NAME
patch —
apply a diff file to an
original
SYNOPSIS
patch |
[-bCcEeflNnRstuv]
[-B
backup-prefix]
[-D
symbol]
[-d
directory]
[-F
max-fuzz]
[-i
patchfile]
[-o
out-file]
[-p
strip-count]
[-r
rej-name]
[-V t |
nil | never |
none] [-x
number]
[-z
backup-ext]
[- -posix]
[origfile
[patchfile]] |
DESCRIPTION
patch will take a patch file containing any of the four forms
of difference listing produced by the
diff(1) program and apply those
differences to an original file, producing a patched version. If
patchfile is omitted, or is a hyphen, the patch will be
read from the standard input.
patch will attempt to determine the type of the diff listing,
unless over-ruled by a
-c,
-e,
-n, or
-u option. Context diffs
(old-style, new-style, and unified) and normal diffs are applied directly by
the
patch program itself, whereas ed diffs are simply fed to
the
ed(1) editor via a pipe.
If the
patchfile 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 determined for each diff listing, and
that the garbage before each diff listing will be examined for interesting
things such as file names and revision level (see the section on
Filename Determination
below).
The options are as follows:
-
-
- -B
backup-prefix,
--prefix
backup-prefix
- Causes the next argument to be interpreted as a prefix to
the backup file name. If this argument is specified, any argument to
-z will be ignored.
-
-
- -b,
--backup
- Save a backup copy of the file before it is modified. By
default the original file is saved with a backup extension of
“.orig” unless the file already has a numbered backup, in
which case a numbered backup is made. This is equivalent to specifying
“-V existing”. This option
is currently the default, unless --posix is
specified.
-
-
- -C,
--check
- Checks that the patch would apply cleanly, but does not
modify anything.
-
-
- -c,
--context
- Forces patch to interpret the patch file
as a context diff.
-
-
- -D
symbol, --ifdef
symbol
- 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
the argument.
-
-
- -d
directory,
--directory
directory
- Causes patch to interpret the next
argument as a directory, and change the working directory to it before
doing anything else.
-
-
- -E,
--remove-empty-files
- Causes patch to remove output files that
are empty after the patches have been applied. This option is useful when
applying patches that create or remove files.
-
-
- -e,
--ed
- Forces patch to interpret the patch file
as an ed(1) script.
-
-
- -F
max-fuzz, --fuzz
max-fuzz
- Sets the maximum fuzz factor. This option 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, ordinarily 3.
-
-
- -f,
--force
- Forces patch to assume that the user
knows exactly what he or she is doing, and to not ask any questions. 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.
-
-
- -i
patchfile, --input
patchfile
- Causes the next argument to be interpreted as the input
file name (i.e., a patchfile). This option may be specified multiple
times.
-
-
- -l,
--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 pattern 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 input file.
-
-
- -N,
--forward
- Causes patch to ignore patches that it
thinks are reversed or already applied. See also
-R.
-
-
- -n,
--normal
- Forces patch to interpret the patch file
as a normal diff.
-
-
- -o
out-file, --output
out-file
- Causes the next argument to be interpreted as the output
file name.
-
-
- -p
strip-count,
--strip
strip-count
- Sets the pathname strip count, which controls how pathnames
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. 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,
supposing the file name in the patch file was
/u/howard/src/blurfl/blurfl.c:
Setting -p0 gives the entire
pathname unmodified.
-p1 gives
u/howard/src/blurfl/blurfl.c
without the leading slash.
-p4 gives
blurfl/blurfl.c
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 option.
-
-
- -R,
--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 option 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 option 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
heuristic.)
-
-
- -r
rej-name,
--reject-file
rej-name
- Causes the next argument to be interpreted as the reject
file name.
-
-
- -s,
--quiet,
--silent
- Makes patch do its work silently, unless
an error occurs.
-
-
- -t,
--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 they are.
-
-
- -u,
--unified
- Forces patch to interpret the patch file
as a unified context diff (a unidiff).
-
-
- -V
t | nil | never |
none,
--version-control t |
nil | never |
none
- 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
PATCH_VERSION_CONTROL
or
VERSION_CONTROL
environment variables, which are
overridden by this option. The -B option overrides this
option, causing the prefix to always be used for making backup file names.
The values of the PATCH_VERSION_CONTROL
and
VERSION_CONTROL
environment variables 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,
numbered
- Always make numbered backups.
