files yields no common lines and one large hunk that +contains all lines of both files. In general, there are many ways to +match up lines between two given files. @command{diff} tries to minimize +the total hunk size by finding large sequences of common lines +interspersed with small hunks of differing lines. + +For example, suppose the file @file{F} contains the three lines +@samp{a}, @samp{b}, @samp{c}, and the file @file{G} contains the same +three lines in reverse order @samp{c}, @samp{b}, @samp{a}. If +@command{diff} finds the line @samp{c} as common, then the command +@samp{diff F G} produces this output: + +@example +1,2d0 +< a +< b +3a2,3 +> b +> a +@end example + +@noindent +But if @command{diff} notices the common line @samp{b} instead, it produces +this output: + +@example +1c1 +< a +--- +> c +3c3 +< c +--- +> a +@end example + +@noindent +It is also possible to find @samp{a} as the common line. @command{diff} +does not always find an optimal matching between the files; it takes +shortcuts to run faster. But its output is usually close to the +shortest possible. You can adjust this tradeoff with the +@option{--minimal} (@option{-d}) option (@pxref{diff Performance}). + +@node White Space +@section Suppressing Differences in Blank and Tab Spacing +@cindex blank and tab difference suppression +@cindex tab and blank difference suppression + +The @option{--ignore-tab-expansion} (@option{-E}) option ignores the +distinction between tabs and spaces on input. A tab is considered to be +equivalent to the number of spaces to the next tab stop (@pxref{Tabs}). + +The @option{--ignore-trailing-space} (@option{-Z}) option ignores white +space at line end. + +The @option{--ignore-space-change} (@option{-b}) option is stronger than +@option{-E} and @option{-Z} combined. +It ignores white space at line end, and considers all other sequences of +one or more white space characters within a line to be equivalent. With this +option, @command{diff} considers the following two lines to be equivalent, +where @samp{$} denotes the line end: + +@example +Here lyeth muche rychnesse in lytell space. -- John Heywood$ +Here lyeth muche rychnesse in lytell space. -- John Heywood $ +@end example + +The @option{--ignore-all-space} (@option{-w}) option is stronger still. +It ignores differences even if one line has white space where +the other line has none. @dfn{White space} characters include +tab, vertical tab, form feed, carriage return, and space; +some locales may define additional characters to be white space. +With this option, @command{diff} considers the +following two lines to be equivalent, where @samp{$} denotes the line +end and @samp{^M} denotes a carriage return: + +@example +Here lyeth muche rychnesse in lytell space.-- John Heywood$ + He relyeth much erychnes seinly tells pace. --John Heywood ^M$ +@end example + +For many other programs newline is also a white space character, but +@command{diff} is a line-oriented program and a newline character +always ends a line. Hence the @option{-w} or +@option{--ignore-all-space} option does not ignore newline-related +changes; it ignores only other white space changes. + +@node Blank Lines +@section Suppressing Differences Whose Lines Are All Blank +@cindex blank line difference suppression + +The @option{--ignore-blank-lines} (@option{-B}) option ignores changes +that consist entirely of blank lines. With this option, for example, a +file containing +@example +1. A point is that which has no part. + +2. A line is breadthless length. +-- Euclid, The Elements, I +@end example +@noindent +is considered identical to a file containing +@example +1. A point is that which has no part. +2. A line is breadthless length. + + +-- Euclid, The Elements, I +@end example + +Normally this option affects only lines that are completely empty, but +if you also specify an option that ignores trailing spaces, +lines are also affected if they look empty but contain white space. +In other words, @option{-B} is equivalent to @samp{-I '^$'} by +default, but it is equivalent to @option{-I '^[[:space:]]*$'} if +@option{-b}, @option{-w} or @option{-Z} is also specified. + +@node Specified Lines +@section Suppressing Differences Whose Lines All Match a Regular Expression +@cindex regular expression suppression + +To ignore insertions and deletions of lines that match a +@command{grep}-style regular expression, use the +@option{--ignore-matching-lines=@var{regexp}} (@option{-I @var{regexp}}) option. +You should escape +regular expressions that contain shell metacharacters to prevent the +shell from expanding them. For example, @samp{diff -I '^[[:digit:]]'} ignores +all changes to lines beginning with a digit. + +However, @option{-I} only ignores the insertion or deletion of lines that +contain the regular expression if every changed line in the hunk---every +insertion and every deletion---matches the regular expression. In other +words, for each nonignorable change, @command{diff} prints the complete set +of changes in its vicinity, including the ignorable ones. + +You can specify more than one regular expression for lines to ignore by +using more than one @option{-I} option. @command{diff} tries to match each +line against each regular expression. + +@node Case Folding +@section Suppressing Case Differences +@cindex case difference suppression + +@acronym{GNU} @command{diff} can treat lower case letters as +equivalent to their upper case counterparts, so that, for example, it +considers @samp{Funky Stuff}, @samp{funky STUFF}, and @samp{fUNKy +stuFf} to all be the same. To request this, use the @option{-i} or +@option{--ignore-case} option. + +@node Brief +@section Summarizing Which Files Differ +@cindex summarizing which files differ +@cindex brief difference reports + +When you only want to find out whether files are different, and you +don't care what the differences are, you can use the summary output +format. In this format, instead of showing the differences between the +files, @command{diff} simply reports whether files differ. The +@option{--brief} (@option{-q}) option selects this output format. + +This format is especially useful when comparing the contents of two +directories. It is also much faster than doing the normal line by line +comparisons, because @command{diff} can stop analyzing the files as soon as +it knows that there are any differences. + +You can also get a brief indication of whether two files differ by using +@command{cmp}. For files that are identical, @command{cmp} produces no +output. When the files differ, by default, @command{cmp} outputs the byte +and line number where the first difference occurs, or reports that one +file is a prefix of the other. You can use +the @option{-s}, @option{--quiet}, or @option{--silent} option to +suppress that information, so that @command{cmp} +produces no output and reports whether the files differ using only its +exit status (@pxref{Invoking cmp}). + +@c Fix this. +Unlike @command{diff}, @command{cmp} cannot compare directories; it can only +compare two files. + +@node Binary +@section Binary Files and Forcing Text Comparisons +@cindex binary file diff +@cindex text versus binary diff + +If @command{diff} thinks that either of the two files it is comparing is +binary (a non-text file), it normally treats that pair of files much as +if the summary output format had been selected (@pxref{Brief}), and +reports only that the binary files are different. This is because line +by line comparisons are usually not meaningful for binary files. +This does not count as trouble, even though the resulting output does +not capture all the differences. + +@command{diff} determines whether a file is text or binary by checking the +first few bytes in the file; the exact number of bytes is system +dependent, but it is typically several thousand. If every byte in +that part of the file is non-null, @command{diff} considers the file to be +text; otherwise it considers the file to be binary. + +Sometimes you might want to force @command{diff} to consider files to be +text. For example, you might be comparing text files that contain +null characters; @command{diff} would erroneously decide that those are +non-text files. Or you might be comparing documents that are in a +format used by a word processing system that uses null characters to +indicate special formatting. You can force @command{diff} to consider all +files to be text files, and compare them line by line, by using the +@option{--text} (@option{-a}) option. If the files you compare using this +option do not in fact contain text, they will probably contain few +newline characters, and the @command{diff} output will consist of hunks +showing differences between long lines of whatever characters the files +contain. + +You can also force @command{diff} to report only whether files differ +(but not how). Use the @option{--brief} (@option{-q}) option for +this. + +In operating systems that distinguish between text and binary files, +@command{diff} normally reads and writes all data as text. Use the +@option{--binary} option to force @command{diff} to read and write binary +data instead. This option has no effect on a @acronym{POSIX}-compliant system +like @acronym{GNU} or traditional Unix. However, many personal computer +operating systems represent the end of a line with a carriage return +followed by a newline. On such systems, @command{diff} normally ignores +these carriage returns on input and generates them at the end of each +output line, but with the @option{--binary} option @command{diff} treats +each carriage return as just another input character, and does not +generate a carriage return at the end of each output line. This can be +useful when dealing with non-text files that are meant to be +interchanged with @acronym{POSIX}-compliant systems. + +The @option{--strip-trailing-cr} causes @command{diff} to treat input +lines that end in carriage return followed by newline as if they end +in plain newline. This can be useful when comparing text that is +imperfectly imported from many personal computer operating systems. +This option affects how lines are read, which in turn affects how they +are compared and output. + +If you want to compare two files byte by byte, you can use the +@command{cmp} program with the @option{--verbose} (@option{-l}) +option to show the values of each differing byte in the two files. +With @acronym{GNU} @command{cmp}, you can also use the @option{-b} or +@option{--print-bytes} option to show the @acronym{ASCII} representation of +those bytes. @xref{Invoking cmp}, for more information. + +If @command{diff3} thinks that any of the files it is comparing is binary +(a non-text file), it normally reports an error, because such +comparisons are usually not useful. @command{diff3} uses the same test as +@command{diff} to decide whether a file is binary. As with @command{diff}, if +the input files contain a few non-text bytes but otherwise are like +text files, you can force @command{diff3} to consider all files to be text +files and compare them line by line by using the @option{-a} or +@option{--text} option. + +@node Output Formats +@chapter @command{diff} Output Formats +@cindex output formats +@cindex format of @command{diff} output + +@command{diff} has several mutually exclusive options for output format. +The following sections describe each format, illustrating how +@command{diff} reports the differences between two sample input files. + +@menu +* Sample diff Input:: Sample @command{diff} input files for examples. +* Context:: Showing differences with the surrounding text. +* Side by Side:: Showing differences in two columns. +* Normal:: Showing differences without surrounding text. +* Scripts:: Generating scripts for other programs. +* If-then-else:: Merging files with if-then-else. +@end menu + +@node Sample diff Input +@section Two Sample Input Files +@cindex @command{diff} sample input +@cindex sample input for @command{diff} + +Here are two sample files that we will use in numerous examples to +illustrate the output of @command{diff} and how various options can change +it. + +This is the file @file{lao}: + +@example +The Way that can be told of is not the eternal Way; +The name that can be named is not the eternal name. +The Nameless is the origin of Heaven and Earth; +The Named is the mother of all things. +Therefore let there always be non-being, + so we may see their subtlety, +And let there always be being, + so we may see their outcome. +The two are the same, +But after they are produced, + they have different names. +@end example + +This is the file @file{tzu}: + +@example +The Nameless is the origin of Heaven and Earth; +The named is the mother of all things. + +Therefore let there always be non-being, + so we may see their subtlety, +And let there always be being, + so we may see their outcome. +The two are the same, +But after they are produced, + they have different names. +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +@end example + +In this example, the first hunk contains just the first two lines of +@file{lao}, the second hunk contains the fourth line of @file{lao} +opposing the second and third lines of @file{tzu}, and the last hunk +contains just the last three lines of @file{tzu}. + +@node Context +@section Showing Differences in Their Context +@cindex context output format +@cindex @samp{!} output format + +Usually, when you are looking at the differences between files, you will +also want to see the parts of the files near the lines that differ, to +help you understand exactly what has changed. These nearby parts of the +files are called the @dfn{context}. + +@acronym{GNU} @command{diff} provides two output formats that show context +around the differing lines: @dfn{context format} and @dfn{unified +format}. It can optionally show in which function or section of the +file the differing lines are found. + +If you are distributing new versions of files to other people in the +form of @command{diff} output, you should use one of the output formats +that show context so that they can apply the diffs even if they have +made small changes of their own to the files. @command{patch} can apply +the diffs in this case by searching in the files for the lines of +context around the differing lines; if those lines are actually a few +lines away from where the diff says they are, @command{patch} can adjust +the line numbers accordingly and still apply the diff correctly. +@xref{Imperfect}, for more information on using @command{patch} to apply +imperfect diffs. + +@menu +* Context Format:: An output format that shows surrounding lines. +* Unified Format:: A more compact output format that shows context. +* Sections:: Showing which sections of the files differences are in. +* Alternate Names:: Showing alternate file names in context headers. +@end menu + +@node Context Format +@subsection Context Format + +The context output format shows several lines of context around the +lines that differ. It is the standard format for distributing updates +to source code. + +To select this output format, use the +@option{--context@r{[}=@var{lines}@r{]}} (@option{-C @var{lines}}) +or @option{-c} option. The +argument @var{lines} that some of these options take is the number of +lines of context to show. If you do not specify @var{lines}, it +defaults to three. For proper operation, @command{patch} typically needs +at least two lines of context. + +@menu +* Example Context:: Sample output in context format. +* Less Context:: Another sample with less context. +* Detailed Context:: A detailed description of the context output format. +@end menu + +@node Example Context +@subsubsection An Example of Context Format + +Here is the output of @samp{diff -c lao tzu} (@pxref{Sample diff Input}, +for the complete contents of the two files). Notice that up to three +lines that are not different are shown around each line that is +different; they are the context lines. Also notice that the first two +hunks have run together, because their contents overlap. + +@example +*** lao 2002-02-21 23:30:39.942229878 -0800 +--- tzu 2002-02-21 23:30:50.442260588 -0800 +*************** +*** 1,7 **** +- The Way that can be told of is not the eternal Way; +- The name that can be named is not the eternal name. + The Nameless is the origin of Heaven and Earth; +! The Named is the mother of all things. + Therefore let there always be non-being, + so we may see their subtlety, + And let there always be being, +--- 1,6 ---- + The Nameless is the origin of Heaven and Earth; +! The named is the mother of all things. +! @- + Therefore let there always be non-being, + so we may see their subtlety, + And let there always be being, +*************** +*** 9,11 **** +--- 8,13 ---- + The two are the same, + But after they are produced, + they have different names. ++ They both may be called deep and profound. ++ Deeper and more profound, ++ The door of all subtleties! +@end example + +@node Less Context +@subsubsection An Example of Context Format with Less Context + +Here is the output of @samp{diff -C 1 lao tzu} (@pxref{Sample diff +Input}, for the complete contents of the two files). Notice that at +most one context line is reported here. + +@example +*** lao 2002-02-21 23:30:39.942229878 -0800 +--- tzu 2002-02-21 23:30:50.442260588 -0800 +*************** +*** 1,5 **** +- The Way that can be told of is not the eternal Way; +- The name that can be named is not the eternal name. + The Nameless is the origin of Heaven and Earth; +! The Named is the mother of all things. + Therefore let there always be non-being, +--- 1,4 ---- + The Nameless is the origin of Heaven and Earth; +! The named is the mother of all things. +! @- + Therefore let there always be non-being, +*************** +*** 11 **** +--- 10,13 ---- + they have different names. ++ They both may be called deep and profound. ++ Deeper and more profound, ++ The door of all subtleties! +@end example + +@node Detailed Context +@subsubsection Detailed Description of Context Format + +The context output format starts with a two-line header, which looks +like this: + +@example +*** @var{from-file} @var{from-file-modification-time} +--- @var{to-file} @var{to-file-modification time} +@end example + +@noindent +@vindex LC_TIME +@cindex time stamp format, context diffs +The time stamp normally looks like @samp{2002-02-21 23:30:39.942229878 +-0800} to indicate the date, time with fractional seconds, and time +zone in @uref{ftp://ftp.isi.edu/in-notes/rfc2822.txt, Internet RFC +2822 format}. (The fractional seconds are omitted on hosts that do +not support fractional time stamps.) However, a traditional time +stamp like @samp{Thu Feb 21 23:30:39 2002} is used if the +@env{LC_TIME} locale category is either @samp{C} or @samp{POSIX}. + +You can change the header's content with the +@option{--label=@var{label}} option; see @ref{Alternate Names}. + +Next come one or more hunks of differences; each hunk shows one area +where the files differ. Context format hunks look like this: + +@example +*************** +*** @var{from-file-line-numbers} **** + @var{from-file-line} + @var{from-file-line}@dots{} +--- @var{to-file-line-numbers} ---- + @var{to-file-line} + @var{to-file-line}@dots{} +@end example + +If a hunk contains two or more lines, its line numbers look like +@samp{@var{start},@var{end}}. Otherwise only its end line number +appears. An empty hunk is considered to end at the line that precedes +the hunk. + +The lines of context around the lines that differ start with two space +characters. The lines that differ between the two files start with one +of the following indicator characters, followed by a space character: + +@table @samp +@item ! +A line that is part of a group of one or more lines that changed between +the two files. There is a corresponding group of lines marked with +@samp{!