OS/2 Shareware BBS: 11 Util/11-Util.zip/DIFFPT.ZIP/PATCH.MAN

Text File | 1991-07-01 | 15KB | 316 lines

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 four
     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 (old-style, new-style, and unified) 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
     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
     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 ([e-mail]).

     -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
          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.

          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.

     -u   forces patch to interpret the patch file as a unified
          context diff (a unidiff).

     -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
     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.