This is Info file diff.info, produced by Makeinfo-1.51 from the input
file ./diff.texi.

   This file documents the the GNU `diff', `diff3', `sdiff', and `cmp'
commands for showing the differences between text files and the `patch'
command for using their output to update files.

   Copyright (C) 1992, 1993 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.


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-column
change indicator to the left of the text.  The first column 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.

   In a line format, ordinary characters represent themselves;
conversion specifications start with `%' and have one of the following
forms.

`%l'
     stands for the 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 the contents of the line, including its trailing
     newline (if any).  If a line is incomplete, this format preserves
     its incompleteness.

`%0'
     stands for a null character.

`%%'
     stands for `%'.

   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.


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 /* not 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 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 just 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 /* not 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: Comparing Directories,  Next: Adjusting Output,  Prev: Output Formats,  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.  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
`-P' or `--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.


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.

* Menu:

* Tabs::		Preserving the alignment of tabstops.
* Pagination::		Page numbering and timestamping `diff' output.


File: diff.info,  Node: Tabs,  Next: Pagination,  Up: Adjusting Output

Preserving Tabstop 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 tabstop, 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 tabstops are set
every 8 columns.  To use this form of output with `patch', you must
give `patch' the `-l' or `--ignore-whitespace' option (*note Changed
Whitespace::., for more information).

   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 tabstops 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':

     Mar 11 13:37 1991  diff -lc lao tzu Page 1


File: diff.info,  Node: diff Performance,  Next: Comparing Three Files,  Prev: Adjusting Output,  Up: Top

`diff' Performance Tradeoffs
****************************

   GNU `diff' runs quite efficiently; however, in some circumstances
you can cause it to run faster or produce a more compact set of changes.
There are two ways that you can affect the performance of GNU `diff' by
changing 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 `-H' or
`--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.


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'.

* Menu:

* 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.  Two spaces
precede each copy of an input line to distinguish it from the commands.
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
together with warnings about conflicts.

   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'.

* Menu:

* 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
newline had been present.


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 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
package `emerge'.  *Note emerge: (emacs)emerge, for more information.

* Menu:

* 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 -H -I REGEXP
     
     --ignore-blank-lines  --ignore-case
     --ignore-matching-lines=REGEXP  --ignore-space-change
     --left-column  --minimal  --speed-large-files
     --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.
Follow each command with RET.

`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.

`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
files instead of distributing the entire file set; your correspondents
can apply `patch' to update their copy of the files with your changes.
`patch' automatically determines the diff format, skips any leading or
trailing headers, and uses the headers to determine which file to
patch.  This lets your correspondents feed an article or message
containing a difference listing directly to `patch'.

   `patch' detects and warns about common problems like forward
patches.  It saves the original version of the files it patches, and
saves any patches that it could not apply.  It can also maintain a
`patchlevel.h' file to ensures 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, saving the original file in `F.orig',
and putting reject hunks (if any) into `F.rej'.

   *Note Invoking patch::, for detailed information on the options to
`patch'.  *Note Backups::, for more information on how `patch' names
backup files.  *Note Rejects::, for more information on where `patch'
puts reject hunks.

* Menu:

* patch Input::		Selecting the type of `patch' input.
* Imperfect::		Dealing with imperfect patches.
* Empty Files::		Removing empty files after patching.
* Multiple Patches::	Handling multiple patches in a file specially.
* patch Messages::	Messages and questions `patch' can produce.


File: diff.info,  Node: patch Input,  Next: Imperfect,  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: Imperfect,  Next: Empty Files,  Prev: patch Input,  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 news article
or mail message directly to `patch', and it should work.  If the entire
diff is indented by a constant amount of whitespace, `patch'
automatically ignores the indentation.

   However, certain other types of imperfect input require user
intervention.

* Menu:

* Changed Whitespace::	When tabs and spaces don't match exactly.
* Reversed Patches::	Applying reversed patches correctly.
* Inexact::		Helping `patch' find close matches.


File: diff.info,  Node: Changed Whitespace,  Next: Reversed Patches,  Up: Imperfect

Applying Patches with Changed Whitespace
----------------------------------------

   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-whitespace' option, which makes `patch' compare whitespace
loosely so that any sequence of whitespace in the patch file matches
any sequence of whitespace in the input files.  Non-whitespace
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 Whitespace,  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.  The `-R' option does not work with `ed' scripts
because there is too little information in them to reconstruct the
reverse operation.