} in the part of this hunk for the other file. + +@item + +An ``inserted'' line in the second file that corresponds to nothing in +the first file. + +@item - +A ``deleted'' line in the first file that corresponds to nothing in the +second file. +@end table + +If all of the changes in a hunk are insertions, the lines of +@var{from-file} are omitted. If all of the changes are deletions, the +lines of @var{to-file} are omitted. + +@node Unified Format +@subsection Unified Format +@cindex unified output format +@cindex @samp{+-} output format + +The unified output format is a variation on the context format that is +more compact because it omits redundant context lines. To select this +output format, use the +@option{--unified@r{[}=@var{lines}@r{]}} (@option{-U @var{lines}}), +or @option{-u} option. +The argument @var{lines} is the number of lines of context to show. +When it is not given, it defaults to three. + +At present, only @acronym{GNU} @command{diff} can produce this format and +only @acronym{GNU} @command{patch} can automatically apply diffs in this +format. For proper operation, @command{patch} typically needs at +least three lines of context. + +@menu +* Example Unified:: Sample output in unified format. +* Detailed Unified:: A detailed description of unified format. +@end menu + +@node Example Unified +@subsubsection An Example of Unified Format + +Here is the output of the command @samp{diff -u lao tzu} +(@pxref{Sample diff Input}, for the complete contents of the two files): + +@example +--- lao 2002-02-21 23:30:39.942229878 -0800 ++++ tzu 2002-02-21 23:30:50.442260588 -0800 +@@@@ -1,7 +1,6 @@@@ +-The Way that can be told of is not the eternal Way; +-The name that can be named is not the eternal name. + The Nameless is the origin of Heaven and Earth; +-The Named is the mother of all things. ++The named is the mother of all things. ++ + Therefore let there always be non-being, + so we may see their subtlety, + And let there always be being, +@@@@ -9,3 +8,6 @@@@ + The two are the same, + But after they are produced, + they have different names. ++They both may be called deep and profound. ++Deeper and more profound, ++The door of all subtleties! +@end example + +@node Detailed Unified +@subsubsection Detailed Description of Unified Format + +The unified output format starts with a two-line header, which looks +like this: + +@example +--- @var{from-file} @var{from-file-modification-time} ++++ @var{to-file} @var{to-file-modification-time} +@end example + +@noindent +@cindex time stamp format, unified diffs +The time stamp looks like @samp{2002-02-21 23:30:39.942229878 -0800} +to indicate the date, time with fractional seconds, and time zone. +The fractional seconds are omitted on hosts that do not support +fractional time stamps. + +You can change the header's content with the +@option{--label=@var{label}} option. @xref{Alternate Names}. + +Next come one or more hunks of differences; each hunk shows one area +where the files differ. Unified format hunks look like this: + +@example +@@@@ @var{from-file-line-numbers} @var{to-file-line-numbers} @@@@ + @var{line-from-either-file} + @var{line-from-either-file}@dots{} +@end example + +If a hunk contains just one line, only its start line number appears. +Otherwise its line numbers look like @samp{@var{start},@var{count}}. +An empty hunk is considered to start at the line that follows the hunk. + +If a hunk and its context contain two or more lines, its +line numbers look like @samp{@var{start},@var{count}}. Otherwise only +its end line number appears. An empty hunk is considered to end at +the line that precedes the hunk. + +The lines common to both files begin with a space character. The lines +that actually differ between the two files have one of the following +indicator characters in the left print column: + +@table @samp +@item + +A line was added here to the first file. + +@item - +A line was removed here from the first file. +@end table + +@node Sections +@subsection Showing Which Sections Differences Are in +@cindex headings +@cindex section headings + +Sometimes you might want to know which part of the files each change +falls in. If the files are source code, this could mean which +function was changed. If the files are documents, it could mean which +chapter or appendix was changed. @acronym{GNU} @command{diff} can +show this by displaying the nearest section heading line that precedes +the differing lines. Which lines are ``section headings'' is +determined by a regular expression. + +@menu +* Specified Headings:: Showing headings that match regular expressions. +* C Function Headings:: Showing headings of C functions. +@end menu + +@node Specified Headings +@subsubsection Showing Lines That Match Regular Expressions +@cindex specified headings +@cindex regular expression matching headings + +To show in which sections differences occur for files that are not +source code for C or similar languages, use the +@option{--show-function-line=@var{regexp}} (@option{-F @var{regexp}}) option. +@command{diff} +considers lines that match the @command{grep}-style regular expression +@var{regexp} to be the beginning +of a section of the file. Here are suggested regular expressions for +some common languages: + +@c Please add to this list, e.g. Fortran, Pascal, Perl, Python. +@table @samp +@item ^[[:alpha:]$_] +C, C++, Prolog +@item ^( +Lisp +@item ^@@node +Texinfo +@end table + +This option does not automatically select an output format; in order to +use it, you must select the context format (@pxref{Context Format}) or +unified format (@pxref{Unified Format}). In other output formats it +has no effect. + +The @option{--show-function-line} (@option{-F}) option finds the nearest +unchanged line that precedes each hunk of differences and matches the +given regular expression. Then it adds that line to the end of the +line of asterisks in the context format, or to the @samp{@@@@} line in +unified format. If no matching line exists, this option leaves the output for +that hunk unchanged. If that line is more than 40 characters long, it +outputs only the first 40 characters. You can specify more than one +regular expression for such lines; @command{diff} tries to match each line +against each regular expression, starting with the last one given. This +means that you can use @option{-p} and @option{-F} together, if you wish. + +@node C Function Headings +@subsubsection Showing C Function Headings +@cindex C function headings +@cindex function headings, C + +To show in which functions differences occur for C and similar +languages, you can use the @option{--show-c-function} (@option{-p}) option. +This option automatically defaults to the context output format +(@pxref{Context Format}), with the default number of lines of context. +You can override that number with @option{-C @var{lines}} elsewhere in the +command line. You can override both the format and the number with +@option{-U @var{lines}} elsewhere in the command line. + +The @option{--show-c-function} (@option{-p}) option is equivalent to +@option{-F '^[[:alpha:]$_]'} if the unified format is specified, otherwise +@option{-c -F '^[[:alpha:]$_]'} (@pxref{Specified Headings}). @acronym{GNU} +@command{diff} provides this option for the sake of convenience. + +@node Alternate Names +@subsection Showing Alternate File Names +@cindex alternate file names +@cindex file name alternates + +If you are comparing two files that have meaningless or uninformative +names, you might want @command{diff} to show alternate names in the header +of the context and unified output formats. To do this, use the +@option{--label=@var{label}} option. The first time +you give this option, its argument replaces the name and date of the +first file in the header; the second time, its argument replaces the +name and date of the second file. If you give this option more than +twice, @command{diff} reports an error. The @option{--label} option does not +affect the file names in the @command{pr} header when the @option{-l} or +@option{--paginate} option is used (@pxref{Pagination}). + +Here are the first two lines of the output from @samp{diff -C 2 +--label=original --label=modified lao tzu}: + +@example +*** original +--- modified +@end example + +@node Side by Side +@section Showing Differences Side by Side +@cindex side by side +@cindex two-column output +@cindex columnar output + +@command{diff} can produce a side by side difference listing of two files. +The files are listed in two columns with a gutter between them. The +gutter contains one of the following markers: + +@table @asis +@item white space +The corresponding lines are in common. That is, either the lines are +identical, or the difference is ignored because of one of the +@option{--ignore} options (@pxref{White Space}). + +@item @samp{|} +The corresponding lines differ, and they are either both complete +or both incomplete. + +@item @samp{<} +The files differ and only the first file contains the line. + +@item @samp{>} +The files differ and only the second file contains the line. + +@item @samp{(} +Only the first file contains the line, but the difference is ignored. + +@item @samp{)} +Only the second file contains the line, but the difference is ignored. + +@item @samp{\} +The corresponding lines differ, and only the first line is incomplete. + +@item @samp{/} +The corresponding lines differ, and only the second line is incomplete. +@end table + +Normally, an output line is incomplete if and only if the lines that it +contains are incomplete. @xref{Incomplete Lines}. However, when an +output line represents two differing lines, one might be incomplete +while the other is not. In this case, the output line is complete, +but its the gutter is marked @samp{\} if the first line is incomplete, +@samp{/} if the second line is. + +Side by side format is sometimes easiest to read, but it has limitations. +It generates much wider output than usual, and truncates lines that are +too long to fit. Also, it relies on lining up output more heavily than +usual, so its output looks particularly bad if you use varying +width fonts, nonstandard tab stops, or nonprinting characters. + +You can use the @command{sdiff} command to interactively merge side by side +differences. @xref{Interactive Merging}, for more information on merging files. + +@menu +* Side by Side Format:: Controlling side by side output format. +* Example Side by Side:: Sample side by side output. +@end menu + +@node Side by Side Format +@subsection Controlling Side by Side Format +@cindex side by side format + +The @option{--side-by-side} (@option{-y}) option selects side by side +format. Because side by side output lines contain two input lines, the +output is wider than usual: normally 130 print columns, which can fit +onto a traditional printer line. You can set the width of the output +with the @option{--width=@var{columns}} (@option{-W @var{columns}}) +option. The output is split into two halves of equal width, separated by a +small gutter to mark differences; the right half is aligned to a tab +stop so that tabs line up. Input lines that are too long to fit in half +of an output line are truncated for output. + +The @option{--left-column} option prints only the left column of two +common lines. The @option{--suppress-common-lines} option suppresses +common lines entirely. + +@node Example Side by Side +@subsection An Example of Side by Side Format + +Here is the output of the command @samp{diff -y -W 72 lao tzu} +(@pxref{Sample diff Input}, for the complete contents of the two files). + +@example +The Way that can be told of is n < +The name that can be named is no < +The Nameless is the origin of He The Nameless is the origin of He +The Named is the mother of all t | The named is the mother of all t + > +Therefore let there always be no Therefore let there always be no + so we may see their subtlety, so we may see their subtlety, +And let there always be being, And let there always be being, + so we may see their outcome. so we may see their outcome. +The two are the same, The two are the same, +But after they are produced, But after they are produced, + they have different names. they have different names. + > They both may be called deep and + > Deeper and more profound, + > The door of all subtleties! +@end example + +@node Normal +@section Showing Differences Without Context +@cindex normal output format +@cindex @samp{<} output format + +The ``normal'' @command{diff} output format shows each hunk of differences +without any surrounding context. Sometimes such output is the clearest +way to see how lines have changed, without the clutter of nearby +unchanged lines (although you can get similar results with the context +or unified formats by using 0 lines of context). However, this format +is no longer widely used for sending out patches; for that purpose, the +context format (@pxref{Context Format}) and the unified format +(@pxref{Unified Format}) are superior. Normal format is the default for +compatibility with older versions of @command{diff} and the @acronym{POSIX} +standard. Use the @option{--normal} option to select this output +format explicitly. + +@menu +* Example Normal:: Sample output in the normal format. +* Detailed Normal:: A detailed description of normal output format. +@end menu + +@node Example Normal +@subsection An Example of Normal Format + +Here is the output of the command @samp{diff lao tzu} +(@pxref{Sample diff Input}, for the complete contents of the two files). +Notice that it shows only the lines that are different between the two +files. + +@example +1,2d0 +< The Way that can be told of is not the eternal Way; +< The name that can be named is not the eternal name. +4c2,3 +< The Named is the mother of all things. +--- +> The named is the mother of all things. +> @- +11a11,13 +> They both may be called deep and profound. +> Deeper and more profound, +> The door of all subtleties! +@end example + +@node Detailed Normal +@subsection Detailed Description of Normal Format + +The normal output format consists of one or more hunks of differences; +each hunk shows one area where the files differ. Normal format hunks +look like this: + +@example +@var{change-command} +< @var{from-file-line} +< @var{from-file-line}@dots{} +--- +> @var{to-file-line} +> @var{to-file-line}@dots{} +@end example + +There are three types of change commands. Each consists of a line +number or comma-separated range of lines in the first file, a single +character indicating the kind of change to make, and a line number or +comma-separated range of lines in the second file. All line numbers are +the original line numbers in each file. The types of change commands +are: + +@table @samp +@item @var{l}a@var{r} +Add the lines in range @var{r} of the second file after line @var{l} of +the first file. For example, @samp{8a12,15} means append lines 12--15 +of file 2 after line 8 of file 1; or, if changing file 2 into file 1, +delete lines 12--15 of file 2. + +@item @var{f}c@var{t} +Replace the lines in range @var{f} of the first file with lines in range +@var{t} of the second file. This is like a combined add and delete, but +more compact. For example, @samp{5,7c8,10} means change lines 5--7 of +file 1 to read as lines 8--10 of file 2; or, if changing file 2 into +file 1, change lines 8--10 of file 2 to read as lines 5--7 of file 1. + +@item @var{r}d@var{l} +Delete the lines in range @var{r} from the first file; line @var{l} is where +they would have appeared in the second file had they not been deleted. +For example, @samp{5,7d3} means delete lines 5--7 of file 1; or, if +changing file 2 into file 1, append lines 5--7 of file 1 after line 3 of +file 2. +@end table + +@node Scripts +@section Making Edit Scripts +@cindex script output formats + +Several output modes produce command scripts for editing @var{from-file} +to produce @var{to-file}. + +@menu +* ed Scripts:: Using @command{diff} to produce commands for @command{ed}. +* Forward ed:: Making forward @command{ed} scripts. +* RCS:: A special @command{diff} output format used by @acronym{RCS}. +@end menu + +@node ed Scripts +@subsection @command{ed} Scripts +@cindex @command{ed} script output format + +@command{diff} can produce commands that direct the @command{ed} text editor +to change the first file into the second file. Long ago, this was the +only output mode that was suitable for editing one file into another +automatically; today, with @command{patch}, it is almost obsolete. Use the +@option{--ed} (@option{-e}) option to select this output format. + +Like the normal format (@pxref{Normal}), this output format does not +show any context; unlike the normal format, it does not include the +information necessary to apply the diff in reverse (to produce the first +file if all you have is the second file and the diff). + +If the file @file{d} contains the output of @samp{diff -e old new}, then +the command @samp{(cat d && echo w) | ed - old} edits @file{old} to make +it a copy of @file{new}. More generally, if @file{d1}, @file{d2}, +@dots{}, @file{dN} contain the outputs of @samp{diff -e old new1}, +@samp{diff -e new1 new2}, @dots{}, @samp{diff -e newN-1 newN}, +respectively, then the command @samp{(cat d1 d2 @dots{} dN && echo w) | +ed - old} edits @file{old} to make it a copy of @file{newN}. + +@menu +* Example ed:: A sample @command{ed} script. +* Detailed ed:: A detailed description of @command{ed} format. +@end menu + +@node Example ed +@subsubsection Example @command{ed} Script + +Here is the output of @samp{diff -e lao tzu} (@pxref{Sample +diff Input}, for the complete contents of the two files): + +@example +11a +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +. +4c +The named is the mother of all things. + +. +1,2d +@end example + +@node Detailed ed +@subsubsection Detailed Description of @command{ed} Format + +The @command{ed} output format consists of one or more hunks of +differences. The changes closest to the ends of the files come first so +that commands that change the number of lines do not affect how +@command{ed} interprets line numbers in succeeding commands. @command{ed} +format hunks look like this: + +@example +@var{change-command} +@var{to-file-line} +@var{to-file-line}@dots{} +. +@end example + +Because @command{ed} uses a single period on a line to indicate the +end of input, @acronym{GNU} @command{diff} protects lines of changes +that contain a single period on a line by writing two periods instead, +then writing a subsequent @command{ed} command to change the two +periods into one. The @command{ed} format cannot represent an +incomplete line, so if the second file ends in a changed incomplete +line, @command{diff} reports an error and then pretends that a newline +was appended. + +There are three types of change commands. Each consists of a line +number or comma-separated range of lines in the first file and a single +character indicating the kind of change to make. All line numbers are +the original line numbers in the file. The types of change commands +are: + +@table @samp +@item @var{l}a +Add text from the second file after line @var{l} in the first file. For +example, @samp{8a} means to add the following lines after line 8 of file +1. + +@item @var{r}c +Replace the lines in range @var{r} in the first file with the following +lines. Like a combined add and delete, but more compact. For example, +@samp{5,7c} means change lines 5--7 of file 1 to read as the text file +2. + +@item @var{r}d +Delete the lines in range @var{r} from the first file. For example, +@samp{5,7d} means delete lines 5--7 of file 1. +@end table + +@node Forward ed +@subsection Forward @command{ed} Scripts +@cindex forward @command{ed} script output format + +@command{diff} can produce output that is like an @command{ed} script, but +with hunks in forward (front to back) order. The format of the commands +is also changed slightly: command characters precede the lines they +modify, spaces separate line numbers in ranges, and no attempt is made +to disambiguate hunk lines consisting of a single period. Like +@command{ed} format, forward @command{ed} format cannot represent incomplete +lines. + +Forward @command{ed} format is not very useful, because neither @command{ed} +nor @command{patch} can apply diffs in this format. It exists mainly for +compatibility with older versions of @command{diff}. Use the @option{-f} or +@option{--forward-ed} option to select it. + +@node RCS +@subsection @acronym{RCS} Scripts +@cindex @acronym{RCS} script output format + +The @acronym{RCS} output format is designed specifically for use by +the Revision Control System, which is a set of free programs used for +organizing different versions and systems of files. Use the +@option{--rcs} (@option{-n}) option to select this output format. It +is like the forward @command{ed} format (@pxref{Forward ed}), but it +can represent arbitrary changes to the contents of a file because it +avoids the forward @command{ed} format's problems with lines +consisting of a single period and with incomplete lines. Instead of +ending text sections with a line consisting of a single period, each +command specifies the number of lines it affects; a combination of the +@samp{a} and @samp{d} commands are used instead of @samp{c}. Also, if +the second file ends in a changed incomplete line, then the output +also ends in an incomplete line. + +Here is the output of @samp{diff -n lao tzu} (@pxref{Sample +diff Input}, for the complete contents of the two files): + +@example +d1 2 +d4 1 +a4 2 +The named is the mother of all things. + +a11 3 +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +@end example + +@node If-then-else +@section Merging Files with If-then-else +@cindex merged output format +@cindex if-then-else output format +@cindex C if-then-else output format +@cindex @command{ifdef} output format + +You can use @command{diff} to merge two files of C source code. The output +of @command{diff} in this format contains all the lines of both files. +Lines common to both files are output just once; the differing parts are +separated by the C preprocessor directives @code{#ifdef @var{name}} or +@code{#ifndef @var{name}}, @code{#else}, and @code{#endif}. When +compiling the output, you select which version to use by either defining +or leaving undefined the macro @var{name}. + +To merge two files, use @command{diff} with the @option{-D @var{name}} or +@option{--ifdef=@var{name}} option. The argument @var{name} is the C +preprocessor identifier to use in the @code{#ifdef} and @code{#ifndef} +directives. + +For example, if you change an instance of @code{wait (&s)} to +@code{waitpid (-1, &s, 0)} and then merge the old and new files with +the @option{--ifdef=HAVE_WAITPID} option, then the affected part of your code +might look like this: + +@example + do @{ +#ifndef HAVE_WAITPID + if ((w = wait (&s)) < 0 && errno != EINTR) +#else /* HAVE_WAITPID */ + if ((w = waitpid (-1, &s, 0)) < 0 && errno != EINTR) +#endif /* HAVE_WAITPID */ + return w; + @} while (w != child); +@end example + +You can specify formats for languages other than C by using line group +formats and line formats, as described in the next sections. + +@menu +* Line Group Formats:: Formats for general if-then-else line groups. +* Line Formats:: Formats for each line in a line group. +* Example If-then-else:: Sample if-then-else format output. +* Detailed If-then-else:: A detailed description of if-then-else format. +@end menu + +@node Line Group Formats +@subsection Line Group Formats +@cindex line group formats +@cindex formats for if-then-else line groups + +Line group formats let you specify formats suitable for many +applications that allow if-then-else input, including programming +languages and text formatting languages. A line