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 patch(1)                                                           patch(1)

 NAME    [Toc]    [Back]
      patch - a program for applying a diff file to an original

 SYNOPSIS    [Toc]    [Back]
    Non-XPG4 version
      patch [options] orig patchfile [+[ options] orig]

      patch <patchfile     # usual form

    XPG4 version    [Toc]    [Back]
      patch [-blNR] [-c|-e|-n] [-d dir] [-D define] [-i patchfile]
           [-o outfile] [-p num] [-r rejectfile] [file]

 DESCRIPTION    [Toc]    [Back]
      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 switch.
      Note that functionality of this option varies for XPG4 version.  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
      standard input.  For XPG4 version, patchfile has to be specified as
      argument to -i switch. 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 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 consistent amount, this will be taken into

      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

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 patch(1)                                                           patch(1)

      maximum fuzz factor is 2.) Note that for XPG4 version 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 XPG4 version
      does not support verbose option. So, most of the diagnostic messages
      are not printed for this version. However user queries will always be

      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 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 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

      (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.

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 patch(1)                                                           patch(1)

      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 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 XPG4 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.

      patch recognizes the following switches:

      -b   causes the next argument to be interpreted as the backup
           extension, to be used in place of ``.orig''.  (For XPG4 version
           this option varies. With this option no argument is required and
           the option only enables the backup process. Always default
           extension is used.)

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

      -d   causes patch to interpret the next argument as a directory, 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.  (For XPG4
           version this option varies. With this version "#ifndef"
           constructor is not used.)

      -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.  (This option is not
           supported by XPG4 version.)

      -F number
           sets the maximum fuzz factor.  This switch only applied 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.  (This option

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 patch(1)                                                           patch(1)

           is not supported by XPG4 version.)

      -i   This option is supported only by XPG4 version. It causes next
           argument to be interpreted as the patch file name.

      -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 output file
           name.  There are some added features for the XPG4 version.
           Multiple patches for a single file will be applied to the
           intermediate versions of the file created by any previous
           patches, and will result in multiple,concatenated versions of the
           file being written to output file.

      -p number
           sets the pathname strip count, which controls how pathnames 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 specifies how many backslashes 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


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


           without the leading slash, -p4 gives


           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

      -R   tells patch that this patch was created with the old and new
           files swapped.  (Yes, I'm afraid that does happen occasionally,

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 patch(1)                                                           patch(1)

           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.  (This
           option is not supported by XPG4 version.)

      -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.  (This option
           is not supported by XPG4 version.)

      -v   causes patch to print out it's revision header and patch level.
           (This option is not supported by XPG4 version.)

      -x number
           sets internal debugging flags, and is of interest only to patch
           patchers.  (This option is not supported by XPG4 version.)

 Environment Variables
      UNIX95 determines which version of patch is used. If this variable is
      set, patch exhibits XPG4 behaviour.

 RETURN VALUE    [Toc]    [Back]
      The following exit values are returned for XPG4 version:

           0   Successful completion.
           1   One or more lines were written to a reject file.
           >1  An error occurred.

      For non-XPG4 version exit values vary as follows:

           0   Successful completion or one or more lines were written to a
               reject file.

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 patch(1)                                                           patch(1)

           1   An error occurred.

 DIAGNOSTICS    [Toc]    [Back]
      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.

      Note that only few diagnostic messages are printed for XPG4 version,
      since it does not support verbose option.

 WARNINGS    [Toc]    [Back]
      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 XPG4 options -c, -e, -n which forces 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.

 FILES    [Toc]    [Back]

 SEE ALSO    [Toc]    [Back]
      diff(1), ed(1).

      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

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 patch(1)                                                           patch(1)

      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.

 BUGS    [Toc]    [Back]
      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 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.

      One more thing to be noted with respect to XPG4 version of patch. 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: XPG4

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