diff.texi

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

with the @option{-W @var{columns}} or @option{--width=@var{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 @option{--left-column} option prints only the left column of two
common lines.  The @option{--suppress-common-lines} option suppresses
common lines entirely.

@node Example Side by Side
@subsection An Example of Side by Side Format

Here is the output of the command @samp{diff -y -W 72 lao tzu}
(@pxref{Sample diff Input}, for the complete contents of the two files).

@example
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!
@end example

@node Normal
@section Showing Differences Without Context
@cindex normal output format
@cindex @samp{<} output format

The ``normal'' @command{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 (@pxref{Context Format}) and the unified format
(@pxref{Unified Format}) are superior.  Normal format is the default for
compatibility with older versions of @command{diff} and the @acronym{POSIX}
standard.  Use the @option{--normal} option to select this output
format explicitly.

@menu
* Example Normal::  Sample output in the normal format.
* Detailed Normal:: A detailed description of normal output format.
@end menu

@node Example Normal
@subsection An Example of Normal Format

Here is the output of the command @samp{diff lao tzu}
(@pxref{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.

@example
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!
@end example

@node Detailed Normal
@subsection 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:

@example
@var{change-command}
< @var{from-file-line}
< @var{from-file-line}@dots{}
---
> @var{to-file-line}
> @var{to-file-line}@dots{}
@end example

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:

@table @samp
@item @var{l}a@var{r}
Add the lines in range @var{r} of the second file after line @var{l} of
the first file.  For example, @samp{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.

@item @var{f}c@var{t}
Replace the lines in range @var{f} of the first file with lines in range
@var{t} of the second file.  This is like a combined add and delete, but
more compact.  For example, @samp{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.

@item @var{r}d@var{l}
Delete the lines in range @var{r} from the first file; line @var{l} is where
they would have appeared in the second file had they not been deleted.
For example, @samp{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.
@end table

@node Scripts
@section Making Edit Scripts
@cindex script output formats

Several output modes produce command scripts for editing @var{from-file}
to produce @var{to-file}.

@menu
* ed Scripts:: Using @command{diff} to produce commands for @command{ed}.
* Forward ed:: Making forward @command{ed} scripts.
* RCS::        A special @command{diff} output format used by @acronym{RCS}.
@end menu

@node ed Scripts
@subsection @command{ed} Scripts
@cindex @command{ed} script output format

@command{diff} can produce commands that direct the @command{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 @command{patch}, it is almost obsolete.  Use the
@option{-e} or @option{--ed} option to select this output format.

Like the normal format (@pxref{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 @file{d} contains the output of @samp{diff -e old new}, then
the command @samp{(cat d && echo w) | ed - old} edits @file{old} to make
it a copy of @file{new}.  More generally, if @file{d1}, @file{d2},
@dots{}, @file{dN} contain the outputs of @samp{diff -e old new1},
@samp{diff -e new1 new2}, @dots{}, @samp{diff -e newN-1 newN},
respectively, then the command @samp{(cat d1 d2 @dots{} dN && echo w) |
ed - old} edits @file{old} to make it a copy of @file{newN}.

@menu
* Example ed::  A sample @command{ed} script.
* Detailed ed:: A detailed description of @command{ed} format.
@end menu

@node Example ed
@subsubsection Example @command{ed} Script

Here is the output of @samp{diff -e lao tzu} (@pxref{Sample
diff Input}, for the complete contents of the two files):

@example
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
@end example

@node Detailed ed
@subsubsection Detailed Description of @command{ed} Format

The @command{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
@command{ed} interprets line numbers in succeeding commands.  @command{ed}
format hunks look like this:

@example
@var{change-command}
@var{to-file-line}
@var{to-file-line}@dots{}
.
@end example

Because @command{ed} uses a single period on a line to indicate the
end of input, @acronym{GNU} @command{diff} protects lines of changes
that contain a single period on a line by writing two periods instead,
then writing a subsequent @command{ed} command to change the two
periods into one.  The @command{ed} format cannot represent an
incomplete line, so if the second file ends in a changed incomplete
line, @command{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:

@table @samp
@item @var{l}a
Add text from the second file after line @var{l} in the first file.  For
example, @samp{8a} means to add the following lines after line 8 of file
1.

@item @var{r}c
Replace the lines in range @var{r} in the first file with the following
lines.  Like a combined add and delete, but more compact.  For example,
@samp{5,7c} means change lines 5--7 of file 1 to read as the text file
2.

@item @var{r}d
Delete the lines in range @var{r} from the first file.  For example,
@samp{5,7d} means delete lines 5--7 of file 1.
@end table

@node Forward ed
@subsection Forward @command{ed} Scripts
@cindex forward @command{ed} script output format

@command{diff} can produce output that is like an @command{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
@command{ed} format, forward @command{ed} format cannot represent incomplete
lines.

Forward @command{ed} format is not very useful, because neither @command{ed}
nor @command{patch} can apply diffs in this format.  It exists mainly for
compatibility with older versions of @command{diff}.  Use the @option{-f} or
@option{--forward-ed} option to select it.

@node RCS
@subsection @acronym{RCS} Scripts
@cindex @acronym{RCS} script output format

The @acronym{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
@option{-n} or @option{--rcs} option to select this output format.  It
is like the forward @command{ed} format (@pxref{Forward ed}), but it
can represent arbitrary changes to the contents of a file because it
avoids the forward @command{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
@samp{a} and @samp{d} commands are used instead of @samp{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 @samp{diff -n lao tzu} (@pxref{Sample
diff Input}, for the complete contents of the two files):

@example
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!
@end example

@node If-then-else
@section Merging Files with If-then-else
@cindex merged output format
@cindex if-then-else output format
@cindex C if-then-else output format
@cindex @command{ifdef} output format

You can use @command{diff} to merge two files of C source code.  The output
of @command{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 @code{#ifdef @var{name}} or
@code{#ifndef @var{name}}, @code{#else}, and @code{#endif}.  When
compiling the output, you select which version to use by either defining
or leaving undefined the macro @var{name}.

To merge two files, use @command{diff} with the @option{-D @var{name}} or
@option{--ifdef=@var{name}} option.  The argument @var{name} is the C
preprocessor identifier to use in the @code{#ifdef} and @code{#ifndef}
directives.

For example, if you change an instance of @code{wait (&s)} to
@code{waitpid (-1, &s, 0)} and then merge the old and new files with
the @option{--ifdef=HAVE_WAITPID} option, then the affected part of your code
might look like this:

@example
    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);
@end example

You can specify formats for languages other than C by using line group
formats and line formats, as described in the next sections.

@menu
* Line Group Formats::    Formats for general if-then-else line groups.
* Line Formats::          Formats for each line in a line group.
* Example If-then-else::  Sample if-then-else format output.
* Detailed If-then-else:: A detailed description of if-then-else format.
@end menu

@node Line Group Formats
@subsection Line Group Formats
@cindex line group formats
@cindex formats for if-then-else line groups

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 @file{old}