group format specifies +the output format for a contiguous group of similar lines. + +For example, the following command compares the TeX files @file{old} +and @file{new}, and outputs a merged file in which old regions are +surrounded by @samp{\begin@{em@}}-@samp{\end@{em@}} lines, and new +regions are surrounded by @samp{\begin@{bf@}}-@samp{\end@{bf@}} lines. + +@example +diff \ + --old-group-format='\begin@{em@} +%<\end@{em@} +' \ + --new-group-format='\begin@{bf@} +%>\end@{bf@} +' \ + old new +@end example + +The following command is equivalent to the above example, but it is a +little more verbose, because it spells out the default line group formats. + +@example +diff \ + --old-group-format='\begin@{em@} +%<\end@{em@} +' \ + --new-group-format='\begin@{bf@} +%>\end@{bf@} +' \ + --unchanged-group-format='%=' \ + --changed-group-format='\begin@{em@} +%<\end@{em@} +\begin@{bf@} +%>\end@{bf@} +' \ + old new +@end example + +Here is a more advanced example, which outputs a diff listing with +headers containing line numbers in a ``plain English'' style. + +@example +diff \ + --unchanged-group-format='' \ + --old-group-format='-------- %dn line%(n=1?:s) deleted at %df: +%<' \ + --new-group-format='-------- %dN line%(N=1?:s) added after %de: +%>' \ + --changed-group-format='-------- %dn line%(n=1?:s) changed at %df: +%<-------- to: +%>' \ + old new +@end example + +To specify a line group format, use @command{diff} with one of the options +listed below. You can specify up to four line group formats, one for +each kind of line group. You should quote @var{format}, because it +typically contains shell metacharacters. + +@table @option +@item --old-group-format=@var{format} +These line groups are hunks containing only lines from the first file. +The default old group format is the same as the changed group format if +it is specified; otherwise it is a format that outputs the line group as-is. + +@item --new-group-format=@var{format} +These line groups are hunks containing only lines from the second +file. The default new group format is same as the changed group +format if it is specified; otherwise it is a format that outputs the +line group as-is. + +@item --changed-group-format=@var{format} +These line groups are hunks containing lines from both files. The +default changed group format is the concatenation of the old and new +group formats. + +@item --unchanged-group-format=@var{format} +These line groups contain lines common to both files. The default +unchanged group format is a format that outputs the line group as-is. +@end table + +In a line group format, ordinary characters represent themselves; +conversion specifications start with @samp{%} and have one of the +following forms. + +@table @samp +@item %< +stands for the lines from the first file, including the trailing newline. +Each line is formatted according to the old line format (@pxref{Line Formats}). + +@item %> +stands for the lines from the second file, including the trailing newline. +Each line is formatted according to the new line format. + +@item %= +stands for the lines common to both files, including the trailing newline. +Each line is formatted according to the unchanged line format. + +@item %% +stands for @samp{%}. + +@item %c'@var{C}' +where @var{C} is a single character, stands for @var{C}. +@var{C} may not be a backslash or an apostrophe. +For example, @samp{%c':'} stands for a colon, even inside +the then-part of an if-then-else format, which a colon would +normally terminate. + +@item %c'\@var{O}' +where @var{O} is a string of 1, 2, or 3 octal digits, +stands for the character with octal code @var{O}. +For example, @samp{%c'\0'} stands for a null character. + +@item @var{F}@var{n} +where @var{F} is a @code{printf} conversion specification and @var{n} is one +of the following letters, stands for @var{n}'s value formatted with @var{F}. + +@table @samp +@item e +The line number of the line just before the group in the old file. + +@item f +The line number of the first line in the group in the old file; +equals @var{e} + 1. + +@item l +The line number of the last line in the group in the old file. + +@item m +The line number of the line just after the group in the old file; +equals @var{l} + 1. + +@item n +The number of lines in the group in the old file; equals @var{l} - @var{f} + 1. + +@item E, F, L, M, N +Likewise, for lines in the new file. + +@end table + +@vindex LC_NUMERIC +The @code{printf} conversion specification can be @samp{%d}, +@samp{%o}, @samp{%x}, or @samp{%X}, specifying decimal, octal, +lower case hexadecimal, or upper case hexadecimal output +respectively. After the @samp{%} the following options can appear in +sequence: a series of zero or more flags; an integer +specifying the minimum field width; and a period followed by an +optional integer specifying the minimum number of digits. +The flags are @samp{-} for left-justification, @samp{'} for separating +the digit into groups as specified by the @env{LC_NUMERIC} locale category, +and @samp{0} for padding with zeros instead of spaces. +For example, @samp{%5dN} prints the number of new lines in the group +in a field of width 5 characters, using the @code{printf} format @code{"%5d"}. + +@item (@var{A}=@var{B}?@var{T}:@var{E}) +If @var{A} equals @var{B} then @var{T} else @var{E}. +@var{A} and @var{B} are each either a decimal constant +or a single letter interpreted as above. +This format spec is equivalent to @var{T} if +@var{A}'s value equals @var{B}'s; otherwise it is equivalent to @var{E}. + +For example, @samp{%(N=0?no:%dN) line%(N=1?:s)} is equivalent to +@samp{no lines} if @var{N} (the number of lines in the group in the +new file) is 0, to @samp{1 line} if @var{N} is 1, and to @samp{%dN lines} +otherwise. +@end table + +@node Line Formats +@subsection Line Formats +@cindex line formats + +Line formats control how each line taken from an input file is +output as part of a line group in if-then-else format. + +For example, the following command outputs text with a one-character +change indicator to the left of the text. The first character of output +is @samp{-} for deleted lines, @samp{|} for added lines, and a space for +unchanged lines. The formats contain newline characters where newlines +are desired on output. + +@example +diff \ + --old-line-format='-%l +' \ + --new-line-format='|%l +' \ + --unchanged-line-format=' %l +' \ + old new +@end example + +To specify a line format, use one of the following options. You should +quote @var{format}, since it often contains shell metacharacters. + +@table @option +@item --old-line-format=@var{format} +formats lines just from the first file. + +@item --new-line-format=@var{format} +formats lines just from the second file. + +@item --unchanged-line-format=@var{format} +formats lines common to both files. + +@item --line-format=@var{format} +formats all lines; in effect, it sets all three above options simultaneously. +@end table + +In a line format, ordinary characters represent themselves; +conversion specifications start with @samp{%} and have one of the +following forms. + +@table @samp +@item %l +stands for the contents of the line, not counting its trailing +newline (if any). This format ignores whether the line is incomplete; +@xref{Incomplete Lines}. + +@item %L +stands for the contents of the line, including its trailing newline +(if any). If a line is incomplete, this format preserves its +incompleteness. + +@item %% +stands for @samp{%}. + +@item %c'@var{C}' +where @var{C} is a single character, stands for @var{C}. +@var{C} may not be a backslash or an apostrophe. +For example, @samp{%c':'} stands for a colon. + +@item %c'\@var{O}' +where @var{O} is a string of 1, 2, or 3 octal digits, +stands for the character with octal code @var{O}. +For example, @samp{%c'\0'} stands for a null character. + +@item @var{F}n +where @var{F} is a @code{printf} conversion specification, +stands for the line number formatted with @var{F}. +For example, @samp{%.5dn} prints the line number using the +@code{printf} format @code{"%.5d"}. @xref{Line Group Formats}, for +more about printf conversion specifications. + +@end table + +The default line format is @samp{%l} followed by a newline character. + +If the input contains tab characters and it is important that they line +up on output, you should ensure that @samp{%l} or @samp{%L} in a line +format is just after a tab stop (e.g.@: by preceding @samp{%l} or +@samp{%L} with a tab character), or you should use the @option{-t} or +@option{--expand-tabs} option. + +Taken together, the line and line group formats let you specify many +different formats. For example, the following command uses a format +similar to normal @command{diff} format. You can tailor this command +to get fine control over @command{diff} output. + +@example +diff \ + --old-line-format='< %l +' \ + --new-line-format='> %l +' \ + --old-group-format='%df%(f=l?:,%dl)d%dE +%<' \ + --new-group-format='%dea%dF%(F=L?:,%dL) +%>' \ + --changed-group-format='%df%(f=l?:,%dl)c%dF%(F=L?:,%dL) +%<--- +%>' \ + --unchanged-group-format='' \ + old new +@end example + +@node Example If-then-else +@subsection An Example of If-then-else Format + +Here is the output of @samp{diff -DTWO lao tzu} (@pxref{Sample +diff Input}, for the complete contents of the two files): + +@example +#ifndef TWO +The Way that can be told of is not the eternal Way; +The name that can be named is not the eternal name. +#endif /* ! TWO */ +The Nameless is the origin of Heaven and Earth; +#ifndef TWO +The Named is the mother of all things. +#else /* TWO */ +The named is the mother of all things. + +#endif /* TWO */ +Therefore let there always be non-being, + so we may see their subtlety, +And let there always be being, + so we may see their outcome. +The two are the same, +But after they are produced, + they have different names. +#ifdef TWO +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +#endif /* TWO */ +@end example + +@node Detailed If-then-else +@subsection Detailed Description of If-then-else Format + +For lines common to both files, @command{diff} uses the unchanged line +group format. For each hunk of differences in the merged output +format, if the hunk contains only lines from the first file, +@command{diff} uses the old line group format; if the hunk contains only +lines from the second file, @command{diff} uses the new group format; +otherwise, @command{diff} uses the changed group format. + +The old, new, and unchanged line formats specify the output format of +lines from the first file, lines from the second file, and lines common +to both files, respectively. + +The option @option{--ifdef=@var{name}} is equivalent to +the following sequence of options using shell syntax: + +@example +--old-group-format='#ifndef @var{name} +%<#endif /* ! @var{name} */ +' \ +--new-group-format='#ifdef @var{name} +%>#endif /* @var{name} */ +' \ +--unchanged-group-format='%=' \ +--changed-group-format='#ifndef @var{name} +%<#else /* @var{name} */ +%>#endif /* @var{name} */ +' +@end example + +You should carefully check the @command{diff} output for proper nesting. +For example, when using the @option{-D @var{name}} or +@option{--ifdef=@var{name}} option, you should check that if the +differing lines contain any of the C preprocessor directives +@samp{#ifdef}, @samp{#ifndef}, @samp{#else}, @samp{#elif}, or +@samp{#endif}, they are nested properly and match. If they don't, you +must make corrections manually. It is a good idea to carefully check +the resulting code anyway to make sure that it really does what you +want it to; depending on how the input files were produced, the output +might contain duplicate or otherwise incorrect code. + +The @command{patch} @option{-D @var{name}} option behaves like +the @command{diff} @option{-D @var{name}} option, except it operates on +a file and a diff to produce a merged file. @xref{patch Options}. + +@node Incomplete Lines +@chapter Incomplete Lines +@cindex incomplete lines +@cindex full lines +@cindex newline treatment by @command{diff} + +When an input file ends in a non-newline character, its last line is +called an @dfn{incomplete line} because its last character is not a +newline. All other lines are called @dfn{full lines} and end in a +newline character. Incomplete lines do not match full lines unless +differences in white space are ignored (@pxref{White Space}). + +An incomplete line is normally distinguished on output from a full +line by a following line that starts with @samp{\}. However, the +@acronym{RCS} format (@pxref{RCS}) outputs the incomplete line as-is, +without any trailing newline or following line. The side by side +format normally represents incomplete lines as-is, but in some cases +uses a @samp{\} or @samp{/} gutter marker. @xref{Side by Side}. The +if-then-else line format preserves a line's incompleteness with +@samp{%L}, and discards the newline with @samp{%l}. @xref{Line Formats}. +Finally, with the @command{ed} and forward @command{ed} +output formats (@pxref{Output Formats}) @command{diff} cannot +represent an incomplete line, so it pretends there was a newline and +reports an error. + +For example, suppose @file{F} and @file{G} are one-byte files that +contain just @samp{f} and @samp{g}, respectively. Then @samp{diff F G} +outputs + +@example +1c1 +< f +\ No newline at end of file +--- +> g +\ No newline at end of file +@end example + +@noindent +(The exact message may differ in non-English locales.) +@samp{diff -n F G} outputs the following without a trailing newline: + +@example +d1 1 +a1 1 +g +@end example + +@noindent +@samp{diff -e F G} reports two errors and outputs the following: + +@example +1c +g +. +@end example + +@node Comparing Directories +@chapter Comparing Directories + +@vindex LC_COLLATE +You can use @command{diff} to compare some or all of the files in two +directory trees. When both file name arguments to @command{diff} are +directories, it compares each file that is contained in both +directories, examining file names in alphabetical order as specified by +the @env{LC_COLLATE} locale category. Normally +@command{diff} is silent about pairs of files that contain no differences, +but if you use the @option{--report-identical-files} (@option{-s}) option, +it reports pairs of identical files. Normally @command{diff} reports +subdirectories common to both directories without comparing +subdirectories' files, but if you use the @option{-r} or +@option{--recursive} option, it compares every corresponding pair of files +in the directory trees, as many levels deep as they go. + +If only one file exists, @command{diff} normally does not show its +contents; it merely reports that one file exists but the other does +not. You can make @command{diff} act as though the missing file is +empty, so that it outputs the entire contents of the file that +actually exists. (It is output as either an insertion or a +deletion, depending on whether the missing file is in the first or the +second position.) To do this, use the @option{--new-file} +(@option{-N}) option. This option affects command-line arguments as +well as files found via directory traversal; for example, @samp{diff +-N a b} treats @file{a} as empty if @file{a} does not exist but +@file{b} does, and similarly @samp{diff -N - b} treats standard input +as empty if it is closed but @file{b} exists. + +If the older directory contains large files that are not in +the newer directory, you can make the patch smaller by using the +@option{--unidirectional-new-file} option instead of @option{-N}. +This option is like @option{-N} except that it inserts the contents only +of files that appear in the second directory but not the first (that is, +files that were added). At the top of the patch, write instructions for +the user applying the patch to remove the files that were deleted before +applying the patch. @xref{Making Patches}, for more discussion of +making patches for distribution. + +To ignore some files while comparing directories, use the +@option{--exclude=@var{pattern}} (@option{-x @var{pattern}}) option. +This option +ignores any files or subdirectories whose base names match the shell +pattern @var{pattern}. Unlike in the shell, a period at the start of +the base of a file name matches a wildcard at the start of a pattern. +You should enclose @var{pattern} in quotes so that the shell does not +expand it. For example, the option @option{-x '*.[ao]'} ignores any file +whose name ends with @samp{.a} or @samp{.o}. + +This option accumulates if you specify it more than once. For example, +using the options @option{-x 'RCS' -x '*,v'} ignores any file or +subdirectory whose base name is @samp{RCS} or ends with @samp{,v}. + +If you need to give this option many times, you can instead put the +patterns in a file, one pattern per line, and use the +@option{--exclude-from=@var{file}} (@option{-X @var{file}}) option. +Trailing white space and empty lines are ignored in the pattern file. + +If you have been comparing two directories and stopped partway through, +later you might want to continue where you left off. You can do this by +using the @option{--starting-file=@var{file}} (@option{-S @var{file}}) +option. This compares only the file @var{file} and all alphabetically +later files in the topmost directory level. + +If two directories differ only in that file names are lower case in +one directory and upper case in the upper, @command{diff} normally +reports many differences because it compares file names in a +case sensitive way. With the @option{--ignore-file-name-case} option, +@command{diff} ignores case differences in file names, so that for example +the contents of the file @file{Tao} in one directory are compared to +the contents of the file @file{TAO} in the other. The +@option{--no-ignore-file-name-case} option cancels the effect of the +@option{--ignore-file-name-case} option, reverting to the default +behavior. + +If an @option{--exclude=@var{pattern}} (@option{-x @var{pattern}}) option, +or an @option{--exclude-from=@var{file}} (@option{-X @var{file}}) option, +is specified while the @option{--ignore-file-name-case} option is in +effect, case is ignored when excluding file names matching the +specified patterns. + +To tell @command{diff} not to follow a symbolic link, use the +@c later: @option{--no-dereference} (@option{-P}). +@option{--no-dereference} option. + +@node Adjusting Output +@chapter Making @command{diff} Output Prettier + +@command{diff} provides several ways to adjust the appearance of its output. +These adjustments can be applied to any output format. + +@menu +* Tabs:: Preserving the alignment of tab stops. +* Trailing Blanks:: Suppressing blanks before empty output lines. +* Pagination:: Page numbering and time-stamping @command{diff} output. +@end menu + +@node Tabs +@section Preserving Tab Stop Alignment +@cindex tab stop alignment +@cindex aligning tab stops + +The lines of text in some of the @command{diff} output formats are +preceded by one or two characters that indicate whether the text is +inserted, deleted, or changed. The addition of those characters can +cause tabs to move to the next tab stop, throwing off the alignment of +columns in the line. @acronym{GNU} @command{diff} provides two ways +to make tab-aligned columns line up correctly. + +The first way is to have @command{diff} convert all tabs into the correct +number of spaces before outputting them; select this method with the +@option{--expand-tabs} (@option{-t}) option. To use this form of output with +@command{patch}, you must give @command{patch} the @option{-l} or +@option{--ignore-white-space} option (@pxref{Changed White Space}, for more +information). @command{diff} normally assumes that tab stops are set +every 8 print columns, but this can be altered by the +@option{--tabsize=@var{columns}} option. + +The other method for making tabs line up correctly is to add a tab +character instead of a space after the indicator character at the +beginning of the line. This ensures that all following tab characters +are in the same position relative to tab stops that they were in the +original files, so that the output is aligned correctly. Its +disadvantage is that it can make long lines too long to fit on one line +of the screen or the paper. It also does not work with the unified +output format, which does not have a space character after the change +type indicator character. Select this method with the @option{-T} or +@option{--initial-tab} option. + +@node Trailing Blanks +@section Omitting trailing blanks +@cindex trailing blanks +When outputting lines in normal or context format, or outputting an +unchanged line in unified format, @command{diff} normally outputs a +blank just before each line. If the line is empty, the output of +@command{diff} therefore contains trailing blanks even though the +input does not contain them. For example, when outputting an +unchanged empty line in context format, @command{diff} normally +outputs a line with two leading spaces. + +Some text editors and email agents routinely delete trailing blanks, +so it can be a problem to deal with diff output files that contain +them. You can avoid this problem with the +@option{--suppress-blank-empty} option. It causes @command{diff} to +omit trailing blanks at the end of output lines in normal, context, +and unified format, unless the trailing blanks were already present in +the input. This changes the output format slightly, so that output +lines are guaranteed to never end in a blank unless an input line ends +in a blank. This format is less likely to be munged by text editors +or by transmission via email. It is accepted by @acronym{GNU} +@command{patch} as well. + +@node Pagination +@section Paginating @command{diff} Output +@cindex paginating @command{diff} output + +It can be convenient to have long output page-numbered