# diff.info   [plain text]

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,
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

(a) The FSF's Back-Cover Text is: "You have freedom to copy and
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,
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

(a) The FSF's Back-Cover Text is: "You have freedom to copy and
the Free Software Foundation raise funds for GNU development."

* 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'.
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.

* 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::,

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.

* 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.

* 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
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

* 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.

* 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
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.

* 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.

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
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
merging files.

* 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.

* 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'.

* 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.

* 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,
%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.

* 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

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

****************************

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
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'.

* 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

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

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'.

* 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

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

* 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.

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
can apply patch' to update their copy of the files with your changes.
patch' automatically determines the diff format, skips any leading or
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'.

* 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.

* 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

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
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.

* 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

* 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.

* 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

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:

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

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.

* 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.

* 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'

--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

--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::.

--ignore-file-name-case'
Ignore case when comparing file names during recursive comparison.
*Note Comparing Directories::.

-l'
--paginate'
Pass the output through pr' to paginate it.  *Note Pagination::.

--label=LABEL'
Use LABEL instead of the file name in the context format (*note
Context Format::) and unified format (*note Unified Format::)

--left-column'
Print only the left column of two common lines in side by side
format.  *Note Side by Side Format::.

--line-format=FORMAT'
Use FORMAT to output all input lines in if-then-else format.
*Note Line Formats::.

-n'
--rcs'
Output RCS-format diffs; like -f' except that each command
specifies the number of lines affected.  *Note RCS::.

-N'
--new-file'
In directory comparison, if a file is found in only one directory,
treat it as present but empty in the other directory.  *Note
Comparing Directories::.

--new-group-format=FORMAT'
Use FORMAT to output a group of lines taken from just the second
file in if-then-else format.  *Note Line Group Formats::.

--new-line-format=FORMAT'
Use FORMAT to output a line taken from just the second file in
if-then-else format.  *Note Line Formats::.

--old-group-format=FORMAT'
Use FORMAT to output a group of lines taken from just the first
file in if-then-else format.  *Note Line Group Formats::.

--old-line-format=FORMAT'
Use FORMAT to output a line taken from just the first file in
if-then-else format.  *Note Line Formats::.

-p'
--show-c-function'
Show which C function each change is in.  *Note C Function

-q'
--brief'
Report only whether the files differ, not the details of the
differences.  *Note Brief::.

-r'
--recursive'
When comparing directories, recursively compare any subdirectories
found.  *Note Comparing Directories::.

-s'
--report-identical-files'
Report when two files are the same.  *Note Comparing Directories::.

-S FILE'
--starting-file=FILE'
used for resuming an aborted comparison.  *Note Comparing
Directories::.

--speed-large-files'
Use heuristics to speed handling of large files that have numerous
scattered small changes.  *Note diff Performance::.

--strip-trailing-cr'
Strip any trailing carriage return at the end of an input line.
*Note Binary::.

--suppress-common-lines'
Do not print common lines in side by side format.  *Note Side by
Side Format::.

-t'
--expand-tabs'
Expand tabs to spaces in the output, to preserve the alignment of
tabs in the input files.  *Note Tabs::.

-T'
--initial-tab'
Output a tab rather than a space before the text of a line in
normal or context format.  This causes the alignment of tabs in
the line to look normal.  *Note Tabs::.

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

-u'
Use the unified output format, showing three lines of context.
*Note Unified Format::.

--unchanged-group-format=FORMAT'
Use FORMAT to output a group of common lines taken from both files
in if-then-else format.  *Note Line Group Formats::.

--unchanged-line-format=FORMAT'
Use FORMAT to output a line common to both files in if-then-else
format.  *Note Line Formats::.

--unidirectional-new-file'
When comparing directories, if a file appears only in the second
directory of the two, treat it as present but empty in the other.
*Note Comparing Directories::.

-U LINES'
--unified[=LINES]'
Use the unified output format, showing LINES (an integer) lines of
context, or three if LINES is not given.  *Note Unified 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 -u'.  POSIX 1003.1-2001 (*note
Standards conformance::) does not allow this; use -U LINES'

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

-w'
--ignore-all-space'
Ignore white space when comparing lines.  *Note White Space::.

-W COLUMNS'
--width=COLUMNS'
Output at most COLUMNS (default 130) print columns per line in
side by side format.  *Note Side by Side Format::.

-x PATTERN'
--exclude=PATTERN'
When comparing directories, ignore files and subdirectories whose
basenames match PATTERN.  *Note Comparing Directories::.

