source: trunk/essentials/sys-apps/diffutils/doc/diff.info@ 3330

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'
     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.

`--unchanged-group-format=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.

   In a line group format, ordinary characters represent themselves;
conversion specifications start with `%' and have one of the following
forms.

`%<'
     stands for the lines from the first file, including the trailing
     newline.  Each line is formatted according to the old line format
     (*note Line Formats::).

`%>'
     stands for the lines from the second file, including the trailing
     newline.  Each line is formatted according to the new line format.

`%='
     stands for the lines common to both files, including the trailing
     newline.  Each line is formatted according to the unchanged line
     format.

`%%'
     stands for `%'.

`%c'C''
     where C is a single character, stands for C.  C may not be a
     backslash or an apostrophe.  For example, `%c':'' stands for a
     colon, even inside the then-part of an if-then-else format, which
     a colon would normally terminate.

`%c'\O''
     where O is a string of 1, 2, or 3 octal digits, stands for the
     character with octal code O.  For example, `%c'\0'' stands for a
     null character.

`FN'
     where F is a `printf' conversion specification and N is one of the
     following letters, stands for N's value formatted with F.

    `e'
          The line number of the line just before the group in the old
          file.

    `f'
          The line number of the first line in the group in the old
          file; equals E + 1.

    `l'
          The line number of the last line in the group in the old file.

    `m'
          The line number of the line just after the group in the old
          file; equals L + 1.

    `n'
          The number of lines in the group in the old file; equals L -
          F + 1.

    `E, F, L, M, N'
          Likewise, for lines in the new file.

     The `printf' conversion specification can be `%d', `%o', `%x', or
     `%X', specifying decimal, octal, lower case hexadecimal, or upper
     case hexadecimal output respectively.  After the `%' 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 `-' for left-justification, `'' for separating the
     digit into groups as specified by the `LC_NUMERIC' locale category,
     and `0' for padding with zeros instead of spaces.  For example,
     `%5dN' prints the number of new lines in the group in a field of
     width 5 characters, using the `printf' format `"%5d"'.

`(A=B?T:E)'
     If A equals B then T else E.  A and B are each either a decimal
     constant or a single letter interpreted as above.  This format
     spec is equivalent to T if A's value equals B's; otherwise it is
     equivalent to E.

     For example, `%(N=0?no:%dN) line%(N=1?:s)' is equivalent to `no
     lines' if N (the number of lines in the group in the the new file)
     is 0, to `1 line' if N is 1, and to `%dN lines' otherwise.


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

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 `-' for deleted lines, `|' for added lines, and a space for
unchanged lines.  The formats contain newline characters where newlines
are desired on output.

     diff \
        --old-line-format='-%l
     ' \
        --new-line-format='|%l
     ' \
        --unchanged-line-format=' %l
     ' \
        old new

   To specify a line format, use one of the following options.  You
should quote FORMAT, since it often contains shell metacharacters.

`--old-line-format=FORMAT'
     formats lines just from the first file.

`--new-line-format=FORMAT'
     formats lines just from the second file.

`--unchanged-line-format=FORMAT'
     formats lines common to both files.

`--line-format=FORMAT'
     formats all lines; in effect, it sets all three above options
     simultaneously.

   In a line format, ordinary characters represent themselves;
conversion specifications start with `%' and have one of the following
forms.

`%l'
     stands for the contents of the line, not counting its trailing
     newline (if any).  This format ignores whether the line is
     incomplete; *Note Incomplete Lines::.

`%L'
     stands for the contents of the line, including its trailing newline
     (if any).  If a line is incomplete, this format preserves its
     incompleteness.

`%%'
     stands for `%'.

`%c'C''
     where C is a single character, stands for C.  C may not be a
     backslash or an apostrophe.  For example, `%c':'' stands for a
     colon.

`%c'\O''
     where O is a string of 1, 2, or 3 octal digits, stands for the
     character with octal code O.  For example, `%c'\0'' stands for a
     null character.

`Fn'
     where F is a `printf' conversion specification, stands for the
     line number formatted with F.  For example, `%.5dn' prints the
     line number using the `printf' format `"%.5d"'.  *Note Line Group
     Formats::, for more about printf conversion specifications.

   The default line format is `%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 `%l' or `%L' in a line format
is just after a tab stop (e.g. by preceding `%l' or `%L' with a tab
character), or you should use the `-t' or `--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 `diff' format.  You can tailor this command to get
fine control over `diff' output.

     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


File: diff.info,  Node: Detailed If-then-else,  Next: Example If-then-else,  Prev: Line Formats,  Up: If-then-else

Detailed Description of If-then-else Format
-------------------------------------------

   For lines common to both files, `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, `diff' uses the old
line group format; if the hunk contains only lines from the second
file, `diff' uses the new group format; otherwise, `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 `--ifdef=NAME' is equivalent to the following sequence of
options using shell syntax:

     --old-group-format='#ifndef NAME
     %<#endif /* ! NAME */
     ' \
     --new-group-format='#ifdef NAME
     %>#endif /* NAME */
     ' \
     --unchanged-group-format='%=' \
     --changed-group-format='#ifndef NAME
     %<#else /* NAME */
     %>#endif /* NAME */
     '

   You should carefully check the `diff' output for proper nesting.
For example, when using the `-D NAME' or `--ifdef=NAME' option, you
should check that if the differing lines contain any of the C
preprocessor directives `#ifdef', `#ifndef', `#else', `#elif', or
`#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 `patch' `-D NAME' option behaves like the `diff' `-D NAME'
option, except it operates on a file and a diff to produce a merged
file; *Note patch Options::.


File: diff.info,  Node: Example If-then-else,  Prev: Detailed If-then-else,  Up: If-then-else

An Example of If-then-else Format
---------------------------------

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

     #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 */


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

Incomplete Lines
****************

   When an input file ends in a non-newline character, its last line is
called an "incomplete line" because its last character is not a
newline.  All other lines are called "full lines" and end in a newline
character.  Incomplete lines do not match full lines unless differences
in white space are ignored (*note White Space::).

   An incomplete line is normally distinguished on output from a full
line by a following line that starts with `\'.  However, the RCS format
(*note 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 `\' or `/' gutter
marker; *Note Side by Side::.  The if-then-else line format preserves a
line's incompleteness with `%L', and discards the newline with `%l';
*Note Line Formats::.  Finally, with the `ed' and forward `ed' output
formats (*note Output Formats::) `diff' cannot represent an incomplete
line, so it pretends there was a newline and reports an error.

   For example, suppose `F' and `G' are one-byte files that contain
just `f' and `g', respectively.  Then `diff F G' outputs

     1c1
     < f
     \ No newline at end of file
     ---
     > g
     \ No newline at end of file

(The exact message may differ in non-English locales.)  `diff -n F G'
outputs the following without a trailing newline:

     d1 1
     a1 1
     g

`diff -e F G' reports two errors and outputs the following:

     1c
     g
     .


