diff.texi

制作2.6内核的CLFS时 使用的diffutils-2.8.7.tar.gz包

\input texinfo @c -*-texinfo-*-
@comment $Id: diff.texi,v 1.25 2004/04/12 07:44:35 eggert Exp $
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@setfilename diff.info
@include version.texi
@settitle Comparing and Merging Files
@syncodeindex vr cp
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@copying
This manual is for GNU Diffutils
(version @value{VERSION}, @value{UPDATED}),
and documents the @acronym{GNU} @command{diff}, @command{diff3},
@command{sdiff}, and @command{cmp} commands for showing the
differences between files and the @acronym{GNU} @command{patch} command for
using their output to update files.

Copyright @copyright{} 1992, 1993, 1994, 1998, 2001, 2002, 2004 Free
Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 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.''
@end quotation
@end copying

@c Debian install-info (up through at least version 1.9.20) uses only the
@c first dircategory.  Put this one first, as it is more useful in practice.
@dircategory Individual utilities
@direntry
* cmp: (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 direntry

@dircategory Text creation and manipulation
@direntry
* Diff: (diff).                 Comparing and merging files.
@end direntry

@titlepage
@title Comparing and Merging Files
@subtitle for Diffutils @value{VERSION} and @code{patch} 2.5.4
@subtitle @value{UPDATED}
@author David MacKenzie, Paul Eggert, and Richard Stallman
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@shortcontents
@contents

@ifnottex
@node Top
@top Comparing and Merging Files

@insertcopying
@end ifnottex

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

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

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

* Interactive Merging::   Interactive merging with @command{sdiff}.

* Merging with patch::    Using @command{patch} to change old files into new ones.
* Making Patches::        Tips for making and using patch distributions.

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

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

* Copying This Manual::   How to make copies of this manual.
* Translations::          Available translations of this manual.
* Index::                 Index.
@end menu

@node Overview
@unnumbered Overview
@cindex overview of @command{diff} and @command{patch}

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

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

You can use the @command{cmp} command to show the byte and line numbers
where two files differ.  @command{cmp} can also show all the bytes
that differ between the two files, side by side.  A way to compare
two files character by character is the Emacs command @kbd{M-x
compare-windows}.  @xref{Other Window, , Other Window, emacs, The @acronym{GNU}
Emacs Manual}, for more information on that command.

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

You can use the @command{sdiff} command to merge two files interactively.

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

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

@acronym{GNU} @command{diff} was written by Paul Eggert, Mike Haertel,
David Hayes, Richard Stallman, and Len Tower.  Wayne Davison designed and
implemented the unified output format.  The basic algorithm is described
by Eugene W. Myers in ``An O(ND) Difference Algorithm and its Variations'',
@cite{Algorithmica} Vol.@: 1 No.@: 2, 1986, pp.@: 251--266; and in ``A File
Comparison Program'', Webb Miller and Eugene W. Myers,
@cite{Software---Practice and Experience} Vol.@: 15 No.@: 11, 1985,
pp.@: 1025--1040.
@c From: "Gene Myers" <[e-mail]>
@c They are about the same basic algorithm; the Algorithmica
@c paper gives a rigorous treatment and the sub-algorithm for
@c delivering scripts and should be the primary reference, but
@c both should be mentioned.
The algorithm was independently discovered as described by E. Ukkonen in
``Algorithms for Approximate String Matching'',
@cite{Information and Control} Vol.@: 64, 1985, pp.@: 100--118.
@c From: "Gene Myers" <[e-mail]>
@c Date: Wed, 29 Sep 1993 08:27:55 MST
@c Ukkonen should be given credit for also discovering the algorithm used
@c in GNU diff.
Unless the @option{--minimal} option is used, @command{diff} uses a
heuristic by Paul Eggert that limits the cost to @math{O(N^1.5 log N)}
at the price of producing suboptimal output for large inputs with many
differences.  Related algorithms are surveyed by Alfred V. Aho in
section 6.3 of ``Algorithms for Finding Patterns in Strings'',
@cite{Handbook of Theoretical Computer Science} (Jan Van Leeuwen,
ed.), Vol.@: A, @cite{Algorithms and Complexity}, Elsevier/MIT Press,
1990, pp.@: 255--300.

@acronym{GNU} @command{diff3} was written by Randy Smith.  @acronym{GNU}
@command{sdiff} was written by Thomas Lord.  @acronym{GNU} @command{cmp}
was written by Torbj@"orn Granlund and David MacKenzie.

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

@node Comparison
@chapter What Comparison Means
@cindex introduction

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

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

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

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

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

@menu
* Hunks::             Groups of differing lines.
* White Space::       Suppressing differences in white space.
* Blank Lines::       Suppressing differences whose lines are all blank.
* Specified Lines::   Suppressing differences whose lines all match a pattern.
* Case Folding::      Suppressing differences in alphabetic case.
* Brief::             Summarizing which files are different.
* Binary::            Comparing binary files or forcing text comparisons.
@end menu

@node Hunks
@section Hunks
@cindex hunks

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

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

@example
1,2d0
< a
< b
3a2,3
> b
> a
@end example

@noindent
But if @command{diff} notices the common line @samp{b} instead, it produces
this output:

@example
1c1
< a
---
> c
3c3
< c
---
> a
@end example

@noindent
It is also possible to find @samp{a} as the common line.  @command{diff}
does not always find an optimal matching between the files; it takes
shortcuts to run faster.  But its output is usually close to the
shortest possible.  You can adjust this tradeoff with the
@option{-d} or @option{--minimal} option (@pxref{diff Performance}).

@node White Space
@section Suppressing Differences in Blank and Tab Spacing
@cindex blank and tab difference suppression
@cindex tab and blank difference suppression

The @option{-E} or @option{--ignore-tab-expansion} option ignores the
distinction between tabs and spaces on input.  A tab is considered to be
equivalent to the number of spaces to the next tab stop (@pxref{Tabs}).

The @option{-b} or @option{--ignore-space-change} option is stronger.
It ignores white space at line end, and considers all other sequences of
one or more white space characters within a line to be equivalent.  With this
option, @command{diff} considers the following two lines to be equivalent,
where @samp{$} denotes the line end:

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

The @option{-w} or @option{--ignore-all-space} option is stronger still.
It ignores differences even if one line has white space where
the other line has none.  @dfn{White space} characters include
tab, newline, vertical tab, form feed, carriage return, and space;
some locales may define additional characters to be white space.
With this option, @command{diff} considers the
following two lines to be equivalent, where @samp{$} denotes the line
end and @samp{^M} denotes a carriage return:

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

@node Blank Lines
@section Suppressing Differences Whose Lines Are All Blank
@cindex blank line difference suppression

The @option{-B} or @option{--ignore-blank-lines} option ignores changes
that consist entirely of blank lines.  With this option, for example, a
file containing
@example
1.  A point is that which has no part.

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