patch(1) General Commands Manual patch(1)
NAME
patch - Applies changes to files
SYNOPSIS
patch [-bflsvNRS] [-c | -e | -n] [-B prefix] [-d directory] [-D define] [-F] [number] [-i patchfile] [-o outfile] [-p number] [-r reject-
file] [original_file] [patchfile] [+] [flags] [original_file]
The patch command takes a patch file that contains any of the three forms of difference listing produced by the diff program (normal, con-
text, or ed-style) and applies those differences to an original file, producing a patched version.
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
patch: XCU5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
OPTIONS
Saves a copy of the original contents of each modified file, before the differences are applied in a file of the same name with the suffix
appended to it. If the file already exists, it is overwritten. If multiple patches are applied to the same file, the file is written only
for the first patch. If -o outfile is also specified, patchfile.orig will not be created, but if outfile already exists, outfile.orig is
created. [Tru64 UNIX] Specifies a prefix to the backup file name. Interprets the patch file as a context diff (the output of diff when
-c or -C is specified). Changes the current directory to directory before processing. Uses the C preprocessor #ifdef define ... #endif
construct to mark changes. The define argument is used as the differentiating symbol. Interprets the patch file as an ed script, rather
than as a diff script. [Tru64 UNIX] Suppresses queries to the user. To suppress commentary, use the -s option. [Tru64 UNIX] Sets the
maximum fuzz factor. This option applies to context diffs only, and causes patch to ignore up to the specified number of lines when deter-
mining where to install a hunk. If the -F option is not specified, the default fuzz factor is 2. If the -F option is specified without a
number argument, the fuzz factor is taken to be 0 (zero). The factor may not be set to more than the number of lines of context in the
context diff (ordinarily 3).
[Tru64 UNIX] Note that a larger fuzz factor increases the odds of a faulty patch. Reads the patch information from the file named
by the specified patchfile, rather than from standard input. Causes any sequence of spaces and tabs (whitespace) in the diff script
to match any sequence of spaces in the input file. Other characters will be matched exactly. Interprets the script as a normal
diff. Ignores patches where the differences have already been applied to the file; by default, already-applied patches are
rejected. (See the -R option.) Instead of modifying the files (specified by the patchfile argument or the diff listings) directly,
write a copy of the file referenced by each patch, with the appropriate differences applied, to outfile. Multiple patches for a
single file are applied to the intermediate versions of the file created by any previous patches, and result in multiple, concate-
nated versions of the file written to outfile. Sets the path name strip count, which controls how path names found in the patch
file are treated. This option is useful if you keep your files in a different directory than that specified by the patch. The
strip count specifies how many slashes are to be stripped from the front of the path name. Any intervening directory names are also
stripped.
For example, if the file name in the patch file was /u/howard/src/blurfl/blurfl.c, entering -p0 leaves the entire path name unmodi-
fied. Entering -p1 results in u/howard/src/blurfl/blurfl.c without the leading slash. Entering -p4 results in blurfl/blurfl.c.
Omitting -p from the patch command line, results in blurfl.c.
The patch command looks for the resulting path name in the current directory, or in the directory specified by the -d option. Spec-
ifies the reject file name. By default, the reject file name has the same name as the output file, with the suffix appended to it.
Reverses the sense of the patch script; that is, patch assumes that the diff script was created from the new version to the old ver-
sion. The patch command tries to reverse each portion of the script before applying it. Rejected differences are saved in swapped
format. The -R option cannot be used with ed scripts because there is too little information to reconstruct the reverse operation.
If this option is not specified, and until a portion of the patch file is successfully applied, patch tries to apply each portion in
its reversed sense as well as in its normal sense. If the attempt is successful, you are prompted to determine if -R should be set.
Note that this method cannot detect a reversed patch if it is a normal diff and if the first command is an append (that is, it
should have been a delete), since appends always succeed because a NULL context matches anywhere. Luckily, most patches add or
change lines rather than delete them, so most reversed normal diffs begin with a delete, which will fail, triggering the heuristic.)
[Tru64 UNIX] Patches silently unless an error occurs. [Tru64 UNIX] Ignores a patch from the patch file, but continues looking for
the next patch in the file. Thus, patch -S + -S + <patchfile
ignores the first and second patches in patchfile (see the description of the + offset that follows). [Tru64 UNIX] Prints out the
revision header and patch level. [Tru64 UNIX] Sets internal debugging flags. (This option is of interest only to patch patchers.)
[Tru64 UNIX] Specifies flags (and possibly another original file name) for the second and subsequent patches. The argument list
for each patch must be preceded with a +. (Note, however, that the argument list for a second or subsequent patch may not specify a
new patch file.)
OPERANDS
The file to be patched.
DESCRIPTION
By default, the patched version is put in place of the original. The original file can be backed up to the same name with the extension by
using the -b option. You may also specify where you want the output to go with the -o option. If the -i patchfile option is not speci-
fied, or if patchfile is a - (dash), the patch is read from standard input.
The patch command attempts to determine the type of the diff listing, unless it is overruled by a -c, -e, or -n option, which specify con-
text, ed, and normal diffs, respectively. Context diffs and normal diffs are applied by the patch program itself, while ed diffs are fed
to the ed editor by means of a pipe.
