This manual is for GNU Diffutils
(version 3.10, 2 January 2023),
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 © 1992–1994, 1998, 2001–2002, 2004, 2006, 2009–2023 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 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”
diff Output Formatsdiff Output Prettierdiff Performance Tradeoffssdiffpatchcmpdiffdiff3patchsdiffdiff Output Formats
diff Output Prettier
diff Performance Tradeoffssdiff
patch
patch Input Formatpatch
patch and the POSIX Standardpatch and Traditional patchcmp
diff
diff3
patch
sdiff
diff and 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 Perhaps one file is a newer version of the other file.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 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. See Other Window in The GNU
Emacs Manual, 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
by Eugene W. Myers in “An O(ND) Difference Algorithm and its Variations”,
Algorithmica Vol. 1, 1986, pp. 251–266,
http://dx.doi.org/10.1007/BF01840446; and in “A File
Comparison Program”, Webb Miller and Eugene W. Myers,
Software—Practice and Experience Vol. 15, 1985,
pp. 1025–1040,
http://dx.doi.org/10.1002/spe.4380151102.
The algorithm was independently discovered as described by Esko Ukkonen in
“Algorithms for Approximate String Matching”,
Information and Control Vol. 64, 1985, pp. 100–118,
http://dx.doi.org/10.1016/S0019-9958(85)80046-2.
Unless the --minimal option is used, diff uses a
heuristic by Paul Eggert that limits the cost to 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”,
Handbook of Theoretical Computer Science (Jan Van Leeuwen,
ed.), Vol. A, Algorithms and Complexity, Elsevier/MIT Press,
1990, pp. 255–300.
GNU diff3 was written by Randy Smith. GNU
sdiff was written by Thomas Lord. GNU cmp
was written by Torbjörn Granlund and David MacKenzie.
GNU 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.
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.
These commands compare input files without necessarily reading them.
For example, if diff is asked simply to report whether two
files differ, and it discovers that the files have different sizes, it
need not read them to do its job.
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 (-d) option (see diff Performance Tradeoffs).
The --ignore-tab-expansion (-E) 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 (see Preserving Tab Stop Alignment).
The --ignore-trailing-space (-Z) option ignores white space at line end.
The --ignore-space-change (-b) option is stronger than
-E and -Z combined.
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, 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 --ignore-all-space (-w) option is stronger still.
It ignores differences even if one line has white space where
the other line has none. White space characters include
tab, vertical tab, form feed, carriage return, and space;
some locales may define additional characters to be white space.
With this option, 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$
For many other programs newline is also a white space character, but
diff is a line-oriented program and a newline character
always ends a line. Hence the -w or
--ignore-all-space option does not ignore newline-related
changes; it ignores only other white space changes.
The --ignore-blank-lines (-B) option ignores changes that consist entirely of blank lines. With this option, 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
Normally this option affects only lines that are completely empty, but if you also specify an option that ignores trailing spaces, lines are also affected if they look empty but contain white space. In other words, -B is equivalent to ‘-I '^$'’ by default, but it is equivalent to -I '^[[:space:]]*$' if -b, -w or -Z is also specified.
To ignore insertions and deletions of lines that match a
grep-style regular expression, use the
--ignore-matching-lines=regexp (-I 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.
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.
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
--brief (-q) option selects 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, or reports that one
file is a prefix of the other. You can use
the -s, --quiet, or --silent option to
suppress that information, so that cmp
produces no output and reports whether the files differ using only its
exit status (see Invoking cmp).
Unlike diff, cmp cannot compare directories; it can only
compare two files.
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 (see Summarizing Which Files Differ), and
reports only that the binary files are different. This is because line
by line comparisons are usually not meaningful for binary files.
This does not count as trouble, even though the resulting output does
not capture all the differences.
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
--text (-a) 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 report only whether files differ
(but not how). Use the --brief (-q) option for
this.
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 --verbose (-l)
option to show the values of each differing byte in the two files.
With GNU cmp, you can also use the -b or
--print-bytes option to show the ASCII representation of
those bytes. See Invoking cmp, for more information.
If diff3 thinks that any of the files it is comparing is binary
(a non-text file), it normally reports an error, because such
comparisons are usually not useful. diff3 uses the same test as
diff to decide whether a file is binary. As with diff, if
the input files contain a few non-text bytes but otherwise are like
text files, you can force diff3 to consider all files to be text
files and compare them line by line by using the -a or
--text option.
diff Output Formats ¶diff has several mutually exclusive options for output format.
The following sections describe each format, illustrating how
diff reports the differences between two sample input files.
Here are two sample files that we will use in numerous examples to
illustrate the output of diff and how various options can change
it.
This is the file lao:
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 outcome. The two are the same, But after they are produced, they have different names.
This is the file tzu:
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 outcome. The two are the same, But after they are produced, they have different names. They both may be called deep and profound. Deeper and more profound, The door of all subtleties!
In this example, the first hunk contains just the first two lines of lao, the second hunk contains the fourth line of lao opposing the second and third lines of tzu, and the last hunk contains just the last three lines of tzu.
Usually, when you are looking at the differences between files, you will also want to see the parts of the files near the lines that differ, to help you understand exactly what has changed. These nearby parts of the files are called the context.
GNU diff provides two output formats that show context
around the differing lines: context format and unified
format. It can optionally show in which function or section of the
file the differing lines are found.
If you are distributing new versions of files to other people in the
form of diff output, you should use one of the output formats
that show context so that they can apply the diffs even if they have
made small changes of their own to the files. patch can apply
the diffs in this case by searching in the files for the lines of
context around the differing lines; if those lines are actually a few
lines away from where the diff says they are, patch can adjust
the line numbers accordingly and still apply the diff correctly.
See Applying Imperfect Patches, for more information on using patch to apply
imperfect diffs.
The context output format shows several lines of context around the lines that differ. It is the standard format for distributing updates to source code.
To select this output format, use the
--context[=lines] (-C lines)
or -c option. The
argument lines that some of these options take is the number of
lines of context to show. If you do not specify lines, it
defaults to three. For proper operation, patch typically needs
at least two lines of context.
Here is the output of ‘diff -c lao tzu’ (see Two Sample Input Files, for the complete contents of the two files). Notice that up to three lines that are not different are shown around each line that is different; they are the context lines. Also notice that the first two hunks have run together, because their contents overlap.
*** lao 2002-02-21 23:30:39.942229878 -0800
--- tzu 2002-02-21 23:30:50.442260588 -0800
***************
*** 1,7 ****
- 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,
--- 1,6 ----
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,
***************
*** 9,11 ****
--- 8,13 ----
The two are the same,
But after they are produced,
they have different names.
+ They both may be called deep and profound.
+ Deeper and more profound,
+ The door of all subtleties!
Here is the output of ‘diff -C 1 lao tzu’ (see Two Sample Input Files, for the complete contents of the two files). Notice that at most one context line is reported here.
*** lao 2002-02-21 23:30:39.942229878 -0800
--- tzu 2002-02-21 23:30:50.442260588 -0800
***************
*** 1,5 ****
- 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,
--- 1,4 ----
The Nameless is the origin of Heaven and Earth;
! The named is the mother of all things.
!
Therefore let there always be non-being,
***************
*** 11 ****
--- 10,13 ----
they have different names.
+ They both may be called deep and profound.
+ Deeper and more profound,
+ The door of all subtleties!
The context output format starts with a two-line header, which looks like this:
*** from-file from-file-modification-time --- to-file to-file-modification time
The timestamp normally looks like ‘2002-02-21 23:30:39.942229878
-0800’ to indicate the date, time with fractional seconds, and time
zone in Internet RFC
2822 format. (The fractional seconds are omitted on hosts that do
not support fractional timestamps.) However, a traditional timestamp
like ‘Thu Feb 21 23:30:39 2002’ is used if the
LC_TIME locale category is either ‘C’ or ‘POSIX’.
You can change the header’s content with the --label=label option; see Showing Alternate File Names.
Next come one or more hunks of differences; each hunk shows one area where the files differ. Context format hunks look like this:
*************** *** from-file-line-numbers **** from-file-line from-file-line... --- to-file-line-numbers ---- to-file-line to-file-line...
If a hunk contains two or more lines, its line numbers look like ‘start,end’. Otherwise only its end line number appears. An empty hunk is considered to end at the line that precedes the hunk.
The lines of context around the lines that differ start with two space characters. The lines that differ between the two files start with one of the following indicator characters, followed by a space character:
A line that is part of a group of one or more lines that changed between the two files. There is a corresponding group of lines marked with ‘!’ in the part of this hunk for the other file.
An “inserted” line in the second file that corresponds to nothing in the first file.
A “deleted” line in the first file that corresponds to nothing in the second file.
If all of the changes in a hunk are insertions, the lines of from-file are omitted. If all of the changes are deletions, the lines of to-file are omitted.
The unified output format is a variation on the context format that is more compact because it omits redundant context lines. To select this output format, use the --unified[=lines] (-U lines), or -u option. The argument lines is the number of lines of context to show. When it is not given, it defaults to three.
In the early 1990s, only GNU diff could produce this format and
only GNU patch could automatically apply diffs in this
format. For proper operation, patch typically needs at
least three lines of context.
Here is the output of the command ‘diff -u lao tzu’ (see Two Sample Input Files, for the complete contents of the two files):
--- lao 2002-02-21 23:30:39.942229878 -0800 +++ tzu 2002-02-21 23:30:50.442260588 -0800 @@ -1,7 +1,6 @@ -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. +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, @@ -9,3 +8,6 @@ The two are the same, But after they are produced, they have different names. +They both may be called deep and profound. +Deeper and more profound, +The door of all subtleties!
