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PATCH(1) NetBSD General Commands Manual PATCH(1)
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patch -- apply a diff file to an original
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]]
patch will take a patch file containing any of the four forms of differ-
ence listing produced by the diff(1) program and apply those differences
to an original file, producing a patched version. If patchfile is omit-
ted, 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
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
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.
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
Checks that the patch would apply cleanly, but does not modify
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 differenti-
ating 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.
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) script.
-F max-fuzz, --fuzz max-fuzz
Sets the maximum fuzz factor. This option only applies to con-
text 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 follow-
ing: 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 com-
mentary; 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
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 -R.
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
-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
Setting -p0 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 path-
name unmodified. Whatever you end up with is looked for either
in the current directory, or the directory specified by the -d
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
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
-s, --quiet, --silent
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).
-V t | nil | never | none, --version-control t | nil | never | none
Causes the next argument to be interpreted as a method for creat-
ing 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
Always make numbered backups.
Make numbered backups of files that already have
them, simple backups of the others.
Always make simple backups.
none No backups are created.
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
-z backup-ext, --suffix backup-ext
Causes the next argument to be interpreted as the backup exten-
sion, to be used in place of ".orig".
Enables strict IEEE Std 1003.1-2004 (``POSIX.1'') conformance,
1. Backup files are not created unless the -b option is speci-
2. If unspecified, the file name used is the first of the old,
new and index files that exists.
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 contain-
ing 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 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 will
put the hunk out to a reject file, which normally is the name of the out-
put file plus ".rej". (Note that the rejected hunk will come out in con-
text 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 dif-
ferent than in the patch file: they reflect the approximate location
patch thinks the failed hunks belong in the new file rather than the old
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
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 uni-
fied 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:
1. 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).
2. 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.
3. 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.
4. 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 con-
taining the patch.
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 environ-
ment 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 con-
text 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
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 sepa-
rate files in case something goes haywire.
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
TMPDIR Directory to put temporary files in; default is
PATCH_VERSION_CONTROL Selects when numbered backup files are made.
VERSION_CONTROL Same as PATCH_VERSION_CONTROL.
$TMPDIR/patch* patch temporary files
/dev/tty used to read input when patch prompts the user
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.
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 specifica-
Larry Wall with many other contributors.
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.
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
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 suc-
ceeded 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.
NetBSD 9.1 November 7, 2015 NetBSD 9.1