and time-stamped. +The @option{--paginate} (@option{-l}) option does this by sending the +@command{diff} output through the @command{pr} program. Here is what the page +header might look like for @samp{diff -lc lao tzu}: + +@example +2002-02-22 14:20 diff -lc lao tzu Page 1 +@end example + +@node diff Performance +@chapter @command{diff} Performance Tradeoffs +@cindex performance of @command{diff} + +@acronym{GNU} @command{diff} runs quite efficiently; however, in some +circumstances you can cause it to run faster or produce a more compact +set of changes. + +One way to improve @command{diff} performance is to use hard or +symbolic links to files instead of copies. This improves performance +because @command{diff} normally does not need to read two hard or +symbolic links to the same file, since their contents must be +identical. For example, suppose you copy a large directory hierarchy, +make a few changes to the copy, and then often use @samp{diff -r} to +compare the original to the copy. If the original files are +read-only, you can greatly improve performance by creating the copy +using hard or symbolic links (e.g., with @acronym{GNU} @samp{cp -lR} or +@samp{cp -sR}). Before editing a file in the copy for the first time, +you should break the link and replace it with a regular copy. + +You can also affect the performance of @acronym{GNU} @command{diff} by +giving it options that change the way it compares files. +Performance has more than one dimension. These options improve one +aspect of performance at the cost of another, or they improve +performance in some cases while hurting it in others. + +The way that @acronym{GNU} @command{diff} determines which lines have +changed always comes up with a near-minimal set of differences. +Usually it is good enough for practical purposes. If the +@command{diff} output is large, you might want @command{diff} to use a +modified algorithm that sometimes produces a smaller set of +differences. The @option{--minimal} (@option{-d}) option does this; +however, it can also cause @command{diff} to run more slowly than +usual, so it is not the default behavior. + +When the files you are comparing are large and have small groups of +changes scattered throughout them, you can use the +@option{--speed-large-files} option to make a different modification to +the algorithm that @command{diff} uses. If the input files have a constant +small density of changes, this option speeds up the comparisons without +changing the output. If not, @command{diff} might produce a larger set of +differences; however, the output will still be correct. + +Normally @command{diff} discards the prefix and suffix that is common to +both files before it attempts to find a minimal set of differences. +This makes @command{diff} run faster, but occasionally it may produce +non-minimal output. The @option{--horizon-lines=@var{lines}} option +prevents @command{diff} from discarding the last @var{lines} lines of the +prefix and the first @var{lines} lines of the suffix. This gives +@command{diff} further opportunities to find a minimal output. + +Suppose a run of changed lines includes a sequence of lines at one end +and there is an identical sequence of lines just outside the other end. +The @command{diff} command is free to choose which identical sequence is +included in the hunk. In this case, @command{diff} normally shifts the +hunk's boundaries when this merges adjacent hunks, or shifts a hunk's +lines towards the end of the file. Merging hunks can make the output +look nicer in some cases. + +@node Comparing Three Files +@chapter Comparing Three Files +@cindex comparing three files +@cindex format of @command{diff3} output + +Use the program @command{diff3} to compare three files and show any +differences among them. (@command{diff3} can also merge files; see +@ref{diff3 Merging}). + +The ``normal'' @command{diff3} output format shows each hunk of +differences without surrounding context. Hunks are labeled depending +on whether they are two-way or three-way, and lines are annotated by +their location in the input files. + +@xref{Invoking diff3}, for more information on how to run @command{diff3}. + +@menu +* Sample diff3 Input:: Sample @command{diff3} input for examples. +* Example diff3 Normal:: Sample output in the normal format. +* Detailed diff3 Normal:: A detailed description of normal output format. +* diff3 Hunks:: The format of normal output format. +@end menu + +@node Sample diff3 Input +@section A Third Sample Input File +@cindex @command{diff3} sample input +@cindex sample input for @command{diff3} + +Here is a third sample file that will be used in examples to illustrate +the output of @command{diff3} and how various options can change it. The +first two files are the same that we used for @command{diff} (@pxref{Sample +diff Input}). This is the third sample file, called @file{tao}: + +@example +The Way that can be told of is not the eternal Way; +The name that can be named is not the eternal name. +The Nameless is the origin of Heaven and Earth; +The named is the mother of all things. + +Therefore let there always be non-being, + so we may see their subtlety, +And let there always be being, + so we may see their result. +The two are the same, +But after they are produced, + they have different names. + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +@end example + +@node Example diff3 Normal +@section An Example of @command{diff3} Normal Format + +Here is the output of the command @samp{diff3 lao tzu tao} +(@pxref{Sample diff3 Input}, for the complete contents of the files). +Notice that it shows only the lines that are different among the three +files. + +@example +====2 +1:1,2c +3:1,2c + The Way that can be told of is not the eternal Way; + The name that can be named is not the eternal name. +2:0a +====1 +1:4c + The Named is the mother of all things. +2:2,3c +3:4,5c + The named is the mother of all things. + @- +====3 +1:8c +2:7c + so we may see their outcome. +3:9c + so we may see their result. +==== +1:11a +2:11,13c + They both may be called deep and profound. + Deeper and more profound, + The door of all subtleties! +3:13,14c + @- + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +@end example + +@node Detailed diff3 Normal +@section Detailed Description of @command{diff3} Normal Format + +Each hunk begins with a line marked @samp{====}. Three-way hunks have +plain @samp{====} lines, and two-way hunks have @samp{1}, @samp{2}, or +@samp{3} appended to specify which of the three input files differ in +that hunk. The hunks contain copies of two or three sets of input +lines each preceded by one or two commands identifying where the lines +came from. + +Normally, two spaces precede each copy of an input line to distinguish +it from the commands. But with the @option{--initial-tab} (@option{-T}) +option, @command{diff3} uses a tab instead of two spaces; this lines up +tabs correctly. @xref{Tabs}, for more information. + +Commands take the following forms: + +@table @samp +@item @var{file}:@var{l}a +This hunk appears after line @var{l} of file @var{file}, and +contains no lines in that file. To edit this file to yield the other +files, one must append hunk lines taken from the other files. For +example, @samp{1:11a} means that the hunk follows line 11 in the first +file and contains no lines from that file. + +@item @var{file}:@var{r}c +This hunk contains the lines in the range @var{r} of file @var{file}. +The range @var{r} is a comma-separated pair of line numbers, or just one +number if there is only one line. To edit this file to yield the +other files, one must change the specified lines to be the lines taken +from the other files. For example, @samp{2:11,13c} means that the hunk +contains lines 11 through 13 from the second file. +@end table + +If the last line in a set of input lines is incomplete +(@pxref{Incomplete Lines}), it is distinguished on output from a full +line by a following line that starts with @samp{\}. + +@node diff3 Hunks +@section @command{diff3} Hunks +@cindex hunks for @command{diff3} +@cindex @command{diff3} hunks + +Groups of lines that differ in two or three of the input files are +called @dfn{diff3 hunks}, by analogy with @command{diff} hunks +(@pxref{Hunks}). If all three input files differ in a @command{diff3} +hunk, the hunk is called a @dfn{three-way hunk}; if just two input files +differ, it is a @dfn{two-way hunk}. + +As with @command{diff}, several solutions are possible. When comparing the +files @samp{A}, @samp{B}, and @samp{C}, @command{diff3} normally finds +@command{diff3} hunks by merging the two-way hunks output by the two +commands @samp{diff A B} and @samp{diff A C}. This does not necessarily +minimize the size of the output, but exceptions should be rare. + +For example, suppose @file{F} contains the three lines @samp{a}, +@samp{b}, @samp{f}, @file{G} contains the lines @samp{g}, @samp{b}, +@samp{g}, and @file{H} contains the lines @samp{a}, @samp{b}, +@samp{h}. @samp{diff3 F G H} might output the following: + +@example +====2 +1:1c +3:1c + a +2:1c + g +==== +1:3c + f +2:3c + g +3:3c + h +@end example + +@noindent +because it found a two-way hunk containing @samp{a} in the first and +third files and @samp{g} in the second file, then the single line +@samp{b} common to all three files, then a three-way hunk containing +the last line of each file. + +@node diff3 Merging +@chapter Merging From a Common Ancestor +@cindex merging from a common ancestor + +When two people have made changes to copies of the same file, +@command{diff3} can produce a merged output that contains both sets of +changes together with warnings about conflicts. + +One might imagine programs with names like @command{diff4} and @command{diff5} +to compare more than three files simultaneously, but in practice the +need rarely arises. You can use @command{diff3} to merge three or more +sets of changes to a file by merging two change sets at a time. + +@command{diff3} can incorporate changes from two modified versions into a +common preceding version. This lets you merge the sets of changes +represented by the two newer files. Specify the common ancestor version +as the second argument and the two newer versions as the first and third +arguments, like this: + +@example +diff3 @var{mine} @var{older} @var{yours} +@end example + +@noindent +You can remember the order of the arguments by noting that they are in +alphabetical order. + +@cindex conflict +@cindex overlap +You can think of this as subtracting @var{older} from @var{yours} and +adding the result to @var{mine}, or as merging into @var{mine} the +changes that would turn @var{older} into @var{yours}. This merging is +well-defined as long as @var{mine} and @var{older} match in the +neighborhood of each such change. This fails to be true when all three +input files differ or when only @var{older} differs; we call this +a @dfn{conflict}. When all three input files differ, we call the +conflict an @dfn{overlap}. + +@command{diff3} gives you several ways to handle overlaps and conflicts. +You can omit overlaps or conflicts, or select only overlaps, +or mark conflicts with special @samp{<<<<<<<} and @samp{>>>>>>>} lines. + +@command{diff3} can output the merge results as an @command{ed} script that +that can be applied to the first file to yield the merged output. +However, it is usually better to have @command{diff3} generate the merged +output directly; this bypasses some problems with @command{ed}. + +@menu +* Which Changes:: Selecting changes to incorporate. +* Marking Conflicts:: Marking conflicts. +* Bypassing ed:: Generating merged output directly. +* Merging Incomplete Lines:: How @command{diff3} merges incomplete lines. +* Saving the Changed File:: Emulating System V behavior. +@end menu + +@node Which Changes +@section Selecting Which Changes to Incorporate +@cindex overlapping change, selection of +@cindex unmerged change + +You can select all unmerged changes from @var{older} to @var{yours} for merging +into @var{mine} with the @option{--ed} (@option{-e}) option. You can +select only the nonoverlapping unmerged changes with +@option{--easy-only} (@option{-3}), +and you can select only the overlapping changes with +@option{--overlap-only} (@option{-x}). + +The @option{-e}, @option{-3} and @option{-x} options select only +@dfn{unmerged changes}, i.e.@: changes where @var{mine} and @var{yours} +differ; they ignore changes from @var{older} to @var{yours} where +@var{mine} and @var{yours} are identical, because they assume that such +changes have already been merged. If this assumption is not a safe +one, you can use the @option{--show-all} (@option{-A}) option +(@pxref{Marking Conflicts}). + +Here is the output of the command @command{diff3} with each of these three +options (@pxref{Sample diff3 Input}, for the complete contents of the files). +Notice that @option{-e} outputs the union of the disjoint sets of changes +output by @option{-3} and @option{-x}. + +Output of @samp{diff3 -e lao tzu tao}: +@example +11a + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +. +8c + so we may see their result. +. +@end example + +Output of @samp{diff3 -3 lao tzu tao}: +@example +8c + so we may see their result. +. +@end example + +Output of @samp{diff3 -x lao tzu tao}: +@example +11a + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +. +@end example + +@node Marking Conflicts +@section Marking Conflicts +@cindex conflict marking +@cindex @samp{<<<<<<<} for marking conflicts + +@command{diff3} can mark conflicts in the merged output by +bracketing them with special marker lines. A conflict +that comes from two files @var{A} and @var{B} is marked as follows: + +@example +<<<<<<< @var{A} +@r{lines from @var{A}} +======= +@r{lines from @var{B}} +>>>>>>> @var{B} +@end example + +A conflict that comes from three files @var{A}, @var{B} and @var{C} is +marked as follows: + +@example +<<<<<<< @var{A} +@r{lines from @var{A}} +||||||| @var{B} +@r{lines from @var{B}} +======= +@r{lines from @var{C}} +>>>>>>> @var{C} +@end example + +The @option{--show-all} (@option{-A}) option acts like the @option{-e} +option, except that it brackets conflicts, and it outputs all changes +from @var{older} to @var{yours}, not just the unmerged changes. Thus, +given the sample input files (@pxref{Sample diff3 Input}), @samp{diff3 +-A lao tzu tao} puts brackets around the conflict where only @file{tzu} +differs: + +@example +<<<<<<< tzu +======= +The Way that can be told of is not the eternal Way; +The name that can be named is not the eternal name. +>>>>>>> tao +@end example + +And it outputs the three-way conflict as follows: + +@example +<<<<<<< lao +||||||| tzu +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +======= + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +>>>>>>> tao +@end example + +The @option{--show-overlap} (@option{-E}) option outputs less information +than the @option{--show-all} (@option{-A}) option, because it outputs only +unmerged changes, and it never outputs the contents of the second +file. Thus the @option{-E} option acts like the @option{-e} option, +except that it brackets the first and third files from three-way +overlapping changes. Similarly, @option{-X} acts like @option{-x}, except +it brackets all its (necessarily overlapping) changes. For example, +for the three-way overlapping change above, the @option{-E} and @option{-X} +options output the following: + +@example +<<<<<<< lao +======= + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +>>>>>>> tao +@end example + +If you are comparing files that have meaningless or uninformative names, +you can use the @option{--label=@var{label}} +option to show alternate names in the @samp{<<<<<<<}, @samp{|||||||} +and @samp{>>>>>>>} brackets. This option can be given up to three +times, once for each input file. Thus @samp{diff3 -A --label X +--label Y --label Z A +B C} acts like @samp{diff3 -A A B C}, except that the output looks like +it came from files named @samp{X}, @samp{Y} and @samp{Z} rather than +from files named @samp{A}, @samp{B} and @samp{C}. + +@node Bypassing ed +@section Generating the Merged Output Directly +@cindex merged @command{diff3} format + +With the @option{--merge} (@option{-m}) option, @command{diff3} outputs the +merged file directly. This is more efficient than using @command{ed} to +generate it, and works even with non-text files that @command{ed} would +reject. If you specify @option{-m} without an @command{ed} script option, +@option{-A} is assumed. + +For example, the command @samp{diff3 -m lao tzu tao} +(@pxref{Sample diff3 Input} for a copy of the input files) would output +the following: + +@example +<<<<<<< tzu +======= +The Way that can be told of is not the eternal Way; +The name that can be named is not the eternal name. +>>>>>>> tao +The Nameless is the origin of Heaven and Earth; +The Named is the mother of all things. +Therefore let there always be non-being, + so we may see their subtlety, +And let there always be being, + so we may see their result. +The two are the same, +But after they are produced, + they have different names. +<<<<<<< lao +||||||| tzu +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties! +======= + + -- The Way of Lao-Tzu, tr. Wing-tsit Chan +>>>>>>> tao +@end example + +@node Merging Incomplete Lines +@section How @command{diff3} Merges Incomplete Lines +@cindex incomplete line merging + +With @option{-m}, incomplete lines (@pxref{Incomplete Lines}) are simply +copied to the output as they are found; if the merged output ends in an +conflict and one of the input files ends in an incomplete +line, succeeding @samp{|||||||}, @samp{=======} or @samp{>>>>>>>} +brackets appear somewhere other than the start of a line because +they are appended to the incomplete line. + +Without @option{-m}, if an @command{ed} script option is specified and an +incomplete line is found, @command{diff3} generates a warning and acts as +if a newline had been present. + +@node Saving the Changed File +@section Saving the Changed File +@cindex System V @command{diff3} compatibility + +Traditional Unix @command{diff3} generates an @command{ed} script without the +trailing @samp{w} and @samp{q} commands that save the changes. +System V @command{diff3} generates these extra commands. @acronym{GNU} +@command{diff3} normally behaves like traditional Unix +@command{diff3}, but with the @option{-i} option it behaves like +System V @command{diff3} and appends the @samp{w} and @samp{q} +commands. + +The @option{-i} option requires one of the @command{ed} script options +@option{-AeExX3}, and is incompatible with the merged output option +@option{-m}. + +@node Interactive Merging +@chapter Interactive Merging with @command{sdiff} +@cindex diff merging +@cindex interactive merging + +With @command{sdiff}, you can merge two files interactively based on a +side-by-side @option{-y} format comparison (@pxref{Side by Side}). Use +@option{--output=@var{file}} (@option{-o @var{file}}) to specify where to +put the merged text. @xref{Invoking sdiff}, for more details on the +options to @command{sdiff}. + +Another way to merge files interactively is to use the Emacs Lisp +package @command{emerge}. @xref{Emerge, , Emerge, emacs, The +@acronym{GNU} Emacs Manual}, for more information. + +@menu +* sdiff Option Summary:: Summary of @command{sdiff} options. +* Merge Commands:: Merging two files interactively. +@end menu + +@node sdiff Option Summary +@section Specifying @command{diff} Options to @command{sdiff} +@cindex @command{sdiff} output format + +The following @command{sdiff} options have the same meaning as for +@command{diff}. @xref{diff Options}, for the use of these options. + +@example +-a -b -d -i -t -v +-B -E -I @var{regexp} -Z + +--expand-tabs +--ignore-blank-lines --ignore-case +--ignore-matching-lines=@var{regexp} --ignore-space-change +--ignore-tab-expansion --ignore-trailing-space +--left-column --minimal --speed-large-files +--strip-trailing-cr --suppress-common-lines +--tabsize=@var{columns} --text --version --width=@var{columns} +@end example + +For historical reasons, @command{sdiff} has alternate names for some +options. The @option{-l} option is equivalent to the +@option{--left-column} option, and similarly @option{-s} is equivalent +to @option{--suppress-common-lines}. The meaning of the @command{sdiff} +@option{-w} and @option{-W} options is interchanged from that of +@command{diff}: with @command{sdiff}, @option{-w @var{columns}} is +equivalent to @option{--width=@var{columns}}, and @option{-W} is +equivalent to @option{--ignore-all-space}. @command{sdiff} without the +@option{-o} option is equivalent to @command{diff} with the +@option{--side-by-side} (@option{-y}) option (@pxref{Side by Side}). + +@node Merge Commands +@section Merge Commands +@cindex merge commands +@cindex merging interactively + +Groups of common lines, with a blank gutter, are copied from the first +file to the output. After each group of differing lines, @command{sdiff} +prompts with @samp{%} and pauses, waiting for one of the following +commands. Follow each command with @key{RET}. + +@table @samp +@item e +Discard both versions. +Invoke a text editor on an empty temporary file, +then copy the resulting file to the output. + +@item eb +Concatenate the two versions, edit the result in a temporary file, +then copy the edited result to the output. + +@item ed +Like @samp{eb}, except precede each version with a header that +shows what file and lines the version came from. + +@item el +@itemx e1 +Edit a copy of the left version, then copy the result to the output. + +@item er +@itemx e2 +Edit a copy of the right version, then copy the result to the output. + +@item l +@itemx 1 +Copy the left version to the output. + +@item q +Quit. + +@item r +@itemx 2 +Copy the right version to the output. + +@item