The unified output format starts with a two-line header, which looks like this:
--- from-file from-file-modification-time +++ to-file to-file-modification-time
The timestamp looks like ‘2002-02-21 23:30:39.942229878 -0800’ to indicate the date, time with fractional seconds, and time zone. The fractional seconds are omitted on hosts that do not support fractional timestamps.
You can change the header’s content with the --label=label option. See Showing Alternate File Names.
Next come one or more hunks of differences; each hunk shows one area where the files differ. Unified format hunks look like this:
@@ from-file-line-numbers to-file-line-numbers @@ line-from-either-file line-from-either-file...
If a hunk contains just one line, only its start line number appears. Otherwise its line numbers look like ‘start,count’. An empty hunk is considered to start at the line that follows the hunk.
If a hunk and its context contain two or more lines, its line numbers look like ‘start,count’. Otherwise only its end line number appears. An empty hunk is considered to end at the line that precedes the hunk.
The lines common to both files begin with a space character. The lines that actually differ between the two files have one of the following indicator characters in the left print column:
A line was added here to the first file.
A line was removed here from the first file.
Sometimes you might want to know which part of the files each change
falls in. If the files are source code, this could mean which
function was changed. If the files are documents, it could mean which
chapter or appendix was changed. GNU diff can
show this by displaying the nearest section heading line that precedes
the differing lines. Which lines are “section headings” is
determined by a regular expression.
To show in which sections differences occur for files that are not
source code for C or similar languages, use the
--show-function-line=regexp (-F regexp) option.
diff
considers lines that match the grep-style regular expression
regexp to be the beginning
of a section of the file. Here are suggested regular expressions for
some common languages:
C, C++, Prolog
Lisp
Texinfo
This option does not automatically select an output format; in order to use it, you must select the context format (see Context Format) or unified format (see Unified Format). In other output formats it has no effect.
The --show-function-line (-F) option finds the nearest
unchanged line that precedes each hunk of differences and matches the
given regular expression. Then it adds that line to the end of the
line of asterisks in the context format, or to the ‘@@’ line in
unified format. If no matching line exists, this option leaves the output for
that hunk unchanged. If that line is more than 40 characters long, it
outputs only the first 40 characters. You can specify more than one
regular expression for such lines; diff tries to match each line
against each regular expression, starting with the last one given. This
means that you can use -p and -F together, if you wish.
To show in which functions differences occur for C and similar languages, you can use the --show-c-function (-p) option. This option automatically defaults to the context output format (see Context Format), with the default number of lines of context. You can override that number with -C lines elsewhere in the command line. You can override both the format and the number with -U lines elsewhere in the command line.
The --show-c-function (-p) option is equivalent to
-F '^[[:alpha:]$_]' if the unified format is specified, otherwise
-c -F '^[[:alpha:]$_]' (see Showing Lines That Match Regular Expressions). GNU
diff provides this option for the sake of convenience.
If you are comparing two files that have meaningless or uninformative
names, you might want diff to show alternate names in the header
of the context and unified output formats. To do this, use the
--label=label option. The first time
you give this option, its argument replaces the name and date of the
first file in the header; the second time, its argument replaces the
name and date of the second file. If you give this option more than
twice, diff reports an error. The --label option does not
affect the file names in the pr header when the -l or
--paginate option is used (see Paginating diff Output).
Here are the first two lines of the output from ‘diff -C 2 --label=original --label=modified lao tzu’:
*** original --- modified
diff can produce a side by side difference listing of two files.
The files are listed in two columns with a gutter between them. The
gutter contains one of the following markers:
The corresponding lines are in common. That is, either the lines are identical, or the difference is ignored because of one of the --ignore options (see Suppressing Differences in Blank and Tab Spacing).
The corresponding lines differ, and they are either both complete or both incomplete.
The files differ and only the first file contains the line.
The files differ and only the second file contains the line.
Only the first file contains the line, but the difference is ignored.
Only the second file contains the line, but the difference is ignored.
The corresponding lines differ, and only the first line is incomplete.
The corresponding lines differ, and only the second line is incomplete.
Normally, an output line is incomplete if and only if the lines that it contains are incomplete. See Incomplete Lines. However, when an output line represents two differing lines, one might be incomplete while the other is not. In this case, the output line is complete, but its the gutter is marked ‘\’ if the first line is incomplete, ‘/’ if the second line is.
Side by side format is sometimes easiest to read, but it has limitations. It generates much wider output than usual, and truncates lines that are too long to fit. Also, it relies on lining up output more heavily than usual, so its output looks particularly bad if you use varying width fonts, nonstandard tab stops, or nonprinting characters.
You can use the sdiff command to interactively merge side by side
differences. See Interactive Merging with sdiff, for more information on merging files.
The --side-by-side (-y) option selects side by side format. Because side by side output lines contain two input lines, the output is wider than usual: normally 130 print columns, which can fit onto a traditional printer line. You can set the width of the output with the --width=columns (-W 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 --left-column option prints only the left column of two common lines. The --suppress-common-lines option suppresses common lines entirely.
Here is the output of the command ‘diff -y -W 72 lao tzu’ (see Two Sample Input Files, for the complete contents of the two files).
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!
The “normal” 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 (see Context Format) and the unified format
(see Unified Format) are superior. Normal format is the default for
compatibility with older versions of diff and the POSIX
standard. Use the --normal option to select this output
format explicitly.
Here is the output of the command ‘diff lao tzu’ (see Two Sample Input Files, for the complete contents of the two files). Notice that it shows only the lines that are different between the two files.
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!
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:
change-command < from-file-line < from-file-line... --- > to-file-line > to-file-line...
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:
Add the lines in range r of the second file after line l of the first file. For example, ‘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.
Replace the lines in range f of the first file with lines in range t of the second file. This is like a combined add and delete, but more compact. For example, ‘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.
Delete the lines in range r from the first file; line l is where they would have appeared in the second file had they not been deleted. For example, ‘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.
Several output modes produce command scripts for editing from-file to produce to-file.
ed Scripts ¶diff can produce commands that direct the 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 patch, it is almost obsolete. Use the
--ed (-e) option to select this output format.
Like the normal format (see Showing Differences Without Context), 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 d contains the output of ‘diff -e old new’, then the command ‘(cat d && echo w) | ed - old’ edits old to make it a copy of new. More generally, if d1, d2, …, dN contain the outputs of ‘diff -e old new1’, ‘diff -e new1 new2’, …, ‘diff -e newN-1 newN’, respectively, then the command ‘(cat d1 d2 … dN && echo w) | ed - old’ edits old to make it a copy of newN.
ed Script ¶Here is the output of ‘diff -e lao tzu’ (see Two Sample Input Files, for the complete contents of the two files):
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
ed Format ¶The 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
ed interprets line numbers in succeeding commands. ed
format hunks look like this:
change-command to-file-line to-file-line... .
Because ed uses a single period on a line to indicate the
end of input, GNU diff protects lines of changes
that contain a single period on a line by writing two periods instead,
then writing a subsequent ed command to change the two
periods into one. The ed format cannot represent an
incomplete line, so if the second file ends in a changed incomplete
line, 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:
Add text from the second file after line l in the first file. For example, ‘8a’ means to add the following lines after line 8 of file 1.
Replace the lines in range r in the first file with the following lines. Like a combined add and delete, but more compact. For example, ‘5,7c’ means change lines 5–7 of file 1 to read as the text file 2.
Delete the lines in range r from the first file. For example, ‘5,7d’ means delete lines 5–7 of file 1.
ed Scripts ¶diff can produce output that is like an 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
ed format, forward ed format cannot represent incomplete
lines.
Forward ed format is not very useful, because neither ed
nor patch can apply diffs in this format. It exists mainly for
compatibility with older versions of diff. Use the -f or
--forward-ed option to select it.
The 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
--rcs (-n) option to select this output format. It
is like the forward ed format (see Forward ed Scripts), but it
can represent arbitrary changes to the contents of a file because it
avoids the forward 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
‘a’ and ‘d’ commands are used instead of ‘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 ‘diff -n lao tzu’ (see Two Sample Input Files, for the complete contents of the two files):
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!
You can use diff to merge two files of C source code. The output
of 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 #ifdef name or
#ifndef name, #else, and #endif. When
compiling the output, you select which version to use by either defining
or leaving undefined the macro name.
To merge two files, use diff with the -D name or
--ifdef=name option. The argument name is the C
preprocessor identifier to use in the #ifdef and #ifndef
directives.
For example, if you change an instance of wait (&s) to
waitpid (-1, &s, 0) and then merge the old and new files with
the --ifdef=HAVE_WAITPID option, then the affected part of your code
might look like this:
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);
You can specify formats for languages other than C by using line group formats and line formats, as described in the next sections.