File: diff.info,  Node: Comparing Directories,  Next: Adjusting Output,  Prev: Incomplete Lines,  Up: Top

Comparing Directories
*********************

   You can use `diff' to compare some or all of the files in two
directory trees.  When both file name arguments to `diff' are
directories, it compares each file that is contained in both
directories, examining file names in alphabetical order as specified by
the `LC_COLLATE' locale category.  Normally `diff' is silent about
pairs of files that contain no differences, but if you use the `-s' or
`--report-identical-files' option, it reports pairs of identical files.
Normally `diff' reports subdirectories common to both directories
without comparing subdirectories' files, but if you use the `-r' or
`--recursive' option, it compares every corresponding pair of files in
the directory trees, as many levels deep as they go.

   For file names that are in only one of the directories, `diff'
normally does not show the contents of the file that exists; it reports
only that the file exists in that directory and not in the other.  You
can make `diff' act as though the file existed but was empty in the
other directory, 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 it is in the first or the second directory given.)
To do this, use the `-N' or `--new-file' option.

   If the older directory contains one or more large files that are not
in the newer directory, you can make the patch smaller by using the
`--unidirectional-new-file' option instead of `-N'.  This option is
like `-N' except that it only inserts the contents 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.  *Note Making Patches::, for more discussion of
making patches for distribution.

   To ignore some files while comparing directories, use the `-x
PATTERN' or `--exclude=PATTERN' option.  This option ignores any files
or subdirectories whose base names match the shell pattern 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
PATTERN in quotes so that the shell does not expand it.  For example,
the option `-x '*.[ao]'' ignores any file whose name ends with `.a' or
`.o'.

   This option accumulates if you specify it more than once.  For
example, using the options `-x 'RCS' -x '*,v'' ignores any file or
subdirectory whose base name is `RCS' or ends with `,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 `-X FILE' or
`--exclude-from=FILE' option.

   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 `-S FILE' or `--starting-file=FILE' option.  This
compares only the file 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, `diff' normally reports many
differences because it compares file names in a case sensitive way.
With the `--ignore-file-name-case' option, `diff' ignores case
differences in file names, so that for example the contents of the file
`Tao' in one directory are compared to the contents of the file `TAO'
in the other.  The `--no-ignore-file-name-case' option cancels the
effect of the `--ignore-file-name-case' option, reverting to the default
behavior.

   If an `-x PATTERN', `--exclude=PATTERN', `-X FILE', or
`--exclude-from=FILE' option is specified while the
`--ignore-file-name-case' option is in effect, case is ignored when
excluding file names matching the specified patterns.


File: diff.info,  Node: Adjusting Output,  Next: diff Performance,  Prev: Comparing Directories,  Up: Top

Making `diff' Output Prettier
*****************************

   `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.
* Pagination:: Page numbering and time-stamping `diff' output.


File: diff.info,  Node: Tabs,  Next: Pagination,  Up: Adjusting Output

Preserving Tab Stop Alignment
=============================

   The lines of text in some of the `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.  GNU `diff' provides two ways to make tab-aligned columns line up
correctly.

   The first way is to have `diff' convert all tabs into the correct
number of spaces before outputting them; select this method with the
`-t' or `--expand-tabs' option.  `diff' assumes that tab stops are set
every 8 print columns.  To use this form of output with `patch', you
must give `patch' the `-l' or `--ignore-white-space' option (*note
Changed White Space::, for more information).

   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 `-T' or
`--initial-tab' option.


File: diff.info,  Node: Pagination,  Prev: Tabs,  Up: Adjusting Output

Paginating `diff' Output
========================

   It can be convenient to have long output page-numbered and
time-stamped.  The `-l' and `--paginate' options do this by sending the
`diff' output through the `pr' program.  Here is what the page header
might look like for `diff -lc lao tzu':

     2002-02-22 14:20                 diff -lc lao tzu                 Page 1


File: diff.info,  Node: diff Performance,  Next: Comparing Three Files,  Prev: Adjusting Output,  Up: Top

`diff' Performance Tradeoffs
****************************

   GNU `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 `diff' performance is to use hard or symbolic
links to files instead of copies.  This improves performance because
`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 `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 GNU `cp -lR' or `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 GNU `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 GNU `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 `diff' output is large, you
might want `diff' to use a modified algorithm that sometimes produces a
smaller set of differences.  The `-d' or `--minimal' option does this;
however, it can also cause `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
`--speed-large-files' option to make a different modification to the
algorithm that `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, `diff' might produce a larger set of
differences; however, the output will still be correct.

   Normally `diff' discards the prefix and suffix that is common to
both files before it attempts to find a minimal set of differences.
This makes `diff' run faster, but occasionally it may produce
non-minimal output.  The `--horizon-lines=LINES' option prevents `diff'
from discarding the last LINES lines of the prefix and the first LINES
lines of the suffix.  This gives `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 `diff' command is free to choose which identical sequence is
included in the hunk.  In this case, `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.


File: diff.info,  Node: Comparing Three Files,  Next: diff3 Merging,  Prev: diff Performance,  Up: Top

Comparing Three Files
*********************

   Use the program `diff3' to compare three files and show any
differences among them.  (`diff3' can also merge files; see *Note diff3
Merging::).

   The "normal" `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.

   *Note Invoking diff3::, for more information on how to run `diff3'.

* Menu:

* Sample diff3 Input::    Sample `diff3' input for examples.
* Detailed diff3 Normal:: A detailed description of normal output format.
* diff3 Hunks::           The format of normal output format.
* Example diff3 Normal::  Sample output in the normal format.


File: diff.info,  Node: Sample diff3 Input,  Next: Detailed diff3 Normal,  Up: Comparing Three Files

A Third Sample Input File
=========================

   Here is a third sample file that will be used in examples to
illustrate the output of `diff3' and how various options can change it.
The first two files are the same that we used for `diff' (*note Sample
diff Input::).  This is the third sample file, called `tao':

     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


File: diff.info,  Node: Detailed diff3 Normal,  Next: diff3 Hunks,  Prev: Sample diff3 Input,  Up: Comparing Three Files

Detailed Description of `diff3' Normal Format
=============================================

   Each hunk begins with a line marked `===='.  Three-way hunks have
plain `====' lines, and two-way hunks have `1', `2', or `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 `-T' or `--initial-tab'
option, `diff3' uses a tab instead of two spaces; this lines up tabs
correctly.  *Note Tabs::, for more information.

   Commands take the following forms:

`FILE:La'
     This hunk appears after line L of file 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,
     `1:11a' means that the hunk follows line 11 in the first file and
     contains no lines from that file.

`FILE:Rc'
     This hunk contains the lines in the range R of file FILE.  The
     range R is a comma-separated pair of line numbers, or just one
     number if the range is a singleton.  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, `2:11,13c' means that
     the hunk contains lines 11 through 13 from the second file.

   If the last line in a set of input lines is incomplete (*note
Incomplete Lines::), it is distinguished on output from a full line by
a following line that starts with `\'.


File: diff.info,  Node: diff3 Hunks,  Next: Example diff3 Normal,  Prev: Detailed diff3 Normal,  Up: Comparing Three Files

`diff3' Hunks
=============

   Groups of lines that differ in two or three of the input files are
called "diff3 hunks", by analogy with `diff' hunks (*note Hunks::).  If
all three input files differ in a `diff3' hunk, the hunk is called a
"three-way hunk"; if just two input files differ, it is a "two-way
hunk".