s +Silently copy common lines. + +@item v +Verbosely copy common lines. This is the default. +@end table + +@vindex EDITOR +The text editor invoked is specified by the @env{EDITOR} environment +variable if it is set. The default is system-dependent. + +@node Merging with patch +@chapter Merging with @command{patch} + +@command{patch} takes comparison output produced by @command{diff} and applies +the differences to a copy of the original file, producing a patched +version. With @command{patch}, you can distribute just the changes to a +set of files instead of distributing the entire file set; your +correspondents can apply @command{patch} to update their copy of the files +with your changes. @command{patch} automatically determines the diff +format, skips any leading or trailing headers, and uses the headers to +determine which file to patch. This lets your correspondents feed a +mail message containing a difference listing directly to +@command{patch}. + +@command{patch} detects and warns about common problems like forward +patches. It saves any patches that it could not apply. It can also maintain a +@code{patchlevel.h} file to ensure that your correspondents apply +diffs in the proper order. + +@command{patch} accepts a series of diffs in its standard input, usually +separated by headers that specify which file to patch. It applies +@command{diff} hunks (@pxref{Hunks}) one by one. If a hunk does not +exactly match the original file, @command{patch} uses heuristics to try to +patch the file as well as it can. If no approximate match can be found, +@command{patch} rejects the hunk and skips to the next hunk. @command{patch} +normally replaces each file @var{f} with its new version, putting reject +hunks (if any) into @samp{@var{f}.rej}. + +@xref{Invoking patch}, for detailed information on the options to +@command{patch}. + +@menu +* patch Input:: Selecting the type of @command{patch} input. +* Revision Control:: Getting files from @acronym{RCS}, @acronym{SCCS}, etc. +* Imperfect:: Dealing with imperfect patches. +* Creating and Removing:: Creating and removing files with a patch. +* Patching Time Stamps:: Updating time stamps on patched files. +* Multiple Patches:: Handling multiple patches in a file. +* patch Directories:: Changing directory and stripping directories. +* Backups:: Whether backup files are made. +* Backup Names:: Backup file names. +* Reject Names:: Reject file names. +* patch Messages:: Messages and questions @command{patch} can produce. +* patch and POSIX:: Conformance to the @acronym{POSIX} standard. +* patch and Tradition:: @acronym{GNU} versus traditional @command{patch}. +@end menu + +@node patch Input +@section Selecting the @command{patch} Input Format +@cindex @command{patch} input format + +@command{patch} normally determines which @command{diff} format the patch +file uses by examining its contents. For patch files that contain +particularly confusing leading text, you might need to use one of the +following options to force @command{patch} to interpret the patch file as a +certain format of diff. The output formats listed here are the only +ones that @command{patch} can understand. + +@table @option +@item -c +@itemx --context +context diff. + +@item -e +@itemx --ed +@command{ed} script. + +@item -n +@itemx --normal +normal diff. + +@item -u +@itemx --unified +unified diff. +@end table + +@node Revision Control +@section Revision Control +@cindex revision control +@cindex version control +@cindex @acronym{RCS} +@cindex ClearCase +@cindex @acronym{SCCS} + +If a nonexistent input file is under a revision control system +supported by @command{patch}, @command{patch} normally asks the user +whether to get (or check out) the file from the revision control +system. Patch currently supports @acronym{RCS}, ClearCase and +@acronym{SCCS}. Under @acronym{RCS} and @acronym{SCCS}, +@command{patch} also asks when the input file is read-only and matches +the default version in the revision control system. + +@vindex PATCH_GET +The @option{--get=@var{num}} (@option{-g @var{num}}) option affects access +to files under supported revision control systems. If @var{num} is +positive, @command{patch} gets the file without asking the user; if +zero, @command{patch} neither asks the user nor gets the file; and if +negative, @command{patch} asks the user before getting the file. The +default value of @var{num} is given by the value of the +@env{PATCH_GET} environment variable if it is set; if not, the default +value is zero if @command{patch} is conforming to @acronym{POSIX}, negative +otherwise. @xref{patch and POSIX}. + +@vindex VERSION_CONTROL +The choice of revision control system is unaffected by the +@env{VERSION_CONTROL} environment variable (@pxref{Backup Names}). + +@node Imperfect +@section Applying Imperfect Patches +@cindex imperfect patch application + +@command{patch} tries to skip any leading text in the patch file, +apply the diff, and then skip any trailing text. Thus you can feed a +mail message directly to @command{patch}, and it should work. If the +entire diff is indented by a constant amount of white space, +@command{patch} automatically ignores the indentation. If a context +diff contains trailing carriage return on each line, @command{patch} +automatically ignores the carriage return. If a context diff has been +encapsulated by prepending @w{@samp{- }} to lines beginning with @samp{-} +as per @uref{ftp://ftp.isi.edu/in-notes/rfc934.txt, Internet RFC 934}, +@command{patch} automatically unencapsulates the input. + +However, certain other types of imperfect input require user +intervention or testing. + +@menu +* Changed White Space:: When tabs and spaces don't match exactly. +* Reversed Patches:: Applying reversed patches correctly. +* Inexact:: Helping @command{patch} find close matches. +* Dry Runs:: Predicting what @command{patch} will do. +@end menu + +@node Changed White Space +@subsection Applying Patches with Changed White Space +@cindex white space in patches + +Sometimes mailers, editors, or other programs change spaces into tabs, +or vice versa. If this happens to a patch file or an input file, the +files might look the same, but @command{patch} will not be able to match +them properly. If this problem occurs, use the @option{-l} or +@option{--ignore-white-space} option, which makes @command{patch} compare +blank characters (i.e.@: spaces and tabs) loosely so that any nonempty +sequence of blanks in the patch file matches any nonempty sequence of +blanks in the input files. Non-blank +characters must still match exactly. Each line of the context must +still match a line in the input file. + +@node Reversed Patches +@subsection Applying Reversed Patches +@cindex reversed patches + +Sometimes people run @command{diff} with the new file first instead of +second. This creates a diff that is ``reversed''. To apply such +patches, give @command{patch} the @option{--reverse} (@option{-R}) option. +@command{patch} then attempts to swap each hunk around before applying it. +Rejects come out in the swapped format. + +Often @command{patch} can guess that the patch is reversed. If the first +hunk of a patch fails, @command{patch} reverses the hunk to see if it can +apply it that way. If it can, @command{patch} asks you if you want to have +the @option{-R} option set; if it can't, @command{patch} continues to apply +the patch normally. This method cannot detect a reversed patch if it is +a normal diff and the first command is an append (which should have been +a delete) since appends always succeed, because a null context matches +anywhere. But most patches add or change lines rather than delete them, +so most reversed normal diffs begin with a delete, which fails, and +@command{patch} notices. + +If you apply a patch that you have already applied, @command{patch} thinks +it is a reversed patch and offers to un-apply the patch. This could be +construed as a feature. If you did this inadvertently and you don't +want to un-apply the patch, just answer @samp{n} to this offer and to +the subsequent ``apply anyway'' question---or type @kbd{C-c} to kill the +@command{patch} process. + +@node Inexact +@subsection Helping @command{patch} Find Inexact Matches +@cindex inexact patches +@cindex fuzz factor when patching + +For context diffs, and to a lesser extent normal diffs, @command{patch} can +detect when the line numbers mentioned in the patch are incorrect, and +it attempts to find the correct place to apply each hunk of the patch. +As a first guess, it takes the line number mentioned in the hunk, plus +or minus any offset used in applying the previous hunk. If that is not +the correct place, @command{patch} scans both forward and backward for a +set of lines matching the context given in the hunk. + +First @command{patch} looks for a place where all lines of the context +match. If it cannot find such a place, and it is reading a context or +unified diff, and the maximum fuzz factor is set to 1 or more, then +@command{patch} makes another scan, ignoring the first and last line of +context. If that fails, and the maximum fuzz factor is set to 2 or +more, it makes another scan, ignoring the first two and last two lines +of context are ignored. It continues similarly if the maximum fuzz +factor is larger. + +The @option{--fuzz=@var{lines}} (@option{-F @var{lines}}) option sets the +maximum fuzz factor to @var{lines}. This option only applies to context +and unified diffs; it ignores up to @var{lines} lines while looking for +the place to install a hunk. Note that a larger fuzz factor increases +the odds of making a faulty patch. The default fuzz factor is 2; there +is no point to setting it to more than the number of lines of context +in the diff, ordinarily 3. + +If @command{patch} cannot find a place to install a hunk of the patch, it +writes the hunk out to a reject file (@pxref{Reject Names}, for information +on how reject files are named). It writes out rejected hunks in context +format no matter what form the input patch is in. If the input is a +normal or @command{ed} diff, many of the contexts are simply null. The +line numbers on the hunks in the reject file may be different from those +in the patch file: they show the approximate location where @command{patch} +thinks the failed hunks belong in the new file rather than in the old +one. + +If the @option{--verbose} option is given, then +as it completes each hunk @command{patch} tells you whether the hunk +succeeded or failed, and if it failed, on which line (in the new file) +@command{patch} thinks the hunk should go. If this is different from the +line number specified in the diff, it tells you the offset. A single +large offset @emph{may} indicate that @command{patch} installed a hunk in +the wrong place. @command{patch} also tells you if it used a fuzz factor +to make the match, in which case you should also be slightly suspicious. + +@command{patch} cannot tell if the line numbers are off in an @command{ed} +script, and can only detect wrong line numbers in a normal diff when it +finds a change or delete command. It may have the same problem with a +context diff using a fuzz factor equal to or greater than the number of +lines of context shown in the diff (typically 3). In these cases, you +should probably look at a context diff between your original and patched +input files to see if the changes make sense. Compiling without errors +is a pretty good indication that the patch worked, but not a guarantee. + +A patch against an empty file applies to a nonexistent file, and vice +versa. @xref{Creating and Removing}. + +@command{patch} usually produces the correct results, even when it must +make many guesses. However, the results are guaranteed only when +the patch is applied to an exact copy of the file that the patch was +generated from. + +@node Dry Runs +@subsection Predicting what @command{patch} will do +@cindex testing @command{patch} +@cindex dry runs for @command{patch} + +It may not be obvious in advance what @command{patch} will do with a +complicated or poorly formatted patch. If you are concerned that the +input might cause @command{patch} to modify the wrong files, you can +use the @option{--dry-run} option, which causes @command{patch} to +print the results of applying patches without actually changing any +files. You can then inspect the diagnostics generated by the dry run +to see whether @command{patch} will modify the files that you expect. +If the patch does not do what you want, you can modify the patch (or +the other options to @command{patch}) and try another dry run. Once +you are satisfied with the proposed patch you can apply it by invoking +@command{patch} as before, but this time without the +@option{--dry-run} option. + +@node Creating and Removing +@section Creating and Removing Files +@cindex creating files +@cindex empty files, removing +@cindex removing empty files + +Sometimes when comparing two directories, a file may exist in one +directory but not the other. If you give @command{diff} the +@option{--new-file} (@option{-N}) option, or if you supply an old or +new file that is named @file{/dev/null} or is empty and is dated the +Epoch (1970-01-01 00:00:00 UTC), @command{diff} outputs a patch that +adds or deletes the contents of this file. When given such a patch, +@command{patch} normally creates a new file or removes the old file. +However, when conforming to @acronym{POSIX} (@pxref{patch and POSIX}), +@command{patch} does not remove the old file, but leaves it empty. +The @option{--remove-empty-files} (@option{-E}) option causes +@command{patch} to remove output files that are empty after applying a +patch, even if the patch does not appear to be one that removed the +file. + +If the patch appears to create a file that already exists, +@command{patch} asks for confirmation before applying the patch. + +@node Patching Time Stamps +@section Updating Time Stamps on Patched Files +@cindex time stamps on patched files + +When @command{patch} updates a file, it normally sets the file's +last-modified time stamp to the current time of day. If you are using +@command{patch} to track a software distribution, this can cause +@command{make} to incorrectly conclude that a patched file is out of +date. For example, if @file{syntax.c} depends on @file{syntax.y}, and +@command{patch} updates @file{syntax.c} and then @file{syntax.y}, then +@file{syntax.c} will normally appear to be out of date with respect to +@file{syntax.y} even though its contents are actually up to date. + +The @option{--set-utc} (@option{-Z}) option causes @command{patch} to +set a patched file's modification and access times to the time stamps +given in context diff headers. If the context diff headers do not +specify a time zone, they are assumed to use Coordinated Universal +Time (@acronym{UTC}, often known as @acronym{GMT}). + +The @option{--set-time} (@option{-T}) option acts like @option{-Z} or +@option{--set-utc}, except that it assumes that the context diff +headers' time stamps use local time instead of @acronym{UTC}. This option +is not recommended, because patches using local time cannot easily be +used by people in other time zones, and because local time stamps are +ambiguous when local clocks move backwards during daylight-saving time +adjustments. If the context diff headers specify a time zone, this +option is equivalent to @option{--set-utc} (@option{-Z}). + +@command{patch} normally refrains from setting a file's time stamps if +the file's original last-modified time stamp does not match the time +given in the diff header, of if the file's contents do not exactly +match the patch. However, if the @option{--force} (@option{-f}) +option is given, the file's time stamps are set regardless. + +Due to the limitations of the current @command{diff} format, +@command{patch} cannot update the times of files whose contents have +not changed. Also, if you set file time stamps to values other than +the current time of day, you should also remove (e.g., with @samp{make +clean}) all files that depend on the patched files, so that later +invocations of @command{make} do not get confused by the patched +files' times. + +@node Multiple Patches +@section Multiple Patches in a File +@cindex multiple patches +@cindex intuiting file names from patches + +If the patch file contains more than one patch, and if you do not +specify an input file on the command line, @command{patch} tries to +apply each patch as if they came from separate patch files. This +means that it determines the name of the file to patch for each patch, +and that it examines the leading text before each patch for file names +and prerequisite revision level (@pxref{Making Patches}, for more on +that topic). + +@command{patch} uses the following rules to intuit a file name from +the leading text before a patch. First, @command{patch} takes an +ordered list of candidate file names as follows: + +@itemize @bullet +@item +If the header is that of a context diff, @command{patch} takes the old +and new file names in the header. A name is ignored if it does not +have enough slashes to satisfy the @option{-p@var{num}} or +@option{--strip=@var{num}} option. The name @file{/dev/null} is also +ignored. + +@item +If there is an @samp{Index:} line in the leading garbage and if either +the old and new names are both absent or if @command{patch} is +conforming to @acronym{POSIX}, @command{patch} takes the name in the +@samp{Index:} line. + +@item +For the purpose of the following rules, the candidate file names are +considered to be in the order (old, new, index), regardless of the +order that they appear in the header. +@end itemize + +@noindent +Then @command{patch} selects a file name from the candidate list as +follows: + +@itemize @bullet +@item +If some of the named files exist, @command{patch} selects the first +name if conforming to @acronym{POSIX}, and the best name otherwise. + +@item +If @command{patch} is not ignoring @acronym{RCS}, ClearCase, and @acronym{SCCS} +(@pxref{Revision Control}), and no named files exist but an @acronym{RCS}, +ClearCase, or @acronym{SCCS} master is found, @command{patch} selects the +first named file with an @acronym{RCS}, ClearCase, or @acronym{SCCS} master. + +@item +If no named files exist, no @acronym{RCS}, ClearCase, or @acronym{SCCS} master +was found, some names are given, @command{patch} is not conforming to +@acronym{POSIX}, and the patch appears to create a file, @command{patch} +selects the best name requiring the creation of the fewest +directories. + +@item +If no file name results from the above heuristics, you are asked for +the name of the file to patch, and @command{patch} selects that name. +@end itemize + +To determine the @dfn{best} of a nonempty list of file names, +@command{patch} first takes all the names with the fewest path name +components; of those, it then takes all the names with the shortest +basename; of those, it then takes all the shortest names; finally, it +takes the first remaining name. + +@xref{patch and POSIX}, to see whether @command{patch} is conforming +to @acronym{POSIX}. + +@node patch Directories +@section Applying Patches in Other Directories +@cindex directories and patch +@cindex patching directories + +The @option{--directory=@var{directory}} (@option{-d @var{directory}}) +option to @command{patch} makes directory @var{directory} the current +directory for interpreting both file names in the patch file, and file +names given as arguments to other options (such as @option{-B} and +@option{-o}). For example, while in a mail reading program, you can patch +a file in the @file{/usr/src/emacs} directory directly from a message +containing the patch like this: + +@example +| patch -d /usr/src/emacs +@end example + +Sometimes the file names given in a patch contain leading directories, +but you keep your files in a directory different from the one given in +the patch. In those cases, you can use the +@option{--strip=@var{number}} (@option{-p@var{number}}) +option to set the file name strip count to @var{number}. The strip +count tells @command{patch} how many slashes, along with the directory +names between them, to strip from the front of file names. A sequence +of one or more adjacent slashes is counted as a single slash. By +default, @command{patch} strips off all leading directories, leaving +just the base file names. + +For example, suppose the file name in the patch file is +@file{/gnu/src/emacs/etc/NEWS}. Using @option{-p0} gives the +entire file name unmodified, @option{-p1} gives +@file{gnu/src/emacs/etc/NEWS} (no leading slash), @option{-p4} gives +@file{etc/NEWS}, and not specifying @option{-p} at all gives @file{NEWS}. + +@command{patch} looks for each file (after any slashes have been stripped) +in the current directory, or if you used the @option{-d @var{directory}} +option, in that directory. + +@node Backups +@section Backup Files +@cindex backup file strategy + +Normally, @command{patch} creates a backup file if the patch does not +exactly match the original input file, because in that case the +original data might not be recovered if you undo the patch with +@samp{patch -R} (@pxref{Reversed Patches}). However, when conforming +to @acronym{POSIX}, @command{patch} does not create backup files by +default. @xref{patch and POSIX}. + +The @option{--backup} (@option{-b}) option causes @command{patch} to +make a backup file regardless of whether the patch matches the +original input. The @option{--backup-if-mismatch} option causes +@command{patch} to create backup files for mismatches files; this is +the default when not conforming to @acronym{POSIX}. The +@option{--no-backup-if-mismatch} option causes @command{patch} to not +create backup files, even for mismatched patches; this is the default +when conforming to @acronym{POSIX}. + +When backing up a file that does not exist, an empty, unreadable +backup file is created as a placeholder to represent the nonexistent +file. + +@node Backup Names +@section Backup File Names +@cindex backup file names + +Normally, @command{patch} renames an original input file into a backup +file by appending to its name the extension @samp{.orig}, or @samp{~} +if using @samp{.orig} would make the backup file name too +long.