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PATCH(1) 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 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 con-
text 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. 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 con-
text. 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 suspi-
cious. 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, 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.
o 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 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 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 say, while in a news interface, some-
thing like 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 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 revi-
sion 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. 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 --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 oth-
erwise 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
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.
--binary
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.
--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 time stamps on the header to deter-
mine whether a file should exist after patching. However, if the input is not a con-
text 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 ques-
tions. 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 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 if patch is conforming to POSIX, negative otherwise.
--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.
-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 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.
-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.
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, Perforce, or SCCS.
o Require that all options precede the files in the command line.
o 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.
-U or --unified-reject-files
Produce unified reject files. The default is to produce context type reject files.
--global-reject-file=rejectfile
Put all rejects into rejectfile instead of creating separate reject files for all files
that have rejects. The rejectfile will contain headers that identify which file each
reject refers to. Note that the global reject file is created even if --dry-run is
specified (while non-global reject files will only be created without --dry-run).
-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 informa-
tion 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.)
-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 con-
text 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, gen-
erate 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 vari-
able, 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 recog-
nizes 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 --suf-
fix 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 SIM-
PLE_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
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 speci-
fied 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 con-
text 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.
ENVIRONMENT
PATCH_GET
This specifies whether patch gets missing or read-only files from RCS, ClearCase, Per-
force, 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)
Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message Encapsulation,
Internet RFC 934 <URL:ftp://ftp.isi.edu/in-notes/rfc934.txt> (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 directories. The names old and new should not con-
tain 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 configure 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
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, 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. 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.
COMPATIBILITY ISSUES
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 to POSIX.
o In traditional patch, the -p option's operand was optional, and a bare -p was equiva-
lent 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 names.
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 con-
forming 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 real trouble.
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.
-c
-d dir
-D define
-e
-l
-n
-N
-o outfile
-pnum
-R
-r rejectfile
BUGS
Please report bugs via email to <bug-patch AT gnu.org>.
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.
COPYING
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 dis-
tributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another lan-
guage, 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 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.
GNU 2002/05/25 PATCH(1)
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