-
-
- nil,
existing
- Make numbered backups of files that already have them,
simple backups of the others.
-
-
- never,
simple
- Always make simple backups.
-
-
- none
- No backups are created.
-
-
- -v,
--version
- Causes patch to print out its revision
header and patch level.
-
-
- -x
number, --debug
number
- Sets internal debugging flags, and is of interest only to
patch patchers.
-
-
- -z
backup-ext,
--suffix
backup-ext
- Causes the next argument to be interpreted as the backup
extension, to be used in place of “.orig”.
-
-
- --posix
- Enables strict IEEE Std 1003.1-2004
(“POSIX.1”) conformance, specifically:
- Backup files are not created unless the
-b option is specified.
- If unspecified, the file name used is the first of the
old, new and index files that exists.
Patch Application
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”. (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 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 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 indication
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
suspicious.
Filename Determination
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. When checking a prospective file name, pathname components are
stripped as specified by the
-p option and the file's
existence and writability are checked relative to the current working
directory (or the directory specified by the
-d option).
If the diff is a context or unified diff,
patch is able to
determine the old and new file names from the diff header. For context diffs,
the “old” file is specified in the line beginning with
“***” and the “new” file is specified in the line
beginning with “---”. For a unified diff, the “old”
file is specified in the line beginning with “---” and the
“new” file is specified in the line beginning with
“+++”. If there is an “Index:” line in the leading
garbage (regardless of the diff type),
patch will use the
file name from that line as the “index” file.
patch will choose the file name by performing the following
steps, with the first match used:
- If patch is operating in strict
IEEE Std 1003.1-2004 (“POSIX.1”) mode,
the first of the “old”, “new” and
“index” file names that exist is used. Otherwise,
patch will examine either the “old” and
“new” file names or, for a non-context diff, the
“index” file name, and choose the file name with the fewest
path components, the shortest basename, and the shortest total file name
length (in that order).
- If no file exists, patch checks for the
existence of the files in an RCS directory using the criteria specified
above. If found, patch will attempt to get or check out
the file.
- If no suitable file was found to patch, the patch file is
a context or unified diff, and the old file was zero length, the new file
name is created and used.
- If the file name still cannot be determined,
patch will prompt the user for the file name to
use.
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.
Backup Files
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”, or as specified by the
-B,
-V, or
-z options. The extension used for
making backup files may also be specified in the
SIMPLE_BACKUP_SUFFIX
environment variable, which is
overridden by the options above.
If the backup file is a symbolic or hard link to the original file,
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 or is not linked to the original file.
You may also specify where you want the output to go with the
-o option; if that file already exists, it is backed up
first.
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 file names right, either in a context
diff header, or with an “Index:” line. If you are patching
something in a subdirectory, be sure to tell the patch user to specify a
-p option 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 target 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.
ENVIRONMENT
POSIXLY_CORRECT
- When set, patch behaves as if the
--posix option has been
specified.
SIMPLE_BACKUP_SUFFIX
- Extension to use for backup file names instead of
“.orig”.
TMPDIR
- Directory to put temporary files in; default is
/tmp.
PATCH_VERSION_CONTROL
- Selects when numbered backup files are made.
VERSION_CONTROL
- Same as
PATCH_VERSION_CONTROL
.
FILES
- $TMPDIR/patch*
- patch temporary files
- /dev/tty
- used to read input when patch prompts the
user
DIAGNOSTICS
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.
The
patch utility exits with one of the following values:
- 0
- Successful completion.
- 1
- One or more lines were written to a reject file.
- >1
- An error occurred.
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.
SEE ALSO
diff(1)
STANDARDS
The
patch utility is compliant with the
IEEE
Std 1003.1-2004 (“POSIX.1”) specification (except as
detailed above for the
--posix option), though the presence
of
patch itself is optional.
The flags [
-CEfstuvBFVxz] and
[
--posix] are extensions to that
specification.
AUTHORS
Larry Wall with many other contributors.
CAVEATS
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 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.
BUGS
Could be smarter about partial matches, excessively deviant offsets and swapped
code, but that would take an extra pass.
Check patch mode (
-C) will fail if you try to check several
patches in succession that build on each other. The entire
patch code would have to be restructured to keep temporary
files around so that it can handle this situation.
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 will think
it is a reversed patch, and offer to un-apply the patch. This could be
construed as a feature.