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 old and new, and outputs a merged file in which old regions are surrounded by ‘\begin{em}’-‘\end{em}’ lines, and new regions are surrounded by ‘\begin{bf}’-‘\end{bf}’ lines.
diff \
--old-group-format='\begin{em}
%<\end{em}
' \
--new-group-format='\begin{bf}
%>\end{bf}
' \
old new
The following command is equivalent to the above example, but it is a little more verbose, because it spells out the default line group formats.
diff \
--old-group-format='\begin{em}
%<\end{em}
' \
--new-group-format='\begin{bf}
%>\end{bf}
' \
--unchanged-group-format='%=' \
--changed-group-format='\begin{em}
%<\end{em}
\begin{bf}
%>\end{bf}
' \
old new
Here is a more advanced example, which outputs a diff listing with headers containing line numbers in a “plain English” style.
diff \ --unchanged-group-format='' \ --old-group-format='-------- %dn line%(n=1?:s) deleted at %df: %<' \ --new-group-format='-------- %dN line%(N=1?:s) added after %de: %>' \ --changed-group-format='-------- %dn line%(n=1?:s) changed at %df: %<-------- to: %>' \ old new
To specify a line group format, use diff with one of the options
listed below. You can specify up to four line group formats, one for
each kind of line group. You should quote format, because it
typically contains shell metacharacters.
These line groups are hunks containing only lines from the first file. The default old group format is the same as the changed group format if it is specified; otherwise it is a format that outputs the line group as-is.
These line groups are hunks containing only lines from the second file. The default new group format is same as the changed group format if it is specified; otherwise it is a format that outputs the line group as-is.
These line groups are hunks containing lines from both files. The default changed group format is the concatenation of the old and new group formats.
These line groups contain lines common to both files. The default unchanged group format is a format that outputs the line group as-is.
In a line group format, ordinary characters represent themselves; conversion specifications start with ‘%’ and have one of the following forms.
stands for the lines from the first file, including the trailing newline. Each line is formatted according to the old line format (see Line Formats).
stands for the lines from the second file, including the trailing newline. Each line is formatted according to the new line format.
stands for the lines common to both files, including the trailing newline. Each line is formatted according to the unchanged line format.
stands for ‘%’.
where C is a single character, stands for C. C may not be a backslash or an apostrophe. For example, ‘%c':'’ stands for a colon, even inside the then-part of an if-then-else format, which a colon would normally terminate.
where O is a string of 1, 2, or 3 octal digits, stands for the character with octal code O. For example, ‘%c'\0'’ stands for a null character.
where F is a printf conversion specification and n is one
of the following letters, stands for n’s value formatted with F.
The line number of the line just before the group in the old file.
The line number of the first line in the group in the old file; equals e + 1.
The line number of the last line in the group in the old file.
The line number of the line just after the group in the old file; equals l + 1.
The number of lines in the group in the old file; equals l - f + 1.
Likewise, for lines in the new file.
The printf conversion specification can be ‘%d’,
‘%o’, ‘%x’, or ‘%X’, specifying decimal, octal,
lower case hexadecimal, or upper case hexadecimal output
respectively. After the ‘%’ the following options can appear in
sequence: a series of zero or more flags; an integer
specifying the minimum field width; and a period followed by an
optional integer specifying the minimum number of digits.
The flags are ‘-’ for left-justification, ‘'’ for separating
the digit into groups as specified by the LC_NUMERIC locale category,
and ‘0’ for padding with zeros instead of spaces.
For example, ‘%5dN’ prints the number of new lines in the group
in a field of width 5 characters, using the printf format "%5d".
If A equals B then T else E. A and B are each either a decimal constant or a single letter interpreted as above. This format spec is equivalent to T if A’s value equals B’s; otherwise it is equivalent to E.
For example, ‘%(N=0?no:%dN) line%(N=1?:s)’ is equivalent to ‘no lines’ if N (the number of lines in the group in the new file) is 0, to ‘1 line’ if N is 1, and to ‘%dN lines’ otherwise.
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-character change indicator to the left of the text. The first character 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.
formats lines just from the first file.
formats lines just from the second file.
formats lines common to both files.
formats all lines; in effect, it sets all three above options simultaneously.
In a line format, ordinary characters represent themselves; conversion specifications start with ‘%’ and have one of the following forms.
stands for the contents of the line, not counting its trailing newline (if any). This format ignores whether the line is incomplete; See Incomplete Lines.
stands for the contents of the line, including its trailing newline (if any). If a line is incomplete, this format preserves its incompleteness.
stands for ‘%’.
where C is a single character, stands for C. C may not be a backslash or an apostrophe. For example, ‘%c':'’ stands for a colon.
where O is a string of 1, 2, or 3 octal digits, stands for the character with octal code O. For example, ‘%c'\0'’ stands for a null character.
where F is a printf conversion specification,
stands for the line number formatted with F.
For example, ‘%.5dn’ prints the line number using the
printf format "%.5d". See Line Group Formats, for
more about printf conversion specifications.
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.
Taken together, the line and line group formats let you specify many
different formats. For example, the following command uses a format
similar to normal diff format. You can tailor this command
to get fine control over diff output.
diff \ --old-line-format='< %l ' \ --new-line-format='> %l ' \ --old-group-format='%df%(f=l?:,%dl)d%dE %<' \ --new-group-format='%dea%dF%(F=L?:,%dL) %>' \ --changed-group-format='%df%(f=l?:,%dl)c%dF%(F=L?:,%dL) %<--- %>' \ --unchanged-group-format='' \ old new
Here is the output of ‘diff -DTWO lao tzu’ (see Two Sample Input Files, 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 /* ! 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 */
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 /* ! 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 -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 like
the diff -D name option, except it operates on
a file and a diff to produce a merged file. See Options to patch.
When an input file ends in a non-newline character, its last line is called an incomplete line because its last character is not a newline. All other lines are called full lines and end in a newline character. Incomplete lines do not match full lines unless differences in white space are ignored (see Suppressing Differences in Blank and Tab Spacing).
An incomplete line is normally distinguished on output from a full
line by a following line that starts with ‘\’. However, the
RCS format (see RCS Scripts) outputs the incomplete line as-is,
without any trailing newline or following line. The side by side
format normally represents incomplete lines as-is, but in some cases
uses a ‘\’ or ‘/’ gutter marker. See Showing Differences Side by Side. The
if-then-else line format preserves a line’s incompleteness with
‘%L’, and discards the newline with ‘%l’. See Line Formats.
Finally, with the ed and forward ed
output formats (see diff Output Formats) diff cannot
represent an incomplete line, so it pretends there was a newline and
reports an error.
For example, suppose F and G are one-byte files that contain just ‘f’ and ‘g’, respectively. Then ‘diff F G’ outputs
1c1 < f \ No newline at end of file --- > g \ No newline at end of file
(The exact message may differ in non-English locales.) ‘diff -n F G’ outputs the following without a trailing newline:
d1 1 a1 1 g
‘diff -e F G’ reports two errors and outputs the following:
1c g .
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 as specified by
the LC_COLLATE locale category. Normally
diff is silent about pairs of files that contain no differences,
but if you use the --report-identical-files (-s) 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.
If only one file exists, diff normally does not show its
contents; it merely reports that one file exists but the other does
not. You can make diff act as though the missing file is
empty, 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 the missing file is in the first or the
second position.) To do this, use the --new-file
(-N) option. This option affects command-line arguments as
well as files found via directory traversal; for example, ‘diff
-N a b’ treats a as empty if a does not exist but
b does.
If the older directory contains large files that are not in the newer directory, you can make the patch smaller by using the --unidirectional-new-file option instead of -N. This option is like -N except that it inserts the contents only 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. See Tips for Making and Using Patches, for more discussion of making patches for distribution.
To ignore some files while comparing directories, use the --exclude=pattern (-x 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 --exclude-from=file (-X file) option. Trailing white space and empty lines are ignored in the pattern file.
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 --starting-file=file (-S file) option. This compares only the file file and all alphabetically later files in the topmost directory level.
If two directories differ only in that file names are lower case in
one directory and upper case in the upper, diff normally
reports many differences because it compares file names in a
case sensitive way. With the --ignore-file-name-case option,
diff ignores case differences in file names, so that for example
the contents of the file Tao in one directory are compared to
the contents of the file TAO in the other. The
--no-ignore-file-name-case option cancels the effect of the
--ignore-file-name-case option, reverting to the default
behavior.
If an --exclude=pattern (-x pattern) option, or an --exclude-from=file (-X file) option, is specified while the --ignore-file-name-case option is in effect, case is ignored when excluding file names matching the specified patterns.
To tell diff not to follow a symbolic link, use the
--no-dereference option.
diff Output Prettier ¶diff provides several ways to adjust the appearance of its output.
These adjustments can be applied to any output format.
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 tab stop, 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
--expand-tabs (-t) option. To use this form of output with
patch, you must give patch the -l or
--ignore-white-space option (see Applying Patches with Changed White Space, for more
information). diff normally assumes that tab stops are set
every 8 print columns, but this can be altered by the
--tabsize=columns option.
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 tab stops 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.
When outputting lines in normal or context format, or outputting an
unchanged line in unified format, diff normally outputs a
blank just before each line. If the line is empty, the output of
diff therefore contains trailing blanks even though the
input does not contain them. For example, when outputting an
unchanged empty line in context format, diff normally
outputs a line with two leading spaces.
Some text editors and email agents routinely delete trailing blanks,
so it can be a problem to deal with diff output files that contain
them. You can avoid this problem with the
--suppress-blank-empty option. It causes diff to
omit trailing blanks at the end of output lines in normal, context,
and unified format, unless the trailing blanks were already present in
the input. This changes the output format slightly, so that output
lines are guaranteed to never end in a blank unless an input line ends
in a blank. This format is less likely to be munged by text editors
or by transmission via email. It is accepted by GNU
patch as well.
diff Output ¶It can be convenient to have long output page-numbered and time-stamped.
