PATCH(1) General Commands Manual PATCH(1)
NAME
patch - apply a diff file to an original
SYNOPSIS
patch [options] [originalfile [patchfile]]
but usually just
patch -pnum <patchfile
DESCRIPTION
patch takes a patch file patchfile containing a difference listing produced by the diff program and applies
those differences to one or more original files, producing patched versions. Normally the patched versions
are put in place of the originals. Backups can be made; see the -b or --backup option. The names of the
files to be patched are usually taken from the patch file, but if there's just one file to be patched it can
be specified on the command line as originalfile.
Upon startup, patch attempts to determine the type of the diff listing, unless overruled by a -c (--context),
-e (--ed), -n (--normal), or -u (--unified) option. Context diffs (old-style, new-style, and unified) and
normal diffs are applied by the patch program itself, while ed diffs are simply fed to the ed(1) editor via a
pipe.
patch tries to skip any leading garbage, apply the diff, and then skip any trailing garbage. Thus you could
feed an article or message containing a diff listing to patch, and it should work. If the entire diff is
indented by a consistent amount, if lines end in CRLF, or if a diff is encapsulated one or more times by
prepending "- " to lines starting with "-" as specified by Internet RFC 934, this is taken into account.
After removing indenting or encapsulation, lines beginning with # are ignored, as they are considered to be
comments.
With context diffs, and to a lesser extent with normal diffs, patch can detect when the line numbers mentioned
in the patch are incorrect, and attempts to find the correct place to apply each hunk of the patch. As a
first guess, it takes the line number mentioned for the hunk, plus or minus any offset used in applying the
previous hunk. If that is not the correct place, patch scans both forwards and backwards 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 no such place is found, and it's a context diff, and the maximum fuzz factor is set to 1 or more, then
another scan takes place ignoring the first and last line of context. If that fails, and the maximum fuzz
factor is set to 2 or more, the first two and last two lines of context are ignored, and another scan is made.
(The default maximum fuzz factor is 2.)
Hunks with less prefix context than suffix context (after applying fuzz) must apply at the start of the file
if their first line number is 1. Hunks with more prefix context than suffix context (after applying fuzz)
must apply at the end of the file.
If patch cannot find a place to install that hunk of the patch, it puts the hunk out to a reject file, which
normally is the name of the output file plus a .rej suffix, or # if .rej would generate a file name that is
too long (if even appending the single character # makes the file name too long, then # replaces the file
name's last character).
The rejected hunk comes out in unified or context diff format. If the input was a normal diff, many of the
contexts are simply null. The line numbers on the hunks in the reject file may be different than in the patch
file: they reflect the approximate location patch thinks the failed hunks belong in the new file rather than
the old one.
As each hunk is completed, you are told if the hunk failed, and if so which line (in the new file) patch
thought the hunk should go on. If the hunk is installed at a different line from the line number specified in
the diff, you are told the offset. A single large offset may indicate that a hunk was installed in the wrong
· If there is an Index: line in the leading garbage and if either the old and new names are both absent or if
patch is conforming to POSIX, patch takes the name in the Index: line.
· For the purpose of the following rules, the candidate file names are considered to be in the order (old,
new, index), regardless of the order that they appear in the header.
Then patch selects a file name from the candidate list as follows:
· If some of the named files exist, patch selects the first name if conforming to POSIX, and the best name
otherwise.
· If patch is not ignoring RCS, ClearCase, Perforce, and SCCS (see the -g num or --get=num option), and no
named files exist but an RCS, ClearCase, Perforce, or SCCS master is found, patch selects the first named
file with an RCS, ClearCase, Perforce, or SCCS master.
· If no named files exist, no RCS, ClearCase, Perforce, or SCCS master was found, some names are given, 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.
· If no file name results from the above heuristics, you are asked for the name of the file to patch, and
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.
Additionally, if the leading garbage contains a Prereq: line, patch takes the first word from the prerequi‐
sites line (normally a version number) and checks the original file to see if that word can be found. If not,
patch asks for confirmation before proceeding.
The upshot of all this is that you should be able to say, while in a news interface, something like the fol‐
lowing:
| patch -d /usr/src/local/blurfl
and patch a file in the blurfl directory directly from the article containing the patch.
If the patch file contains more than one patch, patch tries to apply each of them as if they came from sepa‐
rate patch files. This means, among other things, that it is assumed that the name of the file to patch must
be determined for each diff listing, and that the garbage before each diff listing contains interesting things
such as file names and revision level, as mentioned previously.
OPTIONS
-b or --backup
Make backup files. That is, when patching a file, rename or copy the original instead of removing it.
When backing up a file that does not exist, an empty, unreadable backup file is created as a placeholder to
represent the nonexistent file. See the -V or --version-control option for details about how backup file
names are determined.
