patch(1)

DESCRIPTION

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 option. Note that functionality of this option varies for the UNIX Standard version (see standards(5)). You may also specify where you want the output to go with a -o option. If patchfile is omitted, or is a hyphen, the patch will be read from standard input. For the UNIX Standard (see standards(5)) version, patchfile has to be specified as argument to the -i option. 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 overruled by a -c, -e, or -n option. 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 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 is 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.) Note that for the UNIX Standard (see standards(5)) version, the 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 the UNIX standard (see standards(5)) version does not support verbose option. So, most of the diagnostic messages are not printed for this version. However user queries will always be displayed.

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 file name 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 file name from that line. The context diff header takes precedence over an Index line. If no file name can be intuited from the leading garbage, you will be asked for the name of the file to patch.

(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:

and patch a file in the blurfl directory directly from the article containing the patch.

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 file names and revision level, as mentioned previously. You can give options (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 the UNIX Standard (see standards(5)) 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.

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 will not let them apply patches out of order without some warning. Second, make sure you have 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 does not 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.

RETURN VALUE

The following exit values are returned for the UNIX Standard (see standards(5)) version:

For the non-UNIX Standard version, exit values vary as follows:

DIAGNOSTICS

Most error messages indicate that patch could not 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 the UNIX Standard version, because it does not support the verbose option.

WARNINGS

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 UNIX Standard options -c, -e, and -n, which force 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.

patch 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.

If you apply a patch that you have already applied, patch will think it is a reversed patch, and offer to un-apply the patch. This could be construed as a feature.

UNIX Standard version: 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 patch.

FILES

/var/tmp/patch*

SEE ALSO

diff(1), ed(1), standards(5).

STANDARDS CONFORMANCE

patch: XPG4