The --paginate (-l) option does this by sending the
diff output through the pr program. Here is what the page
header might look like for ‘diff -lc lao tzu’:
2002-02-22 14:20 diff -lc lao tzu Page 1
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.
One way to improve diff performance is to use hard or
symbolic links to files instead of copies. This improves performance
because diff normally does not need to read two hard or
symbolic links to the same file, since their contents must be
identical. For example, suppose you copy a large directory hierarchy,
make a few changes to the copy, and then often use ‘diff -r’ to
compare the original to the copy. If the original files are
read-only, you can greatly improve performance by creating the copy
using hard or symbolic links (e.g., with GNU ‘cp -lR’ or
‘cp -sR’). Before editing a file in the copy for the first time,
you should break the link and replace it with a regular copy.
You can also affect the performance of GNU diff by
giving it options that change 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 --minimal (-d) 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
--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.
Normally diff discards the prefix and suffix that is common to
both files before it attempts to find a minimal set of differences.
This makes diff run faster, but occasionally it may produce
non-minimal output. The --horizon-lines=lines option
prevents diff from discarding the last lines lines of the
prefix and the first lines lines of the suffix. This gives
diff further opportunities to find a minimal output.
Suppose a run of changed lines includes a sequence of lines at one end
and there is an identical sequence of lines just outside the other end.
The diff command is free to choose which identical sequence is
included in the hunk. In this case, diff normally shifts the
hunk’s boundaries when this merges adjacent hunks, or shifts a hunk’s
lines towards the end of the file. Merging hunks can make the output
look nicer in some cases.
Use the program diff3 to compare three files and show any
differences among them. (diff3 can also merge files; see
Merging From a Common Ancestor).
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.
See Invoking diff3, for more information on how to run diff3.
diff3 Normal Formatdiff3 Normal Formatdiff3 HunksHere 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 (see Two Sample Input Files). 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
diff3 Normal Format ¶Here is the output of the command ‘diff3 lao tzu tao’ (see A Third Sample Input File, 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
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.
Normally, two spaces precede each copy of an input line to distinguish
it from the commands. But with the --initial-tab (-T)
option, diff3 uses a tab instead of two spaces; this lines up
tabs correctly. See Preserving Tab Stop Alignment, for more information.
Commands take the following forms:
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.
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 there is only one line. 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 (see Incomplete Lines), it is distinguished on output from a full line by a following line that starts with ‘\’.
diff3 Hunks ¶Groups of lines that differ in two or three of the input files are
called diff3 hunks, by analogy with diff hunks
(see 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.
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.
diff3 Merges Incomplete LinesYou can select all unmerged changes from older to yours for merging into mine with the --ed (-e) option. You can select only the nonoverlapping unmerged changes with --easy-only (-3), and you can select only the overlapping changes with --overlap-only (-x).
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 --show-all (-A) option (see Marking Conflicts).
Here is the output of the command diff3 with each of these three
options (see A Third Sample Input File, 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 .
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 --show-all (-A) 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 (see A Third Sample Input File), ‘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 --show-overlap (-E) option outputs less information than the --show-all (-A) 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 --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 --label X --label Y --label 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’.
With the --merge (-m) 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 is assumed.
For example, the command ‘diff3 -m lao tzu tao’ (see A Third Sample Input File 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
diff3 Merges Incomplete Lines ¶With -m, incomplete lines (see 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.
Traditional Unix diff3 generates an ed script without the
trailing ‘w’ 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.
sdiff ¶With sdiff, you can merge two files interactively based on a
side-by-side -y format comparison (see Showing Differences Side by Side). Use
--output=file (-o file) to specify where to
put the merged text. See Invoking sdiff, for more details on the
options to sdiff.
Another way to merge files interactively is to use the Emacs Lisp
package emerge. See Emerge in The
GNU Emacs Manual, for more information.
diff Options to sdiff ¶The following sdiff options have the same meaning as for
diff. See Options to diff, for the use of these options.
-a -b -d -i -t -v -B -E -I regexp -Z --expand-tabs --ignore-blank-lines --ignore-case --ignore-matching-lines=regexp --ignore-space-change --ignore-tab-expansion --ignore-trailing-space --left-column --minimal --speed-large-files --strip-trailing-cr --suppress-common-lines --tabsize=columns --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
--side-by-side (-y) option (see Showing Differences Side by Side).
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.
Discard both versions. Invoke a text editor on an empty temporary file, then copy the resulting file to the output.
Concatenate the two versions, edit the result in a temporary file, then copy the edited result to the output.
Like ‘eb’, except precede each version with a header that shows what file and lines the version came from.
Edit a copy of the left version, then copy the result to the output.
Edit a copy of the right version, then copy the result to the output.
Copy the left version to the output.
Quit.
Copy the right version to the output.
Silently copy common lines.
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.
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 a
mail message containing a difference listing directly to
patch.
patch detects and warns about common problems like forward
patches. It saves any patches that it could not apply. It can also maintain a
patchlevel.h file to ensure 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 (see 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, putting reject
hunks (if any) into ‘f.rej’.
See Invoking patch, for detailed information on the options to
patch.
patch Input Formatpatchpatch and the POSIX Standardpatch and Traditional patchpatch 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.
context diff.
ed script.
normal diff.
unified diff.
If a nonexistent input file is under a revision control system
supported by patch, patch normally asks the user
whether to get (or check out) the file from the revision control
system. Patch currently supports RCS, ClearCase and
SCCS. Under RCS and SCCS,
patch also asks when the input file is read-only and matches
the default version in the revision control system.
The --get=num (-g num) option affects access
to files under supported revision control systems. If num is
positive, patch gets the file without asking the user; if
zero, patch neither asks the user nor gets the file; and if
negative, patch asks the user before getting the file. The
default value of num is given by the value of the
PATCH_GET environment variable if it is set; if not, the default
value is zero if patch is conforming to POSIX, negative
otherwise. See patch and the POSIX Standard.
The choice of revision control system is unaffected by the
VERSION_CONTROL environment variable (see Backup File Names).
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
mail message directly to patch, and it should work. If the
entire diff is indented by a constant amount of white space,
patch automatically ignores the indentation. If a context
diff contains trailing carriage return on each line, patch
automatically ignores the carriage return. If a context diff has been
encapsulated by prepending ‘- ’ to lines beginning with ‘-’
as per Internet RFC 934,
patch automatically unencapsulates the input.
However, certain other types of imperfect input require user intervention or testing.
patch Find Inexact Matchespatch will doSometimes 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-white-space option, which makes patch compare
blank characters (i.e. spaces and tabs) loosely so that any nonempty
sequence of blanks in the patch file matches any nonempty sequence of
blanks in the input files. Non-blank
characters must still match exactly. Each line of the context must
still match a line in the input file.
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 --reverse (-R) option.
patch then attempts to swap each hunk around before applying it.
Rejects come out in the swapped format.
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.
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 --fuzz=lines (-F 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; there is no point to setting it 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 (see Reject File Names, 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.
If the --verbose option is given, then
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.
A patch against an empty file applies to a nonexistent file, and vice versa. See Creating and Removing Files.
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.
patch will do ¶It may not be obvious in advance what patch will do with a
complicated or poorly formatted patch. If you are concerned that the
input might cause patch to modify the wrong files, you can
use the --dry-run option, which causes patch to
print the results of applying patches without actually changing any
files. You can then inspect the diagnostics generated by the dry run
to see whether patch will modify the files that you expect.
If the patch does not do what you want, you can modify the patch (or
the other options to patch) and try another dry run. Once
you are satisfied with the proposed patch you can apply it by invoking
patch as before, but this time without the
--dry-run option.
Sometimes when comparing two directories, a file may exist in one
directory but not the other. If you give diff the
--new-file (-N) option, or if you supply an old or
new file that is named /dev/null or is empty and is dated the
Epoch (1970-01-01 00:00:00 UTC), diff outputs a patch that
adds or deletes the contents of this file. When given such a patch,
patch normally creates a new file or removes the old file.
However, when conforming to POSIX (see patch and the POSIX Standard),
patch does not remove the old file, but leaves it empty.
The --remove-empty-files (-E) option causes
patch to remove output files that are empty after applying a
patch, even if the patch does not appear to be one that removed the
file.
If the patch appears to create a file that already exists,
patch asks for confirmation before applying the patch.
When patch updates a file, it normally sets the file’s
last-modified timestamp to the current time of day. If you are using
patch to track a software distribution, this can cause
make to incorrectly conclude that a patched file is out of
date. For example, if syntax.c depends on syntax.y, and
patch updates syntax.c and then syntax.y, then
syntax.c will normally appear to be out of date with respect to
syntax.y even though its contents are actually up to date.
The --set-utc (-Z) option causes patch to
set a patched file’s modification and access times to the timestamps
given in context diff headers. If the context diff headers do not
specify a time zone, they are assumed to use Coordinated Universal
Time (UTC, often known as GMT).
The --set-time (-T) option acts like -Z or --set-utc, except that it assumes that the context diff headers’ timestamps use local time instead of UTC. This option is not recommended, because patches using local time cannot easily be used by people in other time zones, and because local timestamps are ambiguous when local clocks move backwards during daylight-saving time adjustments. If the context diff headers specify a time zone, this option is equivalent to --set-utc (-Z).
patch normally refrains from setting a file’s timestamps if
the file’s original last-modified timestamp does not match the time
given in the diff header, of if the file’s contents do not exactly
match the patch. However, if the --force (-f)
option is given, the file’s timestamps are set regardless.
