PATCH(1)	    UNIX Programmer's Manual		 PATCH(1)



NAME
     patch - a program for applying a diff file to an original

SYNOPSIS
     patch [options] orig patchfile [+ [options] orig]

     but usually just

     patch <patchfile

DESCRIPTION
     _P_a_t_c_h will take a patch file containing any of the three
     forms of difference listing produced by the _d_i_f_f program 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 "~" , or as
     specified by the -b switch.  You may also specify where you
     want the output to go with a -o switch.  If _p_a_t_c_h_f_i_l_e is
     omitted, or is a hyphen, the patch will be read from stan-
     dard 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
     _p_a_t_c_h program itself, while ed diffs are simply fed to the
     _e_d editor via a pipe.

     _P_a_t_c_h 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 _p_a_t_c_h, and
     it should work.  If the entire diff is indented by a con-
     sistent amount, this will be taken into account.

     With context diffs, and to a lesser extent with normal
     diffs, _p_a_t_c_h 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, _p_a_t_c_h will scan both forwards
     and backwards for a set of lines matching the context given
     in the hunk.  First _p_a_t_c_h 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 _p_a_t_c_h 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



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     output file plus ".rej" or "#" .  (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 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 one.

     As each hunk is completed, you will be told whether the hunk
     succeeded or failed, and which line (in the new file) _p_a_t_c_h
     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.

     If no original file is specified on the command line, _p_a_t_c_h
     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 win-
     ning.  Only context diffs have lines like that, but if there
     is an "Index:" line in the leading garbage, _p_a_t_c_h 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 patch.

     (If the original file cannot be found, but a suitable SCCS
     or RCS file is handy, _p_a_t_c_h will attempt to get or check out
     the file.)

     Additionally, if the leading garbage contains a "Prereq: "
     line, _p_a_t_c_h 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, _p_a_t_c_h 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.

     If the patch file contains more than one patch, _p_a_t_c_h 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



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     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 separat-
     ing the corresponding argument lists by a '+'.  (The argu-
     ment list for a second or subsequent patch may not specify a
     new patch file, however.)

     _P_a_t_c_h recognizes the following switches:

     -b   causes the next argument to be interpreted as the
	  backup extension, to be used in place of ".orig" or
	  "~".

     -B   causes the next argument to be interpreted as a prefix
	  to the backup file name. If this argument is specified
	  any argument from -b will be ignored.  This argument is
	  an extension to Larry Wall's patch v2.0.1.4, patchlevel
	  8, made by M. Greim (greim@sbsvax.uucp).

     -c   forces _p_a_t_c_h to interpret the patch file as a context
	  diff.

     -d   causes _p_a_t_c_h to interpret the next argument as a direc-
	  tory, and cd to it before doing anything else.

     -D   causes _p_a_t_c_h 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   forces _p_a_t_c_h to interpret the patch file as an ed
	  script.

     -f   forces _p_a_t_c_h 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.

     -F<number>
	  sets the maximum fuzz factor.  This switch only applies
	  to context diffs, and causes _p_a_t_c_h 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.

     -l   causes the pattern matching to be done loosely, in case
	  the tabs and spaces have been munged in your input



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	  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 _p_a_t_c_h to interpret the patch file as a normal
	  diff.

     -N   causes _p_a_t_c_h to ignore patches that it thinks are
	  reversed or already applied.	See also -R .

     -o   causes the next argument to be interpreted as the out-
	  put file name.

     -p<number>
	  sets the pathname strip count, which controls how path-
	  names 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 speci-
	  fies how many slashes 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 file was

	       /u/howard/src/blurfl/blurfl.c

	  setting -p or -p0 gives the entire pathname unmodified,
	  -p1 gives

	       u/howard/src/blurfl/blurfl.c

	  without the leading slash, -p4 gives

	       blurfl/blurfl.c

	  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 name.

     -R   tells _p_a_t_c_h that this patch was created with the old
	  and new files swapped.  (Yes, I'm afraid that does hap-
	  pen occasionally, human nature being what it is.) _P_a_t_c_h
	  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
	  reverse operation.




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	  If the first hunk of a patch fails, _p_a_t_c_h 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 _p_a_t_c_h do its work silently, unless an error
	  occurs.

     -S   causes _p_a_t_c_h 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.

     -v   causes _p_a_t_c_h to print out it's revision header and
	  patch level.

     -x<number>
	  sets internal debugging flags, and is of interest only
	  to _p_a_t_c_h patchers.

ENVIRONMENT
     No environment variables are used by _p_a_t_c_h.

FILES
     /tmp/patch*

SEE ALSO
     diff(1)

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 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



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     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.

DIAGNOSTICS
     Too many to list here, but generally indicative that _p_a_t_c_h
     couldn't parse your patch file.

     The message "Hmm..." indicates that there is unprocessed
     text in the patch file and that _p_a_t_c_h is attempting to
     intuit whether there is a patch in that text and, if so,
     what kind of patch it is.

     _P_a_t_c_h will exit with a non-zero status if any reject files
     were created.  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.

CAVEATS
     _P_a_t_c_h 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 con-
     text 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.

     _P_a_t_c_h 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 gen-
     erated from.

BUGS
     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 OLD-
     CODE ... #else ...  #endif), _p_a_t_c_h 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, _p_a_t_c_h will
     think it is a reversed patch, and offer to un-apply the
     patch.  This could be construed as a feature.



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