--backup-if-mismatch
Back up a file if the patch does not match the file exactly and if backups are not otherwise requested.
This is the default unless patch is conforming to POSIX.
--no-backup-if-mismatch
writes never transform line endings. On Windows, reads and writes do transform line endings by default, and
patches should be generated by diff --binary when line endings are significant.)
-c or --context
Interpret the patch file as a ordinary context diff.
-d dir or --directory=dir
Change to the directory dir immediately, before doing anything else.
-D define or --ifdef=define
Use the #ifdef ... #endif construct to mark changes, with define as the differentiating symbol.
--dry-run
Print the results of applying the patches without actually changing any files.
-e or --ed
Interpret the patch file as an ed script.
-E or --remove-empty-files
Remove output files that are empty after the patches have been applied. Normally this option is unneces‐
sary, since patch can examine the time stamps on the header to determine whether a file should exist after
patching. However, if the input is not a context diff or if patch is conforming to POSIX, patch does not
remove empty patched files unless this option is given. When patch removes a file, it also attempts to
remove any empty ancestor directories.
-f or --force
Assume that the user knows exactly what he or she is doing, and do not ask any questions. Skip patches
whose headers do not say which file is to be patched; patch files even though they have the wrong version
for the Prereq: line in the patch; and assume that patches are not reversed even if they look like they
are. This option does not suppress commentary; use -s for that.
-F num or --fuzz=num
Set the maximum fuzz factor. This option only applies to diffs that have context, and causes patch to
ignore up to that many lines of context in looking for places to install a hunk. Note that a larger fuzz
factor increases the odds of a faulty patch. The default fuzz factor is 2. A fuzz factor greater than or
equal to the number of lines of context in the context diff, ordinarily 3, ignores all context.
-g num or --get=num
This option controls patch's actions when a file is under RCS or SCCS control, and does not exist or is
read-only and matches the default version, or when a file is under ClearCase or Perforce control and does
not exist. If num is positive, patch gets (or checks out) the file from the revision control system; if
zero, patch ignores RCS, ClearCase, Perforce, and SCCS and does not get the file; and if negative, patch
asks the user whether to get the file. The default value of this option is given by the value of the
PATCH_GET environment variable if it is set; if not, the default value is zero.
--help
Print a summary of options and exit.
-i patchfile or --input=patchfile
Read the patch from patchfile. If patchfile is -, read from standard input, the default.
-l or --ignore-whitespace
Match patterns loosely, in case tabs or spaces have been munged in your files. Any sequence of one or more
blanks in the patch file matches any sequence in the original file, and sequences of blanks at the ends of
=======
new lines from the patch
>>>>>>>
The optional argument of --merge determines the output format for conflicts: the diff3 format shows the
||||||| section with the original lines from the patch; in the merge format, this section is missing. The
merge format is the default.
This option implies --forward and does not take the --fuzz=num option into account.
-n or --normal
Interpret the patch file as a normal diff.
-N or --forward
Ignore patches that seem to be reversed or already applied. It is only checked if the first hunk of a patch
can be reversed. See also -R.
-o outfile or --output=outfile
Send output to outfile instead of patching files in place. Do not use this option if outfile is one of the
files to be patched. When outfile is -, send output to standard output, and send any messages that would
usually go to standard output to standard error.
-pnum or --strip=num
Strip the smallest prefix containing num leading slashes from each file name found in the patch file. A
sequence of one or more adjacent slashes is counted as a single slash. This controls how file names found
in the patch file are treated, in case you keep your files in a different directory than the person who
sent out the patch. For example, supposing the file name in the patch file was
/u/howard/src/blurfl/blurfl.c
setting -p0 gives the entire file name unmodified, -p1 gives
u/howard/src/blurfl/blurfl.c
without the leading slash, -p4 gives
blurfl/blurfl.c
and not specifying -p at all just gives you blurfl.c. Whatever you end up with is looked for either in the
current directory, or the directory specified by the -d option.
--posix
Conform more strictly to the POSIX standard, as follows.
· Take the first existing file from the list (old, new, index) when intuiting file names from diff head‐
ers.
· Do not remove files that are empty after patching.
· Do not ask whether to get files from RCS, ClearCase, Perforce, or SCCS.
· Require that all options precede the files in the command line.
· Do not backup files when there is a mismatch.
c Quote names as for a C language string.
escape 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 QUOT‐
ING_STYLE. If that environment variable is not set, the default value is shell.
-r rejectfile or --reject-file=rejectfile
Put rejects into rejectfile instead of the default .rej file. When rejectfile is -, discard rejects.
-R or --reverse
Assume that this patch was created with the old and new files swapped. (Yes, I'm afraid that does happen
occasionally, human nature being what it is.) patch attempts to swap each hunk around before applying it.
Rejects come out in the swapped format. The -R option does not work with ed diff scripts because there is
too little information to reconstruct the reverse operation.