Due to the limitations of the current diff format,
patch cannot update the times of files whose contents have
not changed. Also, if you set file timestamps to values other than
the current time of day, you should also remove (e.g., with ‘make
clean’) all files that depend on the patched files, so that later
invocations of make do not get confused by the patched
files’ times.
If the patch file contains more than one patch, and if you do not
specify an input file on the command line, patch tries to
apply each patch 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 (see Tips for Making and Using Patches, for more on
that topic).
patch uses the following rules to intuit a file name from
the leading text before a patch. First, patch takes an
ordered list of candidate file names as follows:
patch takes the old
and new file names in the header. A name is ignored if it does not
have enough slashes to satisfy the -pnum or
--strip=num option. The name /dev/null is also
ignored.
patch is
conforming to POSIX, patch takes the name in the
‘Index:’ line.
Then patch selects a file name from the candidate list as
follows:
patch selects the first
name if conforming to POSIX, and the best name otherwise.
patch is not ignoring RCS, ClearCase, and SCCS
(see Revision Control), and no named files exist but an RCS,
ClearCase, or SCCS master is found, patch selects the
first named file with an RCS, ClearCase, or SCCS master.
patch is not conforming to
POSIX, and the patch appears to create a file, patch
selects the best name requiring the creation of the fewest
directories.
patch selects that name.
To determine the best of a nonempty list of file names,
patch first takes all the names with the fewest path name
components; of those, it then takes all the names with the shortest
basename; of those, it then takes all the shortest names; finally, it
takes the first remaining name.
See patch and the POSIX Standard, to see whether patch is conforming
to POSIX.
The --directory=directory (-d directory)
option to patch makes directory directory the current
directory for interpreting both file names in the patch file, and file
names given as arguments to other options (such as -B and
-o). For example, while in a mail reading program, you can patch
a file in the /usr/src/emacs directory directly from a message
containing the patch like this:
| patch -d /usr/src/emacs
Sometimes the file names given in a patch contain leading directories,
but you keep your files in a directory different from the one given in
the patch. In those cases, you can use the
--strip=number (-pnumber)
option to set the file name strip count to number. The strip
count tells patch how many slashes, along with the directory
names between them, to strip from the front of file names. A sequence
of one or more adjacent slashes is counted as a single slash. By
default, patch strips off all leading directories, leaving
just the base file names.
For example, suppose the file name in the patch file is /gnu/src/emacs/etc/NEWS. Using -p0 gives the entire file name unmodified, -p1 gives gnu/src/emacs/etc/NEWS (no leading slash), -p4 gives etc/NEWS, and not specifying -p at all gives NEWS.
patch looks for each file (after any slashes have been stripped)
in the current directory, or if you used the -d directory
option, in that directory.
Normally, patch creates a backup file if the patch does not
exactly match the original input file, because in that case the
original data might not be recovered if you undo the patch with
‘patch -R’ (see Applying Reversed Patches). However, when conforming
to POSIX, patch does not create backup files by
default. See patch and the POSIX Standard.
The --backup (-b) option causes patch to
make a backup file regardless of whether the patch matches the
original input. The --backup-if-mismatch option causes
patch to create backup files for mismatches files; this is
the default when not conforming to POSIX. The
--no-backup-if-mismatch option causes patch to not
create backup files, even for mismatched patches; this is the default
when conforming to POSIX.
When backing up a file that does not exist, an empty, unreadable backup file is created as a placeholder to represent the nonexistent file.
Normally, patch renames an original input file into a backup
file by appending to its name the extension ‘.orig’, or ‘~’
if using ‘.orig’ would make the backup file name too
long.1 The -z backup-suffix or
--suffix=backup-suffix option causes patch to
use backup-suffix as the backup extension instead.
Alternately, you can specify the extension for backup files with the
SIMPLE_BACKUP_SUFFIX environment variable, which the options
override.
patch can also create numbered backup files the way
GNU Emacs does. With this method, instead of having a
single backup of each file, patch makes a new backup file
name each time it patches a file. For example, the backups of a file
named sink would be called, successively, sink.~1~,
sink.~2~, sink.~3~, etc.
The -V backup-style or
--version-control=backup-style option takes as an
argument a method for creating backup file names. You can alternately
control the type of backups that patch makes with the
PATCH_VERSION_CONTROL environment variable, which the
-V option overrides. If PATCH_VERSION_CONTROL is not
set, the VERSION_CONTROL environment variable is used instead.
Please note that these options and variables control backup file
names; they do not affect the choice of revision control system
(see Revision Control).
The values of these environment variables and the argument to the
-V option are like the GNU Emacs version-control
variable (see Backup Names in The GNU Emacs Manual,
for more information on backup versions in Emacs). They also
recognize synonyms that are more descriptive. The valid values are
listed below; unique abbreviations are acceptable.
Always make numbered backups.
Make numbered backups of files that already have them, simple backups of the others. This is the default.
Always make simple backups.
You can also tell patch to prepend a prefix, such as a
directory name, to produce backup file names. The
--prefix=prefix (-B prefix) option makes backup
files by prepending prefix to them. The
--basename-prefix=prefix (-Y prefix) prepends
prefix to the last file name component of backup file names
instead; for example, -Y ~ causes the backup name for
dir/file.c to be dir/~file.c. If you use either of
these prefix options, the suffix-based options are ignored.
If you specify the output file with the -o option, that file is the one that is backed up, not the input file.
Options that affect the names of backup files do not affect whether backups are made. For example, if you specify the --no-backup-if-mismatch option, none of the options described in this section have any affect, because no backups are made.
The names for reject files (files containing patches that
patch could not find a place to apply) are normally the name
of the output file with ‘.rej’ appended (or ‘#’ if using
‘.rej’ would make the backup file name too long).
Alternatively, you can tell patch to place all of the rejected
patches in a single file. The -r reject-file or
--reject-file=reject-file option uses reject-file as
the reject file name.
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 produce more or
fewer messages, to have it not ask for keyboard input, and to
affect the way that file names are quoted in messages.
patch exits with status 0 if all hunks are applied successfully,
1 if some hunks cannot be applied, and 2 if there is more serious trouble.
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.
patch ¶You can cause patch to produce more messages by using the
--verbose option. For example, when you give this option,
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 --force (-f) option assumes that you know
what you are doing. It causes patch to do the following:
The --batch (-t) option is similar to -f, in that it suppresses questions, but it makes somewhat different assumptions:
patch Quoting Style ¶When patch outputs a file name in a diagnostic message, it
can format the name in any of several ways. This can be useful to
output file names unambiguously, even if they contain punctuation or
special characters like newlines. The
--quoting-style=word option controls how names are
output. The word should be one of the following:
Output names as-is.
Quote names for the shell if they contain shell metacharacters or would cause ambiguous output.
Quote names for the shell, even if they would normally not require quoting.
Quote names as for a C language string.
Quote as with ‘c’ except omit the surrounding double-quote characters.
You can specify the default value of the --quoting-style
option with the environment variable QUOTING_STYLE. If that
environment variable is not set, the default value is ‘shell’,
but this default may change in a future version of patch.
patch and the POSIX Standard ¶If you specify the --posix option, or set the
POSIXLY_CORRECT environment variable, patch conforms
more strictly to the POSIX standard, as follows:
patch and Traditional patch ¶The current version of GNU patch normally follows the
POSIX standard. See patch and the POSIX Standard, for the few exceptions
to this general rule.
Unfortunately, POSIX redefined the behavior of patch in
several important ways. You should be aware of the following
differences if you must interoperate with traditional patch,
or with GNU patch version 2.1 and earlier.
patch, the -p option’s operand was
optional, and a bare -p was equivalent to -p0. The
-p option now requires an operand, and -p 0 is now
equivalent to -p0. For maximum compatibility, use options
like -p0 and -p1.
Also, traditional patch simply counted slashes when
stripping path prefixes; patch now counts pathname
components. That is, a sequence of one or more adjacent slashes now
counts as a single slash. For maximum portability, avoid sending
patches containing // in file names.
patch, backups were enabled by default. This
behavior is now enabled with the --backup (-b)
option.
Conversely, in POSIX patch, backups are never made,
even when there is a mismatch. In GNU patch, this
behavior is enabled with the --no-backup-if-mismatch option,
or by conforming to POSIX.
The -b suffix option of traditional patch is
equivalent to the ‘-b -z suffix’ options of GNU
patch.
patch used a complicated (and incompletely
documented) method to intuit the name of the file to be patched from
the patch header. This method did not conform to POSIX, and had
a few gotchas. Now patch uses a different, equally
complicated (but better documented) method that is optionally
POSIX-conforming; we hope it has fewer gotchas. The two methods
are compatible if the file names in the context diff header and the
‘Index:’ line are all identical after prefix-stripping. Your
patch is normally compatible if each header’s file names all contain
the same number of slashes.
patch asked the user a question, it sent
the question to standard error and looked for an answer from the first
file in the following list that was a terminal: standard error,
standard output, /dev/tty, and standard input. Now
patch sends questions to standard output and gets answers
from /dev/tty. Defaults for some answers have been changed so
that patch never goes into an infinite loop when using
default answers.
patch exited with a status value that counted
the number of bad hunks, or with status 1 if there was real trouble.
Now patch exits with status 1 if some hunks failed, or with
2 if there was real trouble.
patch,
traditional patch, or a patch that conforms to
POSIX. Spaces are significant in the following list, and
operands are required.
