patch - apply a diff file to an original
patch [options] [originalfile [patchfile]]
but usually just
patch -pnum <patchfile
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 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, or if a context diff contains
lines ending in CRLF or is encapsulated one or more times by prepending
"- " to lines starting with "-" as specified by Internet RFC 934, this
is taken into account.
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.) 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 ordinary context diff form regardless of the
input patch's form. 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 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:
+o 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.
+o 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.
+o 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:
+o If some of the named files exist, patch selects the first name if
conforming to POSIX, and the best name otherwise.
+o If patch is not ignoring RCS, ClearCase, and SCCS (see the -g num or
--get=num option), 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.
+o If no named files exist, no RCS, ClearCase, 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.
+o 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
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 say, while in a
news interface, something like the following:
| patch -d /usr/src/local/blurfl
and patch a file in the blurfl directory directly from the article containing
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.
-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 --ver-
sion-control option for details about how backup file names are
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.
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
Prefix pref to a file name when generating its simple backup file
name. For example, with -B /junk/ the simple backup file name for
src/patch/util.c is /junk/src/patch/util.c.
Read and write all files in binary mode, except for standard output
and /dev/tty. This option has no effect on POSIX-conforming systems.
On systems like DOS where this option makes a difference, the
patch should be generated by diff -a --binary.
-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.
Print the results of applying the patches without actually changing
-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 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 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, and it may not be set to more than the number of lines of context
in the context diff, ordinarily 3.
-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 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, 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 if patch is
conforming to POSIX, negative otherwise.
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.
-n or --normal
Interpret the patch file as a normal diff.
-N or --forward
Ignore patches that seem to be reversed or already applied. See
-o outfile or --output=outfile
Send output to outfile instead of patching files in place.
-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
setting -p0 gives the entire file name unmodified, -p1 gives
without the leading slash, -p4 gives
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.
Conform more strictly to the POSIX standard, as follows.
+o Take the first existing file from the list (old, new, index) when
intuiting file names from diff headers.
+o Do not remove files that are empty after patching.
+o Do not ask whether to get files from RCS, ClearCase, or SCCS.
+o Require that all options precede the files in the command line.
+o Do not backup files when there is a mismatch.
Use style word to quote output names. The word should be one of the
Output names as-is.
shell 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
c Quote names as for a C language string.
escape Quote as with c except omit the surrounding double-quote
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.
-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 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
-s or --silent or --quiet
Work silently, unless an error occurs.
-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, assuming that the context diff
headers use local time. This option 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.
Instead of using this option, 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
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-pre-
fix, 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
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
Prefix pref to the basename of a file name when generating its simple
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 suffix as the simple backup suffix. For example, with -z - the
simple backup file name for src/patch/util.c is src/patch/util.c-.
The backup suffix may also be specified by the SIMPLE_BACKUP_SUFFIX
environment variable, which is overridden by this option.
-Z or --set-utc
Set the modification and access times of patched files from time
stamps given in context diff headers, assuming 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.
This specifies whether patch gets missing or read-only files from
RCS, ClearCase, or SCCS by default; see the -g or --get option.
POSIXLY_CORRECT [Toc] [Back]
If set, patch conforms more strictly to the POSIX standard by
default: see the --posix option.
QUOTING_STYLE [Toc] [Back]
Default value of the --quoting-style option.
SIMPLE_BACKUP_SUFFIX [Toc] [Back]
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
controlling terminal; used to get answers to questions asked of the
Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message
Encapsulation, Internet RFC 934 <URL:ftp://ftp.isi.edu/in-
NOTES FOR PATCH SENDERS [Toc] [Back]
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 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, 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
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 config-
ure where there is a line configure: configure.in 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 generally indicate that patch couldn't parse your patch
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, 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
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.
Until a suitable interactive interface is added, 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.
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
+o 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 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
+o 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.
+o 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; 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.
+o When traditional 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.
+o Traditional 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
+o 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.
Please report bugs via email to <email@example.com>.
patch could be smarter about partial matches, excessively deviant offsets
and swapped code, but that would take an extra pass.
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.
Copyright 1984, 1985, 1986, 1988 Larry Wall.
Copyright 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be included in translations
approved by the copyright holders instead of in the original
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.
GNU 1998/03/21 PATCH(1)
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