   As with `diff', several solutions are possible.  When comparing the
files `A', `B', and `C', `diff3' normally finds `diff3' hunks by
merging the two-way hunks output by the two commands `diff A B' and
`diff A C'.  This does not necessarily minimize the size of the output,
but exceptions should be rare.

   For example, suppose `F' contains the three lines `a', `b', `f', `G'
contains the lines `g', `b', `g', and `H' contains the lines `a', `b',
`h'.  `diff3 F G H' might output the following:

     ====2
     1:1c
     3:1c
       a
     2:1c
       g
     ====
     1:3c
       f
     2:3c
       g
     3:3c
       h

because it found a two-way hunk containing `a' in the first and third
files and `g' in the second file, then the single line `b' common to
all three files, then a three-way hunk containing the last line of each
file.


File: diff.info,  Node: Example diff3 Normal,  Prev: diff3 Hunks,  Up: Comparing Three Files

An Example of `diff3' Normal Format
===================================

   Here is the output of the command `diff3 lao tzu tao' (*note Sample
diff3 Input::, for the complete contents of the files).  Notice that it
shows only the lines that are different among the three files.

     ====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


File: diff.info,  Node: diff3 Merging,  Next: Interactive Merging,  Prev: Comparing Three Files,  Up: Top

Merging From a Common Ancestor
******************************

   When two people have made changes to copies of the same file,
`diff3' can produce a merged output that contains both sets of changes
together with warnings about conflicts.

   One might imagine programs with names like `diff4' and `diff5' to
compare more than three files simultaneously, but in practice the need
rarely arises.  You can use `diff3' to merge three or more sets of
changes to a file by merging two change sets at a time.

   `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:

     diff3 MINE OLDER YOURS

You can remember the order of the arguments by noting that they are in
alphabetical order.

   You can think of this as subtracting OLDER from YOURS and adding the
result to MINE, or as merging into MINE the changes that would turn
OLDER into YOURS.  This merging is well-defined as long as MINE and
OLDER match in the neighborhood of each such change.  This fails to be
true when all three input files differ or when only OLDER differs; we
call this a "conflict".  When all three input files differ, we call the
conflict an "overlap".

   `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 `<<<<<<<' and `>>>>>>>' lines.

   `diff3' can output the merge results as an `ed' script that that can
be applied to the first file to yield the merged output.  However, it
is usually better to have `diff3' generate the merged output directly;
this bypasses some problems with `ed'.

* Menu:

* Which Changes::            Selecting changes to incorporate.
* Marking Conflicts::        Marking conflicts.
* Bypassing ed::             Generating merged output directly.
* Merging Incomplete Lines:: How `diff3' merges incomplete lines.
* Saving the Changed File::  Emulating System V behavior.


File: diff.info,  Node: Which Changes,  Next: Marking Conflicts,  Up: diff3 Merging

Selecting Which Changes to Incorporate
======================================

   You can select all unmerged changes from OLDER to YOURS for merging
into MINE with the `-e' or `--ed' option.  You can select only the
nonoverlapping unmerged changes with `-3' or `--easy-only', and you can
select only the overlapping changes with `-x' or `--overlap-only'.

   The `-e', `-3' and `-x' options select only "unmerged changes", i.e.
changes where MINE and YOURS differ; they ignore changes from OLDER to
YOURS where MINE and 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 `-A' or `--show-all' option (*note Marking
Conflicts::).

   Here is the output of the command `diff3' with each of these three
options (*note Sample diff3 Input::, for the complete contents of the
files).  Notice that `-e' outputs the union of the disjoint sets of
changes output by `-3' and `-x'.

   Output of `diff3 -e lao tzu tao':
     11a
     
       -- The Way of Lao-Tzu, tr. Wing-tsit Chan
     .
     8c
       so we may see their result.
     .

   Output of `diff3 -3 lao tzu tao':
     8c
       so we may see their result.
     .

   Output of `diff3 -x lao tzu tao':
     11a
     
       -- The Way of Lao-Tzu, tr. Wing-tsit Chan
     .


File: diff.info,  Node: Marking Conflicts,  Next: Bypassing ed,  Prev: Which Changes,  Up: diff3 Merging

Marking Conflicts
=================

   `diff3' can mark conflicts in the merged output by bracketing them
with special marker lines.  A conflict that comes from two files A and
B is marked as follows:

     <<<<<<< A
     lines from A
     =======
     lines from B
     >>>>>>> B

   A conflict that comes from three files A, B and C is marked as
follows:

     <<<<<<< A
     lines from A
     ||||||| B
     lines from B
     =======
     lines from C
     >>>>>>> C

   The `-A' or `--show-all' option acts like the `-e' option, except
that it brackets conflicts, and it outputs all changes from OLDER to
YOURS, not just the unmerged changes.  Thus, given the sample input
files (*note Sample diff3 Input::), `diff3 -A lao tzu tao' puts
brackets around the conflict where only `tzu' differs:

     <<<<<<< 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

   And it outputs the three-way conflict as follows:

     <<<<<<< 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

   The `-E' or `--show-overlap' option outputs less information than
the `-A' or `--show-all' option, because it outputs only unmerged
changes, and it never outputs the contents of the second file.  Thus
the `-E' option acts like the `-e' option, except that it brackets the
first and third files from three-way overlapping changes.  Similarly,
`-X' acts like `-x', except it brackets all its (necessarily
overlapping) changes.  For example, for the three-way overlapping
change above, the `-E' and `-X' options output the following:

     <<<<<<< lao
     =======
     
       -- The Way of Lao-Tzu, tr. Wing-tsit Chan
     >>>>>>> tao

   If you are comparing files that have meaningless or uninformative
names, you can use the `-L LABEL' or `--label=LABEL' option to show
alternate names in the `<<<<<<<', `|||||||' and `>>>>>>>' brackets.
This option can be given up to three times, once for each input file.
Thus `diff3 -A -L X -L Y -L Z A B C' acts like `diff3 -A A B C', except
that the output looks like it came from files named `X', `Y' and `Z'
rather than from files named `A', `B' and `C'.


File: diff.info,  Node: Bypassing ed,  Next: Merging Incomplete Lines,  Prev: Marking Conflicts,  Up: diff3 Merging

Generating the Merged Output Directly
=====================================

   With the `-m' or `--merge' option, `diff3' outputs the merged file
directly.  This is more efficient than using `ed' to generate it, and
works even with non-text files that `ed' would reject.  If you specify
`-m' without an `ed' script option, `-A' (`--show-all') is assumed.

   For example, the command `diff3 -m lao tzu tao' (*note Sample diff3
Input:: for a copy of the input files) would output the following:

     <<<<<<< 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


File: diff.info,  Node: Merging Incomplete Lines,  Next: Saving the Changed File,  Prev: Bypassing ed,  Up: diff3 Merging

How `diff3' Merges Incomplete Lines
===================================

   With `-m', incomplete lines (*note 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 `|||||||', `=======' or `>>>>>>>' brackets appear somewhere
other than the start of a line because they are appended to the
incomplete line.

