patch - apply a diff file to an original
patch [options] [origfile [patchfile]] [+ [options] [orig-
but usually just
Patch will take a patch file containing any of the four
forms of difference listing produced by the diff program
and apply those differences to an original file, producing
a patched version. By default, the patched version is put
in place of the original, with the original file backed up
to the same name with the extension ".orig" ("~" on sys-
tems that do not support long filenames), or as specified
by the -b, -B, or -V switches. The extension used for
making backup files may also be specified in the SIM-
PLE_BACKUP_SUFFIX environment variable, which is overrid-
den by above switches.
If the backup file already exists, patch creates a new
backup file name by changing the first lowercase letter in
the last component of the file's name into uppercase. If
there are no more lowercase letters in the name, it
removes the first character from the name. It repeats
this process until it comes up with a backup file that
does not already exist.
You may also specify where you want the output to go with
a -o switch; if that file already exists, it is backed up
If patchfile is omitted, or is a hyphen, the patch will be
read from standard input.
Upon startup, patch will attempt to determine the type of
the diff listing, unless over-ruled by a -c, -e, -n, or -u
switch. 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 editor via a pipe.
Patch will try 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, this will be 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 will attempt 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 will scan
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 will put the hunk out
to a reject file, which normally is the name of the output
file plus ".rej" ("#" on systems that do not support long
filenames). (Note that the rejected hunk will come out in
context diff form whether the input patch was a context
diff or a normal diff. If the input was a normal diff,
many of the contexts will simply be null.) The line num-
bers 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 will be told whether the
hunk succeeded or failed, and which line (in the new file)
patch thought the hunk should go on. If this is different
from the line number specified in the diff you will be
told the offset. A single large offset MAY be an indica-
tion that a hunk was installed in the wrong place. You
will also be told if a fuzz factor was used to make the
match, in which case you should also be slightly suspi-
If no original file is specified on the command line,
patch will try to figure out from the leading garbage what
the name of the file to edit is. In the header of a con-
text diff, the filename is found from lines beginning with
"***" or "---", with the shortest name of an existing file
winning. Only context diffs have lines like that, but if
there is an "Index:" line in the leading garbage, patch
will try to use the filename from that line. The context
diff header takes precedence over an Index line. If no
filename can be intuited from the leading garbage, you
will be asked for the name of the file to patch.
If the original file cannot be found or is read-only, but
a suitable SCCS or RCS file is handy, patch will attempt
to get or check out the file.
Additionally, if the leading garbage contains a "Prereq: "
line, patch will take the first word from the
prerequisites line (normally a version number) and check
the input file to see if that word can be found. If not,
patch will ask for confirmation before proceeding.
The upshot of all this is that you should be able to say,
while in a news interface, the following:
| patch -d /usr/src/local/blurfl
and patch a file in the blurfl directory directly from the
article containing the patch.
If the patch file contains more than one patch, patch will
try 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 deter-
mined for each diff listing, and that the garbage before
each diff listing will be examined for interesting things
such as filenames and revision level, as mentioned previ-
ously. You can give switches (and another original file
name) for the second and subsequent patches by separating
the corresponding argument lists by a '+'. (The argument
list for a second or subsequent patch may not specify a
new patch file, however.)
Patch recognizes the following switches:
-b or --suffix
causes the next argument to be interpreted as the
backup extension, to be used in place of ".orig" or
-B or --prefix
causes the next argument to be interpreted as a pre-
fix to the backup file name. If this argument is
specified any argument from -b will be ignored.
-c or --context
forces patch to interpret the patch file as a context
-C or --check
checks that the patch would apply cleanly, but does
not modify anything.
-d or --directory
causes patch to interpret the next argument as a
directory, and cd to it before doing anything else.
-D or --ifdef
causes patch to use the "#ifdef...#endif" construct
to mark changes. The argument following will be used
as the differentiating symbol. Note that, unlike the
C compiler, there must be a space between the -D and
-e or --ed
forces patch to interpret the patch file as an ed
-E or --remove-empty-files
causes patch to remove output files that are empty
after the patches have been applied.
-f or --force
forces patch to assume that the user knows exactly
what he or she is doing, and to not ask any ques-
tions. It assumes the following: skip patches for
which a file to patch can't be found; 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.
-t or --batch
similar to -f, in that it suppresses questions, but
makes some different assumptions: skip patches for
which a file to patch can't be found (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
-F<number> or --fuzz <number>
sets the maximum fuzz factor. This switch only
applies to context diffs, 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,
-l or --ignore-whitespace
causes the pattern matching to be done loosely, in
case the tabs and spaces have been munged in your
input file. Any sequence of whitespace in the pat-
tern line will match any sequence in the input file.
