source: trunk/essentials/sys-apps/diffutils/doc/diff.info@ 3506

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

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

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

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

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

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


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

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

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

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

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

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

* Overview::              Preliminary information.
* Comparison::            What file comparison means.

* Output Formats::        Formats for two-way difference reports.
* Incomplete Lines::      Lines that lack trailing newlines.
* Comparing Directories:: Comparing files and directories.
* Adjusting Output::      Making `diff' output prettier.
* diff Performance::      Making `diff' smarter or faster.

* Comparing Three Files:: Formats for three-way difference reports.
* diff3 Merging::         Merging from a common ancestor.

* Interactive Merging::   Interactive merging with `sdiff'.

* Merging with patch::    Using `patch' to change old files into new ones.
* Making Patches::        Tips for making and using patch distributions.

* Invoking cmp::          Compare two files byte by byte.
* Invoking diff::         Compare two files line by line.
* Invoking diff3::        Compare three files line by line.
* Invoking patch::        Apply a diff file to an original.
* Invoking sdiff::        Side-by-side merge of file differences.

* Standards conformance:: Conformance to the POSIX standard.
* Projects::              If you've found a bug or other shortcoming.

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


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

Overview
********

   Computer users often find occasion to ask how two files differ.
Perhaps one file is a newer version of the other file.  Or maybe the
two files started out as identical copies but were changed by different
people.

   You can use the `diff' command to show differences between two
files, or each corresponding file in two directories.  `diff' outputs
differences between files line by line in any of several formats,
selectable by command line options.  This set of differences is often
called a "diff" or "patch".  For files that are identical, `diff'
normally produces no output; for binary (non-text) files, `diff'
normally reports only that they are different.

   You can use the `cmp' command to show the byte and line numbers
where two files differ.  `cmp' can also show all the bytes that differ
between the two files, side by side.  A way to compare two files
character by character is the Emacs command `M-x compare-windows'.
*Note Other Window: (emacs)Other Window, for more information on that
command.

   You can use the `diff3' command to show differences among three
files.  When two people have made independent changes to a common
original, `diff3' can report the differences between the original and
the two changed versions, and can produce a merged file that contains
both persons' changes together with warnings about conflicts.

   You can use the `sdiff' command to merge two files interactively.

   You can use the set of differences produced by `diff' to distribute
updates to text files (such as program source code) to other people.
This method is especially useful when the differences are small compared
to the complete files.  Given `diff' output, you can use the `patch'
program to update, or "patch", a copy of the file.  If you think of
`diff' as subtracting one file from another to produce their
difference, you can think of `patch' as adding the difference to one
file to reproduce the other.

   This manual first concentrates on making diffs, and later shows how
to use diffs to update files.

   GNU `diff' was written by Paul Eggert, Mike Haertel, David Hayes,
Richard Stallman, and Len Tower.  Wayne Davison designed and
implemented the unified output format.  The basic algorithm is described
in "An O(ND) Difference Algorithm and its Variations", Eugene W. Myers,
`Algorithmica' Vol. 1 No. 2, 1986, pp. 251-266; and in "A File
Comparison Program", Webb Miller and Eugene W. Myers,
`Software--Practice and Experience' Vol. 15 No. 11, 1985, pp. 1025-1040.
The algorithm was independently discovered as described in "Algorithms
for Approximate String Matching", E. Ukkonen, `Information and Control'
Vol. 64, 1985, pp. 100-118.

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

   `patch' was written mainly by Larry Wall and Paul Eggert; several
GNU enhancements were contributed by Wayne Davison and David MacKenzie.
Parts of this manual are adapted from a manual page written by Larry
Wall, with his permission.


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

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

   There are several ways to think about the differences between two
files.  One way to think of the differences is as a series of lines
that were deleted from, inserted in, or changed in one file to produce
the other file.  `diff' compares two files line by line, finds groups of
lines that differ, and reports each group of differing lines.  It can
report the differing lines in several formats, which have different
purposes.

   GNU `diff' can show whether files are different without detailing
the differences.  It also provides ways to suppress certain kinds of
differences that are not important to you.  Most commonly, such
differences are changes in the amount of white space between words or
lines.  `diff' also provides ways to suppress differences in alphabetic
case or in lines that match a regular expression that you provide.
These options can accumulate; for example, you can ignore changes in
both white space and alphabetic case.

   Another way to think of the differences between two files is as a
sequence of pairs of bytes that can be either identical or different.
`cmp' reports the differences between two files byte by byte, instead
of line by line.  As a result, it is often more useful than `diff' for
comparing binary files.  For text files, `cmp' is useful mainly when
you want to know only whether two files are identical, or whether one
file is a prefix of the other.