-X FILE'
--exclude-from=FILE'
When comparing directories, ignore files and subdirectories whose
basenames match any pattern contained in FILE.  *Note Comparing
Directories::.

-y'
--side-by-side'
Use the side by side output format.  *Note Side by Side Format::.

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

Invoking diff3'
****************

The diff3' command compares three files and outputs descriptions of
their differences.  Its arguments are as follows:

diff3 OPTIONS... MINE OLDER YOURS

The files to compare are MINE, OLDER, and YOURS.  At most one of
these three file names may be -', which tells diff3' to read the
standard input for that file.

An exit status of 0 means diff3' was successful, 1 means some
conflicts were found, and 2 means trouble.

* diff3 Options:: Summary of options to diff3'.

File: diff.info,  Node: diff3 Options,  Up: Invoking diff3

Options to diff3'
==================

Below is a summary of all of the options that GNU diff3' accepts.
Multiple single letter options (unless they take an argument) can be
combined into a single command line argument.

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

-A'
--show-all'
Incorporate all unmerged changes from OLDER to YOURS into MINE,
surrounding conflicts with bracket lines.  *Note Marking
Conflicts::.

--diff-program=PROGRAM'
Use the compatible comparison program PROGRAM to compare files

-e'
--ed'
Generate an ed' script that incorporates all the changes from
OLDER to YOURS into MINE.  *Note Which Changes::.

-E'
--show-overlap'
Like -e', except bracket lines from overlapping changes' first
and third files.  *Note Marking Conflicts::.  With -E', an
overlapping change looks like this:

<<<<<<< MINE
lines from MINE
=======
lines from YOURS
>>>>>>> YOURS

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

-i'
Generate w' and q' commands at the end of the ed' script for
System V compatibility.  This option must be combined with one of
the -AeExX3' options, and may not be combined with -m'.  *Note
Saving the Changed File::.

-L LABEL'
--label=LABEL'
Use the label LABEL for the brackets output by the -A', -E' and
-X' options.  This option may be given up to three times, one for
each input file.  The default labels are the names of the input
files.  Thus diff3 -L X -L Y -L Z -m A B C' acts like diff3 -m 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'.
*Note Marking Conflicts::.

-m'
--merge'
Apply the edit script to the first file and send the result to
standard output.  Unlike piping the output from diff3' to ed',
this works even for binary files and incomplete lines.  -A' is
assumed if no edit script option is specified.  *Note Bypassing
ed::.

-T'
--initial-tab'
Output a tab rather than two spaces before the text of a line in
normal format.  This causes the alignment of tabs in the line to
look normal.  *Note Tabs::.

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

-x'
--overlap-only'
Like -e', except output only the overlapping changes.  *Note
Which Changes::.

-X'
Like -E', except output only the overlapping changes.  In other
words, like -x', except bracket changes as in -E'.  *Note
Marking Conflicts::.

-3'
--easy-only'
Like -e', except output only the nonoverlapping changes.  *Note
Which Changes::.

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

Invoking patch'
****************

Normally patch' is invoked like this:

patch <PATCHFILE

The full format for invoking patch' is:

patch OPTIONS... [ORIGFILE [PATCHFILE]]

You can also specify where to read the patch from with the -i
PATCHFILE' or --input=PATCHFILE' option.  If you do not specify
PATCHFILE, or if PATCHFILE is -', patch' reads the patch (that is,
the diff' output) from the standard input.

If you do not specify an input file on the command line, patch'
tries to intuit from the "leading text" (any text in the patch that
comes before the diff' output) which file to edit.  *Note Multiple
Patches::.

By default, patch' replaces the original input file with the
patched version, possibly after renaming the original file into a
backup file (*note Backup Names::, for a description of how patch'
names backup files).  You can also specify where to put the output with
the -o FILE' or --output=FILE' option; however, do not use this option
if FILE is one of the input files.

* patch Options::     Summary table of options to patch'.

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

Options to patch'
==================

Here is a summary of all of the options that GNU patch' accepts.
*Note patch and Tradition::, for which of these options are safe to use
in older versions of patch'.

Multiple single-letter options that do not take an argument can be
combined into a single command line argument with only one dash.

-b'
--backup'
Back up the original contents of each file, even if backups would
normally not be made.  *Note Backups::.

-B PREFIX'
--prefix=PREFIX'
Prepend PREFIX to backup file names.  *Note Backup Names::.

