# 2.11BSD#431 - /usr/man/cat1/patch.0

    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
         Patch will take a patch file containing any of the three
         forms of difference listing produced by the diff 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 patchfile 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
         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 con-
         sistent 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

    Printed 11/26/99	      LOCAL				1

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

         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) 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.

         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 win-
         ning.  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 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:

    	  | 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, 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

    Printed 11/26/99	      LOCAL				2

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

         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.)

         Patch 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 patch to interpret the patch file as a context
    	  diff.

         -d   causes patch to interpret the next argument as a direc-
    	  tory, 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.

         -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.

         -F<number>
    	  sets the maximum fuzz factor.  This switch 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.

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

    Printed 11/26/99	      LOCAL				3

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

    	  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 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 patch 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.) 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
    	  reverse operation.

    Printed 11/26/99	      LOCAL				4

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

    	  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.

         -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.

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

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

    ENVIRONMENT
         No environment variables are used by patch.

    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

    Printed 11/26/99	      LOCAL				5

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

         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 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.

         Patch 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
         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 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.

         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 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), 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.

    Printed 11/26/99	      LOCAL				6

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