source: trunk/essentials/sys-apps/diffutils/doc/diff.info@ 3074

This is diff.info, produced by makeinfo version 4.2 from diff.texi.

This manual is for GNU Diffutils (version 2.8.1, 5 April 2002), and
documents the GNU `diff', `diff3', `sdiff', and `cmp' commands for
showing the differences between files and the GNU `patch' command for
using their output to update files.

   Copyright (C) 1992, 1993, 1994, 1998, 2001, 2002 Free Software
Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with the Front-Cover texts
     being "A GNU Manual," and with the Back-Cover Texts as in (a)
     below.  A copy of the license is included in the section entitled
     "GNU Free Documentation License."

     (a) The FSF's Back-Cover Text is: "You have freedom to copy and
     modify this GNU Manual, like GNU software.  Copies published by
     the Free Software Foundation raise funds for GNU development."
   
INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* cmp: (diff)Invoking cmp.                      Compare 2 files byte by byte.
* diff: (diff)Invoking diff.                    Compare 2 files line by line.
* diff3: (diff)Invoking diff3.                  Compare 3 files line by line.
* patch: (diff)Invoking patch.                  Apply a patch to a file.
* sdiff: (diff)Invoking sdiff.                  Merge 2 files side-by-side.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU packages
START-INFO-DIR-ENTRY
* Diff: (diff).                 Comparing and merging files.
END-INFO-DIR-ENTRY


File: diff.info,  Node: Top,  Next: Overview,  Up: (dir)

Comparing and Merging Files
***************************

This manual is for GNU Diffutils (version 2.8.1, 5 April 2002), and
documents the GNU `diff', `diff3', `sdiff', and `cmp' commands for
showing the differences between files and the GNU `patch' command for
using their output to update files.

   Copyright (C) 1992, 1993, 1994, 1998, 2001, 2002 Free Software
Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with the Front-Cover texts
     being "A GNU Manual," and with the Back-Cover Texts as in (a)
     below.  A copy of the license is included in the section entitled
     "GNU Free Documentation License."

     (a) The FSF's Back-Cover Text is: "You have freedom to copy and
     modify this GNU Manual, like GNU software.  Copies published by
     the Free Software Foundation raise funds for GNU development."
   
* 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 `diff' output prettier.
* diff Performance::      Making `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 `sdiff'.

* Merging with patch::    Using `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 POSIX standard.
* Projects::              If you've found a bug or other shortcoming.

* Copying This Manual::   How to make copies of this manual.
* Index::                 Index.


File: diff.info,  Node: Overview,  Next: Comparison,  Prev: Top,  Up: Top

Overview
********

   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 `diff' command to show differences between two
files, or each corresponding file in two directories.  `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 "diff" or "patch".  For files that are identical, `diff'
normally produces no output; for binary (non-text) files, `diff'
normally reports only that they are different.

   You can use the `cmp' command to show the byte and line numbers
where two files differ.  `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 `M-x compare-windows'.
*Note Other Window: (emacs)Other Window, for more information on that
command.

   You can use the `diff3' command to show differences among three
files.  When two people have made independent changes to a common
original, `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 `sdiff' command to merge two files interactively.

   You can use the set of differences produced by `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 `diff' output, you can use the `patch'
program to update, or "patch", a copy of the file.  If you think of
`diff' as subtracting one file from another to produce their
difference, you can think of `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.

   GNU `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
in "An O(ND) Difference Algorithm and its Variations", Eugene W. Myers,
`Algorithmica' Vol. 1 No. 2, 1986, pp. 251-266; and in "A File
Comparison Program", Webb Miller and Eugene W. Myers,
`Software--Practice and Experience' Vol. 15 No. 11, 1985, pp. 1025-1040.
The algorithm was independently discovered as described in "Algorithms
for Approximate String Matching", E. Ukkonen, `Information and Control'
Vol. 64, 1985, pp. 100-118.

   GNU `diff3' was written by Randy Smith.  GNU `sdiff' was written by
Thomas Lord.  GNU `cmp' was written by Torbjorn Granlund and David
MacKenzie.