--backup-if-mismatch'
Back up the original contents of each file if the patch does not
exactly match the file.  This is the default behavior when not
conforming to POSIX.  *Note Backups::.

--binary'
Read and write all files in binary mode, except for standard output
and /dev/tty'.  This option has no effect on POSIX-conforming
systems like GNU/Linux.  On systems where this option makes a
difference, the patch should be generated by diff -a --binary'.
*Note Binary::.

-c'
--context'
Interpret the patch file as a context diff.  *Note patch Input::.

-d DIRECTORY'
--directory=DIRECTORY'
Make directory DIRECTORY the current directory for interpreting
both file names in the patch file, and file names given as
arguments to other options.  *Note patch Directories::.

-D NAME'
--ifdef=NAME'
Make merged if-then-else output using NAME.  *Note If-then-else::.

--dry-run'
Print the results of applying the patches without actually changing
any files.  *Note Dry Runs::.

-e'
--ed'
Interpret the patch file as an ed' script.  *Note patch Input::.

-E'
--remove-empty-files'
Remove output files that are empty after the patches have been
applied.  *Note Creating and Removing::.

-f'
--force'
Assume that the user knows exactly what he or she is doing, and do
not ask any questions.  *Note patch Messages::.

-F LINES'
--fuzz=LINES'
Set the maximum fuzz factor to LINES.  *Note Inexact::.

-g NUM'
--get=NUM'
If NUM is positive, get input files from a revision control system
as necessary; if zero, do not get the files; if negative, ask the
user whether to get the files.  *Note Revision Control::.

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

-i PATCHFILE'
--input=PATCHFILE'
Read the patch from PATCHFILE rather than from standard input.
*Note patch Options::.

-l'
--ignore-white-space'
Let any sequence of blanks (spaces or tabs) in the patch file match
any sequence of blanks in the input file.  *Note Changed White
Space::.

-n'
--normal'
Interpret the patch file as a normal diff.  *Note patch Input::.

-N'
--forward'
Ignore patches that patch' thinks are reversed or already applied.
See also -R'.  *Note Reversed Patches::.

--no-backup-if-mismatch'
Do not back up the original contents of files.  This is the default
behavior when conforming to POSIX.  *Note Backups::.

-o FILE'
--output=FILE'
Use FILE as the output file name.  *Note patch Options::.

-pNUMBER'
--strip=NUMBER'
Set the file name strip count to NUMBER.  *Note patch
Directories::.

--posix'
Conform to POSIX, as if the POSIXLY_CORRECT' environment variable
had been set.  *Note patch and POSIX::.

--quoting-style=WORD'
Use style WORD to quote names in diagnostics, as if the
QUOTING_STYLE' environment variable had been set to WORD.  *Note
patch Quoting Style::.

-r REJECT-FILE'
--reject-file=REJECT-FILE'
Use REJECT-FILE as the reject file name.  *Note Reject Names::.

-R'
--reverse'
Assume that this patch was created with the old and new files
swapped.  *Note Reversed Patches::.

-s'
--quiet'
--silent'
Work silently unless an error occurs.  *Note patch Messages::.

-t'
--batch'
Do not ask any questions.  *Note patch Messages::.

-T'
--set-time'
Set the modification and access times of patched files from time
stamps given in context diff headers, assuming that the context
diff headers use local time.  *Note Patching Time Stamps::.

-u'
--unified'
Interpret the patch file as a unified diff.  *Note patch Input::.

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

-V BACKUP-STYLE'
--version=control=BACKUP-STYLE'
Select the naming convention for backup file names.  *Note Backup
Names::.

--verbose'
Print more diagnostics than usual.  *Note patch Messages::.

-x NUMBER'
--debug=NUMBER'
Set internal debugging flags.  Of interest only to patch'
patchers.

-Y PREFIX'
--basename-prefix=PREFIX'
Prepend PREFIX to base names of backup files.  *Note Backup
Names::.

-z SUFFIX'
--suffix=SUFFIX'
Use SUFFIX as the backup extension instead of .orig' or ~'.
*Note Backup Names::.

-Z'
--set-utc'
Set the modification and access times of patched files from time
stamps given in context diff headers, assuming that the context
diff headers use UTC.  *Note Patching Time Stamps::.