The patch file must contain zero or more lines of header information followed by one or more patches. Each patch must contain zero or more
lines of file name identification in the format produced by diff -c, and one or more sets of diff output, which are customarily called
"hunks".
The patch command tries to skip any leading text, apply the diff, and then skip any trailing text. Thus, you could feed an article or mes-
sage containing a diff listing to patch, and it would work. If the entire diff is indented by a consistent amount, patch takes this into
account.
If no original file is specified on the command line, patch tries to figure out the name of the file to edit from the leading text. In the
header of a context diff, the file name is found from lines beginning with *** (the name of the file from which the patches arose) or ---
(the name of the file to which the patches should be applied), with the shortest name of an existing file being selected. If there is an
Index: line in the leading text, patch tries to use the file name from that line. The context diff header takes precedence over an Index:
line. If no file name can be determined from the leading text, patch asks you for the name of the file to patch.
If the original file cannot be found, but a suitable SCCS or RCS file is available, patch attempts to get or check out the file.
Additionally, if the leading text contains a Prereq: line, patch takes the first word from the prerequisites line (normally a version num-
ber) and checks the input file to see if that word can be found. If not, patch asks for confirmation before proceeding.
If the patch file contains more than one patch, patch tries to apply each of them as if they came from separate patch files. In this case,
the name of the file to patch must be determined for each diff listing, and the header text before each diff listing is examined for infor-
mation such as file names and revision level. You can give options (and another original file name) for the second and subsequent patches
by separating the corresponding argument lists with a +.
For each hunk, patch 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 scans both forwards and backwards for a set of lines matching the context given in the hunk. The patch com-
mand looks for a place where all lines of the context match.
If no such place is found, and patch is performing a context diff, and the maximum fuzz factor is set to 1 or more, patch performs another
scan that ignores the first and last line of context. If that scan fails, and the maximum fuzz factor is set to 2 or more, patch ignores
the first two and last two lines of context, and makes another scan. (The default maximum fuzz factor is 2.)
If patch cannot find a place to install that hunk of the patch, it places the hunk in a reject file (normally, with the same name as the
output file and the suffix hunk is written in context diff form, regardless of the format of the patch file. If the input was a normal or
ed-style diff, the reject file may contain diffs with zero lines of context. The line numbers on the hunks in the reject file may be dif-
ferent from the line numbers in the patch file; the reject file line numbers reflect the approximate locations for the failed hunks in the
new file rather than the old one.
As each hunk is completed, patch tells you whether the hunk succeeded or failed, and on which line in the new file patch assumed the hunk
should go. If this is different from the line number specified in the diff, patch tells you the offset. A single large offset may be an
indication that a hunk was installed in the wrong place. The patch command also tells you if a fuzz factor was used to make the match, in
which case you should be slightly suspicious.
NOTES
There are several things you should bear in mind if you are going to be sending out patches: [Tru64 UNIX] It is recommended that you keep
a <patchlevel.h> file that 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, users will not be able to apply patches out of order without some warning. [Tru64 UNIX] Make sure you specify the
file names correctly, 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. [Tru64 UNIX] You can create a file by sending out a diff that compares a null file
to the file you want to create. This works only if the file you want to create does not already exist in the target directory. [Tru64
UNIX] Take care not to send out reversed patches, since this makes users wonder whether they already applied the patch. [Tru64
UNIX] While you may be able to put many diff listings into one file, it is advisable to group related patches into separate files. [Tru64
UNIX] The patch command 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.
[Tru64 UNIX] A context diff using a fuzz factor of 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 make sense. Compiling without errors is a pretty good
indication that the patch worked, but this is not an infallible indicator. [Tru64 UNIX] The results of the patch command are guar-
anteed to be correct only when the patch is applied to exactly the same version of the file from which the patch was generated.
[Tru64 UNIX] If the code has been duplicated (for example, with #ifdef OLDCODE ... #else ... #endif), patch is incapable of
patching both versions, and, if patch works at all, it will likely patch the wrong version and tell you that it succeeded. If you
apply a patch you've already applied, patch assumes it is a reversed patch, and offers to undo it.
DIAGNOSTICS
[Tru64 UNIX] The message Hmm... indicates that there is unprocessed text in the patch file and that patch is attempting to determine
whether there is a patch in that text and, if so, what kind of patch it is.
[Tru64 UNIX] The patch command exits with a nonzero status if any reject files were created. When applying a set of patches in a loop,
you should check this exit status, so you don't apply a later patch to a partially patched file.
EXIT STATUS
The following exit values are returned: Successful completion. One or more lines were written to a reject file. An error occurred.
ENVIRONMENT VARIABLES
The following environment variables affect the execution of patch: Provides a default value for the internationalization variables that are
unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari-
ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value,
overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the for-
mat and contents of diagnostic messages written to standard error. Determines the locale for recognizing the format of time stamps written
by the diff command. Determines the location of message catalogues for the processing of LC_MESSAGES.
FILES
SEE ALSO
Commands: diff(1)
Standards: standards(5)
patch(1)