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 pro-
duced by the diff program and applies those differences to one or more
original files, producing patched versions. Normally the patched ver-
sions 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 email message containing a
diff listing to patch, and it should work. If the entire diff is in-
dented by a consistent amount, if lines end in CRLF, or if a diff is en-
capsulated 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 an-
other 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 indi-
cate that a hunk was installed in the wrong place. You are also told if
a fuzz factor was used to make the match, in which case you should also
be slightly suspicious. If the --verbose option is given, you are also
told about hunks that match exactly.
If no original file origfile is specified on the command line, patch
tries to figure out from the leading garbage what the name of the file
to edit is, using the following rules.
First, patch takes an ordered list of candidate file names as follows:
• If the header is that of a context diff, 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.
• 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 mas-
ter.
• If no named files exist, no RCS, ClearCase, Perforce, or SCCS mas-
ter 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 prerequisites 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 run something like
the following shell command:
patch -d /usr/src/local/blurfl
and patch a file in the blurfl directory directly from a patch that is
read from standard input.
If the patch file contains more than one patch, patch tries to apply
each of them as if they came from separate patch files. This means,
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 be-
fore 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. See the -V or --version-control op-
tion 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
Do not back up a file if the patch does not match the file exactly
and if backups are not otherwise requested. This is the default if
patch is conforming to POSIX.
-B pref or --prefix=pref
Use the simple method to determine backup file names (see the -V
method or --version-control method option), and append pref to a file
name when generating its backup file name. For example, with
-B /junk/ the simple backup file name for src/patch/util.c is
/junk/src/patch/util.c.
--binary
Write all files in binary mode, except for standard output and
/dev/tty. When reading, disable the heuristic for transforming CRLF
line endings into LF line endings. This option is needed on POSIX
systems when applying patches generated on non-POSIX systems to non-
POSIX files. (On POSIX systems, file reads and writes never trans-
form 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 ap-
plied. Normally this option is unnecessary, since patch can examine
the timestamps 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 con-
text.
-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 nega-
tive, 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 lines are ignored. Normal characters must still match
exactly. Each line of the context must still match a line in the
original file.
--merge or --merge=merge or --merge=diff3
Merge a patch file into the original files similar to diff3(1) or
merge(1). If a conflict is found, patch outputs a warning and brack-
ets the conflict with <<<<<<< and >>>>>>> lines. A typical conflict
will look like this:
<<<<<<<
lines from the original file
|||||||
original lines from the patch
=======
new lines from the patch
>>>>>>>
The optional argument of --merge determines the output format for
conflicts: the diff3 format shows the ||||||| section with the origi-
nal lines from the patch; in the merge format, this section is miss-
ing. 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
When a patch does not apply, patch usually checks if the patch looks
like it has been applied already by trying to reverse-apply the first
hunk. The --forward option prevents that. 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 adja-
cent 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 headers.
• 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.
--quoting-style=word
Use style word to quote output names. The word should be one of the
following:
literal
Output names as-is.
shell Quote names for the shell if they contain shell metacharacters
or would cause ambiguous output.
shell-always
Quote names for the shell, even if they would normally not re-
quire quoting.
c Quote names as for a C language string.
escape Quote as with c except omit the surrounding double-quote char-
acters.
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.
-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 na-
ture being what it is.) patch attempts to swap each hunk around be-
fore 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 ap-
plied normally. (Note: this method cannot detect a reversed patch if
it is a normal diff and if the first command 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 uni-
fied). 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 timestamps 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 timestamps are
ambiguous when local clocks move backwards during daylight-saving
time adjustments. Make sure that timestamps include time zones, or
generate patches with UTC and use the -Z or --set-utc option instead.
-u or --unified
Interpret the patch file as a unified context diff.
-v or --version
Print out patch's revision header and patch level, and exit.
-V method or --version-control=method
Use method to determine backup file names. The method can also be
given by the PATCH_VERSION_CONTROL (or, if that's not set, the VER-
SION_CONTROL) environment variable, which is overridden by this op-
tion. The method does not affect whether backup files are made; it
affects only the names of any backup files that are made.
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 Univer-
sal 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 op-
tion.
POSIXLY_CORRECT
If set, patch conforms more strictly to the POSIX standard by de-
fault: see the --posix option.
QUOTING_STYLE
Default value of the --quoting-style option.
SIMPLE_BACKUP_SUFFIX
Extension to use for simple backup file names instead of .orig.
TMPDIR, TMP, TEMP
Directory to put temporary files in; patch uses the first environment
variable in this list that is set. If none are set, the default is
system-dependent; it is normally /tmp on Unix hosts.
VERSION_CONTROL or PATCH_VERSION_CONTROL
Selects version control style; see the -v or --version-control op-
tion.
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 <https://data-
tracker.ietf.org/doc/html/rfc934> (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. When using a version control system
this should be easy; for example, with Git you can use git diff. Other-
wise, 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.
If the patch should communicate file timestamps as well as file con-
tents, its diff commands' headers should have dates and times in Univer-
sal Time using traditional Unix format, so that patch recipients can use
the -Z or --set-utc option. Here is an example command to generate such
headers, using Bourne shell syntax:
LC_ALL=C TZ=UTC0 diff -Naur myprog-2.7 myprog-2.8
Tell your recipients how to apply the patch by telling them which direc-
tory 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 2024
+++ prog/README Mon Mar 17 14:58:22 2024
because the two file names have different numbers of slashes, and dif-
ferent 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 2024
+++ v2.0.30/prog/README Mon Mar 17 14:58:22 2024
Avoid sending patches that compare backup file names like README.orig,
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.
Take care not to send out reversed patches, since it makes people wonder
whether they already applied the patch.
Try not to have your patch modify derived files (e.g. the file configure
where there is a line configure: configure.ac in your makefile), since
the recipient should be able to regenerate the derived files anyway. If
you must send diffs of derived files, generate the diffs using UTC, have
the recipients apply the patch with the -Z or --set-utc option, and have
them remove any unpatched files that depend on patched files (e.g. with
make clean).
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, permis-
sions, 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 GNU patch.
• In POSIX patch when -b is not used, backups are not 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.
• When intuiting the name of the file to be patched from the patch
header, patch uses a complicated method that is optionally POSIX-
conforming. The method is equivalent to POSIX 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.
• Limit yourself to the following options when sending instructions
meant to be executed by anyone running GNU patch or a patch that
conforms to POSIX. Spaces are optional in the following list.
-b
-c
-d dir
-D define
-e
-i patchfile
-l
-n
-N
-o outfile
-p num
-R
-r rejectfile
-u
BUGS
Please report bugs via email to <bug-patch@gnu.org>.
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 re-
versed 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 © 1989–2025 Free Software Foundation, Inc.
Copyright © 1984–1986, 1988 Larry Wall.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are pre-
served on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the en-
tire resulting derived work is distributed under the terms of a permis-
sion 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 ap-
proved 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
contributors include Wayne Davison, who added unidiff support, and David
MacKenzie, who added configuration and backup support. Andreas Gruen-
bacher added support for merging.
GNU PATCH(1)
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