@footnote{A coding error in @acronym{GNU} @command{patch} version +2.5.4 causes it to always use @samp{~}, but this should be fixed in +the next release.} The @option{-z @var{backup-suffix}} or +@option{--suffix=@var{backup-suffix}} option causes @command{patch} to +use @var{backup-suffix} as the backup extension instead. + +@vindex SIMPLE_BACKUP_SUFFIX +Alternately, you can specify the extension for backup files with the +@env{SIMPLE_BACKUP_SUFFIX} environment variable, which the options +override. + +@command{patch} can also create numbered backup files the way +@acronym{GNU} Emacs does. With this method, instead of having a +single backup of each file, @command{patch} makes a new backup file +name each time it patches a file. For example, the backups of a file +named @file{sink} would be called, successively, @file{sink.~1~}, +@file{sink.~2~}, @file{sink.~3~}, etc. + +@vindex PATCH_VERSION_CONTROL +@vindex VERSION_CONTROL +The @option{-V @var{backup-style}} or +@option{--version-control=@var{backup-style}} option takes as an +argument a method for creating backup file names. You can alternately +control the type of backups that @command{patch} makes with the +@env{PATCH_VERSION_CONTROL} environment variable, which the +@option{-V} option overrides. If @env{PATCH_VERSION_CONTROL} is not +set, the @env{VERSION_CONTROL} environment variable is used instead. +Please note that these options and variables control backup file +names; they do not affect the choice of revision control system +(@pxref{Revision Control}). + +The values of these environment variables and the argument to the +@option{-V} option are like the @acronym{GNU} Emacs @code{version-control} +variable (@pxref{Backup Names, , , emacs, The @acronym{GNU} Emacs Manual}, +for more information on backup versions in Emacs). They also +recognize synonyms that are more descriptive. The valid values are +listed below; unique abbreviations are acceptable. + +@table @option +@item t +@itemx numbered +Always make numbered backups. + +@item nil +@itemx existing +Make numbered backups of files that already have them, simple backups of +the others. This is the default. + +@item never +@itemx simple +Always make simple backups. +@end table + +You can also tell @command{patch} to prepend a prefix, such as a +directory name, to produce backup file names. The +@option{--prefix=@var{prefix}} (@option{-B @var{prefix}}) option makes backup +files by prepending @var{prefix} to them. The +@option{--basename-prefix=@var{prefix}} (@option{-Y @var{prefix}}) prepends +@var{prefix} to the last file name component of backup file names +instead; for example, @option{-Y ~} causes the backup name for +@file{dir/file.c} to be @file{dir/~file.c}. If you use either of +these prefix options, the suffix-based options are ignored. + +If you specify the output file with the @option{-o} option, that file is +the one that is backed up, not the input file. + +Options that affect the names of backup files do not affect whether +backups are made. For example, if you specify the +@option{--no-backup-if-mismatch} option, none of the options described +in this section have any affect, because no backups are made. + +@node Reject Names +@section Reject File Names +@cindex reject file names + +The names for reject files (files containing patches that +@command{patch} could not find a place to apply) are normally the name +of the output file with @samp{.rej} appended (or @samp{#} if using +@samp{.rej} would make the backup file name too long). + +Alternatively, you can tell @command{patch} to place all of the rejected +patches in a single file. The @option{-r @var{reject-file}} or +@option{--reject-file=@var{reject-file}} option uses @var{reject-file} as +the reject file name. + +@node patch Messages +@section Messages and Questions from @command{patch} +@cindex @command{patch} messages and questions +@cindex diagnostics from @command{patch} +@cindex messages from @command{patch} + +@command{patch} can produce a variety of messages, especially if it +has trouble decoding its input. In a few situations where it's not +sure how to proceed, @command{patch} normally prompts you for more +information from the keyboard. There are options to produce more or +fewer messages, to have it not ask for keyboard input, and to +affect the way that file names are quoted in messages. + +@menu +* More or Fewer Messages:: Controlling the verbosity of @command{patch}. +* patch and Keyboard Input:: Inhibiting keyboard input. +* patch Quoting Style:: Quoting file names in diagnostics. +@end menu + +@command{patch} exits with status 0 if all hunks are applied successfully, +1 if some hunks cannot be applied, and 2 if there is more serious trouble. +When applying a set of patches in a loop, you should check the +exit status, so you don't apply a later patch to a partially patched +file. + +@node More or Fewer Messages +@subsection Controlling the Verbosity of @command{patch} +@cindex verbose messages from @command{patch} +@cindex inhibit messages from @command{patch} + +You can cause @command{patch} to produce more messages by using the +@option{--verbose} option. For example, when you give this option, +the message @samp{Hmm...} indicates that @command{patch} is reading text in +the patch file, attempting to determine whether there is a patch in that +text, and if so, what kind of patch it is. + +You can inhibit all terminal output from @command{patch}, unless an error +occurs, by using the @option{-s}, @option{--quiet}, or @option{--silent} +option. + +@node patch and Keyboard Input +@subsection Inhibiting Keyboard Input +@cindex keyboard input to @command{patch} + +There are two ways you can prevent @command{patch} from asking you any +questions. The @option{--force} (@option{-f}) option assumes that you know +what you are doing. It causes @command{patch} to do the following: + +@itemize @bullet +@item +Skip patches that do not contain file names in their headers. + +@item +Patch files even though they have the wrong version for the +@samp{Prereq:} line in the patch; + +@item +Assume that patches are not reversed even if they look like they are. +@end itemize + +@noindent +The @option{--batch} (@option{-t}) option is similar to @option{-f}, in that +it suppresses questions, but it makes somewhat different assumptions: + +@itemize @bullet +@item +Skip patches that do not contain file names in their headers +(the same as @option{-f}). + +@item +Skip patches for which the file has the wrong version for the +@samp{Prereq:} line in the patch; + +@item +Assume that patches are reversed if they look like they are. +@end itemize + +@node patch Quoting Style +@subsection @command{patch} Quoting Style +@cindex quoting style + +When @command{patch} outputs a file name in a diagnostic message, it +can format the name in any of several ways. This can be useful to +output file names unambiguously, even if they contain punctuation or +special characters like newlines. The +@option{--quoting-style=@var{word}} option controls how names are +output. The @var{word} should be one of the following: + +@table @samp +@item literal +Output names as-is. +@item shell +Quote names for the shell if they contain shell metacharacters or would +cause ambiguous output. +@item shell-always +Quote names for the shell, even if they would normally not require quoting. +@item c +Quote names as for a C language string. +@item escape +Quote as with @samp{c} except omit the surrounding double-quote +characters. +@c The following are not yet implemented in patch 2.5.4. +@c @item clocale +@c Quote as with @samp{c} except use quotation marks appropriate for the +@c locale. +@c @item locale +@c @c Use @t instead of @samp to avoid duplicate quoting in some output styles. +@c Like @samp{clocale}, but quote @t{'like this'} instead of @t{"like +@c this"} in the default C locale. This looks nicer on many displays. +@end table + +@vindex QUOTING_STYLE +You can specify the default value of the @option{--quoting-style} +option with the environment variable @env{QUOTING_STYLE}. If that +environment variable is not set, the default value is @samp{shell}, +but this default may change in a future version of @command{patch}. + +@node patch and POSIX +@section @command{patch} and the @acronym{POSIX} Standard +@cindex @acronym{POSIX} + +@vindex POSIXLY_CORRECT +If you specify the @option{--posix} option, or set the +@env{POSIXLY_CORRECT} environment variable, @command{patch} conforms +more strictly to the @acronym{POSIX} standard, as follows: + +@itemize @bullet +@item +Take the first existing file from the list (old, new, index) +when intuiting file names from diff headers. @xref{Multiple Patches}. + +@item +Do not remove files that are removed by a diff. +@xref{Creating and Removing}. + +@item +Do not ask whether to get files from @acronym{RCS}, ClearCase, or +@acronym{SCCS}. @xref{Revision Control}. + +@item +Require that all options precede the files in the command line. + +@item +Do not backup files, even when there is a mismatch. @xref{Backups}. + +@end itemize + +@node patch and Tradition +@section @acronym{GNU} @command{patch} and Traditional @command{patch} +@cindex traditional @command{patch} + +The current version of @acronym{GNU} @command{patch} normally follows the +@acronym{POSIX} standard. @xref{patch and POSIX}, for the few exceptions +to this general rule. + +Unfortunately, @acronym{POSIX} redefined the behavior of @command{patch} in +several important ways. You should be aware of the following +differences if you must interoperate with traditional @command{patch}, +or with @acronym{GNU} @command{patch} version 2.1 and earlier. + +@itemize @bullet +@item +In traditional @command{patch}, the @option{-p} option's operand was +optional, and a bare @option{-p} was equivalent to @option{-p0}. The +@option{-p} option now requires an operand, and @option{-p@ 0} is now +equivalent to @option{-p0}. For maximum compatibility, use options +like @option{-p0} and @option{-p1}. + +Also, traditional @command{patch} simply counted slashes when +stripping path prefixes; @command{patch} now counts pathname +components. That is, a sequence of one or more adjacent slashes now +counts as a single slash. For maximum portability, avoid sending +patches containing @file{//} in file names. + +@item +In traditional @command{patch}, backups were enabled by default. This +behavior is now enabled with the @option{--backup} (@option{-b}) +option. + +Conversely, in @acronym{POSIX} @command{patch}, backups are never made, +even when there is a mismatch. In @acronym{GNU} @command{patch}, this +behavior is enabled with the @option{--no-backup-if-mismatch} option, +or by conforming to @acronym{POSIX}. + +The @option{-b@ @var{suffix}} option of traditional @command{patch} is +equivalent to the @samp{-b -z@ @var{suffix}} options of @acronym{GNU} +@command{patch}. + +@item +Traditional @command{patch} used a complicated (and incompletely +documented) method to intuit the name of the file to be patched from +the patch header. This method did not conform to @acronym{POSIX}, and had +a few gotchas. Now @command{patch} uses a different, equally +complicated (but better documented) method that is optionally +@acronym{POSIX}-conforming; we hope it has fewer gotchas. The two methods +are compatible if the file names in the context diff header and the +@samp{Index:} line are all identical after prefix-stripping. Your +patch is normally compatible if each header's file names all contain +the same number of slashes. + +@item +When traditional @command{patch} asked the user a question, it sent +the question to standard error and looked for an answer from the first +file in the following list that was a terminal: standard error, +standard output, @file{/dev/tty}, and standard input. Now +@command{patch} sends questions to standard output and gets answers +from @file{/dev/tty}. Defaults for some answers have been changed so +that @command{patch} never goes into an infinite loop when using +default answers. + +@item +Traditional @command{patch} exited with a status value that counted +the number of bad hunks, or with status 1 if there was real trouble. +Now @command{patch} exits with status 1 if some hunks failed, or with +2 if there was real trouble. + +@item +Limit yourself to the following options when sending instructions +meant to be executed by anyone running @acronym{GNU} @command{patch}, +traditional @command{patch}, or a @command{patch} that conforms to +@acronym{POSIX}. Spaces are significant in the following list, and +operands are required. + +@example +@option{-c} +@option{-d @var{dir}} +@option{-D @var{define}} +@option{-e} +@option{-l} +@option{-n} +@option{-N} +@option{-o @var{outfile}} +@option{-p@var{num}} +@option{-R} +@option{-r @var{rejectfile}} +@end example + +@end itemize + +@node Making Patches +@chapter Tips for Making and Using Patches + +Use some common sense when making and using patches. For example, +when sending bug fixes to a program's maintainer, send several small +patches, one per independent subject, instead of one large, +harder-to-digest patch that covers all the subjects. + +Here are some other things you should keep in mind if you are going to +distribute patches for updating a software package. + +@menu +* Tips for Patch Producers:: Advice for making patches. +* Tips for Patch Consumers:: Advice for using patches. +* Avoiding Common Mistakes:: Avoiding common mistakes when using @command{patch}. +* Generating Smaller Patches:: How to generate smaller patches. +@end menu + +@node Tips for Patch Producers +@section Tips for Patch Producers +@cindex patch producer tips + +To create a patch that changes an older version of a package into a +newer version, first make a copy of the older and newer versions in +adjacent subdirectories. It is common to do that by unpacking +@command{tar} archives of the two versions. + +To generate the patch, use the command @samp{diff -Naur @var{old} +@var{new}} where @var{old} and @var{new} identify the old and new +directories. The names @var{old} and @var{new} should not contain any +slashes. The @option{-N} option lets the patch create and remove +files; @option{-a} lets the patch update non-text files; @option{-u} +generates useful time stamps and enough context; and @option{-r} lets +the patch update subdirectories. Here is an example command, using +Bourne shell syntax: + +@example +diff -Naur gcc-3.0.3 gcc-3.0.4 +@end example + +Tell your recipients how to apply the patches. This should include +which working directory to use, and which @command{patch} options to +use; the option @samp{-p1} is recommended. Test your procedure by +pretending to be a recipient and applying your patches to a copy of +the original files. + +@xref{Avoiding Common Mistakes}, for how to avoid common mistakes when +generating a patch. + +@node Tips for Patch Consumers +@section Tips for Patch Consumers +@cindex patch consumer tips + +A patch producer should tell recipients how to apply the patches, so +the first rule of thumb for a patch consumer is to follow the +instructions supplied with the patch. + +@acronym{GNU} @command{diff} can analyze files with arbitrarily long lines +and files that end in incomplete lines. However, older versions of +@command{patch} cannot patch such files. If you are having trouble +applying such patches, try upgrading to a recent version of @acronym{GNU} +@command{patch}. + +@node Avoiding Common Mistakes +@section Avoiding Common Mistakes +@cindex common mistakes with patches +@cindex patch, common mistakes + +When producing a patch for multiple files, apply @command{diff} to +directories whose names do not have slashes. This reduces confusion +when the patch consumer specifies the @option{-p@var{number}} option, +since this option can have surprising results when the old and new +file names have different numbers of slashes. For example, do not +send a patch with a header that looks like this: + +@example +diff -Naur v2.0.29/prog/README prog/README +--- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800 ++++ prog/README 2002-03-17 20:49:32.442260588 -0800 +@end example + +@noindent +because the two file names have different numbers of slashes, and +different versions of @command{patch} interpret the file names +differently. To avoid confusion, send output that looks like this +instead: + +@example +diff -Naur v2.0.29/prog/README v2.0.30/prog/README +--- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800 ++++ v2.0.30/prog/README 2002-03-17 20:49:32.442260588 -0800 +@end example + +Make sure you have specified the file names correctly, either in a +context diff header or with an @samp{Index:} line. Take care to not send out +reversed patches, since these make people wonder whether they have +already applied the patch. + +Avoid sending patches that compare backup file names like +@file{README.orig} or @file{README~}, since this might confuse +@command{patch} into patching a backup file instead of the real file. +Instead, send patches that compare the same base file names in +different directories, e.g.@: @file{old/README} and @file{new/README}. + +To save people from partially applying a patch before other patches that +should have gone before it, you can make the first patch in the patch +file update a file with a name like @file{patchlevel.h} or +@file{version.c}, which contains a patch level or version number. If +the input file contains the wrong version number, @command{patch} will +complain immediately. + +An even clearer way to prevent this problem is to put a @samp{Prereq:} +line before the patch. If the leading text in the patch file contains a +line that starts with @samp{Prereq:}, @command{patch} takes the next word +from that line (normally a version number) and checks whether the next +input file contains that word, preceded and followed by either +white space or a newline. If not, @command{patch} prompts you for +confirmation before proceeding. This makes it difficult to accidentally +apply patches in the wrong order. + +@node Generating Smaller Patches +@section Generating Smaller Patches +@cindex patches, shrinking + +The simplest way to generate a patch is to use @samp{diff -Naur} +(@pxref{Tips for Patch Producers}), but you might be able to reduce +the size of the patch by renaming or removing some files before making +the patch. If the older version of the package contains any files +that the newer version does not, or if any files have been renamed +between the two versions, make a list of @command{rm} and @command{mv} +commands for the user to execute in the old version directory before +applying the patch. Then run those commands yourself in the scratch +directory. + +If there are any files that you don't need to include in the patch +because they can easily be rebuilt from other files (for example, +@file{TAGS} and output from @command{yacc} and @command{makeinfo}), +exclude them from the patch by giving @command{diff} the @option{-x +@var{pattern}} option (@pxref{Comparing Directories}). If you want +your patch to modify a derived file because your recipients lack tools +to build it, make sure that the patch for the derived file follows any +patches for files that it depends on, so that the recipients' time +stamps will not confuse @command{make}. + +Now you can create the patch using @samp{diff -Naur}. Make sure to +specify the scratch directory first and the newer directory second. + +Add to the top of the patch a note telling the user any @command{rm} and +@command{mv} commands to run before applying the patch. Then you can +remove the scratch directory. + +You can also shrink the patch size by using fewer lines of context, +but bear in mind that @command{patch} typically needs at least two +lines for proper operation when patches do not exactly match the input +files. + +@node Invoking cmp +@chapter Invoking @command{cmp} +@cindex invoking @command{cmp} +@cindex @command{cmp} invocation + +The @command{cmp} command compares two files, and if they differ, +tells the first byte and line number where they differ or reports +that one file is a prefix of the other. Bytes and +lines are numbered starting with 1. The arguments of @command{cmp} +are as follows: + +@example +cmp @var{options}@dots{} @var{from-file} @r{[}@var{to-file} @r{[}@var{from-skip} @r{[}@var{to-skip}@r{]}@r{]}@r{]} +@end example + +The file name @file{-} is always the standard input. @command{cmp} +also uses the standard input if one file name is omitted. The +@var{from-skip} and @var{to-skip} operands specify how many bytes to +ignore at the start of each file; they are equivalent to the +@option{--ignore-initial=@var{from-skip}:@var{to-skip}} option. + +By default, @command{cmp} outputs nothing if the two files have the +same contents. If one file is a prefix of the other, @command{cmp} +prints to standard error a message of the following form: + +@example +cmp: EOF on @var{shorter-file} +@end example + +Otherwise, @command{cmp} prints to standard output a message of the +following form: + +@example +@var{from-file} @var{to-file} differ: char @var{byte-number}, line @var{line-number} +@end example + +The message formats can differ outside the @acronym{POSIX} locale. +Also, @acronym{POSIX} allows the @acronym{EOF} message to be followed +by a blank and some additional information. + +An exit status of 0 means no differences were found, 1 means some +differences were