   `patch' was written mainly by Larry Wall and Paul Eggert; several
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.


File: diff.info,  Node: Comparison,  Next: Output Formats,  Prev: Overview,  Up: Top

What Comparison Means
*********************

   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.  `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.

   GNU `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.  `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.
`cmp' reports the differences between two files byte by byte, instead
of line by line.  As a result, it is often more useful than `diff' for
comparing binary files.  For text files, `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, `diff' will report that a blank line has
been added to the file, while `cmp' will report that almost every byte
of the two files differs.

   `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.

* Menu:

* Hunks::             Groups of differing lines.
* White Space::       Suppressing differences in white space.
* Blank Lines::       Suppressing differences in blank lines.
* Case Folding::      Suppressing differences in alphabetic case.
* Specified Folding:: Suppressing differences that match regular expressions.
* Brief::             Summarizing which files are different.
* Binary::            Comparing binary files or forcing text comparisons.


File: diff.info,  Node: Hunks,  Next: White Space,  Up: Comparison

Hunks
=====

   When comparing two files, `diff' finds sequences of lines common to
both files, interspersed with groups of differing lines called "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.  `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 `F' contains the three lines `a', `b',
`c', and the file `G' contains the same three lines in reverse order
`c', `b', `a'.  If `diff' finds the line `c' as common, then the command
`diff F G' produces this output:

     1,2d0
     < a
     < b
     3a2,3
     > b
     > a

But if `diff' notices the common line `b' instead, it produces this
output:

     1c1
     < a
     ---
     > c
     3c3
     < c
     ---
     > a

It is also possible to find `a' as the common line.  `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 `--minimal' option
(*note diff Performance::).


File: diff.info,  Node: White Space,  Next: Blank Lines,  Prev: Hunks,  Up: Comparison

Suppressing Differences in Blank and Tab Spacing
================================================

   The `-E' and `--ignore-tab-expansion' options ignore 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.  `diff' assumes that tab
stops are set every 8 print columns.

   The `-b' and `--ignore-space-change' options are stronger.  They
ignore white space at line end, and consider all other sequences of one
or more white space characters to be equivalent.  With these options,
`diff' considers the following two lines to be equivalent, where `$'
denotes the line end:

     Here lyeth  muche rychnesse  in lytell space.   -- John Heywood$
     Here lyeth muche rychnesse in lytell space. -- John Heywood   $

   The `-w' and `--ignore-all-space' options are stronger still.  They
ignore difference even if one line has white space where the other line
has none.  "White space" characters include tab, newline, vertical tab,
form feed, carriage return, and space; some locales may define
additional characters to be white space.  With these options, `diff'
considers the following two lines to be equivalent, where `$' denotes
the line end and `^M' denotes a carriage return:

     Here lyeth  muche  rychnesse in lytell space.--  John Heywood$
       He relyeth much erychnes  seinly tells pace.  --John Heywood   ^M$


File: diff.info,  Node: Blank Lines,  Next: Case Folding,  Prev: White Space,  Up: Comparison

Suppressing Differences in Blank Lines
======================================

   The `-B' and `--ignore-blank-lines' options ignore insertions or
deletions of blank lines.  These options affect only lines that are
completely empty; they do not affect lines that look empty but contain
space or tab characters.  With these options, for example, a file
containing
     1.  A point is that which has no part.
     
     2.  A line is breadthless length.
     -- Euclid, The Elements, I

is considered identical to a file containing
     1.  A point is that which has no part.
     2.  A line is breadthless length.
     
     
     -- Euclid, The Elements, I


File: diff.info,  Node: Case Folding,  Next: Specified Folding,  Prev: Blank Lines,  Up: Comparison

Suppressing Case Differences
============================

   GNU `diff' can treat lower case letters as equivalent to their upper
case counterparts, so that, for example, it considers `Funky Stuff',
`funky STUFF', and `fUNKy stuFf' to all be the same.  To request this,
use the `-i' or `--ignore-case' option.