If the first hunk of a patch fails, patch reverses the hunk to see if it can be applied that way. If it
can, you are asked if you want to have the -R option set. If it can't, the patch continues to be applied
normally. (Note: this method cannot detect a reversed patch if it is a normal diff and if the first com‐
mand is an append (i.e. it should have been a delete) since appends always succeed, due to the fact that a
null context matches anywhere. Luckily, most patches add or change lines rather than delete them, so most
reversed normal diffs begin with a delete, which fails, triggering the heuristic.)
--read-only=behavior
Behave as requested when trying to modify a read-only file: ignore the potential problem, warn about it
(the default), or fail.
--reject-format=format
Produce reject files in the specified format (either context or unified). Without this option, rejected
hunks come out in unified diff format if the input patch was of that format, otherwise in ordinary context
diff form.
-s or --silent or --quiet
Work silently, unless an error occurs.
--follow-symlinks
When looking for input files, follow symbolic links. Replaces the symbolic links, instead of modifying the
files the symbolic links point to. Git-style patches to symbolic links will no longer apply. This option
exists for backwards compatibility with previous versions of patch; its use is discouraged.
-t or --batch
Suppress questions like -f, but make some different assumptions: skip patches whose headers do not contain
file names (the same as -f); skip patches for which the file has the wrong version for the Prereq: line in
the patch; and assume that patches are reversed if they look like they are.
-T or --set-time
Set the modification and access times of patched files from time stamps given in context diff headers.
Unless specified in the time stamps, assume that the context diff headers use local time.
Use of this option with time stamps that do not include time zones is not recommended, because patches
using local time cannot easily be used by people in other time zones, and because local time stamps are
ambiguous when local clocks move backwards during daylight-saving time adjustments. Make sure that time
stamps include time zones, or generate patches with UTC and use the -Z or --set-utc option instead.
The value of method is like the GNU Emacs `version-control' variable; patch also recognizes synonyms that
are more descriptive. The valid values for method are (unique abbreviations are accepted):
existing or nil
Make numbered backups of files that already have them, otherwise simple backups. This is the default.
numbered or t
Make numbered backups. The numbered backup file name for F is F.~N~ where N is the version number.
simple or never
Make simple backups. The -B or --prefix, -Y or --basename-prefix, and -z or --suffix options specify
the simple backup file name. If none of these options are given, then a simple backup suffix is used;
it is the value of the SIMPLE_BACKUP_SUFFIX environment variable if set, and is .orig otherwise.
With numbered or simple backups, if the backup file name is too long, the backup suffix ~ is used instead;
if even appending ~ would make the name too long, then ~ replaces the last character of the file name.
--verbose
Output extra information about the work being done.
-x num or --debug=num
Set internal debugging flags of interest only to patch patchers.
-Y pref or --basename-prefix=pref
Use the simple method to determine backup file names (see the -V method or --version-control method
option), and prefix pref to the basename of a file name when generating its backup file name. For example,
with -Y .del/ the simple backup file name for src/patch/util.c is src/patch/.del/util.c.
-z suffix or --suffix=suffix
Use the simple method to determine backup file names (see the -V method or --version-control method
option), and use suffix as the suffix. For example, with -z - the backup file name for src/patch/util.c is
src/patch/util.c-.
-Z or --set-utc
Set the modification and access times of patched files from time stamps given in context diff headers.
Unless specified in the time stamps, assume that the context diff headers use Coordinated Universal Time
(UTC, often known as GMT). Also see the -T or --set-time option.
The -Z or --set-utc and -T or --set-time options normally refrain from setting a file's time if the file's
original time does not match the time given in the patch header, or if its contents do not match the patch
exactly. However, if the -f or --force option is given, the file time is set regardless.
Due to the limitations of diff output format, these options cannot update the times of files whose contents
have not changed. Also, if you use these options, you should 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.
ENVIRONMENT
PATCH_GET
This specifies whether patch gets missing or read-only files from RCS, ClearCase, Perforce, or SCCS by
default; see the -g or --get option.
POSIXLY_CORRECT
If set, patch conforms more strictly to the POSIX standard by default: see the --posix option.
Selects version control style; see the -v or --version-control option.
FILES
$TMPDIR/p*
temporary files
/dev/tty
controlling terminal; used to get answers to questions asked of the user
SEE ALSO
diff(1), ed(1), merge(1).
Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message Encapsulation, Internet RFC 934
<URL:ftp://ftp.isi.edu/in-notes/rfc934.txt> (1985-01).
NOTES FOR PATCH SENDERS
There are several things you should bear in mind if you are going to be sending out patches.