   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,  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; it may not be set 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 Rejects::., 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.

   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.

   `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: Empty Files,  Next: Multiple Patches,  Prev: Imperfect,  Up: Merging with patch

Removing Empty Files
====================

   Sometimes when comparing two directories, the first directory
contains a file that the second directory does not.  If you give `diff'
the `-N' or `--new-file' option, it outputs a diff that deletes the
contents of this file.  By default, `patch' leaves an empty file after
applying such a diff.  The `-E' or `--remove-empty-files' option to
`patch' deletes output files that are empty after applying the diff.


File: diff.info,  Node: Multiple Patches,  Next: patch Messages,  Prev: Empty Files,  Up: Merging with patch

Multiple Patches in a File
==========================

   If the patch file contains more than one patch, `patch' tries to
apply each of them 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).

   For the second and subsequent patches in the patch file, you can give
options and another original file name by separating their argument
lists with a `+'.  However, the argument list for a second or
subsequent patch may not specify a new patch file, since that does not
make sense.

   For example, to tell `patch' to strip the first three slashes from
the name of the first patch in the patch file and none from subsequent
patches, and to use `code.c' as the first input file, you can use:

     patch -p3 code.c + -p0 < patchfile

   The `-S' or `--skip' option ignores the current patch from the patch
file, but continue looking for the next patch in the file.  Thus, to
ignore the first and third patches in the patch file, you can use:

     patch -S + + -S + < patch file


File: diff.info,  Node: patch Messages,  Prev: Multiple Patches,  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 suppress printing non-fatal messages
and stopping for keyboard input.

   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.

   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 assumes the following:

   * skip patches for which it can't find a file to patch;

   * 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 for which it can't find a file to patch (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.

   `patch' exits with a non-zero status if it creates any reject files.
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: Making Patches,  Next: Invoking cmp,  Prev: Merging with patch,  Up: Top

Tips for Making Patch Distributions
***********************************

   Here are some things you should keep in mind if you are going to
distribute patches for updating a software package.

   Make sure you have specified the file names correctly, either in a
context diff header or with an `Index:' line.  If you are patching
files in a subdirectory, be sure to tell the patch user to specify a
`-p' or `--strip' option as needed.  Take care to not send out reversed
patches, since these make people wonder whether they have already
applied the patch.

   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 whitespace or a
newline.  If not, `patch' prompts you for confirmation before
proceeding.  This makes it difficult to accidentally apply patches in
the wrong order.

   Since `patch' does not handle incomplete lines properly, make sure
that all the source files in your program end with a newline whenever
you release a version.

   To create a patch that changes an older version of a package into a
newer version, first make a copy of the older version in a scratch
directory.  Typically you do that by unpacking a `tar' or `shar'
archive of the older version.

   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'), replace the versions in
the scratch directory with the newer versions, using `rm' and `ln' or
`cp'.

   Now you can create the patch.  The de-facto standard `diff' format
for patch distributions is context format with two lines of context,
produced by giving `diff' the `-C 2' option.  Give `diff' the `-N'
option in case the newer version of the package contains any files that
the older one does not.  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.


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.  Its arguments are as
follows:

     cmp OPTIONS... FROM-FILE [TO-FILE]

   The file name `-' is always the standard input.  `cmp' also uses the
standard input if one file name is omitted.

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

* Menu:

* 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: `-cl' is equivalent to
`-c -l'.

`-c'
     Print the differing characters.  Display control characters as a
     `^' followed by a letter of the alphabet and precede characters
     that have the high bit set with `M-' (which stands for "meta").

`-l'
     Print the (decimal) offsets and (octal) values of all differing
     bytes.

`--print-chars'
     Print the differing characters.  Display control characters as a
     `^' followed by a letter of the alphabet and precede characters
     that have the high bit set with `M-' (which stands for "meta").

`--quiet'
`-s'
`--silent'
     Do not print anything; only return an exit status indicating
     whether the files differ.

`--verbose'
     Print the (decimal) offsets and (octal) values of all differing
     bytes.


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... FROM-FILE TO-FILE

   In the simplest case, `diff' compares the contents of the two files
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 FROM-FILE is a directory and TO-FILE is not, `diff' compares the
file in FROM-FILE whose file name is that of TO-FILE, and vice versa.
The non-directory file must not be `-'.

   If both FROM-FILE and TO-FILE 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.

   `diff' 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 `-'.

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

* Menu:

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