-c -d dir -D define -e -l -n -N -o outfile -pnum -R -r rejectfile
Use some common sense when making and using patches. For example, when sending bug fixes to a program’s maintainer, send several small patches, one per independent subject, instead of one large, harder-to-digest patch that covers all the subjects.
Here are some other things you should keep in mind if you are going to distribute patches for updating a software package.
To create a patch that changes an older version of a package into a
newer version, first make a copy of the older and newer versions in
adjacent subdirectories. It is common to do that by unpacking
tar archives of the two versions.
To generate the patch, use the command ‘diff -Naur old new’ where old and new identify the old and new directories. The names old and new should not contain any slashes. The -N option lets the patch create and remove files; -a lets the patch update non-text files; -u generates useful timestamps and enough context; and -r lets the patch update subdirectories. Here is an example command, using Bourne shell syntax:
diff -Naur gcc-3.0.3 gcc-3.0.4
Tell your recipients how to apply the patches. This should include
which working directory to use, and which patch options to
use; the option ‘-p1’ is recommended. Test your procedure by
pretending to be a recipient and applying your patches to a copy of
the original files.
See Avoiding Common Mistakes, for how to avoid common mistakes when generating a patch.
A patch producer should tell recipients how to apply the patches, so the first rule of thumb for a patch consumer is to follow the instructions supplied with the patch.
GNU diff can analyze files with arbitrarily long lines
and files that end in incomplete lines. However, older versions of
patch cannot patch such files. If you are having trouble
applying such patches, try upgrading to a recent version of GNU
patch.
When producing a patch for multiple files, apply diff to
directories whose names do not have slashes. This reduces confusion
when the patch consumer specifies the -pnumber option,
since this option can have surprising results when the old and new
file names have different numbers of slashes. For example, do not
send a patch with a header that looks like this:
diff -Naur v2.0.29/prog/README prog/README --- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800 +++ prog/README 2002-03-17 20:49:32.442260588 -0800
because the two file names have different numbers of slashes, and
different versions of patch interpret the file names
differently. To avoid confusion, send output that looks like this
instead:
diff -Naur v2.0.29/prog/README v2.0.30/prog/README --- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800 +++ v2.0.30/prog/README 2002-03-17 20:49:32.442260588 -0800
Make sure you have specified the file names correctly, either in a context diff header or with an ‘Index:’ line. Take care to not send out reversed patches, since these make people wonder whether they have already applied the patch.
Avoid sending patches that compare backup file names like
README.orig or README~, since this might confuse
patch into patching a backup file instead of the real file.
Instead, send patches that compare the same base file names in
different directories, e.g. old/README and new/README.
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
white space or a newline. If not, patch prompts you for
confirmation before proceeding. This makes it difficult to accidentally
apply patches in the wrong order.
The simplest way to generate a patch is to use ‘diff -Naur’
(see Tips for Patch Producers), but 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),
exclude them from the patch by giving diff the -x
pattern option (see Comparing Directories). If you want
your patch to modify a derived file because your recipients lack tools
to build it, make sure that the patch for the derived file follows any
patches for files that it depends on, so that the recipients’
timestamps will not confuse make.
Now you can create the patch using ‘diff -Naur’. 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.
You can also shrink the patch size by using fewer lines of context,
but bear in mind that patch typically needs at least two
lines for proper operation when patches do not exactly match the input
files.
cmp ¶The cmp command compares two files, and if they differ,
tells the first byte and line number where they differ or reports
that one file is a prefix of the other. Bytes and
lines are numbered starting with 1. The arguments of cmp
are as follows:
cmp options... from-file [to-file [from-skip [to-skip]]]
The file name - is always the standard input. cmp
also uses the standard input if one file name is omitted. The
from-skip and to-skip operands specify how many bytes to
ignore at the start of each file; they are equivalent to the
--ignore-initial=from-skip:to-skip option.
By default, cmp outputs nothing if the two files have the
same contents. If the two files have bytes that differ, cmp
reports the location of the first difference to standard output:
from-file to-file differ: char byte-number, line line-number
If one file is a prefix of the other, cmp reports the
shorter file’s name to standard error, followed by a blank and extra
information about the shorter file:
cmp: EOF on shorter-file extra-info
The message formats can differ outside the POSIX locale. POSIX allows but does not require the EOF diagnostic’s file name to be followed by a blank and additional information.
An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble.
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: -bl is equivalent to -b -l.
Print the differing bytes. Display control bytes as a ‘^’ followed by a letter of the alphabet and precede bytes that have the high bit set with ‘M-’ (which stands for “meta”).
Output a summary of usage and then exit.
Ignore any differences in the first skip bytes of the input files. Treat files with fewer than skip bytes as if they are empty. If skip is of the form from-skip:to-skip, skip the first from-skip bytes of the first input file and the first to-skip bytes of the second.
Output the (decimal) byte numbers and (octal) values of all differing bytes, instead of the default standard output. Each output line contains a differing byte’s number relative to the start of the input, followed by the differing byte values. Byte numbers start at 1. Also, output the EOF message if one file is shorter than the other.
Compare at most count input bytes.
Do not print anything; only return an exit status indicating whether the files differ.
Output version information and then exit.
In the above table, operands that are byte counts are normally decimal, but may be preceded by ‘0’ for octal and ‘0x’ for hexadecimal.
A byte count can be followed by a suffix to specify a multiple of that count; in this case an omitted integer is understood to be 1. A bare size letter, or one followed by ‘iB’, specifies a multiple using powers of 1024. A size letter followed by ‘B’ specifies powers of 1000 instead. For example, -n 4M and -n 4MiB are equivalent to -n 4194304, whereas -n 4MB is equivalent to -n 4000000. This notation is upward compatible with the SI prefixes for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.
The following suffixes are defined. Large sizes like 1Y may be
rejected by your computer due to limitations of its arithmetic.
kilobyte: 10^3 = 1000.
kibibyte: 2^10 = 1024. ‘K’ is special: the SI prefix is ‘k’ and the IEC 60027-2 prefix is ‘Ki’, but tradition and POSIX use ‘k’ to mean ‘KiB’.
megabyte: 10^6 = 1,000,000.
mebibyte: 2^20 = 1,048,576.
gigabyte: 10^9 = 1,000,000,000.
gibibyte: 2^30 = 1,073,741,824.
terabyte: 10^12 = 1,000,000,000,000.
tebibyte: 2^40 = 1,099,511,627,776.
petabyte: 10^15 = 1,000,000,000,000,000.
pebibyte: 2^50 = 1,125,899,906,842,624.
exabyte: 10^18 = 1,000,000,000,000,000,000.
exbibyte: 2^60 = 1,152,921,504,606,846,976.
zettabyte: 10^21 = 1,000,000,000,000,000,000,000
2^70 = 1,180,591,620,717,411,303,424. (‘Zi’ is a GNU extension to IEC 60027-2.)
yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000.
2^80 = 1,208,925,819,614,629,174,706,176. (‘Yi’ is a GNU extension to IEC 60027-2.)
diff ¶The format for running the diff command is:
diff options... files...
In the simplest case, two file names from-file and
to-file are given, and diff compares the contents of
from-file and to-file. A file name of - stands for
the standard input.
If one file is a directory and the other is not, diff compares
the file in the directory whose name is that of the non-directory.
The non-directory file must not be -.
If two file names are given and both are directories,
diff compares corresponding files in both directories, in
alphabetical order; this comparison is not recursive unless the
--recursive (-r) 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.
If the --from-file=file option is given, the number of file names is arbitrary, and file is compared to each named file. Similarly, if the --to-file=file option is given, each named file is compared to file.
diff options begin with ‘-’, so normally file names
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.
diff ¶Below is a summary of all of the options that GNU
diff 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: -ac is equivalent to -a -c. Long
named options can be abbreviated to any unique prefix of their name.
Brackets ([ and ]) indicate that an option takes an optional argument.
Treat all files as text and compare them line-by-line, even if they do not seem to be text. See Binary Files and Forcing Text Comparisons.
Ignore changes in amount of white space. See Suppressing Differences in Blank and Tab Spacing.
Ignore changes that just insert or delete blank lines. See Suppressing Differences Whose Lines Are All Blank.
Read and write data in binary mode. See Binary Files and Forcing Text Comparisons.
Use the context output format, showing three lines of context. See Context Format.
Specify whether to use color for distinguishing different contexts, like header, added or removed lines. when may be omitted, or one of:
Specifying --color and no when is equivalent to --color=auto.
Use the context output format, showing lines (an integer) lines of
context, or three if lines is not given. See Context Format.
For proper operation, patch typically needs at least two lines of
context.
For compatibility diff also supports an obsolete option
syntax -lines that has effect when combined with
-c, -p, or -u. New scripts should use
-U lines (-C lines) instead.
Use format to output a line group containing differing lines from both files in if-then-else format. See Line Group Formats.
Change the algorithm perhaps find a smaller set of changes. This makes
diff slower (sometimes much slower). See diff Performance Tradeoffs.
Make merged ‘#ifdef’ format output, conditional on the preprocessor macro name. See Merging Files with If-then-else.
Make output that is a valid ed script. See ed Scripts.
Ignore changes due to tab expansion. See Suppressing Differences in Blank and Tab Spacing.
Make output that looks vaguely like an ed script but has changes
in the order they appear in the file. See Forward ed Scripts.
In context and unified format, for each hunk of differences, show some of the last preceding line that matches regexp. See Showing Lines That Match Regular Expressions.
Compare file to each operand; file may be a directory.
Output a summary of usage and then exit.