File: diff.info,  Node: Invoking sdiff,  Next: Standards conformance,  Prev: Invoking patch,  Up: Top

Invoking sdiff'
****************

The sdiff' command merges two files and interactively outputs the
results.  Its arguments are as follows:

sdiff -o OUTFILE OPTIONS... FROM-FILE TO-FILE

This merges FROM-FILE with TO-FILE, with output to OUTFILE.  If
FROM-FILE is a directory and TO-FILE is not, sdiff' compares the file
in FROM-FILE whose file name is that of TO-FILE, and vice versa.
FROM-FILE and TO-FILE may not both be directories.

sdiff' options begin with -', so normally FROM-FILE and TO-FILE
may not begin with -'.  However, --' as an argument by itself treats
the remaining arguments as file names even if they begin with -'.  You
may not use -' as an input file.

sdiff' without -o' (or --output') produces a side-by-side
difference.  This usage is obsolete; use the -y' or --side-by-side'

An exit status of 0 means no differences were found, 1 means some
differences were found, and 2 means trouble.

* sdiff Options:: Summary of options to diff'.

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

Options to sdiff'
==================

Below is a summary of all of the options that GNU sdiff' accepts.
Each option has 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 argument.  Long named
options can be abbreviated to any unique prefix of their name.

-a'
--text'
Treat all files as text and compare them line-by-line, even if they
do not appear 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::.

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

--diff-program=PROGRAM'
Use the compatible comparison program PROGRAM to compare files

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

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

-i'
--ignore-case'
Ignore changes in case; consider upper- and lower-case to be the
same.  *Note Case Folding::.

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

-l'
--left-column'
Print only the left column of two common lines.  *Note Side by
Side Format::.

-o FILE'
--output=FILE'
Put merged output into FILE.  This option is required for merging.

-s'
--suppress-common-lines'
Do not print common lines.  *Note Side by Side Format::.

--speed-large-files'
Use heuristics to speed handling of large files that have numerous
scattered small changes.  *Note diff Performance::.

--strip-trailing-cr'
Strip any trailing carriage return at the end of an input line.
*Note Binary::.

-t'
--expand-tabs'
Expand tabs to spaces in the output, to preserve the alignment of
tabs in the input files.  *Note Tabs::.

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

-w COLUMNS'
--width=COLUMNS'
Output at most COLUMNS (default 130) print columns per line.
*Note Side by Side Format::.  Note that for historical reasons,
this option is -W' in diff', -w' in sdiff'.

-W'
--ignore-all-space'
Ignore white space when comparing lines.  *Note White Space::.
Note that for historical reasons, this option is -w' in diff',
-W' in sdiff'.

File: diff.info,  Node: Standards conformance,  Next: Projects,  Prev: Invoking sdiff,  Up: Top

Standards conformance
*********************

In a few cases, the GNU utilities' default behavior is incompatible
with the POSIX standard.  To suppress these incompatibilities, define
the POSIXLY_CORRECT' environment variable.  Unless you are checking
for POSIX conformance, you probably do not need to define
POSIXLY_CORRECT'.

Normally options and operands can appear in any order, and programs
act as if all the options appear before any operands.  For example,
diff lao tzu -C 2' acts like diff -C 2 lao tzu', since 2' is an
option-argument of -C'.  However, if the POSIXLY_CORRECT' environment
variable is set, options must appear before operands, unless otherwise
specified for a particular command.

Newer versions of POSIX are occasionally incompatible with older
versions.  For example, older versions of POSIX allowed the command
diff -c -10' to have the same meaning as diff -C 10', but POSIX
1003.1-2001 diff' no longer allows digit-string options like -10'.

The GNU utilities normally conform to the version of POSIX that is
standard for your system.  To cause them to conform to a different
version of POSIX, define the _POSIX2_VERSION' environment variable to
a value of the form YYYYMM specifying the year and month the standard
was adopted.  Two values are currently supported for _POSIX2_VERSION':
199209' stands for POSIX 1003.2-1992, and 200112' stands for POSIX
1003.1-2001.  For example, if you are running older software that
assumes an older version of POSIX and uses diff -c -10', you can work
around the compatibility problems by setting _POSIX2_VERSION=199209'

File: diff.info,  Node: Projects,  Next: Copying This Manual,  Prev: Standards conformance,  Up: Top

Future Projects
***************

Here are some ideas for improving GNU diff' and patch'.  The GNU
project has identified some improvements as potential programming
projects for volunteers.  You can also help by reporting any bugs that
you find.

If you are a programmer and would like to contribute something to the
GNU project, please consider volunteering for one of these projects.
If you are seriously contemplating work, please write to <gnu@gnu.org>
to coordinate with other volunteers.

* Shortcomings:: Suggested projects for improvements.
* Bugs::         Reporting bugs.