File: diff.info,  Node: Specified Folding,  Next: Brief,  Prev: Case Folding,  Up: Comparison

Suppressing Lines Matching a Regular Expression
===============================================

   To ignore insertions and deletions of lines that match a
`grep'-style regular expression, use the `-I REGEXP' or
`--ignore-matching-lines=REGEXP' option.  You should escape regular
expressions that contain shell metacharacters to prevent the shell from
expanding them.  For example, `diff -I '^[[:digit:]]'' ignores all
changes to lines beginning with a digit.

   However, `-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, `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 `-I' option.  `diff' tries to match each line
against each regular expression.


File: diff.info,  Node: Brief,  Next: Binary,  Prev: Specified Folding,  Up: Comparison

Summarizing Which Files Differ
==============================

   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, `diff' simply reports whether files differ.  The `-q' and
`--brief' options select 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 `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 `cmp'.  For files that are identical, `cmp' produces no output.
When the files differ, by default, `cmp' outputs the byte and line
number where the first difference occurs.  You can use the `-s' option
to suppress that information, so that `cmp' produces no output and
reports whether the files differ using only its exit status (*note
Invoking cmp::).

   Unlike `diff', `cmp' cannot compare directories; it can only compare
two files.


File: diff.info,  Node: Binary,  Prev: Brief,  Up: Comparison

Binary Files and Forcing Text Comparisons
=========================================

   If `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 (*note Brief::), and
reports only that the binary files are different.  This is because line
by line comparisons are usually not meaningful for binary files.

   `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, `diff' considers the file to be text;
otherwise it considers the file to be binary.

   Sometimes you might want to force `diff' to consider files to be
text.  For example, you might be comparing text files that contain null
characters; `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 `diff' to consider all files to be
text files, and compare them line by line, by using the `-a' or
`--text' option.  If the files you compare using this option do not in
fact contain text, they will probably contain few newline characters,
and the `diff' output will consist of hunks showing differences between
long lines of whatever characters the files contain.

   You can also force `diff' to consider all files to be binary files,
and report only whether they differ (but not how).  Use the `-q' or
`--brief' option for this.

   Differing binary files are considered to cause trouble because the
resulting `diff' output does not capture all the differences.  This
trouble causes `diff' to exit with status 2.  However, this trouble
cannot occur with the `--a' or `--text' option, or with the `-q' or
`--brief' option, as these options both cause `diff' to treat binary
files like text files.

   In operating systems that distinguish between text and binary files,
`diff' normally reads and writes all data as text.  Use the `--binary'
option to force `diff' to read and write binary data instead.  This
option has no effect on a POSIX-compliant system like 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, `diff' normally ignores these carriage
returns on input and generates them at the end of each output line, but
with the `--binary' option `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 POSIX-compliant systems.

   The `--strip-trailing-cr' causes `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 `cmp'
program with the `-l' option to show the values of each differing byte
in the two files.  With GNU `cmp', you can also use the `-b' option to
show the ASCII representation of those bytes.  *Note Invoking cmp::,
for more information.

   If `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.  `diff3' uses the same test as `diff' to decide
whether a file is binary.  As with `diff', if the input files contain a
few non-text bytes but otherwise are like text files, you can force
`diff3' to consider all files to be text files and compare them line by
line by using the `-a' or `--text' options.


File: diff.info,  Node: Output Formats,  Next: Incomplete Lines,  Prev: Comparison,  Up: Top

`diff' Output Formats
*********************

   `diff' has several mutually exclusive options for output format.
The following sections describe each format, illustrating how `diff'
reports the differences between two sample input files.

* Menu:

* Sample diff Input:: Sample `diff' input files for examples.
* Normal::            Showing differences without surrounding text.
* Context::           Showing differences with the surrounding text.
* Side by Side::      Showing differences in two columns.
* Scripts::           Generating scripts for other programs.
* If-then-else::      Merging files with if-then-else.


