patch - apply a diff file to an original
patch [options] [origfile [patchfile]]
patch <patchfile
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, newstyle,
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
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 but
that will
change in a future release.
-B, --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.
-c, --context
Forces patch to interpret the patch file as a context diff.
-C, --check
Checks that the patch would apply cleanly, but does
not modify
anything.
-d, --directory
Causes patch to interpret the next argument as a directory, and
cd(1) to it before doing anything else.
-D, --ifdef
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.
-e, --ed
Forces patch to interpret the patch file as an ed(1)
script.
-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.
-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.
-F<number>, --fuzz <number>
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.
-i, --input
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, --normal
Forces patch to interpret the patch file as a normal
diff.
-N, --forward
Causes patch to ignore patches that it thinks are
reversed or already
applied. See also -R.
-o, --output
Causes the next argument to be interpreted as the
output file
name.
-p<number>, --strip <number>
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, --reject-file
Causes the next argument to be interpreted as the
reject file
name.
-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.)
-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, --version
Causes patch to print out its revision header and
patch level.
-V, --version-control
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.
-x<number>, --debug <number>
Sets internal debugging flags, and is of interest
only to patch
patchers.
-z, --suffix
Causes the next argument to be interpreted as the
backup extension,
to be used in place of ".orig".
--posix
Enables strict IEEE Std 1003.2 (``POSIX.2'') conformance, specifically:
1. Backup files are not created unless the -b option is specified.
2. If unspecified, the file name used is the first
of the old,
new and index files that exists.
Patch Application [Toc] [Back]
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 [Toc] [Back]
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:
1. If patch is operating in strict IEEE Std 1003.2
(``POSIX.2'') 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
SCCS or RCS directory (using the appropriate prefix or
suffix) 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 containing
the patch.
Backup Files [Toc] [Back]
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 [Toc] [Back]
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.
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.
$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.
diff(1)
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
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.
OpenBSD 3.6 July 23, 2003
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