File: diff.info,  Node: Shortcomings,  Next: Bugs,  Up: Projects

Suggested Projects for Improving GNU diff' and patch'
=======================================================

One should be able to use GNU diff' to generate a patch from any
pair of directory trees, and given the patch and a copy of one such
tree, use patch' to generate a faithful copy of the other.
Unfortunately, some changes to directory trees cannot be expressed using
current patch formats; also, patch' does not handle some of the
existing formats.  These shortcomings motivate the following suggested
projects.

* Internationalization:: Handling multibyte and varying-width characters.
* Changing Structure::   Handling changes to the directory structure.
* Special Files::        Handling symbolic links, device special files, etc.
* Unusual File Names::   Handling file names that contain unusual characters.
* Time Stamp Order::     Outputting diffs in time stamp order.
* Ignoring Changes::     Ignoring certain changes while showing others.
* Speedups::             Improving performance.

File: diff.info,  Node: Internationalization,  Next: Changing Structure,  Up: Shortcomings

Handling Multibyte and Varying-Width Characters
-----------------------------------------------

diff', diff3' and sdiff' treat each line of input as a string of
unibyte characters.  This can mishandle multibyte characters in some
cases.  For example, when asked to ignore spaces, diff' does not
properly ignore a multibyte space character.

Also, diff' currently assumes that each byte is one column wide,
and this assumption is incorrect in some locales, e.g., locales that
use UTF-8 encoding.  This causes problems with the -y' or
--side-by-side' option of diff'.

These problems need to be fixed without unduly affecting the
performance of the utilities in unibyte environments.

The IBM GNU/Linux Technology Center Internationalization Team has
proposed some patches to support internationalized diff'
http://oss.software.ibm.com/developer/opensource/linux/patches/i18n/diffutils-2.7.2-i18n-0.1.patch.gz'.
Unfortunately, these patches are incomplete and are to an older version
of diff', so more work needs to be done in this area.

File: diff.info,  Node: Changing Structure,  Next: Special Files,  Prev: Internationalization,  Up: Shortcomings

Handling Changes to the Directory Structure
-------------------------------------------

diff' and patch' do not handle some changes to directory
structure.  For example, suppose one directory tree contains a directory
named D' with some subsidiary files, and another contains a file with
the same name D'.  diff -r' does not output enough information for
patch' to transform the directory subtree into the file.

There should be a way to specify that a file has been removed without
having to include its entire contents in the patch file.  There should
also be a way to tell patch' that a file was renamed, even if there is
no way for diff' to generate such information.  There should be a way
to tell patch' that a file's time stamp has changed, even if its
contents have not changed.

These problems can be fixed by extending the diff' output format to
represent changes in directory structure, and extending patch' to
understand these extensions.

File: diff.info,  Node: Special Files,  Next: Unusual File Names,  Prev: Changing Structure,  Up: Shortcomings

Files that are Neither Directories Nor Regular Files
----------------------------------------------------

Some files are neither directories nor regular files: they are
unusual files like symbolic links, device special files, named pipes,
and sockets.  Currently, diff' treats symbolic links like regular
files; it treats other special files like regular files if they are
specified at the top level, but simply reports their presence when
comparing directories.  This means that patch' cannot represent changes
to such files.  For example, if you change which file a symbolic link
points to, diff' outputs the difference between the two files, instead
of the change to the symbolic link.

diff' should optionally report changes to special files specially,
and patch' should be extended to understand these extensions.

File: diff.info,  Node: Unusual File Names,  Next: Time Stamp Order,  Prev: Special Files,  Up: Shortcomings

File Names that Contain Unusual Characters
------------------------------------------

When a file name contains an unusual character like a newline or
white space, diff -r' generates a patch that patch' cannot parse.
The problem is with format of diff' output, not just with patch',
because with odd enough file names one can cause diff' to generate a
patch that is syntactically correct but patches the wrong files.  The
format of diff' output should be extended to handle all possible file
names.

File: diff.info,  Node: Time Stamp Order,  Next: Ignoring Changes,  Prev: Unusual File Names,  Up: Shortcomings

Outputting Diffs in Time Stamp Order
------------------------------------

Applying patch' to a multiple-file diff can result in files whose
time stamps are out of order.  GNU patch' has options to restore the
time stamps of the updated files (*note Patching Time Stamps::), but
sometimes it is useful to generate a patch that works even if the
recipient does not have GNU patch, or does not use these options.  One
way to do this would be to implement a diff' option to output diffs in
time stamp order.