Do not discard the last lines lines of the common prefix
and the first lines lines of the common suffix.
See diff Performance Tradeoffs.
Ignore changes in case; consider upper- and lower-case letters equivalent. See Suppressing Case Differences.
Ignore changes that just insert or delete lines that match regexp. See Suppressing Differences Whose Lines All Match a Regular Expression.
Ignore case when comparing file names. For example, recursive comparison of d to e might compare the contents of d/Init and e/inIt. At the top level, ‘diff d inIt’ might compare the contents of d/Init and inIt. See Comparing Directories.
Pass the output through pr to paginate it. See Paginating diff Output.
Use label instead of the file name in the context format (see Context Format) and unified format (see Unified Format) headers. See RCS Scripts.
Print only the left column of two common lines in side by side format. See Controlling Side by Side Format.
Use format to output all input lines in if-then-else format. See Line Formats.
Output RCS-format diffs; like -f except that each command specifies the number of lines affected. See RCS Scripts.
If one file is missing, treat it as present but empty. See Comparing Directories.
Use format to output a group of lines taken from just the second file in if-then-else format. See Line Group Formats.
Use format to output a line taken from just the second file in if-then-else format. See Line Formats.
Act on symbolic links themselves instead of what they point to. Two symbolic links are deemed equal only when each points to precisely the same name.
Use format to output a group of lines taken from just the first file in if-then-else format. See Line Group Formats.
Use format to output a line taken from just the first file in if-then-else format. See Line Formats.
Show which C function each change is in. See Showing C Function Headings.
Specify what color palette to use when colored output is enabled. It defaults to ‘rs=0:hd=1:ad=32:de=31:ln=36’ for red deleted lines, green added lines, cyan line numbers, bold header.
Supported capabilities are as follows.
Report only whether the files differ, not the details of the differences. See Summarizing Which Files Differ.
When comparing directories, recursively compare any subdirectories found. See Comparing Directories.
Report when two files are the same. See Comparing Directories.
When comparing directories, start with the file file. This is used for resuming an aborted comparison. See Comparing Directories.
Use heuristics to speed handling of large files that have numerous
scattered small changes. See diff Performance Tradeoffs.
Strip any trailing carriage return at the end of an input line. See Binary Files and Forcing Text Comparisons.
Do not print common lines in side by side format. See Controlling Side by Side Format.
Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. See Preserving Tab Stop Alignment.
Output a tab rather than a space before the text of a line in normal or context format. This causes the alignment of tabs in the line to look normal. See Preserving Tab Stop Alignment.
Assume that tab stops are set every columns (default 8) print columns. See Preserving Tab Stop Alignment.
Suppress any blanks before newlines when printing the representation of an empty line, when outputting normal, context, or unified format. See Omitting trailing blanks.
Compare each operand to file; file may be a directory.
Use the unified output format, showing three lines of context. See Unified Format.
Use format to output a group of common lines taken from both files in if-then-else format. See Line Group Formats.
Use format to output a line common to both files in if-then-else format. See Line Formats.
If a first file is missing, treat it as present but empty. See Comparing Directories.
Use the unified output format, showing lines (an integer) lines of
context, or three if lines is not given. See Unified Format.
For proper operation, patch typically needs at least two lines of
context.
On older systems, diff supports an obsolete option
-lines that has effect when combined with -u.
POSIX 1003.1-2001 (see Standards conformance) does not allow
this; use -U lines instead.
Output version information and then exit.
Ignore white space when comparing lines. See Suppressing Differences in Blank and Tab Spacing.
Output at most columns (default 130) print columns per line in side by side format. See Controlling Side by Side Format.
When comparing directories, ignore files and subdirectories whose basenames match pattern. See Comparing Directories.
When comparing directories, ignore files and subdirectories whose basenames match any pattern contained in file. See Comparing Directories.
Use the side by side output format. See Controlling Side by Side Format.
Ignore white space at line end. See Suppressing Differences in Blank and Tab Spacing.
diff3 ¶The diff3 command compares three files and outputs descriptions
of their differences. Its arguments are as follows:
diff3 options... mine older yours
The files to compare are mine, older, and yours.
At most one of these three file names may be -,
which tells diff3 to read the standard input for that file.
An exit status of 0 means diff3 was successful, 1 means some
conflicts were found, and 2 means trouble.
diff3 ¶Below is a summary of all of the options that GNU diff3
accepts. Multiple single letter options (unless they take an argument)
can be combined into a single command line argument.
Treat all files as text and compare them line-by-line, even if they do not appear to be text. See Binary Files and Forcing Text Comparisons.
Incorporate all unmerged changes from older to yours into mine, surrounding conflicts with bracket lines. See Marking Conflicts.
Use the compatible comparison program program to compare files
instead of diff.
Generate an ed script that incorporates all the changes from
older to yours into mine. See Selecting Which Changes to Incorporate.
Like -e, except bracket lines from overlapping changes’ first and third files. See Marking Conflicts. With -E, an overlapping change looks like this:
<<<<<<< mine lines from mine ======= lines from yours >>>>>>> yours
Output a summary of usage and then exit.
Generate ‘w’ and ‘q’ commands at the end of the ed
script for System V compatibility. This option must be combined with
one of the -AeExX3 options, and may not be combined with -m.
See Saving the Changed File.
Use the label label for the brackets output by the -A, -E and -X options. This option may be given up to three times, one for each input file. The default labels are the names of the input files. Thus ‘diff3 --label X --label Y --label Z -m A B C’ acts like ‘diff3 -m 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’. See Marking Conflicts.
Apply the edit script to the first file and send the result to standard
output. Unlike piping the output from diff3 to ed, this
works even for binary files and incomplete lines. -A is assumed
if no edit script option is specified. See Generating the Merged Output Directly.
Strip any trailing carriage return at the end of an input line. See Binary Files and Forcing Text Comparisons.
Output a tab rather than two spaces before the text of a line in normal format. This causes the alignment of tabs in the line to look normal. See Preserving Tab Stop Alignment.
Output version information and then exit.
Like -e, except output only the overlapping changes. See Selecting Which Changes to Incorporate.
Like -E, except output only the overlapping changes. In other words, like -x, except bracket changes as in -E. See Marking Conflicts.
Like -e, except output only the nonoverlapping changes. See Selecting Which Changes to Incorporate.
patch ¶Normally patch is invoked like this:
patch <patchfile
The full format for invoking patch is:
patch options... [origfile [patchfile]]
You can also specify where to read the patch from with the -i
patchfile or --input=patchfile option.
If you do not specify patchfile, or if patchfile is
-, patch reads the patch (that is, the diff output)
from the standard input.
If you do not specify an input file on the command line, patch
tries to intuit from the leading text (any text in the patch
that comes before the diff output) which file to edit.
See Multiple Patches in a File.
By default, patch replaces the original input file with the
patched version, possibly after renaming the original file into a
backup file (see Backup File Names, for a description of how
patch names backup files). You can also specify where to
put the output with the -o file or
--output=file option; however, do not use this option
if file is one of the input files.
patch ¶Here is a summary of all of the options that GNU patch
accepts. See GNU patch and Traditional patch, for which of these options are
safe to use in older versions of patch.
Multiple single-letter options that do not take an argument can be combined into a single command line argument with only one dash.
Back up the original contents of each file, even if backups would normally not be made. See Backup Files.
Prepend prefix to backup file names. See Backup File Names.
Back up the original contents of each file if the patch does not exactly match the file. This is the default behavior when not conforming to POSIX. See Backup Files.
Read and write all files in binary mode, except for standard output and /dev/tty. This option has no effect on POSIX-conforming systems like GNU/Linux. On systems where this option makes a difference, the patch should be generated by ‘diff -a --binary’. See Binary Files and Forcing Text Comparisons.
Interpret the patch file as a context diff. See Selecting the patch Input Format.
Make directory directory the current directory for interpreting both file names in the patch file, and file names given as arguments to other options. See Applying Patches in Other Directories.
Make merged if-then-else output using name. See Merging Files with If-then-else.
Print the results of applying the patches without actually changing
any files. See Predicting what patch will do.
Interpret the patch file as an ed script. See Selecting the patch Input Format.
Remove output files that are empty after the patches have been applied. See Creating and Removing Files.
Assume that the user knows exactly what he or she is doing, and do not
ask any questions. See Messages and Questions from patch.
Set the maximum fuzz factor to lines. See Helping patch Find Inexact Matches.
If num is positive, get input files from a revision control system as necessary; if zero, do not get the files; if negative, ask the user whether to get the files. See Revision Control.
Output a summary of usage and then exit.
Read the patch from patchfile rather than from standard input.
See Options to patch.
Let any sequence of blanks (spaces or tabs) in the patch file match any sequence of blanks in the input file. See Applying Patches with Changed White Space.
Interpret the patch file as a normal diff. See Selecting the patch Input Format.
Ignore patches that patch thinks are reversed or already applied.
See also -R. See Applying Reversed Patches.
Do not back up the original contents of files. This is the default behavior when conforming to POSIX. See Backup Files.
Use file as the output file name. See Options to patch.
Set the file name strip count to number. See Applying Patches in Other Directories.
Conform to POSIX, as if the POSIXLY_CORRECT environment
variable had been set. See patch and the POSIX Standard.
Use style word to quote names in diagnostics, as if the
QUOTING_STYLE environment variable had been set to word.
See patch Quoting Style.
Use reject-file as the reject file name. See Reject File Names.