File: diff.info,  Node: Sample diff Input,  Next: Normal,  Up: Output Formats

Two Sample Input Files
======================

   Here are two sample files that we will use in numerous examples to
illustrate the output of `diff' and how various options can change it.

   This is the file `lao':

     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.

   This is the file `tzu':

     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!

   In this example, the first hunk contains just the first two lines of
`lao', the second hunk contains the fourth line of `lao' opposing the
second and third lines of `tzu', and the last hunk contains just the
last three lines of `tzu'.


File: diff.info,  Node: Normal,  Next: Context,  Prev: Sample diff Input,  Up: Output Formats

Showing Differences Without Context
===================================

   The "normal" `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 (*note Context Format::) and the unified format (*note
Unified Format::) are superior.  Normal format is the default for
compatibility with older versions of `diff' and the POSIX standard.
Use the `--normal' option to select this output format explicitly.

* Menu:

* Detailed Normal:: A detailed description of normal output format.
* Example Normal::  Sample output in the normal format.


File: diff.info,  Node: Detailed Normal,  Next: Example Normal,  Up: Normal

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:

     CHANGE-COMMAND
     < FROM-FILE-LINE
     < FROM-FILE-LINE...
     ---
     > TO-FILE-LINE
     > TO-FILE-LINE...

   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:

`LaR'
     Add the lines in range R of the second file after line L of the
     first file.  For example, `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.

`FcT'
     Replace the lines in range F of the first file with lines in range
     T of the second file.  This is like a combined add and delete, but
     more compact.  For example, `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.

`RdL'
     Delete the lines in range R from the first file; line L is where
     they would have appeared in the second file had they not been
     deleted.  For example, `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.


File: diff.info,  Node: Example Normal,  Prev: Detailed Normal,  Up: Normal

An Example of Normal Format
---------------------------

   Here is the output of the command `diff lao tzu' (*note 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.

     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!


File: diff.info,  Node: Context,  Next: Side by Side,  Prev: Normal,  Up: Output Formats

Showing Differences in Their Context
====================================

   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 "context".

   GNU `diff' provides two output formats that show context around the
differing lines: "context format" and "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 `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.  `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, `patch' can adjust the line numbers
accordingly and still apply the diff correctly.  *Note Imperfect::, for
more information on using `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.


File: diff.info,  Node: Context Format,  Next: Unified Format,  Up: Context

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 `-C LINES',
`--context[=LINES]', or `-c' option.  The argument LINES that some of
these options take is the number of lines of context to show.  If you
do not specify LINES, it defaults to three.  For proper operation,
`patch' typically needs at least two lines of context.

* Menu:

* Detailed Context:: A detailed description of the context output format.
* Example Context::  Sample output in context format.
* Less Context::     Another sample with less context.


File: diff.info,  Node: Detailed Context,  Next: Example Context,  Up: Context Format

Detailed Description of Context Format
......................................

   The context output format starts with a two-line header, which looks
like this:

     *** FROM-FILE FROM-FILE-MODIFICATION-TIME
     --- TO-FILE TO-FILE-MODIFICATION TIME

The time stamp normally looks like `2002-02-21 23:30:39.942229878
-0800' to indicate the date, time with fractional seconds, and time
zone in Internet RFC 2822 format
(ftp://ftp.isi.edu/in-notes/rfc2822.txt).  However, a traditional time
stamp like `Thu Feb 21 23:30:39 2002' is used if the `LC_TIME' locale
category is either `C' or `POSIX'.

   You can change the header's content with the `--label=LABEL' option;
see *Note 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:

     ***************
     *** FROM-FILE-LINE-RANGE ****
       FROM-FILE-LINE
       FROM-FILE-LINE...
     --- TO-FILE-LINE-RANGE ----
       TO-FILE-LINE
       TO-FILE-LINE...

   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:

`!'
     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 `!' in the part of this hunk for the other file.

`+'
     An "inserted" line in the second file that corresponds to nothing
     in the first file.

