Computer Science
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 context diff 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 fac-
tor 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 fac-
tor 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.
+o If the header is that of a context diff, patch takes
the old and new file names in the header. Any
/dev/null names are ignored.
+o If there is an Index: line in the leading garbage and
if either the old and new names are both absent or the
POSIXLY_CORRECT environment variable is set, patch
takes the name in the Index: line.
+o For the purpose of the following rules, the names are
considered to be in the order (old, new, index),
regardless of the order that they appear in the header.
+o If some of the named files exist, patch uses the first
name if the POSIXLY_CORRECT environment variable is
set, and the best name otherwise.
+o If patch is not ignoring RCS and SCCS (see the -g num
or --get=num option), and no named files exist but an
RCS or SCCS master is found, patch uses the first named
file with an RCS or SCCS master.
+o If no named files exist, no RCS or SCCS master was
found, some names are given, POSIXLY_CORRECT is not
set, and the patch appears to create a file, patch uses
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.
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 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 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 deter-
mined 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.
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 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 the POSIXLY_CORRECT environ-
ment variable is set.
--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 the POSIXLY_CORRECT
environment variable is set.
-B pref or --prefix=pref
Prefix pref to a file name when generating its simple
backup file name. For example, with -B /junk/ the sim-
ple 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-compliant 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 actu-
ally 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 unneces-
sary, 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 the POSIXLY_CORRECT environment variable is set,
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. If num is
positive, patch gets (or checks out) the file from the
revision control system; if zero, patch ignores RCS 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 POSIXLY_CORRECT is set,
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.
-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.
-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 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 information to reconstruct the reverse opera-
tion.
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 nor-
mally. (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, trigger-
ing 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 context diff headers, assum-
ing 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 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-con-
trol' 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 spec-
ify 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 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 gener-
ating 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 suf-
fix 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, assum-
ing that the context diff headers use Coordinated Uni-
versal 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 nor-
mally 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 or SCCS by default; see the -g or --get
option.
POSIXLY_CORRECT
If set, patch conforms more strictly to the POSIX stan-
dard: it takes the first existing file from the list
(old, new, index) when intuiting file names from diff
headers, it does not remove files that are empty after
patching, it does not ask whether to get files from RCS
or SCCS, it requires that all options precede the files
in the command line, and it does not backup files when
there is a mismatch.
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 --ver-
sion-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
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 patch-
level.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 the POSIXLY_CORRECT environ-
ment variable is set 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: config-
ure.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 hay-
wire.
DIAGNOSTICS
Diagnostics generally indicate that patch couldn't parse
your patch file.
If the --verbose option is given, the message Hmm... indi-
cates 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 success-
fully, 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 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
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 ver-
sions 2.1 and earlier, which are not POSIX-compliant.
+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 equiva-
lent 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 com-
ponents. 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 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 was not
POSIX-compliant, and had a few gotchas. Now patch uses
a different, equally complicated (but better docu-
mented) method that is optionally POSIX-compliant; we
hope it has fewer gotchas. The two methods are compat-
ible if the file names in the context diff header and
the Index: line are all identical after prefix-strip-
ping. 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 ques-
tions 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 trou-
ble.
+o Limit yourself to the following options when sending
instructions meant to be executed by anyone running GNU
patch, traditional patch, or a POSIX-compliant patch.
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
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 OLD-
CODE ... #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 1984, 1985, 1986, 1988 Larry Wall.
Copyright 1997 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 ver-
sions 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 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
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 sup-
port.
GNU 1997/07/16 1
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