File: diff.info,  Node: Ignoring Changes,  Next: Speedups,  Prev: Time Stamp Order,  Up: Shortcomings

Ignoring Certain Changes
------------------------

It would be nice to have a feature for specifying two strings, one in
FROM-FILE and one in TO-FILE, which should be considered to match.
Thus, if the two strings are foo' and bar', then if two lines differ
only in that foo' in file 1 corresponds to bar' in file 2, the lines
are treated as identical.

It is not clear how general this feature can or should be, or what
syntax should be used for it.

A partial substitute is to filter one or both files before comparing,
e.g.:

sed 's/foo/bar/g' file1 | diff - file2

However, this outputs the filtered text, not the original.

File: diff.info,  Node: Speedups,  Prev: Ignoring Changes,  Up: Shortcomings

Improving Performance
---------------------

When comparing two large directory structures, one of which was
originally copied from the other with time stamps preserved (e.g., with
cp -pR'), it would greatly improve performance if an option told
diff' to assume that two files with the same size and time stamps have
the same content.  *Note diff Performance::.

File: diff.info,  Node: Bugs,  Prev: Shortcomings,  Up: Projects

Reporting Bugs
==============

If you think you have found a bug in GNU cmp', diff', diff3', or
sdiff', please report it by electronic mail to the GNU utilities bug
report mailing list
(http://mail.gnu.org/mailman/listinfo/bug-gnu-utils)
<bug-gnu-utils@gnu.org>.  Please send bug reports for GNU patch' to
<bug-patch@gnu.org>.  Send as precise a description of the problem as
you can, including the output of the --version' option and sample
input files that produce the bug, if applicable.  If you have a
nontrivial fix for the bug, please send it as well.  If you have a
patch, please send it too.  It may simplify the maintainer's job if the
patch is relative to a recent test release, which you can find in the
directory ftp://alpha.gnu.org/gnu/diffutils/'.

File: diff.info,  Node: Copying This Manual,  Next: Index,  Prev: Projects,  Up: Top

Copying This Manual
*******************

File: diff.info,  Node: GNU Free Documentation License,  Up: Copying This Manual

==============================

Version 1.1, March 2000
Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other
written document "free" in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially.  Secondarily,
this License preserves for the author and publisher a way to get
credit for their work, while not being considered responsible for

This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft

We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does.  But this License is not limited to
software manuals; it can be used for any textual work, regardless
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We recommend this License principally for works whose purpose is
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----------------------------------------------------

To use this License in a document you have written, include a copy of
notices just after the title page:

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
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If you have no Invariant Sections, write "with no Invariant Sections"
instead of saying which ones are invariant.  If you have no Front-Cover
Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being
LIST"; likewise for Back-Cover Texts.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
permit their use in free software.

