patch - apply a diff file to an original
patch [options] [originalfile [patchfile]]
but usually just
patch -pnum (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 directo
ries. The names old and new should not contain any slashes. The 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, using Bourne shell syn
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 recipi
ent 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
wont 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 doesnt
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 diffs -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 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 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 won
der 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 any
way. 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 couldnt 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 attempt
ing to intuit whether there is a patch in that text and, if so, what
kind of patch it is.
patchs 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 dont 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 prob
lem. Until a suitable interactive interface is added, you should prob
ably 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 patchs tradi
tional behavior. You should be aware of these differences if you must
interoperate with patch versions 2.1 and earlier, which do not conform
In traditional patch, the -p options 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 compatibil
ity, 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
In traditional patch, backups were enabled by default. This behav
ior 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 vari
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 bet
ter 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 identi
cal after prefix-stripping. Your patch is normally compatible if
each headers file names all contain the same number of slashes.
When traditional patch asked the user a question, it sent the ques
tion 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.
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
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 .
patch could be smarter about partial matches, excessively deviant off
sets 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 youve already applied, patch thinks it is a
reversed patch, and offers to un-apply the patch. This could be con
strued as a feature.
Copyright (C) 1984, 1985, 1986, 1988 Larry Wall.
Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
1998, 1999, 2000, 2001, 2002 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 per
mission notice identical to this one.
Permission is granted to copy and distribute translations of this man
ual into another language, under the above conditions for modified ver
sions, except that this permission notice may be included in transla
tions approved by the copyright holders instead of in the original
Larry Wall wrote the original version of patch. Paul Eggert removed
patchs 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 2002/05/25 PATCH(1)