   Without `-m', if an `ed' script option is specified and an
incomplete line is found, `diff3' generates a warning and acts as if a
newline had been present.


File: diff.info,  Node: Saving the Changed File,  Prev: Merging Incomplete Lines,  Up: diff3 Merging

Saving the Changed File
=======================

   Traditional Unix `diff3' generates an `ed' script without the
trailing `w' and `q' commands that save the changes.  System V `diff3'
generates these extra commands.  GNU `diff3' normally behaves like
traditional Unix `diff3', but with the `-i' option it behaves like
System V `diff3' and appends the `w' and `q' commands.

   The `-i' option requires one of the `ed' script options `-AeExX3',
and is incompatible with the merged output option `-m'.


File: diff.info,  Node: Interactive Merging,  Next: Merging with patch,  Prev: diff3 Merging,  Up: Top

Interactive Merging with `sdiff'
********************************

   With `sdiff', you can merge two files interactively based on a
side-by-side `-y' format comparison (*note Side by Side::).  Use `-o
FILE' or `--output=FILE' to specify where to put the merged text.
*Note Invoking sdiff::, for more details on the options to `sdiff'.

   Another way to merge files interactively is to use the Emacs Lisp
package `emerge'.  *Note emerge: (emacs)emerge, for more information.

* Menu:

* sdiff Option Summary:: Summary of `sdiff' options.
* Merge Commands::       Merging two files interactively.


File: diff.info,  Node: sdiff Option Summary,  Next: Merge Commands,  Up: Interactive Merging

Specifying `diff' Options to `sdiff'
====================================

   The following `sdiff' options have the same meaning as for `diff'.
*Note diff Options::, for the use of these options.

     -a -b -d -i -t -v
     -B -E -I REGEXP
     
     --ignore-blank-lines  --ignore-case
     --ignore-matching-lines=REGEXP  --ignore-space-change
     --ignore-tab-expansion
     --left-column  --minimal  --speed-large-files
     --strip-trailing-cr  --suppress-common-lines  --expand-tabs
     --text  --version  --width=COLUMNS

   For historical reasons, `sdiff' has alternate names for some
options.  The `-l' option is equivalent to the `--left-column' option,
and similarly `-s' is equivalent to `--suppress-common-lines'.  The
meaning of the `sdiff' `-w' and `-W' options is interchanged from that
of `diff': with `sdiff', `-w COLUMNS' is equivalent to
`--width=COLUMNS', and `-W' is equivalent to `--ignore-all-space'.
`sdiff' without the `-o' option is equivalent to `diff' with the `-y'
or `--side-by-side' option (*note Side by Side::).


File: diff.info,  Node: Merge Commands,  Prev: sdiff Option Summary,  Up: Interactive Merging

Merge Commands
==============

   Groups of common lines, with a blank gutter, are copied from the
first file to the output.  After each group of differing lines, `sdiff'
prompts with `%' and pauses, waiting for one of the following commands.
Follow each command with <RET>.

`e'
     Discard both versions.  Invoke a text editor on an empty temporary
     file, then copy the resulting file to the output.

`eb'
     Concatenate the two versions, edit the result in a temporary file,
     then copy the edited result to the output.

`ed'
     Like `eb', except precede each version with a header that shows
     what file and lines the version came from.

`el'
     Edit a copy of the left version, then copy the result to the
     output.

`er'
     Edit a copy of the right version, then copy the result to the
     output.

`l'
     Copy the left version to the output.

`q'
     Quit.

`r'
     Copy the right version to the output.

`s'
     Silently copy common lines.

`v'
     Verbosely copy common lines.  This is the default.

   The text editor invoked is specified by the `EDITOR' environment
variable if it is set.  The default is system-dependent.


File: diff.info,  Node: Merging with patch,  Next: Making Patches,  Prev: Interactive Merging,  Up: Top

Merging with `patch'
********************

   `patch' takes comparison output produced by `diff' and applies the
differences to a copy of the original file, producing a patched
version.  With `patch', you can distribute just the changes to a set of
files instead of distributing the entire file set; your correspondents
can apply `patch' to update their copy of the files with your changes.
`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 `patch'.

   `patch' detects and warns about common problems like forward
patches.  It saves any patches that it could not apply.  It can also
maintain a `patchlevel.h' file to ensure that your correspondents apply
diffs in the proper order.

   `patch' accepts a series of diffs in its standard input, usually
separated by headers that specify which file to patch.  It applies
`diff' hunks (*note Hunks::) one by one.  If a hunk does not exactly
match the original file, `patch' uses heuristics to try to patch the
file as well as it can.  If no approximate match can be found, `patch'
rejects the hunk and skips to the next hunk.  `patch' normally replaces
each file F with its new version, putting reject hunks (if any) into
`F.rej'.

   *Note Invoking patch::, for detailed information on the options to
`patch'.

* Menu:

* patch Input::            Selecting the type of `patch' input.
* Revision Control::       Getting files from RCS, 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 `patch' can produce.
* patch and POSIX::        Conformance to the POSIX standard.
* patch and Tradition::    GNU versus traditional `patch'.


File: diff.info,  Node: patch Input,  Next: Revision Control,  Up: Merging with patch

Selecting the `patch' Input Format
==================================

   `patch' normally determines which `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 `patch' to interpret the patch file as a certain
format of diff.  The output formats listed here are the only ones that
`patch' can understand.

`-c'
`--context'
     context diff.

`-e'
`--ed'
     `ed' script.

`-n'
`--normal'
     normal diff.

`-u'
`--unified'
     unified diff.


File: diff.info,  Node: Revision Control,  Next: Imperfect,  Prev: patch Input,  Up: Merging with patch

Revision Control
================

   If a nonexistent input file is under a revision control system
supported by `patch', `patch' normally asks the user whether to get (or
check out) the file from the revision control system.  Patch currently
supports RCS, ClearCase and SCCS.  Under RCS and SCCS, `patch' also
asks when the input file is read-only and matches the default version
in the revision control system.

   The `-g NUM' or `--get=NUM' affects access to files under supported
revision control systems.  If NUM is positive, `patch' gets the file
without asking the user; if zero, `patch' neither asks the user nor
gets the file; and if negative, `patch' asks the user before getting
the file.  The default value of NUM is given by the value of the
`PATCH_GET' environment variable if it is set; if not, the default
value is zero if `patch' is conforming to POSIX, negative otherwise.
*Note patch and POSIX::.

   The choice of revision control system is unaffected by the
`VERSION_CONTROL' environment variable (*note Backup Names::).


File: diff.info,  Node: Imperfect,  Next: Creating and Removing,  Prev: Revision Control,  Up: Merging with patch

Applying Imperfect Patches
==========================

   `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 `patch', and it should work.  If the entire diff is
indented by a constant amount of white space, `patch' automatically
ignores the indentation.  If a context diff contains trailing carriage
return on each line, `patch' automatically ignores the carriage return.
If a context diff has been encapsulated by prepending `- ' to lines
beginning with `-' as per Internet RFC 934
(ftp://ftp.isi.edu/in-notes/rfc934.txt), `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 `patch' find close matches.
* Dry Runs::            Predicting what `patch' will do.