File: diff.info,  Node: Index,  Prev: Copying This Manual,  Up: Top

Index
*****

* ! output format:                       Context.
* +- output format:                      Unified Format.
* < output format:                       Normal.
* <<<<<<< for marking conflicts:         Marking Conflicts.
* _POSIX2_VERSION:                       Standards conformance.
* aligning tab stops:                    Tabs.
* alternate file names:                  Alternate Names.
* backup file names:                     Backup Names.
* backup file strategy:                  Backups.
* binary file diff:                      Binary.
* blank and tab difference suppression:  White Space.
* blank line difference suppression:     Blank Lines.
* brief difference reports:              Brief.
* bug reports:                           Bugs.
* C if-then-else output format:          If-then-else.
* case difference suppression:           Case Folding.
* ClearCase:                             Revision Control.
* cmp invocation:                        Invoking cmp.
* cmp options:                           cmp Options.
* columnar output:                       Side by Side.
* common mistakes with patches:          Avoiding Common Mistakes.
* comparing three files:                 Comparing Three Files.
* conflict:                              diff3 Merging.
* conflict marking:                      Marking Conflicts.
* context output format:                 Context.
* creating files:                        Creating and Removing.
* diagnostics from patch:                patch Messages.
* diff invocation:                       Invoking diff.
* diff merging:                          Interactive Merging.
* diff options:                          diff Options.
* diff sample input:                     Sample diff Input.
* diff3 hunks:                           diff3 Hunks.
* diff3 invocation:                      Invoking diff3.
* diff3 options:                         diff3 Options.
* diff3 sample input:                    Sample diff3 Input.
* directories and patch:                 patch Directories.
* directory structure changes:           Changing Structure.
* dry runs for patch:                    Dry Runs.
* ed script output format:               ed Scripts.
* EDITOR:                                Merge Commands.
* empty files, removing:                 Creating and Removing.
* exabyte, definition of:                cmp Options.
* exbibyte, definition of:               cmp Options.
* file name alternates:                  Alternate Names.
* file names with unusual characters:    Unusual File Names.
* format of diff output:                 Output Formats.
* format of diff3 output:                Comparing Three Files.
* formats for if-then-else line groups:  Line Group Formats.
* forward ed script output format:       Forward ed.
* full lines:                            Incomplete Lines.
* fuzz factor when patching:             Inexact.
* gibibyte, definition of:               cmp Options.
* gigabyte, definition of:               cmp Options.
* hunks:                                 Hunks.
* hunks for diff3:                       diff3 Hunks.
* if-then-else output format:            If-then-else.
* ifdef output format:                   If-then-else.
* imperfect patch application:           Imperfect.
* incomplete line merging:               Merging Incomplete Lines.
* incomplete lines:                      Incomplete Lines.
* inexact patches:                       Inexact.
* inhibit messages from patch:           More or Fewer Messages.
* interactive merging:                   Interactive Merging.
* introduction:                          Comparison.
* intuiting file names from patches:     Multiple Patches.
* invoking cmp:                          Invoking cmp.
* invoking diff:                         Invoking diff.
* invoking diff3:                        Invoking diff3.
* invoking patch:                        Invoking patch.
* invoking sdiff:                        Invoking sdiff.
* keyboard input to patch:               patch and Keyboard Input.
* kibibyte, definition of:               cmp Options.
* kilobyte, definition of:               cmp Options.
* LC_COLLATE:                            Comparing Directories.
* LC_NUMERIC:                            Line Group Formats.
* LC_TIME:                               Detailed Context.
* line formats:                          Line Formats.
* line group formats:                    Line Group Formats.
* mebibyte, definition of:               cmp Options.
* megabyte, definition of:               cmp Options.
* merge commands:                        Merge Commands.
* merged diff3 format:                   Bypassing ed.
* merged output format:                  If-then-else.
* merging from a common ancestor:        diff3 Merging.
* merging interactively:                 Merge Commands.
* messages from patch:                   patch Messages.
* multibyte characters:                  Internationalization.
* multiple patches:                      Multiple Patches.
* newline treatment by diff:             Incomplete Lines.
* normal output format:                  Normal.
* options for cmp:                       cmp Options.
* options for diff:                      diff Options.
* options for diff3:                     diff3 Options.
* options for patch:                     patch Options.
* options for sdiff:                     sdiff Options.
* output formats:                        Output Formats.
* overlap:                               diff3 Merging.
* overlapping change, selection of:      Which Changes.
* overview of diff and patch:            Overview.
* paginating diff output:                Pagination.
* patch consumer tips:                   Tips for Patch Consumers.
* patch input format:                    patch Input.
* patch invocation:                      Invoking patch.
* patch messages and questions:          patch Messages.
* patch options:                         patch Options.
* patch producer tips:                   Tips for Patch Producers.
* patch, common mistakes:                Avoiding Common Mistakes.
* PATCH_GET:                             Revision Control.
* PATCH_VERSION_CONTROL:                 Backup Names.
* patches, shrinking:                    Generating Smaller Patches.
* patching directories:                  patch Directories.
* pebibyte, definition of:               cmp Options.
* performance of diff:                   diff Performance.
* petabyte, definition of:               cmp Options.
* POSIX <1>:                             Standards conformance.
* POSIX:                                 patch and POSIX.
* POSIXLY_CORRECT <1>:                   patch and POSIX.
* POSIXLY_CORRECT:                       Standards conformance.
* projects for directories:              Shortcomings.
* quoting style:                         patch Quoting Style.
* QUOTING_STYLE:                         patch Quoting Style.
* RCS:                                   Revision Control.
* RCS script output format:              RCS.
* regular expression suppression:        Specified Folding.
* reject file names:                     Reject Names.
* removing empty files:                  Creating and Removing.
* reporting bugs:                        Bugs.
* reversed patches:                      Reversed Patches.
* revision control:                      Revision Control.
* sample input for diff:                 Sample diff Input.
* sample input for diff3:                Sample diff3 Input.
* SCCS:                                  Revision Control.
* script output formats:                 Scripts.
* sdiff invocation:                      Invoking sdiff.
* sdiff options:                         sdiff Options.
* sdiff output format:                   sdiff Option Summary.
* side by side:                          Side by Side.
* side by side format:                   Side by Side Format.
* SIMPLE_BACKUP_SUFFIX:                  Backup Names.
* special files:                         Special Files.
* summarizing which files differ:        Brief.
* System V diff3 compatibility:          Saving the Changed File.
* tab and blank difference suppression:  White Space.
* tab stop alignment:                    Tabs.
* tebibyte, definition of:               cmp Options.
* terabyte, definition of:               cmp Options.
* testing patch:                         Dry Runs.
* text versus binary diff:               Binary.
* time stamp format, context diffs:      Detailed Context.
* time stamp format, unified diffs:      Detailed Unified.
* time stamps on patched files:          Patching Time Stamps.
* two-column output:                     Side by Side.
* unified output format:                 Unified Format.
* unmerged change:                       Which Changes.
* varying-width characters:              Internationalization.
* verbose messages from patch:           More or Fewer Messages.
* version control:                       Revision Control.
* VERSION_CONTROL <1>:                   Backup Names.
* VERSION_CONTROL:                       Revision Control.
* white space in patches:                Changed White Space.
* yottabyte, definition of:              cmp Options.
* zettabyte, definition of:              cmp Options.