`-'
     A "deleted" line in the first file that corresponds to nothing in
     the second file.

   If all of the changes in a hunk are insertions, the lines of
FROM-FILE are omitted.  If all of the changes are deletions, the lines
of TO-FILE are omitted.


File: diff.info,  Node: Example Context,  Next: Less Context,  Prev: Detailed Context,  Up: Context Format

An Example of Context Format
............................

   Here is the output of `diff -c lao tzu' (*note 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.

     *** 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!


File: diff.info,  Node: Less Context,  Prev: Example Context,  Up: Context Format

An Example of Context Format with Less Context
..............................................

   Here is the output of `diff -C 1 lao tzu' (*note Sample diff
Input::, for the complete contents of the two files).  Notice that at
most one context line is reported here.

     *** 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!


File: diff.info,  Node: Unified Format,  Next: Sections,  Prev: Context Format,  Up: Context

Unified 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 `-U LINES', `--unified[=LINES]', or `-u'
option.  The argument LINES is the number of lines of context to show.
When it is not given, it defaults to three.

   At present, only GNU `diff' can produce this format and only GNU
`patch' can automatically apply diffs in this format.  For proper
operation, `patch' typically needs at least three lines of context.

* Menu:

* Detailed Unified:: A detailed description of unified format.
* Example Unified::  Sample output in unified format.


File: diff.info,  Node: Detailed Unified,  Next: Example Unified,  Up: Unified Format

Detailed Description of Unified Format
......................................

   The unified output format starts with a two-line header, which looks
like this:

     --- FROM-FILE FROM-FILE-MODIFICATION-TIME
     +++ TO-FILE TO-FILE-MODIFICATION-TIME

The time stamp looks like `2002-02-21 23:30:39.942229878 -0800' to
indicate the date, time with fractional seconds, and time zone.

   You can change the header's content with the `--label=LABEL' option;
see *Note 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:

     @@ FROM-FILE-RANGE TO-FILE-RANGE @@
      LINE-FROM-EITHER-FILE
      LINE-FROM-EITHER-FILE...

   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:

`+'
     A line was added here to the first file.

`-'
     A line was removed here from the first file.


File: diff.info,  Node: Example Unified,  Prev: Detailed Unified,  Up: Unified Format

An Example of Unified Format
............................

   Here is the output of the command `diff -u lao tzu' (*note Sample
diff Input::, for the complete contents of the two files):

     --- 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!


File: diff.info,  Node: Sections,  Next: Alternate Names,  Prev: Unified Format,  Up: Context

Showing Which Sections Differences Are in
-----------------------------------------

   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.  GNU `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.


File: diff.info,  Node: Specified Headings,  Next: C Function Headings,  Up: Sections

Showing Lines That Match Regular Expressions
............................................

   To show in which sections differences occur for files that are not
source code for C or similar languages, use the `-F REGEXP' or
`--show-function-line=REGEXP' option.  `diff' considers lines that
match the `grep'-style regular expression REGEXP to be the beginning of
a section of the file.  Here are suggested regular expressions for some
common languages:

`^[[:alpha:]$_]'
     C, C++, Prolog

`^('
     Lisp

`^@node'
     Texinfo

   This option does not automatically select an output format; in order
to use it, you must select the context format (*note Context Format::)
or unified format (*note Unified Format::).  In other output formats it
has no effect.

   The `-F' and `--show-function-line' options find the nearest
unchanged line that precedes each hunk of differences and matches the
given regular expression.  Then they add that line to the end of the
line of asterisks in the context format, or to the `@@' line in unified
format.  If no matching line exists, they leave the output for that
hunk unchanged.  If that line is more than 40 characters long, they
output only the first 40 characters.  You can specify more than one
regular expression for such lines; `diff' tries to match each line
against each regular expression, starting with the last one given.  This
means that you can use `-p' and `-F' together, if you wish.


File: diff.info,  Node: C Function Headings,  Prev: Specified Headings,  Up: Sections

Showing C Function Headings
...........................