File: diff.info,  Node: Changed White Space,  Next: Reversed Patches,  Up: Imperfect

Applying Patches with Changed White Space
-----------------------------------------

   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 `patch' will not be able to match
them properly.  If this problem occurs, use the `-l' or
`--ignore-white-space' option, which makes `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.


File: diff.info,  Node: Reversed Patches,  Next: Inexact,  Prev: Changed White Space,  Up: Imperfect

Applying Reversed Patches
-------------------------

   Sometimes people run `diff' with the new file first instead of
second.  This creates a diff that is "reversed".  To apply such
patches, give `patch' the `-R' or `--reverse' option.  `patch' then
attempts to swap each hunk around before applying it.  Rejects come out
in the swapped format.

   Often `patch' can guess that the patch is reversed.  If the first
hunk of a patch fails, `patch' reverses the hunk to see if it can apply
it that way.  If it can, `patch' asks you if you want to have the `-R'
option set; if it can't, `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 `patch'
notices.

   If you apply a patch that you have already applied, `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 `n' to this offer and to the
subsequent "apply anyway" question--or type `C-c' to kill the `patch'
process.


File: diff.info,  Node: Inexact,  Next: Dry Runs,  Prev: Reversed Patches,  Up: Imperfect

Helping `patch' Find Inexact Matches
------------------------------------

   For context diffs, and to a lesser extent normal diffs, `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, `patch' scans both forward and backward for a set of
lines matching the context given in the hunk.

   First `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
`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 `-F LINES' or `--fuzz=LINES' option sets the maximum fuzz factor
to LINES.  This option only applies to context and unified diffs; it
ignores up to 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 `patch' cannot find a place to install a hunk of the patch, it
writes the hunk out to a reject file (*note 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 `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 `patch' thinks the failed hunks belong in the new file
rather than in the old one.

   If the `--verbose' option is given, then as it completes each hunk
`patch' tells you whether the hunk succeeded or failed, and if it
failed, on which line (in the new file) `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 _may_ indicate that
`patch' installed a hunk in the wrong place.  `patch' also tells you if
it used a fuzz factor to make the match, in which case you should also
be slightly suspicious.

   `patch' cannot tell if the line numbers are off in an `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.  *Note Creating and Removing::.

   `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.


File: diff.info,  Node: Dry Runs,  Prev: Inexact,  Up: Imperfect

Predicting what `patch' will do
-------------------------------

   It may not be obvious in advance what `patch' will do with a
complicated or poorly formatted patch.  If you are concerned that the
input might cause `patch' to modify the wrong files, you can use the
`--dry-run' option, which causes `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 `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 `patch')
and try another dry run.  Once you are satisfied with the proposed
patch you can apply it by invoking `patch' as before, but this time
without the `--dry-run' option.


File: diff.info,  Node: Creating and Removing,  Next: Patching Time Stamps,  Prev: Imperfect,  Up: Merging with patch

Creating and Removing Files
===========================

   Sometimes when comparing two directories, a file may exist in one
directory but not the other.  If you give `diff' the `-N' or
`--new-file' option, or if you supply an old or new file that is named
`/dev/null' or is empty and is dated the Epoch (1970-01-01 00:00:00
UTC), `diff' outputs a patch that adds or deletes the contents of this
file.  When given such a patch, `patch' normally creates a new file or
removes the old file.  However, when conforming to POSIX (*note patch
and POSIX::), `patch' does not remove the old file, but leaves it empty.
The `-E' or `--remove-empty-files' option causes `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, `patch'
asks for confirmation before applying the patch.


File: diff.info,  Node: Patching Time Stamps,  Next: Multiple Patches,  Prev: Creating and Removing,  Up: Merging with patch

Updating Time Stamps on Patched Files
=====================================

   When `patch' updates a file, it normally sets the file's
last-modified time stamp to the current time of day.  If you are using
`patch' to track a software distribution, this can cause `make' to
incorrectly conclude that a patched file is out of date.  For example,
if `syntax.c' depends on `syntax.y', and `patch' updates `syntax.c' and
then `syntax.y', then `syntax.c' will normally appear to be out of date
with respect to `syntax.y' even though its contents are actually up to
date.

   The `-Z' or `--set-utc' option causes `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 (UTC,
often known as GMT).

   The `-T' or `--set-time' option acts like `-Z' or `--set-utc',
except that it assumes that the context diff headers' time stamps use
local time instead of 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 `-Z' or
`--set-utc'.

   `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 `-f' or `--force' option is given, the file's
time stamps are set regardless.

   Due to the limitations of the current `diff' format, `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 `make clean') all files that depend
on the patched files, so that later invocations of `make' do not get
confused by the patched files' times.


File: diff.info,  Node: Multiple Patches,  Next: patch Directories,  Prev: Patching Time Stamps,  Up: Merging with patch

Multiple Patches in a File
==========================

   If the patch file contains more than one patch, and if you do not
specify an input file on the command line, `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 (*note Making Patches::, for more on that
topic).

   `patch' uses the following rules to intuit a file name from the
leading text before a patch.  First, `patch' takes an ordered list of
candidate file names as follows:

   * If the header is that of a context diff, `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 `-pNUM' or `--strip=NUM'
     option.  The name `/dev/null' is also ignored.

   * If there is an `Index:' line in the leading garbage and if either
     the old and new names are both absent or if `patch' is conforming
     to POSIX, `patch' takes the name in the `Index:' line.

   * 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.

Then `patch' selects a file name from the candidate list as follows:

   * If some of the named files exist, `patch' selects the first name
     if conforming to POSIX, and the best name otherwise.

   * If `patch' is not ignoring RCS, ClearCase, and SCCS (*note
     Revision Control::), and no named files exist but an RCS,
     ClearCase, or SCCS master is found, `patch' selects the first
     named file with an RCS, ClearCase, or SCCS master.

   * If no named files exist, no RCS, ClearCase, or SCCS master was
     found, some names are given, `patch' is not conforming to POSIX,
     and the patch appears to create a file, `patch' selects the best
     name requiring the creation of the fewest directories.

   * If no file name results from the above heuristics, you are asked
     for the name of the file to patch, and `patch' selects that name.

   To determine the "best" of a nonempty list of file names, `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.

   *Note patch and POSIX::, to see whether `patch' is conforming to
POSIX.


File: diff.info,  Node: patch Directories,  Next: Backups,  Prev: Multiple Patches,  Up: Merging with patch

Applying Patches in Other Directories
=====================================

   The `-d DIRECTORY' or `--directory=DIRECTORY' option to `patch'
makes directory DIRECTORY the current directory for interpreting both
file names in the patch file, and file names given as arguments to
other options (such as `-B' and `-o').  For example, while in a mail
reading program, you can patch a file in the `/usr/src/emacs' directory
directly from a message containing the patch like this:

     | patch -d /usr/src/emacs

   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 `-pNUMBER' or
`--strip=NUMBER' option to set the file name strip count to NUMBER.
The strip count tells `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, `patch' strips off all leading directories, leaving just the
base file names.