Tag Table:
Node: Top1653
Node: Overview4045
Node: Comparison7202
Node: Hunks9888
Node: White Space11313
Node: Blank Lines12807
Node: Case Folding13562
Node: Specified Folding13977
Node: Brief15052
Node: Binary16295
Node: Output Formats20358
Node: Sample diff Input21076
Node: Normal22569
Node: Detailed Normal23564
Node: Example Normal25289
Node: Context26011
Node: Context Format27567
Node: Detailed Context28345
Node: Example Context30234
Node: Less Context31748
Node: Unified Format32894
Node: Detailed Unified33676
Node: Example Unified34787
Node: Sections35807
Node: Alternate Names38908
Node: Side by Side39808
Node: Side by Side Format41947
Node: Example Side by Side42836
Node: Scripts44162
Node: ed Scripts44563
Node: Detailed ed45756
Node: Example ed47497
Node: Forward ed47934
Node: RCS48696
Node: If-then-else49904
Node: Line Group Formats51572
Node: Line Formats57437
Node: Detailed If-then-else60693
Node: Example If-then-else62583
Node: Incomplete Lines63632
Node: Comparing Directories65263
Node: Tabs69645
Node: Pagination71177
Node: diff Performance71626
Node: Comparing Three Files74708
Node: Sample diff3 Input75580
Node: Detailed diff3 Normal76528
Node: diff3 Hunks78307
Node: Example diff3 Normal79593
Node: diff3 Merging80616
Node: Which Changes82854
Node: Marking Conflicts84258
Node: Bypassing ed86714
Node: Merging Incomplete Lines88068
Node: Saving the Changed File88784
Node: Interactive Merging89390
Node: sdiff Option Summary90094
Node: Merge Commands91242
Node: Merging with patch92503
Node: patch Input94867
Node: Revision Control95537
Node: Imperfect96689
Node: Changed White Space97825
Node: Reversed Patches98606
Node: Inexact100056
Node: Dry Runs103599
Node: Creating and Removing104447
Node: Patching Time Stamps105486
Node: Multiple Patches107677
Node: patch Directories110328
Node: Backups111942
Node: Backup Names112996
Ref: Backup Names-Footnote-1115955
Node: Reject Names116082
Node: patch Messages116660
Node: More or Fewer Messages117706
Node: patch and Keyboard Input118319
Node: patch Quoting Style119332
Node: patch and POSIX120464
Node: Making Patches124734
Node: Tips for Patch Producers125552
Node: Tips for Patch Consumers126796
Node: Avoiding Common Mistakes127421
Node: Generating Smaller Patches129934
Node: Invoking cmp131683
Node: cmp Options132532
Node: Invoking diff135896
Node: diff Options137599
Node: Invoking diff3145722
Node: diff3 Options146352
Node: Invoking patch149255
Node: patch Options150455
Node: Invoking sdiff155669
Node: sdiff Options156808
Node: Standards conformance159561
Node: Projects161299
Node: Shortcomings162002
Node: Internationalization163092
Node: Changing Structure164247
Node: Special Files165336
Node: Unusual File Names166282
Node: Time Stamp Order166904
Node: Ignoring Changes167531
Node: Speedups168285
Node: Bugs168733
Node: Copying This Manual169574