Normal characters must still match exactly. Each
line of the context must still match a line in the
-n or --normal
forces patch to interpret the patch file as a normal
-N or --forward
causes patch to ignore patches that it thinks are
reversed or already applied. See also -R .
-o or --output
causes the next argument to be interpreted as the
output file name.
-p<number> or --strip <number>
sets the pathname strip count, which controls how
pathnames found in the patch file are treated, in
case the you keep your files in a different directory
than the person who sent out the patch. The strip
count specifies how many slashes are to be stripped
from the front of the pathname. (Any intervening
directory names also go away.) For example, suppos-
ing the filename in the patch file was
setting -p or -p0 gives the entire pathname unmodi-
fied, -p1 gives
without the leading slash, -p4 gives
and not specifying -p at all just gives you
"blurfl.c", unless all of the directories in the
leading path (u/howard/src/blurfl) exist and that
path is relative, in which case you get the entire
pathname unmodified. Whatever you end up with is
looked for either in the current directory, or the
directory specified by the -d switch.
-r or --reject-file
causes the next argument to be interpreted as the
reject file name.
-R or --reverse
tells patch 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 will attempt to swap each hunk around before
applying it. Rejects will come out in the swapped
format. The -R switch will 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 will
reverse the hunk to see if it can be applied that
way. If it can, you will be asked if you want to
have the -R switch set. If it can't, the patch will
continue 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 will match anywhere.
Luckily, most patches add or change lines rather than
delete them, so most reversed normal diffs will begin
with a delete, which will fail, triggering the
-s or --quiet or --silent
makes patch do its work silently, unless an error
-S or --skip
causes patch to ignore this patch from the patch
file, but continue on looking for the next patch in
the file. Thus
patch -S + -S + <patchfile
will ignore the first and second of three patches.
-u or --unified
forces patch to interpret the patch file as a unified
context diff (a unidiff).
-v or --version
causes patch to print out its revision header and
-V or --version-control
causes the next argument to be interpreted as a
method for creating backup file names. The type of
backups made can also be given in the VERSION_CONTROL
environment variable, which is overridden by this
option. The -B option overrides this option, causing
the prefix to always be used for making backup file
names. The value of the VERSION_CONTROL environment
variable and the argument to the -V option are like
the GNU Emacs `version-control' variable; they also
recognize synonyms that are more descriptive. The
valid values are (unique abbreviations are accepted):
`t' or `numbered'
Always make numbered backups.
`nil' or `existing'
Make numbered backups of files that already
have them, simple backups of the others. This
is the default.
`never' or `simple'
Always make simple backups.
-x<number> or --debug <number>
sets internal debugging flags, and is of interest
only to patch patchers.
Larry Wall <email@example.com>
with many other contributors.
TMPDIR Directory to put temporary files in; default is
Extension to use for backup file names instead of
".orig" or "~".
Selects when numbered backup files are made.
NOTES FOR PATCH SENDERS
There are several things you should bear in mind if you
are going to be sending out patches. First, 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. Second, make sure you've
specified the filenames right, either in a context diff
header, or with an Index: line. If you are patching some-
thing in a subdirectory, be sure to tell the patch user to
specify a -p switch as needed. Third, you can create a
file by sending out a diff that compares a null file to
the file you want to create. This will only work if the
file you want to create doesn't exist already in the tar-
get directory. Fourth, take care not to send out reversed
patches, since it makes people wonder whether they already
applied the patch. Fifth, while you may be able to get
away with putting 582 diff listings into one file, it is
probably wiser to group related patches into separate
files in case something goes haywire.
Too many to list here, but generally indicative that patch
couldn't parse your patch file.
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 will exit with a non-zero status if any reject files
were created. 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.
Patch cannot tell if the line numbers are off in an ed
script, and can only detect bad line numbers in a normal
diff when it finds a "change" or a "delete" command. A
context diff using fuzz factor 3 may have the same prob-
lem. 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
Could be smarter about partial matches, excessively
deviant offsets and swapped code, but that would take an
Check patch mode ( -C) will fail if you try to check sev-
eral patches in succession that build on each other. The
whole code of patch would have to be restructured to keep
temporary files around so that it can handle this situa-
If code has been duplicated (for instance with #ifdef OLD-
CODE ... #else ... #endif), patch is incapable of patch-
ing both versions, and, if it works at all, will likely
patch the wrong one, and tell you that it succeeded to
If you apply a patch you've already applied, patch will
think it is a reversed patch, and offer to un-apply the
patch. This could be construed as a feature.
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.