   For example, suppose the file name in the patch file is
`/gnu/src/emacs/etc/NEWS'.  Using `-p0' gives the entire file name
unmodified, `-p1' gives `gnu/src/emacs/etc/NEWS' (no leading slash),
`-p4' gives `etc/NEWS', and not specifying `-p' at all gives `NEWS'.

   `patch' looks for each file (after any slashes have been stripped)
in the current directory, or if you used the `-d DIRECTORY' option, in
that directory.


File: diff.info,  Node: Backups,  Next: Backup Names,  Prev: patch Directories,  Up: Merging with patch

Backup Files
============

   Normally, `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 `patch
-R' (*note Reversed Patches::).  However, when conforming to POSIX,
`patch' does not create backup files by default.  *Note patch and
POSIX::.

   The `-b' or `--backup' option causes `patch' to make a backup file
regardless of whether the patch matches the original input.  The
`--backup-if-mismatch' option causes `patch' to create backup files for
mismatches files; this is the default when not conforming to POSIX.  The
`--no-backup-if-mismatch' option causes `patch' to not create backup
files, even for mismatched patches; this is the default when conforming
to 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.


File: diff.info,  Node: Backup Names,  Next: Reject Names,  Prev: Backups,  Up: Merging with patch

Backup File Names
=================

   Normally, `patch' renames an original input file into a backup file
by appending to its name the extension `.orig', or `~' if using `.orig'
would make the backup file name too long.(1)  The `-z BACKUP-SUFFIX' or
`--suffix=BACKUP-SUFFIX' option causes `patch' to use BACKUP-SUFFIX as
the backup extension instead.

   Alternately, you can specify the extension for backup files with the
`SIMPLE_BACKUP_SUFFIX' environment variable, which the options override.

   `patch' can also create numbered backup files the way GNU Emacs
does.  With this method, instead of having a single backup of each file,
`patch' makes a new backup file name each time it patches a file.  For
example, the backups of a file named `sink' would be called,
successively, `sink.~1~', `sink.~2~', `sink.~3~', etc.

   The `-V BACKUP-STYLE' or `--version-control=BACKUP-STYLE' option
takes as an argument a method for creating backup file names.  You can
alternately control the type of backups that `patch' makes with the
`PATCH_VERSION_CONTROL' environment variable, which the `-V' option
overrides.  If `PATCH_VERSION_CONTROL' is not set, the
`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 (*note Revision Control::).

   The values of these environment variables and the argument to the
`-V' option are like the GNU Emacs `version-control' variable (*note
Backup Names: (emacs)Backup Names., 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.

`t'
`numbered'
     Always make numbered backups.

`nil'
`existing'
     Make numbered backups of files that already have them, simple
     backups of the others.  This is the default.

`never'
`simple'
     Always make simple backups.

   You can also tell `patch' to prepend a prefix, such as a directory
name, to produce backup file names.  The `-B PREFIX' or
`--prefix=PREFIX' option makes backup files by prepending PREFIX to
them.  The `-Y PREFIX' or `--basename-prefix=PREFIX' prepends PREFIX to
the last file name component of backup file names instead; for example,
`-Y ~' causes the backup name for `dir/file.c' to be `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 `-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
`--no-backup-if-mismatch' option, none of the options described in this
section have any affect, because no backups are made.

   ---------- Footnotes ----------

   (1) A coding error in GNU `patch' version 2.5.4 causes it to always
use `~', but this should be fixed in the next release.


File: diff.info,  Node: Reject Names,  Next: patch Messages,  Prev: Backup Names,  Up: Merging with patch

Reject File Names
=================

   The names for reject files (files containing patches that `patch'
could not find a place to apply) are normally the name of the output
file with `.rej' appended (or `#' if if using `.rej' would make the
backup file name too long).

   Alternatively, you can tell `patch' to place all of the rejected
patches in a single file.  The `-r REJECT-FILE' or
`--reject-file=REJECT-FILE' option uses REJECT-FILE as the reject file
name.


File: diff.info,  Node: patch Messages,  Next: patch and POSIX,  Prev: Reject Names,  Up: Merging with patch

Messages and Questions from `patch'
===================================

   `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, `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 `patch'.
* patch and Keyboard Input::  Inhibiting keyboard input.
* patch Quoting Style::       Quoting file names in diagnostics.

   `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.


File: diff.info,  Node: More or Fewer Messages,  Next: patch and Keyboard Input,  Up: patch Messages

Controlling the Verbosity of `patch'
------------------------------------

   You can cause `patch' to produce more messages by using the
`--verbose' option.  For example, when you give this option, the
message `Hmm...' indicates that `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 `patch', unless an error
occurs, by using the `-s', `--quiet', or `--silent' option.


File: diff.info,  Node: patch and Keyboard Input,  Next: patch Quoting Style,  Prev: More or Fewer Messages,  Up: patch Messages

Inhibiting Keyboard Input
-------------------------

   There are two ways you can prevent `patch' from asking you any
questions.  The `-f' or `--force' option assumes that you know what you
are doing.  It causes `patch' to do the following:

   * Skip patches that do not contain file names in their headers.

   * Patch files even though they have the wrong version for the
     `Prereq:' line in the patch;

   * Assume that patches are not reversed even if they look like they
     are.

The `-t' or `--batch' option is similar to `-f', in that it suppresses
questions, but it makes somewhat different assumptions:

   * Skip patches that do not contain file names in their headers (the
     same as `-f').

   * Skip patches for which the file has the wrong version for the
     `Prereq:' line in the patch;

   * Assume that patches are reversed if they look like they are.


File: diff.info,  Node: patch Quoting Style,  Prev: patch and Keyboard Input,  Up: patch Messages

`patch' Quoting Style
---------------------

   When `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 `--quoting-style=WORD' option controls
how names are output.  The WORD should be one of the following:

`literal'
     Output names as-is.

`shell'
     Quote names for the shell if they contain shell metacharacters or
     would cause ambiguous output.

`shell-always'
     Quote names for the shell, even if they would normally not require
     quoting.

`c'
     Quote names as for a C language string.

`escape'
     Quote as with `c' except omit the surrounding double-quote
     characters.

   You can specify the default value of the `--quoting-style' option
with the environment variable `QUOTING_STYLE'.  If that environment
variable is not set, the default value is `shell', but this default may
change in a future version of `patch'.


File: diff.info,  Node: patch and POSIX,  Next: patch and Tradition,  Prev: patch Messages,  Up: Merging with patch

`patch' and the POSIX Standard
==============================

   If you specify the `--posix' option, or set the `POSIXLY_CORRECT'
environment variable, `patch' conforms more strictly to the POSIX
standard, as follows:

   * Take the first existing file from the list (old, new, index) when
     intuiting file names from diff headers.  *Note Multiple Patches::.

   * Do not remove files that are removed by a diff.  *Note Creating
     and Removing::.

   * Do not ask whether to get files from RCS, ClearCase, or SCCS.
     *Note Revision Control::.

   * Require that all options precede the files in the command line.

   * Do not backup files, even when there is a mismatch.  *Note
     Backups::.



