patch - a program for applying a diff file to an original
patch [options] orig patchfile [+[ options] orig]
patch <<<<patchfile # usual form
patch [-blNR] [-c|-e|-n] [-d dir] [-D define] [-i patchfile]
[-o outfile] [-p num] [-r rejectfile] [file]
patch will take a patch file containing any of the three forms of
difference listing produced by the diff program (normal, context or in
the style of ed) and apply those differences to an original file,
producing a patched version. 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 switch.
Note that functionality of this option varies for XPG4 version. You
may also specify where you want the output to go with a -o switch. If
patchfile is omitted, or is a hyphen, the patch will be read from
standard input. For XPG4 version, patchfile has to be specified as
argument to -i switch. If this option is omitted or a hyphen is
specified as argument, the patch will read from standard input.
Upon startup, patch will attempt to determine the type of the diff
listing, unless over-ruled by a -c, -e, or -n switch. Context diffs
and normal diffs are applied by the patch program itself, while ed
diffs are simply fed to the ed editor via a pipe.
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
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
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maximum fuzz factor is 2.) Note that for XPG4 version maximum fuzz
factor can not be specified as an option and the default maximum fuzz
factor is used. 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. Note that XPG4 version
does not support verbose option. So, most of the diagnostic messages
are not printed for this version. However user queries will always 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. In the header of a context diff, the filename is found from
lines beginning with ``***'' or ``---'', with the shortest name of an
existing file winning. Only context diffs have lines like that, but
if there is an ``Index:'' line in the leading garbage, patch will try
to use the filename from that line. The context diff header takes
precedence over an Index line. If no filename can be intuited from
the leading garbage, you will be asked for the name of the file to
(If the original file cannot be found, but a suitable SCCS or RCS file
is handy, patch will attempt to get or check out the file.)
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.
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If the patch file 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 filenames and revision level, as mentioned previously.
You can give switches (and another original file name) for the second
and subsequent patches by separating the corresponding argument lists
by a ``+''. (The argument list for a second or subsequent patch may
not specify a new patch file, however.)
With XPG4 version, processing of multiple patches varies considerably.
You can not specify different options for different patches. Options
remain same for all the patches. This also affects the contents of
output file specified with the -o option. See the description of this
option for more details.
patch recognizes the following switches:
-b causes the next argument to be interpreted as the backup
extension, to be used in place of ``.orig''. (For XPG4 version
this option varies. With this option no argument is required and
the option only enables the backup process. Always default
extension is used.)
-c forces patch to interpret the patch file as a context diff.
-d causes patch to interpret the next argument as a directory, and
cd to it before doing anything else.
-D 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. (For XPG4
version this option varies. With this version "#ifndef"
constructor is not used.)
-e forces patch to interpret the patch file as an ed script.
-f forces patch to assume that the user knows exactly what he or she
is doing, and to not ask any questions. It does not suppress
commentary, however. Use -s for that. (This option is not
supported by XPG4 version.)
sets the maximum fuzz factor. This switch only applied 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. (This option
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is not supported by XPG4 version.)
-i This option is supported only by XPG4 version. It causes next
argument to be interpreted as the patch file name.
-l 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 forces patch to interpret the patch file as a normal diff.
-N causes patch to ignore patches that it thinks are reversed or
already applied. See also -R.
-o causes the next argument to be interpreted as the output file
name. There are some added features for the XPG4 version.
Multiple patches for a single file will be applied to the
intermediate versions of the file created by any previous
patches, and will result in multiple,concatenated versions of the
file being written to output file.
sets the pathname strip count, which controls how pathnames found
in the patch file are treated, in case the you keep your files in
a different directory than the person who sent out the patch.
The strip count specifies how many backslashes are to be stripped
from the front of the pathname. (Any intervening directory names
also go away.) For example, supposing the filename in the patch
setting -p or -p0 gives the entire pathname unmodified, -p1 gives
without the leading slash, -p4 gives
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 switch.
-r causes the next argument to be interpreted as the reject file
-R tells patch that this patch was created with the old and new
files swapped. (Yes, I'm afraid that does happen occasionally,
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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 switch 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 switch 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 makes patch do its work silently, unless an error occurs. (This
option is not supported by XPG4 version.)
-S causes patch to ignore this patch from the patch file, but
continue on looking for the next patch in the file. Thus
patch -S + -S + <<<<patchfile
will ignore the first and second of three patches. (This option
is not supported by XPG4 version.)
-v causes patch to print out it's revision header and patch level.
(This option is not supported by XPG4 version.)
sets internal debugging flags, and is of interest only to patch
patchers. (This option is not supported by XPG4 version.)
UNIX95 determines which version of patch is used. If this variable is
set, patch exhibits XPG4 behaviour.
The following exit values are returned for XPG4 version:
0 Successful completion.
1 One or more lines were written to a reject file.
>>>>1 An error occurred.
For non-XPG4 version exit values vary as follows:
0 Successful completion or one or more lines were written to a
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1 An error occurred.
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.
Note that only few diagnostic messages are printed for XPG4 version,
since it does not support verbose option.
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.
The result obtained from the XPG4 options -c, -e, -n which forces the
patch command to interpret the diff file either as a context diff or
as an ed script or as a normal diff respectively is unspecified. For
example, if one forces the patch command to treat the context diff
file as an ed script, the result is unspecified. The same is true if
one forces patch to treat an ed script as a context file and so on..
When a diff is forced with the above options, the diff file is
searched for patterns that are specific to that type of diff file. If
the diff file is not what was specified by the option, the file is
checked for ed commands. If ed commands are present in the diff file,
then the file is assumed to be an ed_diff file and the patch proceeds.
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
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order without some warning. Second, make sure you've specified the
filenames 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 switch 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.
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 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.
One more thing to be noted with respect to XPG4 version of patch. If
you are using multiple patches for different files, group patches that
have to be applied to a single file. Otherwise, intermediate versions
of the previous patches of a file will not be used for the current
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