   To show in which functions differences occur for C and similar
languages, you can use the `-p' or `--show-c-function' option.  This
option automatically defaults to the context output format (*note
Context Format::), with the default number of lines of context.  You
can override that number with `-C LINES' elsewhere in the command line.
You can override both the format and the number with `-U LINES'
elsewhere in the command line.

   The `-p' and `--show-c-function' options are equivalent to `-F
'^[[:alpha:]$_]'' if the unified format is specified, otherwise `-c -F
'^[[:alpha:]$_]'' (*note Specified Headings::).  GNU `diff' provides
them for the sake of convenience.


File: diff.info,  Node: Alternate Names,  Prev: Sections,  Up: Context

Showing Alternate File Names
----------------------------

   If you are comparing two files that have meaningless or uninformative
names, you might want `diff' to show alternate names in the header of
the context and unified output formats.  To do this, use the
`--label=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, `diff' reports an
error.  The `--label' option does not affect the file names in the `pr'
header when the `-l' or `--paginate' option is used (*note
Pagination::).

   Here are the first two lines of the output from `diff -C 2
--label=original --label=modified lao tzu':

     *** original
     --- modified


File: diff.info,  Node: Side by Side,  Next: Scripts,  Prev: Context,  Up: Output Formats

Showing Differences Side by Side
================================

   `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:

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
     `--ignore' options (*note White Space::).

`|'
     The corresponding lines differ, and they are either both complete
     or both incomplete.

`<'
     The files differ and only the first file contains the line.

`>'
     The files differ and only the second file contains the line.

`('
     Only the first file contains the line, but the difference is
     ignored.

`)'
     Only the second file contains the line, but the difference is
     ignored.

`\'
     The corresponding lines differ, and only the first line is
     incomplete.

`/'
     The corresponding lines differ, and only the second line is
     incomplete.

   Normally, an output line is incomplete if and only if the lines that
it contains are incomplete; *Note 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 `\' if the first line is incomplete, `/' 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 `sdiff' command to interactively merge side by side
differences.  *Note 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.


File: diff.info,  Node: Side by Side Format,  Next: Example Side by Side,  Up: Side by Side

Controlling Side by Side Format
-------------------------------

   The `-y' or `--side-by-side' 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
`-W COLUMNS' or `--width=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 `--left-column' option prints only the left column of two common
lines.  The `--suppress-common-lines' option suppresses common lines
entirely.


File: diff.info,  Node: Example Side by Side,  Prev: Side by Side Format,  Up: Side by Side

An Example of Side by Side Format
---------------------------------

   Here is the output of the command `diff -y -W 72 lao tzu' (*note
Sample diff Input::, for the complete contents of the two files).

     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!


File: diff.info,  Node: Scripts,  Next: If-then-else,  Prev: Side by Side,  Up: Output Formats

Making Edit Scripts
===================

   Several output modes produce command scripts for editing FROM-FILE
to produce TO-FILE.

* Menu:

* ed Scripts:: Using `diff' to produce commands for `ed'.
* Forward ed:: Making forward `ed' scripts.
* RCS::        A special `diff' output format used by RCS.


File: diff.info,  Node: ed Scripts,  Next: Forward ed,  Up: Scripts

`ed' Scripts
------------

   `diff' can produce commands that direct the `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 `patch', it is almost obsolete.  Use the
`-e' or `--ed' option to select this output format.

   Like the normal format (*note 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 `d' contains the output of `diff -e old new', then the
command `(cat d && echo w) | ed - old' edits `old' to make it a copy of
`new'.  More generally, if `d1', `d2', ..., `dN' contain the outputs of
`diff -e old new1', `diff -e new1 new2', ..., `diff -e newN-1 newN',
respectively, then the command `(cat d1 d2 ... dN && echo w) | ed -
old' edits `old' to make it a copy of `newN'.

* Menu:

* Detailed ed:: A detailed description of `ed' format.
* Example ed::  A sample `ed' script.