Assume that this patch was created with the old and new files swapped. See Applying Reversed Patches.
Work silently unless an error occurs. See Messages and Questions from patch.
Do not ask any questions. See Messages and Questions from patch.
Set the modification and access times of patched files from timestamps given in context diff headers, assuming that the context diff headers use local time. See Updating Timestamps on Patched Files.
Interpret the patch file as a unified diff. See Selecting the patch Input Format.
Output version information and then exit.
Select the naming convention for backup file names. See Backup File Names.
Print more diagnostics than usual. See Messages and Questions from patch.
Set internal debugging flags. Of interest only to patch
patchers.
Prepend prefix to base names of backup files. See Backup File Names.
Use suffix as the backup extension instead of ‘.orig’ or ‘~’. See Backup File Names.
Set the modification and access times of patched files from timestamps given in context diff headers, assuming that the context diff headers use UTC. See Updating Timestamps on Patched Files.
sdiff ¶The sdiff command merges two files and interactively outputs the
results. Its arguments are as follows:
sdiff -o outfile options... from-file to-file
This merges from-file with to-file, with output to outfile.
If from-file is a directory and to-file is not, sdiff
compares the file in from-file whose file name is that of to-file,
and vice versa. from-file and to-file may not both be
directories.
sdiff 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 ‘-’. You may not use - as an input file.
sdiff without --output (-o) produces a
side-by-side difference. This usage is obsolete; use the
--side-by-side (-y) option of diff instead.
An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble.
sdiff ¶Below is a summary of all of the options that GNU
sdiff accepts. Each option has 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 argument. Long named options can be abbreviated to any unique
prefix of their name.
Treat all files as text and compare them line-by-line, even if they do not appear to be text. See Binary Files and Forcing Text Comparisons.
Ignore changes in amount of white space. See Suppressing Differences in Blank and Tab Spacing.
Ignore changes that just insert or delete blank lines. See Suppressing Differences Whose Lines Are All Blank.
Change the algorithm to perhaps find a smaller set of changes. This
makes sdiff slower (sometimes much slower). See diff Performance Tradeoffs.
Use the compatible comparison program program to compare files
instead of diff.
Ignore changes due to tab expansion. See Suppressing Differences in Blank and Tab Spacing.
Output a summary of usage and then exit.
Ignore changes in case; consider upper- and lower-case to be the same. See Suppressing Case Differences.
Ignore changes that just insert or delete lines that match regexp. See Suppressing Differences Whose Lines All Match a Regular Expression.
Print only the left column of two common lines. See Controlling Side by Side Format.
Put merged output into file. This option is required for merging.
Do not print common lines. See Controlling Side by Side Format.
Use heuristics to speed handling of large files that have numerous
scattered small changes. See diff Performance Tradeoffs.
Strip any trailing carriage return at the end of an input line. See Binary Files and Forcing Text Comparisons.
Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. See Preserving Tab Stop Alignment.
Assume that tab stops are set every columns (default 8) print columns. See Preserving Tab Stop Alignment.
Output version information and then exit.
Output at most columns (default 130) print columns per line.
See Controlling Side by Side Format. Note that for historical reasons, this
option is -W in diff, -w in sdiff.
Ignore white space when comparing lines. See Suppressing Differences in Blank and Tab Spacing.
Note that for historical reasons, this option is -w in diff,
-W in sdiff.
Ignore white space at line end. See Suppressing Differences in Blank and Tab Spacing.
In a few cases, the GNU utilities’ default behavior is
incompatible with the POSIX standard. To suppress these
incompatibilities, define the POSIXLY_CORRECT environment
variable. Unless you are checking for POSIX conformance, you
probably do not need to define POSIXLY_CORRECT.
Normally options and operands can appear in any order, and programs act
as if all the options appear before any operands. For example,
‘diff lao tzu -C 2’ acts like ‘diff -C 2 lao tzu’, since
‘2’ is an option-argument of -C. However, if the
POSIXLY_CORRECT environment variable is set, options must appear
before operands, unless otherwise specified for a particular command.
Newer versions of POSIX are occasionally incompatible with older versions. For example, older versions of POSIX allowed the command ‘diff -c -10’ to have the same meaning as ‘diff -C 10’, but POSIX 1003.1-2001 ‘diff’ no longer allows digit-string options like -10.
The GNU utilities normally conform to the version of POSIX
that is standard for your system. To cause them to conform to a
different version of POSIX, define the _POSIX2_VERSION
environment variable to a value of the form yyyymm specifying
the year and month the standard was adopted. Two values are currently
supported for _POSIX2_VERSION: ‘199209’ stands for
POSIX 1003.2-1992, and ‘200112’ stands for POSIX
1003.1-2001. For example, if you are running older software that
assumes an older version of POSIX and uses ‘diff -c -10’,
you can work around the compatibility problems by setting
‘_POSIX2_VERSION=199209’ in your environment.
Here are some ideas for improving GNU diff and
patch. The GNU project has identified some
improvements as potential programming projects for volunteers. You
can also help by reporting any bugs that you find.
If you are a programmer and would like to contribute something to the GNU project, please consider volunteering for one of these projects. If you are seriously contemplating work, please write to gvc@gnu.org to coordinate with other volunteers.
diff and patch ¶One should be able to use GNU diff to generate a
patch from any pair of directory trees, and given the patch and a copy
of one such tree, use patch to generate a faithful copy of
the other. Unfortunately, some changes to directory trees cannot be
expressed using current patch formats; also, patch does not
handle some of the existing formats. These shortcomings motivate the
following suggested projects.
diff, diff3 and sdiff treat each line of
input as a string of unibyte characters. This can mishandle multibyte
characters in some cases. For example, when asked to ignore spaces,
diff does not properly ignore a multibyte space character.
Also, diff currently assumes that each byte is one column
wide, and this assumption is incorrect in some locales, e.g., locales
that use UTF-8 encoding. This causes problems with the -y or
--side-by-side option of diff.
These problems need to be fixed without unduly affecting the performance of the utilities in unibyte environments.
The IBM GNU/Linux Technology Center Internationalization Team has
proposed
patches
to support internationalized diff.
Unfortunately, these patches are incomplete and are to an older
version of diff, so more work needs to be done in this area.
diff and patch do not handle some changes to directory
structure. For example, suppose one directory tree contains a directory
named ‘D’ with some subsidiary files, and another contains a file
with the same name ‘D’. ‘diff -r’ does not output enough
information for patch to transform the directory subtree into
the file.
There should be a way to specify that a file has been removed without
having to include its entire contents in the patch file. There should
also be a way to tell patch that a file was renamed, even if
there is no way for diff to generate such information.
There should be a way to tell patch that a file’s timestamp
has changed, even if its contents have not changed.
These problems can be fixed by extending the diff output format
to represent changes in directory structure, and extending patch
to understand these extensions.
Some files are neither directories nor regular files: they are unusual
files like symbolic links, device special files, named pipes, and
sockets. Currently, diff treats symbolic links as if they
were the pointed-to files, except that a recursive diff
reports an error if it detects infinite loops of symbolic links (e.g.,
symbolic links to ..). diff treats other special
files like regular files if they are specified at the top level, but
simply reports their presence when comparing directories. This means
that patch cannot represent changes to such files. For
example, if you change which file a symbolic link points to,
diff outputs the difference between the two files, instead
of the change to the symbolic link.
diff should optionally report changes to special files specially,
and patch should be extended to understand these extensions.
When a file name contains an unusual character like a newline or
white space, ‘diff -r’ generates a patch that patch cannot
parse. The problem is with format of diff output, not just with
patch, because with odd enough file names one can cause
diff to generate a patch that is syntactically correct but
patches the wrong files. The format of diff output should be
extended to handle all possible file names.
Applying patch to a multiple-file diff can result in files
whose timestamps are out of order. GNU patch has
options to restore the timestamps of the updated files
(see Updating Timestamps on Patched Files), but sometimes it is useful to generate
a patch that works even if the recipient does not have GNU patch,
or does not use these options. One way to do this would be to
implement a diff option to output diffs in timestamp order.
It would be nice to have a feature for specifying two strings, one in from-file and one in to-file, which should be considered to match. Thus, if the two strings are ‘foo’ and ‘bar’, then if two lines differ only in that ‘foo’ in file 1 corresponds to ‘bar’ in file 2, the lines are treated as identical.
It is not clear how general this feature can or should be, or what syntax should be used for it.
A partial substitute is to filter one or both files before comparing, e.g.:
sed 's/foo/bar/g' file1 | diff - file2
However, this outputs the filtered text, not the original.
When comparing two large directory structures, one of which was
originally copied from the other with timestamps preserved (e.g.,
with ‘cp -pR’), it would greatly improve performance if an option
told diff to assume that two files with the same size and
timestamps have the same content. See diff Performance Tradeoffs.
If you think you have found a bug in GNU cmp,
diff, diff3, or sdiff, please report it
by electronic mail to the
GNU utilities
bug report mailing list bug-diffutils@gnu.org. Please send
bug reports for GNU patch to
bug-patch@gnu.org. Send as precise a description of the
problem as you can, including the output of the --version
option and sample input files that produce the bug, if applicable. If
you have a nontrivial fix for the bug, please send it as well. If you
have a patch, please send it too. It may simplify the maintainer’s
job if the patch is relative to a recent test release, which you can
find in the directory ftp://alpha.gnu.org/gnu/diffutils/.
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A coding error in GNU patch version
2.5.4 causes it to always use ‘~’, but this should be fixed in
the next release.