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Manual: patch

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 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 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 re‐
flect 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 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 ig‐
nored 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 other‐
wise.

• 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 cre‐
ation 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 short‐
est 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 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. 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
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 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 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 ances‐
tor 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 Pre‐
req: 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 lines are ig‐
nored. Normal characters must still match exactly. Each line of the context must still match a line in the orig‐
inal 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 brackets 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 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
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 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 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 require quoting.

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 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 occa‐
sionally, 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 in‐
formation 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 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 de‐
fault), 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 timestamps given in context diff headers. Unless
specified in the timestamps, 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 VERSION_CONTROL) environment variable, which is overridden by this option. 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 sim‐
ple 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 timestamps given in context diff headers. Unless spec‐
ified in the timestamps, 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 origi‐
nal 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.

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 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 (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. Otherwise, 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 contents, its diff commands' headers 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 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 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 2024
+++ prog/README Mon Mar 17 14:58:22 2024

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 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 di‐
rectories, 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: config‐
ure.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, 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 proba‐
bly 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 guar‐
anteed to be correct only when the patch is applied to exactly the same version of the file that the patch was gener‐
ated 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 be‐
havior 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 .

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 succeeded 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.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this
permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copy‐
ing, 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 con‐
ditions 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 bi‐
nary 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
Gruenbacher added support for merging.

GNU PATCH(1)

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