File: diff.info,  Node: patch and Tradition,  Prev: patch and POSIX,  Up: Merging with patch

GNU `patch' and Traditional `patch'
===================================

   The current version of GNU `patch' normally follows the POSIX
standard.  *Note patch and POSIX::, for the few exceptions to this
general rule.

   Unfortunately, POSIX redefined the behavior of `patch' in several
important ways.  You should be aware of the following differences if
you must interoperate with traditional `patch', or with GNU `patch'
version 2.1 and earlier.

   * In traditional `patch', the `-p' option's operand was optional,
     and a bare `-p' was equivalent to `-p0'.  The `-p' option now
     requires an operand, and `-p 0' is now equivalent to `-p0'.  For
     maximum compatibility, use options like `-p0' and `-p1'.

     Also, traditional `patch' simply counted slashes when stripping
     path prefixes; `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
     `//' in file names.

   * In traditional `patch', backups were enabled by default.  This
     behavior is now enabled with the `-b' or `--backup' option.

     Conversely, in POSIX `patch', backups are never made, even when
     there is a mismatch.  In GNU `patch', this behavior is enabled
     with the `--no-backup-if-mismatch' option, or by conforming to
     POSIX.

     The `-b SUFFIX' option of traditional `patch' is equivalent to the
     `-b -z SUFFIX' options of GNU `patch'.

   * Traditional `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 POSIX, and
     had a few gotchas.  Now `patch' uses a different, equally
     complicated (but better documented) method that is optionally
     POSIX-conforming; we hope it has fewer gotchas.  The two methods
     are compatible if the file names in the context diff header and the
     `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.

   * When traditional `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, `/dev/tty', and standard input.  Now `patch'
     sends questions to standard output and gets answers from
     `/dev/tty'.  Defaults for some answers have been changed so that
     `patch' never goes into an infinite loop when using default
     answers.

   * Traditional `patch' exited with a status value that counted the
     number of bad hunks, or with status 1 if there was real trouble.
     Now `patch' exits with status 1 if some hunks failed, or with 2 if
     there was real trouble.

   * Limit yourself to the following options when sending instructions
     meant to be executed by anyone running GNU `patch', traditional
     `patch', or a `patch' that conforms to POSIX.  Spaces are
     significant in the following list, and operands are required.

          `-c'
          `-d DIR'
          `-D DEFINE'
          `-e'
          `-l'
          `-n'
          `-N'
          `-o OUTFILE'
          `-pNUM'
          `-R'
          `-r REJECTFILE'



File: diff.info,  Node: Making Patches,  Next: Invoking cmp,  Prev: Merging with patch,  Up: Top

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 `patch'.
* Generating Smaller Patches::  How to generate smaller patches.


File: diff.info,  Node: Tips for Patch Producers,  Next: Tips for Patch Consumers,  Up: Making Patches

Tips for Patch Producers
========================

   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 `tar'
archives of the two versions.

   To generate the patch, use the command `diff -Naur OLD NEW' where
OLD and NEW identify the old and new directories.  The names OLD and
NEW should not contain any slashes.  The `-N' option lets the patch
create and remove files; `-a' lets the patch update non-text files; `-u'
generates useful time stamps and enough context; and `-r' lets the
patch update subdirectories.  Here is an example command, using Bourne
shell syntax:

     diff -Naur gcc-3.0.3 gcc-3.0.4

   Tell your recipients how to apply the patches.  This should include
which working directory to use, and which `patch' options to use; the
option `-p1' is recommended.  Test your procedure by pretending to be a
recipient and applying your patches to a copy of the original files.

   *Note Avoiding Common Mistakes::, for how to avoid common mistakes
when generating a patch.


File: diff.info,  Node: Tips for Patch Consumers,  Next: Avoiding Common Mistakes,  Prev: Tips for Patch Producers,  Up: Making Patches

Tips for Patch Consumers
========================

   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.

   GNU `diff' can analyze files with arbitrarily long lines and files
that end in incomplete lines.  However, older versions of `patch'
cannot patch such files.  If you are having trouble applying such
patches, try upgrading to a recent version of GNU `patch'.


File: diff.info,  Node: Avoiding Common Mistakes,  Next: Generating Smaller Patches,  Prev: Tips for Patch Consumers,  Up: Making Patches

Avoiding Common Mistakes
========================

   When producing a patch for multiple files, apply `diff' to
directories whose names do not have slashes.  This reduces confusion
when the patch consumer specifies the `-pNUMBER' 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:

     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

because the two file names have different numbers of slashes, and
different versions of `patch' interpret the file names differently.  To
avoid confusion, send output that looks like this instead:

     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

   Make sure you have specified the file names correctly, either in a
context diff header or with an `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
`README.orig' or `README~', since this might confuse `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.
`old/README' and `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 `patchlevel.h' or
`version.c', which contains a patch level or version number.  If the
input file contains the wrong version number, `patch' will complain
immediately.

   An even clearer way to prevent this problem is to put a `Prereq:'
line before the patch.  If the leading text in the patch file contains a
line that starts with `Prereq:', `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, `patch' prompts you for confirmation before
proceeding.  This makes it difficult to accidentally apply patches in
the wrong order.


File: diff.info,  Node: Generating Smaller Patches,  Prev: Avoiding Common Mistakes,  Up: Making Patches

Generating Smaller Patches
==========================

   The simplest way to generate a patch is to use `diff -Naur' (*note
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 `rm' and `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,
`TAGS' and output from `yacc' and `makeinfo'), exclude them from the
patch by giving `diff' the `-x PATTERN' option (*note 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 `make'.

   Now you can create the patch using `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 `rm' and
`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 `patch' typically needs at least two lines for
proper operation when patches do not exactly match the input files.


File: diff.info,  Node: Invoking cmp,  Next: Invoking diff,  Prev: Making Patches,  Up: Top

Invoking `cmp'
**************

   The `cmp' command compares two files, and if they differ, tells the
first byte and line number where they differ.  Bytes and lines are
numbered starting with 1.  The arguments of `cmp' are as follows:

     cmp OPTIONS... FROM-FILE [TO-FILE [FROM-SKIP [TO-SKIP]]]

   The file name `-' is always the standard input.  `cmp' also uses the
standard input if one file name is omitted.  The FROM-SKIP and TO-SKIP
operands specify how many bytes to ignore at the start of each file;
they are equivalent to the `--ignore-initial=FROM-SKIP:TO-SKIP' option.

   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 `cmp'.


File: diff.info,  Node: cmp Options,  Up: Invoking cmp

Options to `cmp'
================

   Below is a summary of all of the options that GNU `cmp' accepts.
Most options have two equivalent names, one of which is a single letter
preceded by `-', and the other of which is a long name preceded by
`--'.  Multiple single letter options (unless they take an argument)
can be combined into a single command line word: `-bl' is equivalent to
`-b -l'.

`-b'
`--print-bytes'
     Print the differing bytes.  Display control bytes as a `^'
     followed by a letter of the alphabet and precede bytes that have
     the high bit set with `M-' (which stands for "meta").

`--help'
     Output a summary of usage and then exit.