   To illustrate the effect that considering changes byte by byte can
have compared with considering them line by line, think of what happens
if a single newline character is added to the beginning of a file.  If
that file is then compared with an otherwise identical file that lacks
the newline at the beginning, `diff' will report that a blank line has
been added to the file, while `cmp' will report that almost every byte
of the two files differs.

   `diff3' normally compares three input files line by line, finds
groups of lines that differ, and reports each group of differing lines.
Its output is designed to make it easy to inspect two different sets of
changes to the same file.

* Menu:

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


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

Hunks
=====

   When comparing two files, `diff' finds sequences of lines common to
both files, interspersed with groups of differing lines called "hunks".
Comparing two identical files yields one sequence of common lines and
no hunks, because no lines differ.  Comparing two entirely different
files yields no common lines and one large hunk that contains all lines
of both files.  In general, there are many ways to match up lines
between two given files.  `diff' tries to minimize the total hunk size
by finding large sequences of common lines interspersed with small
hunks of differing lines.

   For example, suppose the file `F' contains the three lines `a', `b',
`c', and the file `G' contains the same three lines in reverse order
`c', `b', `a'.  If `diff' finds the line `c' as common, then the command
`diff F G' produces this output:

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

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

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

It is also possible to find `a' as the common line.  `diff' does not
always find an optimal matching between the files; it takes shortcuts
to run faster.  But its output is usually close to the shortest
possible.  You can adjust this tradeoff with the `--minimal' option
(*note diff Performance::).


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

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

   The `-E' and `--ignore-tab-expansion' options ignore the distinction
between tabs and spaces on input.  A tab is considered to be equivalent
to the number of spaces to the next tab stop.  `diff' assumes that tab
stops are set every 8 print columns.

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

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

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

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


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

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

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

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


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

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

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


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

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

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

   However, `-I' only ignores the insertion or deletion of lines that
contain the regular expression if every changed line in the hunk--every
insertion and every deletion--matches the regular expression.  In other
words, for each nonignorable change, `diff' prints the complete set of
changes in its vicinity, including the ignorable ones.

   You can specify more than one regular expression for lines to ignore
by using more than one `-I' option.  `diff' tries to match each line
against each regular expression.


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

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

   When you only want to find out whether files are different, and you
don't care what the differences are, you can use the summary output
format.  In this format, instead of showing the differences between the
files, `diff' simply reports whether files differ.  The `-q' and
`--brief' options select this output format.

   This format is especially useful when comparing the contents of two
directories.  It is also much faster than doing the normal line by line
comparisons, because `diff' can stop analyzing the files as soon as it
knows that there are any differences.

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

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


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

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

   If `diff' thinks that either of the two files it is comparing is
binary (a non-text file), it normally treats that pair of files much as
if the summary output format had been selected (*note Brief::), and
reports only that the binary files are different.  This is because line
by line comparisons are usually not meaningful for binary files.

   `diff' determines whether a file is text or binary by checking the
first few bytes in the file; the exact number of bytes is system
dependent, but it is typically several thousand.  If every byte in that
part of the file is non-null, `diff' considers the file to be text;
otherwise it considers the file to be binary.

   Sometimes you might want to force `diff' to consider files to be
text.  For example, you might be comparing text files that contain null
characters; `diff' would erroneously decide that those are non-text
files.  Or you might be comparing documents that are in a format used
by a word processing system that uses null characters to indicate
special formatting.  You can force `diff' to consider all files to be
text files, and compare them line by line, by using the `-a' or
`--text' option.  If the files you compare using this option do not in
fact contain text, they will probably contain few newline characters,
and the `diff' output will consist of hunks showing differences between
long lines of whatever characters the files contain.

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

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

   In operating systems that distinguish between text and binary files,
`diff' normally reads and writes all data as text.  Use the `--binary'
option to force `diff' to read and write binary data instead.  This
option has no effect on a POSIX-compliant system like GNU or
traditional Unix.  However, many personal computer operating systems
represent the end of a line with a carriage return followed by a
newline.  On such systems, `diff' normally ignores these carriage
returns on input and generates them at the end of each output line, but
with the `--binary' option `diff' treats each carriage return as just
another input character, and does not generate a carriage return at the
end of each output line.  This can be useful when dealing with non-text
files that are meant to be interchanged with POSIX-compliant systems.

   The `--strip-trailing-cr' causes `diff' to treat input lines that
end in carriage return followed by newline as if they end in plain
newline.  This can be useful when comparing text that is imperfectly
imported from many personal computer operating systems.  This option
affects how lines are read, which in turn affects how they are compared
and output.

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

   If `diff3' thinks that any of the files it is comparing is binary (a