Create your patch systematically. A good method is 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 diff command's head‐
ers should have dates and times in Universal Time using traditional Unix format, so that patch recipients can
use the -Z or --set-utc option. Here is an example command, using Bourne shell syntax:
LC_ALL=C TZ=UTC0 diff -Naur gcc-2.7 gcc-2.8
Tell your recipients how to apply the patch by telling them which directory to cd to, and which patch options
to use. The option string -Np1 is recommended. Test your procedure by pretending to be a recipient and
applying your patch to a copy of the original files.
You can save people a lot of grief by keeping a patchlevel.h file which is patched to increment the patch
level as the first diff in the patch file you send out. If you put a Prereq: line in with the patch, it won't
let them apply patches out of order without some warning.
You can create a file by sending out a diff that compares /dev/null or an empty file dated the Epoch
(1970-01-01 00:00:00 UTC) to the file you want to create. This only works if the file you want to create
doesn't exist already in the target directory. Conversely, you can remove a file by sending out a context
diff that compares the file to be deleted with an empty file dated the Epoch. The file will be removed unless
patch is conforming to POSIX and the -E or --remove-empty-files option is not given. An easy way to generate
patches that create and remove files is to use GNU diff's -N or --new-file option.
If the recipient is supposed to use the -pN option, do not send output that looks like this:
diff -Naur v2.0.29/prog/README prog/README
--- v2.0.29/prog/README Mon Mar 10 15:13:12 1997
+++ prog/README Mon Mar 17 14:58:22 1997
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 Mon Mar 10 15:13:12 1997
+++ v2.0.30/prog/README Mon Mar 17 14:58:22 1997
While you may be able to get away with putting 582 diff listings into one file, it may be wiser to group
related patches into separate files in case something goes haywire.
DIAGNOSTICS
Diagnostics generally indicate that patch couldn't parse your patch file.
If the --verbose option is given, the message Hmm... indicates that there is unprocessed text in the patch
file and that patch is attempting to intuit whether there is a patch in that text and, if so, what kind of
patch it is.
patch's exit status is 0 if all hunks are applied successfully, 1 if some hunks cannot be applied or there
were merge conflicts, and 2 if there is more serious trouble. When applying a set of patches in a loop it
behooves you to check this exit status so you don't apply a later patch to a partially patched file.
CAVEATS
Context diffs cannot reliably represent the creation or deletion of empty files, empty directories, or special
files such as symbolic links. Nor can they represent changes to file metadata like ownership, permissions, or
whether one file is a hard link to another. If changes like these are also required, separate instructions
(e.g. a shell script) to accomplish them should accompany the patch.
patch cannot tell if the line numbers are off in an ed script, and can detect bad line numbers in a normal
diff only when it finds a change or deletion. A context diff using fuzz factor 3 may have the same problem.
You should probably do a context diff in these cases to see if the changes made sense. Of course, compiling
without errors is a pretty good indication that the patch worked, but not always.
patch usually produces the correct results, even when it has to do a lot of guessing. However, the results
are guaranteed to be correct only when the patch is applied to exactly the same version of the file that the
patch was generated from.
COMPATIBILITY ISSUES
The POSIX standard specifies behavior that differs from patch's traditional behavior. You should be aware of
these differences if you must interoperate with patch versions 2.1 and earlier, which do not conform to POSIX.
· In traditional 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 com‐
ponents. 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.
· In traditional patch, backups were enabled by default. This behavior is now enabled with the -b or
--backup 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 with the --posix
option or by setting the POSIXLY_CORRECT environment variable.
The -b suffix option of traditional patch is equivalent to the -b -z suffix options of GNU patch.
· Traditional 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;
trouble.
· Limit yourself to the following options when sending instructions meant to be executed by anyone running
GNU 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
BUGS
Please report bugs via email to <[email protected]>.
If code has been duplicated (for instance with #ifdef OLDCODE ... #else ... #endif), patch is incapable of
patching both versions, and, if it works at all, will likely patch the wrong one, and tell you that it suc‐
ceeded to boot.
If you apply a patch you've already applied, patch thinks it is a reversed patch, and offers to un-apply the
patch. This could be construed as a feature.
Computing how to merge a hunk is significantly harder than using the standard fuzzy algorithm. Bigger hunks,
more context, a bigger offset from the original location, and a worse match all slow the algorithm down.
COPYING
Copyright (C) 1984, 1985, 1986, 1988 Larry Wall.
Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2009 Free
Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and
this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verba‐
tim copying, provided that the entire resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language, under the
above conditions for modified versions, except that this permission notice may be included in translations
approved by the copyright holders instead of in the original English.
AUTHORS
Larry Wall wrote the original version of patch. Paul Eggert removed patch's arbitrary limits; added support
for binary files, setting file times, and deleting files; and made it conform better to POSIX. Other contrib‐
utors include Wayne Davison, who added unidiff support, and David MacKenzie, who added configuration and
backup support. Andreas Grünbacher added support for merging.
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