found, and 2 means trouble. + +@menu +* cmp Options:: Summary of options to @command{cmp}. +@end menu + +@node cmp Options +@section Options to @command{cmp} +@cindex @command{cmp} options +@cindex options for @command{cmp} + +Below is a summary of all of the options that @acronym{GNU} +@command{cmp} accepts. Most options have two equivalent names, one of +which is a single letter preceded by @samp{-}, and the other of which +is a long name preceded by @samp{--}. Multiple single letter options +(unless they take an argument) can be combined into a single command +line word: @option{-bl} is equivalent to @option{-b -l}. + +@table @option +@item -b +@itemx --print-bytes +Print the differing bytes. Display control bytes as a +@samp{^} followed by a letter of the alphabet and precede bytes +that have the high bit set with @samp{M-} (which stands for ``meta''). + +@item --help +Output a summary of usage and then exit. + +@item -i @var{skip} +@itemx --ignore-initial=@var{skip} +Ignore any differences in the first @var{skip} bytes of the input +files. Treat files with fewer than @var{skip} bytes as if they are +empty. If @var{skip} is of the form +@option{@var{from-skip}:@var{to-skip}}, skip the first @var{from-skip} +bytes of the first input file and the first @var{to-skip} bytes of the +second. + +@item -l +@itemx --verbose +Output the (decimal) byte numbers and (octal) values of all differing bytes, +instead of the default standard output. +Each output line contains a differing byte's number relative to the +start of the input, followed by the differing byte values. +Byte numbers start at 1. +Also, output the @acronym{EOF} message if one file is shorter than the other. + +@item -n @var{count} +@itemx --bytes=@var{count} +Compare at most @var{count} input bytes. + +@item -s +@itemx --quiet +@itemx --silent +Do not print anything; only return an exit status indicating whether +the files differ. + +@item -v +@itemx --version +Output version information and then exit. +@end table + +In the above table, operands that are byte counts are normally +decimal, but may be preceded by @samp{0} for octal and @samp{0x} for +hexadecimal. + +A byte count can be followed by a suffix to specify a multiple of that +count; in this case an omitted integer is understood to be 1. A bare +size letter, or one followed by @samp{iB}, specifies a multiple using +powers of 1024. A size letter followed by @samp{B} specifies powers +of 1000 instead. For example, @option{-n 4M} and @option{-n 4MiB} are +equivalent to @option{-n 4194304}, whereas @option{-n 4MB} is +equivalent to @option{-n 4000000}. This notation is upward compatible +with the @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI +prefixes} for decimal multiples and with the +@uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2 +prefixes for binary multiples}. + +The following suffixes are defined. Large sizes like @code{1Y} may be +rejected by your computer due to limitations of its arithmetic. + +@table @samp +@item kB +@cindex kilobyte, definition of +kilobyte: @math{10^3 = 1000}. +@item k +@itemx K +@itemx KiB +@cindex kibibyte, definition of +kibibyte: @math{2^10 = 1024}. @samp{K} is special: the SI prefix is +@samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and +@acronym{POSIX} use @samp{k} to mean @samp{KiB}. +@item MB +@cindex megabyte, definition of +megabyte: @math{10^6 = 1,000,000}. +@item M +@itemx MiB +@cindex mebibyte, definition of +mebibyte: @math{2^20 = 1,048,576}. +@item GB +@cindex gigabyte, definition of +gigabyte: @math{10^9 = 1,000,000,000}. +@item G +@itemx GiB +@cindex gibibyte, definition of +gibibyte: @math{2^30 = 1,073,741,824}. +@item TB +@cindex terabyte, definition of +terabyte: @math{10^12 = 1,000,000,000,000}. +@item T +@itemx TiB +@cindex tebibyte, definition of +tebibyte: @math{2^40 = 1,099,511,627,776}. +@item PB +@cindex petabyte, definition of +petabyte: @math{10^15 = 1,000,000,000,000,000}. +@item P +@itemx PiB +@cindex pebibyte, definition of +pebibyte: @math{2^50 = 1,125,899,906,842,624}. +@item EB +@cindex exabyte, definition of +exabyte: @math{10^18 = 1,000,000,000,000,000,000}. +@item E +@itemx EiB +@cindex exbibyte, definition of +exbibyte: @math{2^60 = 1,152,921,504,606,846,976}. +@item ZB +@cindex zettabyte, definition of +zettabyte: @math{10^21 = 1,000,000,000,000,000,000,000} +@item Z +@itemx ZiB +@math{2^70 = 1,180,591,620,717,411,303,424}. +(@samp{Zi} is a GNU extension to IEC 60027-2.) +@item YB +@cindex yottabyte, definition of +yottabyte: @math{10^24 = 1,000,000,000,000,000,000,000,000}. +@item Y +@itemx YiB +@math{2^80 = 1,208,925,819,614,629,174,706,176}. +(@samp{Yi} is a GNU extension to IEC 60027-2.) +@end table + +@node Invoking diff +@chapter Invoking @command{diff} +@cindex invoking @command{diff} +@cindex @command{diff} invocation + +The format for running the @command{diff} command is: + +@example +diff @var{options}@dots{} @var{files}@dots{} +@end example + +In the simplest case, two file names @var{from-file} and +@var{to-file} are given, and @command{diff} compares the contents of +@var{from-file} and @var{to-file}. A file name of @file{-} stands for +the standard input. + +If one file is a directory and the other is not, @command{diff} compares +the file in the directory whose name is that of the non-directory. +The non-directory file must not be @file{-}. + +If two file names are given and both are directories, +@command{diff} compares corresponding files in both directories, in +alphabetical order; this comparison is not recursive unless the +@option{--recursive} (@option{-r}) option is given. @command{diff} never +compares the actual contents of a directory as if it were a file. The +file that is fully specified may not be standard input, because standard +input is nameless and the notion of ``file with the same name'' does not +apply. + +If the @option{--from-file=@var{file}} option is given, the number of +file names is arbitrary, and @var{file} is compared to each named file. +Similarly, if the @option{--to-file=@var{file}} option is given, each +named file is compared to @var{file}. + +@command{diff} options begin with @samp{-}, so normally file names +may not begin with @samp{-}. However, @option{--} as an +argument by itself treats the remaining arguments as file names even if +they begin with @samp{-}. + +An exit status of 0 means no differences were found, 1 means some +differences were found, and 2 means trouble. + +@menu +* diff Options:: Summary of options to @command{diff}. +@end menu + +@node diff Options +@section Options to @command{diff} +@cindex @command{diff} options +@cindex options for @command{diff} + +Below is a summary of all of the options that @acronym{GNU} +@command{diff} accepts. Most options have two equivalent names, one +of which is a single letter preceded by @samp{-}, and the other of +which is a long name preceded by @samp{--}. Multiple single letter +options (unless they take an argument) can be combined into a single +command line word: @option{-ac} is equivalent to @option{-a -c}. Long +named options can be abbreviated to any unique prefix of their name. +Brackets ([ and ]) indicate that an option takes an optional argument. + +@table @option +@item -a +@itemx --text +Treat all files as text and compare them line-by-line, even if they +do not seem to be text. @xref{Binary}. + +@item -b +@itemx --ignore-space-change +Ignore changes in amount of white space. @xref{White Space}. + +@item -B +@itemx --ignore-blank-lines +Ignore changes that just insert or delete blank lines. @xref{Blank +Lines}. + +@item --binary +Read and write data in binary mode. @xref{Binary}. + +@item -c +Use the context output format, showing three lines of context. +@xref{Context Format}. + +@item --color [=@var{when}] +@cindex color, distinguishing different context +Specify whether to use color for distinguishing different contexts, +like header, added or removed lines. @var{when} may be omitted, or +one of: +@itemize @bullet +@item none +@vindex none @r{color option} +Do not use color at all. This is the default when no --color option +is specified. +@item auto +@vindex auto @r{color option} +@cindex terminal, using color iff +Use color only if standard output is a terminal. +@item always +@vindex always @r{color option} +Always use color. +@end itemize +Specifying @option{--color} and no @var{when} is equivalent to +@option{--color=auto}. + +@item -C @var{lines} +@itemx --context@r{[}=@var{lines}@r{]} +Use the context output format, showing @var{lines} (an integer) lines of +context, or three if @var{lines} is not given. @xref{Context Format}. +For proper operation, @command{patch} typically needs at least two lines of +context. + +For compatibility @command{diff} also supports an obsolete option +syntax @option{-@var{lines}} that has effect when combined with +@option{-c}, @option{-p}, or @option{-u}. New scripts should use +@option{-U @var{lines}} (@option{-C @var{lines}}) instead. + +@item --changed-group-format=@var{format} +Use @var{format} to output a line group containing differing lines from +both files in if-then-else format. @xref{Line Group Formats}. + +@item -d +@itemx --minimal +Change the algorithm perhaps find a smaller set of changes. This makes +@command{diff} slower (sometimes much slower). @xref{diff Performance}. + +@item -D @var{name} +@itemx --ifdef=@var{name} +Make merged @samp{#ifdef} format output, conditional on the preprocessor +macro @var{name}. @xref{If-then-else}. + +@item -e +@itemx --ed +Make output that is a valid @command{ed} script. @xref{ed Scripts}. + +@item -E +@itemx --ignore-tab-expansion +Ignore changes due to tab expansion. +@xref{White Space}. + +@item -f +@itemx --forward-ed +Make output that looks vaguely like an @command{ed} script but has changes +in the order they appear in the file. @xref{Forward ed}. + +@item -F @var{regexp} +@itemx --show-function-line=@var{regexp} +In context and unified format, for each hunk of differences, show some +of the last preceding line that matches @var{regexp}. @xref{Specified +Headings}. + +@item --from-file=@var{file} +Compare @var{file} to each operand; @var{file} may be a directory. + +@item --help +Output a summary of usage and then exit. + +@item --horizon-lines=@var{lines} +Do not discard the last @var{lines} lines of the common prefix +and the first @var{lines} lines of the common suffix. +@xref{diff Performance}. + +@item -i +@itemx --ignore-case +Ignore changes in case; consider upper- and lower-case letters +equivalent. @xref{Case Folding}. + +@item -I @var{regexp} +@itemx --ignore-matching-lines=@var{regexp} +Ignore changes that just insert or delete lines that match @var{regexp}. +@xref{Specified Lines}. + +@item --ignore-file-name-case +Ignore case when comparing file names. For example, recursive +comparison of @file{d} to @file{e} might compare the contents of +@file{d/Init} and @file{e/inIt}. At the top level, @samp{diff d inIt} +might compare the contents of @file{d/Init} and @file{inIt}. +@xref{Comparing Directories}. + +@item -l +@itemx --paginate +Pass the output through @command{pr} to paginate it. @xref{Pagination}. + +@item -L @var{label} +@itemx --label=@var{label} +Use @var{label} instead of the file name in the context format +(@pxref{Context Format}) and unified format (@pxref{Unified Format}) +headers. @xref{RCS}. + +@item --left-column +Print only the left column of two common lines in side by side format. +@xref{Side by Side Format}. + +@item --line-format=@var{format} +Use @var{format} to output all input lines in if-then-else format. +@xref{Line Formats}. + +@item -n +@itemx --rcs +Output @acronym{RCS}-format diffs; like @option{-f} except that each command +specifies the number of lines affected. @xref{RCS}. + +@item -N +@itemx --new-file +If one file is missing, treat it as present but empty. +@xref{Comparing Directories}. + +@item --new-group-format=@var{format} +Use @var{format} to output a group of lines taken from just the second +file in if-then-else format. @xref{Line Group Formats}. + +@item --new-line-format=@var{format} +Use @var{format} to output a line taken from just the second file in +if-then-else format. @xref{Line Formats}. + +@item --no-dereference +Act on symbolic links themselves instead of what they point to. +Two symbolic links are deemed equal only when each points to +precisely the same name. + +@item --old-group-format=@var{format} +Use @var{format} to output a group of lines taken from just the first +file in if-then-else format. @xref{Line Group Formats}. + +@item --old-line-format=@var{format} +Use @var{format} to output a line taken from just the first file in +if-then-else format. @xref{Line Formats}. + +@item -p +@itemx --show-c-function +Show which C function each change is in. @xref{C Function Headings}. + +@item --palette=@var{palette} +Specify what color palette to use when colored output is enabled. It +defaults to @samp{rs=0:hd=1:ad=32:de=31:ln=36} for red deleted lines, +green added lines, cyan line numbers, bold header. + +Supported capabilities are as follows. + +@table @code +@item ad=32 +@vindex ad @r{capability} + +SGR substring for added lines. +The default is green foreground. + +@item de=31 +@vindex de @r{capability} + +SGR substring for deleted lines. +The default is red foreground. + +@item hd=1 +@vindex hd @r{capability} + +SGR substring for chunk header. +The default is bold foreground. + +@item ln=36 +@vindex ln @r{capability} + +SGR substring for line numbers. +The default is cyan foreground. +@end table + + +@item -q +@itemx --brief +Report only whether the files differ, not the details of the +differences. @xref{Brief}. + +@item -r +@itemx --recursive +When comparing directories, recursively compare any subdirectories +found. @xref{Comparing Directories}. + +@item -s +@itemx --report-identical-files +Report when two files are the same. @xref{Comparing Directories}. + +@item -S @var{file} +@itemx --starting-file=@var{file} +When comparing directories, start with the file @var{file}. This is +used for resuming an aborted comparison. @xref{Comparing Directories}. + +@item --speed-large-files +Use heuristics to speed handling of large files that have numerous +scattered small changes. @xref{diff Performance}. + +@item --strip-trailing-cr +Strip any trailing carriage return at the end of an input line. +@xref{Binary}. + +@item --suppress-common-lines +Do not print common lines in side by side format. +@xref{Side by Side Format}. + +@item -t +@itemx --expand-tabs +Expand tabs to spaces in the output, to preserve the alignment of tabs +in the input files. @xref{Tabs}. + +@item -T +@itemx --initial-tab +Output a tab rather than a space before the text of a line in normal or +context format. This causes the alignment of tabs in the line to look +normal. @xref{Tabs}. + +@item --tabsize=@var{columns} +Assume that tab stops are set every @var{columns} (default 8) print +columns. @xref{Tabs}. + +@item --suppress-blank-empty +Suppress any blanks before newlines when printing the representation +of an empty line, when outputting normal, context, or unified format. +@xref{Trailing Blanks}. + +@item --to-file=@var{file} +Compare each operand to @var{file}; @var{file} may be a directory. + +@item -u +Use the unified output format, showing three lines of context. +@xref{Unified Format}. + +@item --unchanged-group-format=@var{format} +Use @var{format} to output a group of common lines taken from both files +in if-then-else format. @xref{Line Group Formats}. + +@item --unchanged-line-format=@var{format} +Use @var{format} to output a line common to both files in if-then-else +format. @xref{Line Formats}. + +@item --unidirectional-new-file +If a first file is missing, treat it as present but empty. +@xref{Comparing Directories}. + +@item -U @var{lines} +@itemx --unified@r{[}=@var{lines}@r{]} +Use the unified output format, showing @var{lines} (an integer) lines of +context, or three if @var{lines} is not given. @xref{Unified Format}. +For proper operation, @command{patch} typically needs at least two lines of +context. + +On older systems, @command{diff} supports an obsolete option +@option{-@var{lines}} that has effect when combined with @option{-u}. +@acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not allow +this; use @option{-U @var{lines}} instead. + +@item -v +@itemx --version +Output version information and then exit. + +@item -w +@itemx --ignore-all-space +Ignore white space when comparing lines. @xref{White Space}. + +@item -W @var{columns} +@itemx --width=@var{columns} +Output at most @var{columns} (default 130) print columns per line in +side by side format. @xref{Side by Side Format}. + +@item -x @var{pattern} +@itemx --exclude=@var{pattern} +When comparing directories, ignore files and subdirectories whose basenames +match @var{pattern}. @xref{Comparing Directories}. + +@item -X @var{file} +@itemx --exclude-from=@var{file} +When comparing directories, ignore files and subdirectories whose basenames +match any pattern contained in @var{file}. @xref{Comparing Directories}. + +@item -y +@itemx --side-by-side +Use the side by side output format. @xref{Side by Side Format}. + +@item -Z +@itemx --ignore-trailing-space +Ignore white space at line end. @xref{White Space}. +@end table + +@node Invoking diff3 +@chapter Invoking @command{diff3} +@cindex invoking @command{diff3} +@cindex @command{diff3} invocation + +The @command{diff3} command compares three files and outputs descriptions +of their differences. Its arguments are as follows: + +@example +diff3 @var{options}@dots{} @var{mine} @var{older} @var{yours} +@end example + +The files to compare are @var{mine}, @var{older}, and @var{yours}. +At most one of these three file names may be @file{-}, +which tells @command{diff3} to read the standard input for that file. + +An exit status of 0 means @command{diff3} was successful, 1 means some +conflicts were found, and 2 means trouble. + +@menu +* diff3 Options:: Summary of options to @command{diff3}. +@end menu + +@node diff3 Options +@section Options to @command{diff3} +@cindex @command{diff3} options +@cindex options for @command{diff3} + +Below is a summary of all of the options that @acronym{GNU} @command{diff3} +accepts. Multiple single letter options (unless they take an argument) +can be combined into a single command line argument. + +@table @option +@item -a +@itemx --text +Treat all files as text and compare them line-by-line, even if they +do not appear to be text. @xref{Binary}. + +@item -A +@itemx --show-all +Incorporate all unmerged changes from @var{older} to @var{yours} into +@var{mine}, surrounding conflicts with bracket lines. +@xref{Marking Conflicts}. + +@item --diff-program=@var{program} +Use the compatible comparison program @var{program} to compare files +instead of @command{diff}. + +@item -e +@itemx --ed +Generate an @command{ed} script that incorporates all the changes from +@var{older} to @var{yours} into @var{mine}. @xref{Which Changes}. + +@item -E +@itemx --show-overlap +Like @option{-e}, except bracket lines from overlapping changes' first +and third files. +@xref{Marking Conflicts}. +With @option{-E}, an overlapping change looks like this: + +@example +<<<<<<< @var{mine} +@r{lines from @var{mine}} +======= +@r{lines from @var{yours}} +>>>>>>> @var{yours} +@end example + +@item --help +Output a summary of usage and then exit. + +@item -i +Generate @samp{w} and @samp{q} commands at the end of the @command{ed} +script for System V compatibility. This option must be combined with +one of the @option{-AeExX3} options, and may not be combined with @option{-m}. +@xref{Saving the Changed File}. + +@item --label=@var{label} +Use the label @var{label} for the brackets output by the @option{-A}, +@option{-E} and @option{-X} options. This option may be given up to three +times, one for each input file. The default labels are the names of +the input files. Thus @samp{diff3 --label X --label Y --label Z -m A +B C} acts like +@samp{diff3 -m A B C}, except that the output looks like it came from +files named @samp{X}, @samp{Y} and @samp{Z} rather than from files +named @samp{A}, @samp{B} and @samp{C}. @xref{Marking Conflicts}. + +@item -m +@itemx --merge +Apply the edit script to the first file and send the result to standard +output. Unlike piping the output from @command{diff3} to @command{ed}, this +works even for binary files and incomplete lines. @option{-A} is assumed +if no edit script option is specified. @xref{Bypassing ed}. + +@item --strip-trailing-cr +Strip any trailing carriage return at the end of an input line. +@xref{Binary}. + +@item -T +@itemx --initial-tab +Output a tab rather than two spaces before the text of a line in normal format. +This causes the alignment of tabs in the line to look normal. @xref{Tabs}. + +@item -v +@itemx --version +Output version information and then exit. + +@item -x +@itemx --overlap-only +Like @option{-e}, except output only the overlapping changes. +@xref{Which Changes}. + +@item -X +Like @option{-E}, except output only the overlapping changes. +In other words, like @option{-x}, except bracket changes as in @option{-E}. +@xref{Marking Conflicts}. + +@item -3 +@itemx --easy-only +Like @option{-e}, except output only the nonoverlapping changes. +@xref{Which Changes}. +@end table + +@node Invoking patch +@chapter Invoking @command{patch} +@cindex invoking @command{patch} +@cindex @command{patch} invocation + +Normally @command{patch} is invoked like this: + +@example +patch <@var{patchfile} +@end example + +The full format for invoking @command{patch} is: + +@example +patch @var{options}@dots{} @r{[}@var{origfile} @r{[}@var{patchfile}@r{]}@r{]} +@end example + +You can also specify where to read the patch from with the @option{-i +@var{patchfile}} or @option{--input=@var{patchfile}} option. +If you do not specify @var{patchfile}, or