diff.texi

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename diff.info
@settitle Comparing and Merging Files
@setchapternewpage odd
@c %**end of header

@ifinfo
This file documents the the GNU @code{diff}, @code{diff3}, @code{sdiff},
and @code{cmp} commands for showing the differences between text files
and the @code{patch} command for using their output to update files.

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

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end ifinfo

@titlepage
@title Comparing and Merging Files
@subtitle @code{diff}, @code{diff3}, @code{sdiff}, @code{cmp}, and @code{patch}
@subtitle Edition 1.3, for @code{diff} 2.5 and @code{patch} 2.1
@subtitle September 1993
@author by David MacKenzie, Paul Eggert, and Richard Stallman

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1992, 1993, 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the Foundation.
@end titlepage

@node Top, , , (dir)

@ifinfo
This file documents the the GNU @code{diff}, @code{diff3}, @code{sdiff},
and @code{cmp} commands for showing the differences between text files
and the @code{patch} command for using their output to update files.

This is Edition 1.2, for @code{diff} 2.4 and @code{patch} 2.1.
@end ifinfo

@menu
* Overview::		Preliminary information.

* Comparison::		What file comparison means.
* Output Formats::	Formats for difference reports.
* Comparing Directories::	Comparing files and directories.
* Adjusting Output::	Making @code{diff} output prettier.
* diff Performance::	Making @code{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 @code{sdiff}.
* Merging with patch::	Using @code{patch} to change old files into new ones.
* Making Patches::	Tips for making patch distributions.

* Invoking cmp::	How to run @code{cmp} and a summary of its options.
* Invoking diff::	How to run @code{diff} and a summary of its options.
* Invoking diff3::	How to run @code{diff3} and a summary of its options.
* Invoking patch::	How to run @code{patch} and a summary of its options.
* Invoking sdiff::	How to run @code{sdiff} and a summary of its options.

* Incomplete Lines::	Lines that lack trailing newlines.
* Projects::		If you think you've found a bug or other shortcoming.

* Concept Index::	Index of concepts.
@end menu

@node Overview, Comparison, , Top
@unnumbered Overview
@cindex overview of @code{diff} and @code{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 @code{diff} command to show differences between two
files, or each corresponding file in two directories.  @code{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,
@code{diff} normally produces no output; for binary (non-text) files,
@code{diff} normally reports only that they are different.

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

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

You can use the set of differences produced by @code{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 @code{diff} output, you can use the
@code{patch} program to update, or @dfn{patch}, a copy of the file.  If you
think of @code{diff} as subtracting one file from another to produce
their difference, you can think of @code{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 @code{diff} was written by Mike Haertel, David Hayes, Richard
Stallman, Len Tower, and Paul Eggert.  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,
@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 in
``Algorithms for Approximate String Matching'',
E. Ukkonen, @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.

GNU @code{diff3} was written by Randy Smith.  GNU @code{sdiff} was
written by Thomas Lord.  GNU @code{cmp} was written by Torbjorn Granlund
and David MacKenzie.

@code{patch} was written mainly by Larry Wall; the GNU enhancements were
written mainly 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, Output Formats, Overview, Top
@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.  @code{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 @code{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.  @code{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 characters that can be either identical or
different.  @code{cmp} reports the differences between two files
character by character, instead of line by line.  As a result, it is
more useful than @code{diff} for comparing binary files.  For text
files, @code{cmp} is useful mainly when you want to know only whether
two files are identical.

To illustrate the effect that considering changes character by character
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, @code{diff} will report that a
blank line has been added to the file, while @code{cmp} will report that
almost every character of the two files differs.

@code{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.
@end menu

@node Hunks, White Space, , Comparison
@section Hunks
@cindex hunks

When comparing two files, @code{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.  @code{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
@code{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 @code{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.  @code{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
@samp{--minimal} option (@pxref{diff Performance}).

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

The @samp{-b} and @samp{--ignore-space-change} options ignore white space
at line end, and considers all other sequences of one or more
white space characters to be equivalent.  With these options,
@code{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 @samp{-w} and @samp{--ignore-all-space} options are stronger than
@samp{-b}.  They ignore difference even if one file has white space where
the other file 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 these options, @code{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, Case Folding, White Space, Comparison
@section Suppressing Differences in Blank Lines
@cindex blank line difference suppression

The @samp{-B} and @samp{--ignore-blank-lines} options ignore insertions
or deletions of blank lines.  These options normally 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
@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.
2.  A line is breadthless length.


-- Euclid, The Elements, I
@end example

@node Case Folding, Specified Folding, Blank Lines, Comparison
@section Suppressing Case Differences
@cindex case difference suppression