File: diff.info,  Node: Detailed ed,  Next: Example ed,  Up: ed Scripts

Detailed Description of `ed' Format
...................................

   The `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 `ed'
interprets line numbers in succeeding commands.  `ed' format hunks look
like this:

     CHANGE-COMMAND
     TO-FILE-LINE
     TO-FILE-LINE...
     .

   Because `ed' uses a single period on a line to indicate the end of
input, GNU `diff' protects lines of changes that contain a single
period on a line by writing two periods instead, then writing a
subsequent `ed' command to change the two periods into one.  The `ed'
format cannot represent an incomplete line, so if the second file ends
in a changed incomplete line, `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:

`La'
     Add text from the second file after line L in the first file.  For
     example, `8a' means to add the following lines after line 8 of file
     1.

`Rc'
     Replace the lines in range R in the first file with the following
     lines.  Like a combined add and delete, but more compact.  For
     example, `5,7c' means change lines 5-7 of file 1 to read as the
     text file 2.

`Rd'
     Delete the lines in range R from the first file.  For example,
     `5,7d' means delete lines 5-7 of file 1.


File: diff.info,  Node: Example ed,  Prev: Detailed ed,  Up: ed Scripts

Example `ed' Script
...................

   Here is the output of `diff -e lao tzu' (*note Sample diff Input::,
for the complete contents of the two files):

     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


File: diff.info,  Node: Forward ed,  Next: RCS,  Prev: ed Scripts,  Up: Scripts

Forward `ed' Scripts
--------------------

   `diff' can produce output that is like an `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 `ed'
format, forward `ed' format cannot represent incomplete lines.

   Forward `ed' format is not very useful, because neither `ed' nor
`patch' can apply diffs in this format.  It exists mainly for
compatibility with older versions of `diff'.  Use the `-f' or
`--forward-ed' option to select it.


File: diff.info,  Node: RCS,  Prev: Forward ed,  Up: Scripts

RCS Scripts
-----------

   The 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 `-n' or
`--rcs' option to select this output format.  It is like the forward
`ed' format (*note Forward ed::), but it can represent arbitrary
changes to the contents of a file because it avoids the forward `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 `a' and `d' commands are used
instead of `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 `diff -n lao tzu' (*note Sample diff Input::,
for the complete contents of the two files):

     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!


File: diff.info,  Node: If-then-else,  Prev: Scripts,  Up: Output Formats

Merging Files with If-then-else
===============================

   You can use `diff' to merge two files of C source code.  The output
of `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 `#ifdef NAME' or `#ifndef
NAME', `#else', and `#endif'.  When compiling the output, you select
which version to use by either defining or leaving undefined the macro
NAME.

   To merge two files, use `diff' with the `-D NAME' or `--ifdef=NAME'
option.  The argument NAME is the C preprocessor identifier to use in
the `#ifdef' and `#ifndef' directives.

   For example, if you change an instance of `wait (&s)' to `waitpid
(-1, &s, 0)' and then merge the old and new files with the
`--ifdef=HAVE_WAITPID' option, then the affected part of your code
might look like this:

         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);

   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.
* Detailed If-then-else:: A detailed description of if-then-else format.
* Example If-then-else::  Sample if-then-else format output.


File: diff.info,  Node: Line Group Formats,  Next: Line Formats,  Up: If-then-else

Line Group Formats
------------------

   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 `old' and
`new', and outputs a merged file in which old regions are surrounded by
`\begin{em}'-`\end{em}' lines, and new regions are surrounded by
`\begin{bf}'-`\end{bf}' lines.

     diff \
        --old-group-format='\begin{em}
     %<\end{em}
     ' \
        --new-group-format='\begin{bf}
     %>\end{bf}
     ' \
        old new

   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.

     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

   Here is a more advanced example, which outputs a diff listing with
headers containing line numbers in a "plain English" style.

     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

   To specify a line group format, use `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 FORMAT, because it typically
contains shell metacharacters.

`--old-group-format=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.

`--new-group-format=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.

`--changed-group-format=FORMAT'