if @var{patchfile} is +@file{-}, @command{patch} reads the patch (that is, the @command{diff} output) +from the standard input. + +If you do not specify an input file on the command line, @command{patch} +tries to intuit from the @dfn{leading text} (any text in the patch +that comes before the @command{diff} output) which file to edit. +@xref{Multiple Patches}. + +By default, @command{patch} replaces the original input file with the +patched version, possibly after renaming the original file into a +backup file (@pxref{Backup Names}, for a description of how +@command{patch} names backup files). You can also specify where to +put the output with the @option{-o @var{file}} or +@option{--output=@var{file}} option; however, do not use this option +if @var{file} is one of the input files. + +@menu +* patch Options:: Summary table of options to @command{patch}. +@end menu + +@node patch Options +@section Options to @command{patch} +@cindex @command{patch} options +@cindex options for @command{patch} + +Here is a summary of all of the options that @acronym{GNU} @command{patch} +accepts. @xref{patch and Tradition}, for which of these options are +safe to use in older versions of @command{patch}. + +Multiple single-letter options that do not take an argument can be +combined into a single command line argument with only one dash. + +@table @option +@item -b +@itemx --backup +Back up the original contents of each file, even if backups would +normally not be made. @xref{Backups}. + +@item -B @var{prefix} +@itemx --prefix=@var{prefix} +Prepend @var{prefix} to backup file names. @xref{Backup Names}. + +@item --backup-if-mismatch +Back up the original contents of each file if the patch does not +exactly match the file. This is the default behavior when not +conforming to @acronym{POSIX}. @xref{Backups}. + +@item --binary +Read and write all files in binary mode, except for standard output +and @file{/dev/tty}. This option has no effect on +@acronym{POSIX}-conforming systems like @acronym{GNU}/Linux. On systems where +this option makes a difference, the patch should be generated by +@samp{diff -a --binary}. @xref{Binary}. + +@item -c +@itemx --context +Interpret the patch file as a context diff. @xref{patch Input}. + +@item -d @var{directory} +@itemx --directory=@var{directory} +Make directory @var{directory} the current directory for interpreting +both file names in the patch file, and file names given as arguments to +other options. @xref{patch Directories}. + +@item -D @var{name} +@itemx --ifdef=@var{name} +Make merged if-then-else output using @var{name}. @xref{If-then-else}. + +@item --dry-run +Print the results of applying the patches without actually changing +any files. @xref{Dry Runs}. + +@item -e +@itemx --ed +Interpret the patch file as an @command{ed} script. @xref{patch Input}. + +@item -E +@itemx --remove-empty-files +Remove output files that are empty after the patches have been applied. +@xref{Creating and Removing}. + +@item -f +@itemx --force +Assume that the user knows exactly what he or she is doing, and do not +ask any questions. @xref{patch Messages}. + +@item -F @var{lines} +@itemx --fuzz=@var{lines} +Set the maximum fuzz factor to @var{lines}. @xref{Inexact}. + +@item -g @var{num} +@itemx --get=@var{num} +If @var{num} is positive, get input files from a revision control +system as necessary; if zero, do not get the files; if negative, ask +the user whether to get the files. @xref{Revision Control}. + +@item --help +Output a summary of usage and then exit. + +@item -i @var{patchfile} +@itemx --input=@var{patchfile} +Read the patch from @var{patchfile} rather than from standard input. +@xref{patch Options}. + +@item -l +@itemx --ignore-white-space +Let any sequence of blanks (spaces or tabs) in the patch file match +any sequence of blanks in the input file. @xref{Changed White Space}. + +@item -n +@itemx --normal +Interpret the patch file as a normal diff. @xref{patch Input}. + +@item -N +@itemx --forward +Ignore patches that @command{patch} thinks are reversed or already applied. +See also @option{-R}. @xref{Reversed Patches}. + +@item --no-backup-if-mismatch +Do not back up the original contents of files. This is the default +behavior when conforming to @acronym{POSIX}. @xref{Backups}. + +@item -o @var{file} +@itemx --output=@var{file} +Use @var{file} as the output file name. @xref{patch Options}. + +@item -p@var{number} +@itemx --strip=@var{number} +Set the file name strip count to @var{number}. @xref{patch Directories}. + +@item --posix +Conform to @acronym{POSIX}, as if the @env{POSIXLY_CORRECT} environment +variable had been set. @xref{patch and POSIX}. + +@item --quoting-style=@var{word} +Use style @var{word} to quote names in diagnostics, as if the +@env{QUOTING_STYLE} environment variable had been set to @var{word}. +@xref{patch Quoting Style}. + +@item -r @var{reject-file} +@itemx --reject-file=@var{reject-file} +Use @var{reject-file} as the reject file name. @xref{Reject Names}. + +@item -R +@itemx --reverse +Assume that this patch was created with the old and new files swapped. +@xref{Reversed Patches}. + +@item -s +@itemx --quiet +@itemx --silent +Work silently unless an error occurs. @xref{patch Messages}. + +@item -t +@itemx --batch +Do not ask any questions. @xref{patch Messages}. + +@item -T +@itemx --set-time +Set the modification and access times of patched files from time +stamps given in context diff headers, assuming that the context diff +headers use local time. @xref{Patching Time Stamps}. + +@item -u +@itemx --unified +Interpret the patch file as a unified diff. @xref{patch Input}. + +@item -v +@itemx --version +Output version information and then exit. + +@item -V @var{backup-style} +@itemx --version=control=@var{backup-style} +Select the naming convention for backup file names. @xref{Backup Names}. + +@item --verbose +Print more diagnostics than usual. @xref{patch Messages}. + +@item -x @var{number} +@itemx --debug=@var{number} +Set internal debugging flags. Of interest only to @command{patch} +patchers. + +@item -Y @var{prefix} +@itemx --basename-prefix=@var{prefix} +Prepend @var{prefix} to base names of backup files. @xref{Backup Names}. + +@item -z @var{suffix} +@itemx --suffix=@var{suffix} +Use @var{suffix} as the backup extension instead of @samp{.orig} or +@samp{~}. @xref{Backup Names}. + +@item -Z +@itemx --set-utc +Set the modification and access times of patched files from time +stamps given in context diff headers, assuming that the context diff +headers use @acronym{UTC}. @xref{Patching Time Stamps}. + +@end table + +@node Invoking sdiff +@chapter Invoking @command{sdiff} +@cindex invoking @command{sdiff} +@cindex @command{sdiff} invocation + +The @command{sdiff} command merges two files and interactively outputs the +results. Its arguments are as follows: + +@example +sdiff -o @var{outfile} @var{options}@dots{} @var{from-file} @var{to-file} +@end example + +This merges @var{from-file} with @var{to-file}, with output to @var{outfile}. +If @var{from-file} is a directory and @var{to-file} is not, @command{sdiff} +compares the file in @var{from-file} whose file name is that of @var{to-file}, +and vice versa. @var{from-file} and @var{to-file} may not both be +directories. + +@command{sdiff} options begin with @samp{-}, so normally @var{from-file} +and @var{to-file} may not begin with @samp{-}. However, @option{--} as an +argument by itself treats the remaining arguments as file names even if +they begin with @samp{-}. You may not use @file{-} as an input file. + +@command{sdiff} without @option{--output} (@option{-o}) produces a +side-by-side difference. This usage is obsolete; use the +@option{--side-by-side} (@option{-y}) option of @command{diff} instead. + +An exit status of 0 means no differences were found, 1 means some +differences were found, and 2 means trouble. + +@menu +* sdiff Options:: Summary of options to @command{diff}. +@end menu + +@node sdiff Options +@section Options to @command{sdiff} +@cindex @command{sdiff} options +@cindex options for @command{sdiff} + +Below is a summary of all of the options that @acronym{GNU} +@command{sdiff} accepts. Each option has two equivalent names, one of +which is a single letter preceded by @samp{-}, and the other of which +is a long name preceded by @samp{--}. Multiple single letter options +(unless they take an argument) can be combined into a single command +line argument. Long named options can be abbreviated to any unique +prefix of their name. + +@table @option +@item -a +@itemx --text +Treat all files as text and compare them line-by-line, even if they +do not appear to be text. @xref{Binary}. + +@item -b +@itemx --ignore-space-change +Ignore changes in amount of white space. @xref{White Space}. + +@item -B +@itemx --ignore-blank-lines +Ignore changes that just insert or delete blank lines. @xref{Blank +Lines}. + +@item -d +@itemx --minimal +Change the algorithm to perhaps find a smaller set of changes. This +makes @command{sdiff} slower (sometimes much slower). @xref{diff +Performance}. + +@item --diff-program=@var{program} +Use the compatible comparison program @var{program} to compare files +instead of @command{diff}. + +@item -E +@itemx --ignore-tab-expansion +Ignore changes due to tab expansion. +@xref{White Space}. + +@item --help +Output a summary of usage and then exit. + +@item -i +@itemx --ignore-case +Ignore changes in case; consider upper- and lower-case to be the same. +@xref{Case Folding}. + +@item -I @var{regexp} +@itemx --ignore-matching-lines=@var{regexp} +Ignore changes that just insert or delete lines that match @var{regexp}. +@xref{Specified Lines}. + +@item -l +@itemx --left-column +Print only the left column of two common lines. +@xref{Side by Side Format}. + +@item -o @var{file} +@itemx --output=@var{file} +Put merged output into @var{file}. This option is required for merging. + +@item -s +@itemx --suppress-common-lines +Do not print common lines. @xref{Side by Side Format}. + +@item --speed-large-files +Use heuristics to speed handling of large files that have numerous +scattered small changes. @xref{diff Performance}. + +@item --strip-trailing-cr +Strip any trailing carriage return at the end of an input line. +@xref{Binary}. + +@item -t +@itemx --expand-tabs +Expand tabs to spaces in the output, to preserve the alignment of tabs +in the input files. @xref{Tabs}. + +@item --tabsize=@var{columns} +Assume that tab stops are set every @var{columns} (default 8) print +columns. @xref{Tabs}. + +@item -v +@itemx --version +Output version information and then exit. + +@item -w @var{columns} +@itemx --width=@var{columns} +Output at most @var{columns} (default 130) print columns per line. +@xref{Side by Side Format}. Note that for historical reasons, this +option is @option{-W} in @command{diff}, @option{-w} in @command{sdiff}. + +@item -W +@itemx --ignore-all-space +Ignore white space when comparing lines. @xref{White Space}. +Note that for historical reasons, this option is @option{-w} in @command{diff}, +@option{-W} in @command{sdiff}. + +@item -Z +@itemx --ignore-trailing-space +Ignore white space at line end. @xref{White Space}. +@end table + +@node Standards conformance +@chapter Standards conformance +@cindex @acronym{POSIX} + +@vindex POSIXLY_CORRECT +In a few cases, the @acronym{GNU} utilities' default behavior is +incompatible with the @acronym{POSIX} standard. To suppress these +incompatibilities, define the @env{POSIXLY_CORRECT} environment +variable. Unless you are checking for @acronym{POSIX} conformance, you +probably do not need to define @env{POSIXLY_CORRECT}. + +Normally options and operands can appear in any order, and programs act +as if all the options appear before any operands. For example, +@samp{diff lao tzu -C 2} acts like @samp{diff -C 2 lao tzu}, since +@samp{2} is an option-argument of @option{-C}. However, if the +@env{POSIXLY_CORRECT} environment variable is set, options must appear +before operands, unless otherwise specified for a particular command. + +Newer versions of @acronym{POSIX} are occasionally incompatible with older +versions. For example, older versions of @acronym{POSIX} allowed the +command @samp{diff -c -10} to have the same meaning as @samp{diff -C +10}, but @acronym{POSIX} 1003.1-2001 @samp{diff} no longer allows +digit-string options like @option{-10}. + +@vindex _POSIX2_VERSION +The @acronym{GNU} utilities normally conform to the version of @acronym{POSIX} +that is standard for your system. To cause them to conform to a +different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION} +environment variable to a value of the form @var{yyyymm} specifying +the year and month the standard was adopted. Two values are currently +supported for @env{_POSIX2_VERSION}: @samp{199209} stands for +@acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX} +1003.1-2001. For example, if you are running older software that +assumes an older version of @acronym{POSIX} and uses @samp{diff -c -10}, +you can work around the compatibility problems by setting +@samp{_POSIX2_VERSION=199209} in your environment. + +@node Projects +@chapter Future Projects + +Here are some ideas for improving @acronym{GNU} @command{diff} and +@command{patch}. The @acronym{GNU} project has identified some +improvements as potential programming projects for volunteers. You +can also help by reporting any bugs that you find. + +If you are a programmer and would like to contribute something to the +@acronym{GNU} project, please consider volunteering for one of these +projects. If you are seriously contemplating work, please write to +@email{gvc@@gnu.org} to coordinate with other volunteers. + +@menu +* Shortcomings:: Suggested projects for improvements. +* Bugs:: Reporting bugs. +@end menu + +@node Shortcomings +@section Suggested Projects for Improving @acronym{GNU} @command{diff} and @command{patch} +@cindex projects for directories + +One should be able to use @acronym{GNU} @command{diff} to generate a +patch from any pair of directory trees, and given the patch and a copy +of one such tree, use @command{patch} to generate a faithful copy of +the other. Unfortunately, some changes to directory trees cannot be +expressed using current patch formats; also, @command{patch} does not +handle some of the existing formats. These shortcomings motivate the +following suggested projects. + +@menu +* Internationalization:: Handling multibyte and varying-width characters. +* Changing Structure:: Handling changes to the directory structure. +* Special Files:: Handling symbolic links, device special files, etc. +* Unusual File Names:: Handling file names that contain unusual characters. +* Time Stamp Order:: Outputting diffs in time stamp order. +* Ignoring Changes:: Ignoring certain changes while showing others. +* Speedups:: Improving performance. +@end menu + +@node Internationalization +@subsection Handling Multibyte and Varying-Width Characters +@cindex multibyte characters +@cindex varying-width characters + +@command{diff}, @command{diff3} and @command{sdiff} treat each line of +input as a string of unibyte characters. This can mishandle multibyte +characters in some cases. For example, when asked to ignore spaces, +@command{diff} does not properly ignore a multibyte space character. + +Also, @command{diff} currently assumes that each byte is one column +wide, and this assumption is incorrect in some locales, e.g., locales +that use UTF-8 encoding. This causes problems with the @option{-y} or +@option{--side-by-side} option of @command{diff}. + +These problems need to be fixed without unduly affecting the +performance of the utilities in unibyte environments. + +The IBM GNU/Linux Technology Center Internationalization Team has +proposed +@uref{http://oss.software.ibm.com/developer/opensource/linux/patches/i18n/diffutils-2.7.2-i18n-0.1.patch.gz,patches +to support internationalized @command{diff}}. +Unfortunately, these patches are incomplete and are to an older +version of @command{diff}, so more work needs to be done in this area. + +@node Changing Structure +@subsection Handling Changes to the Directory Structure +@cindex directory structure changes + +@command{diff} and @command{patch} do not handle some changes to directory +structure. For example, suppose one directory tree contains a directory +named @samp{D} with some subsidiary files, and another contains a file +with the same name @samp{D}. @samp{diff -r} does not output enough +information for @command{patch} to transform the directory subtree into +the file. + +There should be a way to specify that a file has been removed without +having to include its entire contents in the patch file. There should +also be a way to tell @command{patch} that a file was renamed, even if +there is no way for @command{diff} to generate such information. +There should be a way to tell @command{patch} that a file's time stamp +has changed, even if its contents have not changed. + +These problems can be fixed by extending the @command{diff} output format +to represent changes in directory structure, and extending @command{patch} +to understand these extensions. + +@node Special Files +@subsection Files that are Neither Directories Nor Regular Files +@cindex special files + +Some files are neither directories nor regular files: they are unusual +files like symbolic links, device special files, named pipes, and +sockets. Currently, @command{diff} treats symbolic links as if they +were the pointed-to files, except that a recursive @command{diff} +reports an error if it detects infinite loops of symbolic links (e.g., +symbolic links to @file{..}). @command{diff} treats other special +files like regular files if they are specified at the top level, but +simply reports their presence when comparing directories. This means +that @command{patch} cannot represent changes to such files. For +example, if you change which file a symbolic link points to, +@command{diff} outputs the difference between the two files, instead +of the change to the symbolic link. + +@c This might not be a good idea; is it wise for root to install devices +@c this way? +@command{diff} should optionally report changes to special files specially, +and @command{patch} should be extended to understand these extensions. + +@node Unusual File Names +@subsection File Names that Contain Unusual Characters +@cindex file names with unusual characters + +When a file name contains an unusual character like a newline or +white space, @samp{diff -r} generates a patch that @command{patch} cannot +parse. The problem is with format of @command{diff} output, not just with +@command{patch}, because with odd enough file names one can cause +@command{diff} to generate a patch that is syntactically correct but +patches the wrong files. The format of @command{diff} output should be +extended to handle all possible file names. + +@node Time Stamp Order +@subsection Outputting Diffs in Time Stamp Order + +Applying @command{patch} to a multiple-file diff can result in files +whose time stamps are out of order. @acronym{GNU} @command{patch} has +options to restore the time stamps of the updated files +(@pxref{Patching Time Stamps}), but sometimes it is useful to generate +a patch that works even if the recipient does not have @acronym{GNU} patch, +or does not use these options. One way to do this would be to +implement a @command{diff} option to output diffs in time stamp order. + +@node Ignoring Changes +@subsection Ignoring Certain Changes + +It would be nice to have a feature for specifying two strings, one in +@var{from-file} and one in @var{to-file}, which should be considered to +match. Thus, if the two strings are @samp{foo} and @samp{bar}, then if +two lines differ only in that @samp{foo} in file 1 corresponds to +@samp{bar} in file 2, the lines are treated as identical. + +It is not clear how general this feature can or should be, or +what syntax should be used for it. + +A partial substitute is to filter one or both files before comparing, +e.g.: + +@example +sed 's/foo/bar/g' file1 | diff - file2 +@end example + +However, this outputs the filtered text, not the original. + +@node Speedups +@subsection Improving Performance + +When comparing two large directory structures, one of which was +originally copied from the other with time stamps preserved (e.g., +with @samp{cp -pR}), it would greatly improve performance if an option +told @command{diff} to assume that two files with the same size and +time stamps have the same content. @xref{diff Performance}. + +@node Bugs +@section Reporting Bugs +@cindex bug reports +@cindex reporting bugs + +If you think you have found a bug in @acronym{GNU} @command{cmp}, +@command{diff}, @command{diff3}, or @command{sdiff}, please report it +by electronic mail to the +@uref{http://mail.gnu.org/mailman/listinfo/bug-diffutils,GNU utilities +bug report mailing list} @email{bug-diffutils@@gnu.org}. Please send +bug reports for @acronym{GNU} @command{patch} to +@email{bug-patch@@gnu.org}. Send as precise a description of the +problem as you can, including the output of the @option{--version} +option and sample input files that produce the bug, if applicable. If +you have a nontrivial fix for the bug, please send it as well. If you +have a patch, please send it too. It may simplify the maintainer's +job if the patch is relative to a recent test release, which you can +find in the directory @uref{ftp://alpha.gnu.org/gnu/diffutils/}. + +@node Copying This Manual +@appendix Copying This Manual +@include fdl.texi + +@node Translations +@appendix Translations of This Manual + +Nishio Futoshi of the GNUjdoc project has prepared a Japanese +translation of this manual. Its most recent version can be found at +@uref{http://openlab.ring.gr.jp/gnujdoc/cvsweb/cvsweb.cgi/gnujdoc/}. + +@node Index +@appendix Index + +@printindex cp + +@bye |