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PATCH(1)                                                 PATCH(1)

       patch - apply a diff file to an original

       patch [options] [origfile [patchfile]] [+ [options] [orig-

       but usually just

       patch <patchfile

       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" ("~" on sys-
       tems that do not support long filenames), or as  specified
       by  the  -b,  -B,  or -V switches.  The extension used for
       making backup files may also  be  specified  in  the  SIM-
       PLE_BACKUP_SUFFIX  environment variable, which is overrid-
       den by above switches.

       If the backup file already exists,  patch  creates  a  new
       backup file name by changing the first lowercase letter in
       the last component of the file's name into uppercase.   If
       there  are  no  more  lowercase  letters  in  the name, it
       removes the first character from  the  name.   It  repeats
       this  process  until  it  comes up with a backup file that
       does not already exist.

       You may also specify where you want the output to go  with
       a  -o switch; if that file already exists, it is backed up

       If patchfile is omitted, or is a hyphen, the patch will be
       read from standard input.

       Upon  startup, patch will attempt to determine the type of
       the diff listing, unless over-ruled by a -c, -e, -n, or -u
       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 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


PATCH(1)                                                 PATCH(1)

       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" ("#" on systems that do not support long
       filenames).  (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 num-
       bers 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 indica-
       tion 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  suspi-

       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 con-
       text 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 patch.

       If  the original file cannot be found or is read-only, 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


PATCH(1)                                                 PATCH(1)

       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  deter-
       mined  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 previ-
       ously.  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.)

       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  pre-
            fix  to  the  backup  file  name. If this argument is
            specified any argument from -b will be ignored.

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

       -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.

       -e   forces patch to interpret the patch  file  as  an  ed

       -E   causes  patch  to  remove output files that are empty
            after the patches have been applied.

       -f   forces patch to assume that the  user  knows  exactly


PATCH(1)                                                 PATCH(1)

            what  he  or  she  is doing, and to not ask any ques-
            tions.  It assumes the following:  skip  patches  for
            which  a  file  to  patch can't be found; patch files
            even though they  have  the  wrong  version  for  the
            ``Prereq:''  line  in  the  patch;  and  assume  that
            patches are not reversed even if they look like  they
            are.   This  option does not suppress commentary; use
            -s for that.

       -t   similar to -f, in that it suppresses  questions,  but
            makes  some  different  assumptions: skip patches for
            which a file to patch can't be  found  (the  same  as
            -f);  skip  patches  for which the file has the wrong
            version for the ``Prereq:'' line in  the  patch;  and
            assume  that  patches  are reversed if they look like
            they are.

            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 pat-
            tern 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

       -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.

            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 slashes are to  be  stripped
            from  the  front  of  the pathname.  (Any intervening
            directory names also go away.)  For example,  suppos-
            ing the filename in the patch file was


PATCH(1)                                                 PATCH(1)


            setting  -p  or -p0 gives the entire pathname unmodi-
            fied, -p1 gives


            without the leading slash, -p4 gives


            and  not  specifying  -p  at  all  just   gives   you
            "blurfl.c",  unless  all  of  the  directories in the
            leading path  (u/howard/src/blurfl)  exist  and  that
            path  is  relative,  in which case you get the entire
            pathname unmodified.  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
            happen  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

       -s   makes patch do its work  silently,  unless  an  error

       -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


PATCH(1)                                                 PATCH(1)

            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  its  revision  header  and
            patch level.

       -V   causes  the  next  argument  to  be  interpreted as a
            method for creating backup file names.  The  type  of
            backups made can also be given in the VERSION_CONTROL
            environment variable, which  is  overridden  by  this
            option.  The -B option overrides this option, causing
            the prefix to always be used for making  backup  file
            names.   The value of the VERSION_CONTROL environment
            variable and the argument to the -V option  are  like
            the  GNU  Emacs `version-control' variable; they also
            recognize synonyms that are  more  descriptive.   The
            valid values are (unique abbreviations are accepted):

            `t' or `numbered'
                   Always make numbered backups.

            `nil' or `existing'
                   Make numbered backups of  files  that  already
                   have them, simple backups of the others.  This
                   is the default.

            `never' or `simple'
                   Always make simple backups.

            sets internal debugging flags,  and  is  of  interest
            only to patch patchers.

       Larry Wall <>
       with many other contributors.

       TMPDIR Directory  to  put  temporary  files in; default is

              Extension to use for backup file names  instead  of
              ".orig" or "~".

              Selects when numbered backup files are made.



PATCH(1)                                                 PATCH(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
       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 some-
       thing 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  tar-
       get 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.

       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.

       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  prob-
       lem.  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


PATCH(1)                                                 PATCH(1)

       generated from.

       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  patch-
       ing  both  versions,  and, if it works at all, will likely
       patch the wrong one, and tell you  that  it  succeeded  to

       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.



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