— apply a
diff file to an original
[-V t | nil | never]
will take a patch file containing any of the
four forms of difference listing produced by the
program and apply those
differences to an original file, producing a patched version. If
is omitted, or is a hyphen, the
patch will be read from the standard input.
will attempt to determine the type of the
diff listing, unless overruled by a -c
If the patchfile
contains more than one 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
The options are as follows:
- 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.
- 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
existing”. This option is currently
the default, unless --posix is
- Checks that the patch would apply cleanly, but does not
- Forces patch to interpret the
patch file as a context diff.
- 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.
- Causes patch to interpret the
next argument as a directory, and change working directory to it before
doing anything else.
- 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.
- Forces patch to interpret the
patch file as an ed(1)
- 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.
- 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.
- Causes the next argument to be interpreted as the input
file name (i.e. a patchfile). This option may be specified multiple
- 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.
- Causes patch to ignore patches
that it thinks are reversed or already applied. See also
- Forces patch to interpret the
patch file as a normal diff.
- Causes the next argument to be interpreted as the output
- 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
gives the entire pathname unmodified.
without the leading slash.
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
- 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
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.)
- Causes the next argument to be interpreted as the reject
- Makes patch do its work
silently, unless an error occurs.
- 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.
- Forces patch to interpret the
patch file as a unified context diff (a unidiff).
- 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
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
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):
- Always make numbered backups.
- Make numbered backups of files that already have them,
simple backups of the others.
- Always make simple backups.
- Causes patch to print out its
revision header and patch level.
- Sets internal debugging flags, and is of interest only to
- Causes the next argument to be interpreted as the backup
extension, to be used in place of “.orig”.
- Enables strict IEEE Std
1003.1-2008 (“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.
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,
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.)
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.
If no original file is specified on the command line,
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
option and the file's existence and
writability are checked relative to the current working directory (or the
directory specified by the -d
If the diff is a context or unified diff, patch
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),
will use the file name from that line as
the “index” file.
will choose the file name by performing the
following steps, with the first match used:
- If patch is operating in
strict IEEE Std 1003.1-2008
(“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 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
Additionally, if the leading garbage contains a “Prereq: ”
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
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
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
, or -z
The extension used for making backup files may also be specified in the
which is overridden by the options above.
If the backup file is a symbolic or hard link to the original file,
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
You may also specify where you want the output to go with the
option; if that file already exists, it is
backed up first.
There are several things you should bear in mind if you are going to be sending
First, you can save people a lot of grief by keeping a
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
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.
- When set, patch behaves as if
option has been specified.
- Extension to use for backup file names instead of
- Directory to put temporary files in; default is
- Selects when numbered backup files are made.
- Same as
- patch temporary files
- used to read input when patch
prompts the user
utility exits with one of the following
- Successful completion.
- One or more lines were written to a reject file.
- 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.
Too many to list here, but generally indicative that
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
utility is compliant with the
IEEE Std 1003.1-2008
specification, except as detailed above for
The flags [-BCEFfstVvxz
extensions to that specification.
with many other contributors.
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.
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.
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
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 ...
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.