`-i SKIP'
`--ignore-initial=SKIP'
     Ignore any differences in the first SKIP bytes of the input files.
     Treat files with fewer than SKIP bytes as if they are empty.  If
     SKIP is of the form `FROM-SKIP:TO-SKIP', skip the first FROM-SKIP
     bytes of the first input file and the first TO-SKIP bytes of the
     second.

`-l'
`--verbose'
     Print the (decimal) byte numbers and (octal) values of all
     differing bytes.

`-n COUNT'
`--bytes=COUNT'
     Compare at most COUNT input bytes.

`-s'
`--quiet'
`--silent'
     Do not print anything; only return an exit status indicating
     whether the files differ.

`-v'
`--version'
     Output version information and then exit.

   In the above table, operands that are byte counts are normally
decimal, but may be preceded by `0' for octal and `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 `iB', specifies a multiple using
powers of 1024.  A size letter followed by `B' specifies powers of 1000
instead.  For example, `-n 4M' and `-n 4MiB' are equivalent to `-n
4194304', whereas `-n 4MB' is equivalent to `-n 4000000'.  This
notation is upward compatible with the SI prefixes
(http://www.bipm.fr/enus/3_SI/si-prefixes.html) for decimal multiples
and with the IEC 60027-2 prefixes for binary multiples
(http://physics.nist.gov/cuu/Units/binary.html).

   The following suffixes are defined.  Large sizes like `1Y' may be
rejected by your computer due to limitations of its arithmetic.

`kB'
     kilobyte: 10^3 = 1000.

`k'
`K'
`KiB'
     kibibyte: 2^10 = 1024.  `K' is special: the SI prefix is `k' and
     the IEC 60027-2 prefix is `Ki', but tradition and POSIX use `k' to
     mean `KiB'.

`MB'
     megabyte: 10^6 = 1,000,000.

`M'
`MiB'
     mebibyte: 2^20 = 1,048,576.

`GB'
     gigabyte: 10^9 = 1,000,000,000.

`G'
`GiB'
     gibibyte: 2^30 = 1,073,741,824.

`TB'
     terabyte:  10^12 = 1,000,000,000,000.

`T'
`TiB'
     tebibyte: 2^40 = 1,099,511,627,776.

`PB'
     petabyte: 10^15 = 1,000,000,000,000,000.

`P'
`PiB'
     pebibyte: 2^50 = 1,125,899,906,842,624.

`EB'
     exabyte: 10^18 = 1,000,000,000,000,000,000.

`E'
`EiB'
     exbibyte: 2^60 = 1,152,921,504,606,846,976.

`ZB'
     zettabyte: 10^21 = 1,000,000,000,000,000,000,000

`Z'
`ZiB'
     2^70 = 1,180,591,620,717,411,303,424.  (`Zi' is a GNU extension to
     IEC 60027-2.)

`YB'
     yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000.

`Y'
`YiB'
     2^80 = 1,208,925,819,614,629,174,706,176.  (`Yi' is a GNU
     extension to IEC 60027-2.)


File: diff.info,  Node: Invoking diff,  Next: Invoking diff3,  Prev: Invoking cmp,  Up: Top

Invoking `diff'
***************

   The format for running the `diff' command is:

     diff OPTIONS... FILES...

   In the simplest case, two file names FROM-FILE and TO-FILE are
given, and `diff' compares the contents of FROM-FILE and TO-FILE.  A
file name of `-' stands for text read from the standard input.  As a
special case, `diff - -' compares a copy of standard input to itself.

   If one file is a directory and the other is not, `diff' compares the
file in the directory whose name is that of the non-directory.  The
non-directory file must not be `-'.

   If two file names are given and both are directories, `diff'
compares corresponding files in both directories, in alphabetical
order; this comparison is not recursive unless the `-r' or
`--recursive' option is given.  `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 `--from-file=FILE' option is given, the number of file names
is arbitrary, and FILE is compared to each named file.  Similarly, if
the `--to-file=FILE' option is given, each named file is compared to
FILE.

   `diff' options begin with `-', so normally file names may not begin
with `-'.  However, `--' as an argument by itself treats the remaining
arguments as file names even if they begin with `-'.

   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 `diff'.


File: diff.info,  Node: diff Options,  Up: Invoking diff

Options to `diff'
=================

   Below is a summary of all of the options that GNU `diff' accepts.
Most options have two equivalent names, one of which is a single letter
preceded by `-', and the other of which is a long name preceded by
`--'.  Multiple single letter options (unless they take an argument)
can be combined into a single command line word: `-ac' is equivalent to
`-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.

`-a'
`--text'
     Treat all files as text and compare them line-by-line, even if they
     do not seem to be text.  *Note Binary::.

`-b'
`--ignore-space-change'
     Ignore changes in amount of white space.  *Note White Space::.

`-B'
`--ignore-blank-lines'
     Ignore changes that just insert or delete blank lines.  *Note
     Blank Lines::.

`--binary'
     Read and write data in binary mode.  *Note Binary::.

`-c'
     Use the context output format, showing three lines of context.
     *Note Context Format::.

`-C LINES'
`--context[=LINES]'
     Use the context output format, showing LINES (an integer) lines of
     context, or three if LINES is not given.  *Note Context Format::.
     For proper operation, `patch' typically needs at least two lines of
     context.

     On older systems, `diff' supports an obsolete option `-LINES' that
     has effect when combined with `-c' or `-p'.  POSIX 1003.1-2001
     (*note Standards conformance::) does not allow this; use `-C LINES'
     instead.

`--changed-group-format=FORMAT'
     Use FORMAT to output a line group containing differing lines from
     both files in if-then-else format.  *Note Line Group Formats::.

`-d'
`--minimal'
     Change the algorithm perhaps find a smaller set of changes.  This
     makes `diff' slower (sometimes much slower).  *Note diff
     Performance::.

`-D NAME'
`--ifdef=NAME'
     Make merged `#ifdef' format output, conditional on the preprocessor
     macro NAME.  *Note If-then-else::.

`-e'
`--ed'
     Make output that is a valid `ed' script.  *Note ed Scripts::.

`-E'
`--ignore-tab-expansion'
     Ignore changes due to tab expansion.  *Note White Space::.

`-f'
`--forward-ed'
     Make output that looks vaguely like an `ed' script but has changes
     in the order they appear in the file.  *Note Forward ed::.

`-F REGEXP'
`--show-function-line=REGEXP'
     In context and unified format, for each hunk of differences, show
     some of the last preceding line that matches REGEXP.  *Note
     Specified Headings::.

`--from-file=FILE'
     Compare FILE to each operand; FILE may be a directory.

`--help'
     Output a summary of usage and then exit.

`--horizon-lines=LINES'
     Do not discard the last LINES lines of the common prefix and the
     first LINES lines of the common suffix.  *Note diff Performance::.

`-i'
`--ignore-case'
     Ignore changes in case; consider upper- and lower-case letters
     equivalent.  *Note Case Folding::.

`-I REGEXP'
`--ignore-matching-lines=REGEXP'
     Ignore changes that just insert or delete lines that match REGEXP.
     *Note Specified Folding::.