patch - apply a diff file to an original


   patch [options] [originalfile [patchfile]]

   but usually just

   patch -pnum <patchfile


   patch  takes  a  patch  file  patchfile containing a difference listing
   produced by the diff program and applies those differences  to  one  or
   more  original files, producing patched versions.  Normally the patched
   versions are put in place of the originals.  Backups can be  made;  see
   the  -b  or  --backup option.  The names of the files to be patched are
   usually taken from the patch file, but if there's just one file  to  be
   patched it can be specified on the command line as originalfile.

   Upon startup, patch attempts to determine the type of the diff listing,
   unless overruled by a -c (--context), -e (--ed), -n (--normal),  or  -u
   (--unified)  option.  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(1) editor via a pipe.

   patch  tries 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, if lines end in CRLF, or if  a
   diff  is  encapsulated  one  or  more times by prepending "- " to lines
   starting with "-" as specified by Internet RFC 934, this is taken  into
   account.   After  removing  indenting or encapsulation, lines beginning
   with # are ignored, as they are considered to be comments.

   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
   attempts 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 scans 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.)

   Hunks with less prefix context  than  suffix  context  (after  applying
   fuzz)  must  apply  at the start of the file if their first line number
   is 1.  Hunks with  more  prefix  context  than  suffix  context  (after
   applying fuzz) must apply at the end of the file.

   If patch cannot find a place to install that hunk of the patch, it puts
   the hunk out to a reject file, which normally is the name of the output
   file  plus  a .rej suffix, or # if .rej would generate a file name that
   is too long (if even appending the single character #  makes  the  file
   name too long, then # replaces the file name's last character).

   The  rejected hunk comes out in unified or context diff format.  If the
   input was a normal diff, many of the contexts  are  simply  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 are told if the hunk failed, and if so
   which line (in the new file) patch thought the hunk should go  on.   If
   the  hunk  is  installed  at  a  different  line  from  the line number
   specified in the diff, you are told the offset.  A single large  offset
   may  indicate  that  a  hunk was installed in the wrong place.  You are
   also told if a fuzz factor was used to make the match,  in  which  case
   you  should  also  be  slightly suspicious.  If the --verbose option is
   given, you are also told about hunks that match exactly.

   If no original file origfile is specified on the  command  line,  patch
   tries  to figure out from the leading garbage what the name of the file
   to edit is, using the following rules.

   First, patch takes an ordered list of candidate file names as follows:

    * If the header is that of a context diff, patch takes the old and new
      file  names  in  the  header.  A name is ignored if it does not have
      enough slashes to satisfy the -pnum or --strip=num option.  The name
      /dev/null is also ignored.

    * If  there is an Index: line in the leading garbage and if either the
      old and new names are both absent  or  if  patch  is  conforming  to
      POSIX, patch takes the name in the Index: line.

    * For the purpose of the following rules, the candidate file names are
      considered to be in the order (old, new, index), regardless  of  the
      order that they appear in the header.

   Then patch selects a file name from the candidate list as follows:

    * If  some  of  the named files exist, patch selects the first name if
      conforming to POSIX, and the best name otherwise.

    * If patch is not ignoring RCS, ClearCase, Perforce, and SCCS (see the
      -g num  or  --get=num  option), and no named files exist but an RCS,
      ClearCase, Perforce, or SCCS master  is  found,  patch  selects  the
      first named file with an RCS, ClearCase, Perforce, or SCCS master.

    * If no named files exist, no RCS, ClearCase, Perforce, or SCCS master
      was found, some names are given, patch is not conforming  to  POSIX,
      and  the patch appears to create a file, patch selects the best name
      requiring the creation of the fewest directories.

    * If no file name results from the above heuristics, you are asked for
      the name of the file to patch, and patch selects that name.

   To  determine  the  best  of a nonempty list of file names, patch first
   takes all the names with the fewest path name components; of those,  it
   then  takes all the names with the shortest basename; of those, it then
   takes all the shortest names; finally, it  takes  the  first  remaining

   Additionally,  if  the  leading  garbage contains a Prereq: line, patch
   takes the first word from the prerequisites line  (normally  a  version
   number)  and checks the original file to see if that word can be found.
   If not, patch asks for confirmation before proceeding.

   The upshot of all this is that you should be able to say,  while  in  a
   news interface, something like 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  tries  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 contains interesting things such as file names
   and revision level, as mentioned previously.


   -b  or  --backup
      Make  backup  files.   That is, when patching a file, rename or copy
      the  original   instead   of   removing   it.    See   the   -V   or
      --version-control option for details about how backup file names are

      Back up a file if the patch does not match the file exactly  and  if
      backups  are  not  otherwise  requested.  This is the default unless
      patch is conforming to POSIX.

      Do not back up a file if the patch does not match the  file  exactly
      and  if backups are not otherwise requested.  This is the default if
      patch is conforming to POSIX.

   -B pref  or  --prefix=pref
      Use the simple method to determine backup file  names  (see  the  -V
      method  or  --version-control  method  option), and append pref to a
      file name when generating its backup file name.  For  example,  with
      -B /junk/  the  simple  backup  file  name  for  src/patch/util.c is

      Write all files in binary  mode,  except  for  standard  output  and
      /dev/tty.  When reading, disable the heuristic for transforming CRLF
      line endings into LF line endings.  This option is needed  on  POSIX
      systems when applying patches generated on non-POSIX systems to non-
      POSIX files.   (On  POSIX  systems,  file  reads  and  writes  never
      transform  line  endings.  On Windows, reads and writes do transform
      line  endings  by  default,  and  patches  should  be  generated  by
      diff --binary when line endings are significant.)

   -c  or  --context
      Interpret the patch file as a ordinary context diff.

   -d dir  or  --directory=dir
      Change to the directory dir immediately, before doing anything else.

   -D define  or  --ifdef=define
      Use  the #ifdef ... #endif construct to mark changes, with define as
      the differentiating symbol.

      Print the results of applying the patches without actually  changing
      any files.

   -e  or  --ed
      Interpret the patch file as an ed script.

   -E  or  --remove-empty-files
      Remove  output  files  that  are  empty  after the patches have been
      applied.  Normally this  option  is  unnecessary,  since  patch  can
      examine  the  time  stamps on the header to determine whether a file
      should exist after patching.  However, if the input is not a context
      diff or if patch is conforming to POSIX, patch does not remove empty
      patched files unless this option is given.   When  patch  removes  a
      file, it also attempts to remove any empty ancestor directories.

   -f  or  --force
      Assume  that  the user knows exactly what he or she is doing, and do
      not ask any questions.  Skip patches whose headers do not say  which
      file  is  to be patched; 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.

   -F num  or  --fuzz=num
      Set the maximum fuzz factor.  This option only applies to diffs that
      have  context,  and  causes patch to ignore up to that many lines of
      context 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.  A fuzz factor greater than or equal to the  number  of
      lines  of  context  in  the  context diff, ordinarily 3, ignores all

   -g num  or  --get=num
      This option controls patch's actions when a file  is  under  RCS  or
      SCCS  control,  and  does  not exist or is read-only and matches the
      default version, or when a  file  is  under  ClearCase  or  Perforce
      control  and  does  not  exist.   If num is positive, patch gets (or
      checks out) the file from the  revision  control  system;  if  zero,
      patch  ignores  RCS,  ClearCase, Perforce, and SCCS and does not get
      the file; and if negative, patch asks the user whether  to  get  the
      file.  The default value of this option is given by the value of the
      PATCH_GET environment variable if it is set;  if  not,  the  default
      value is zero.

      Print a summary of options and exit.

   -i patchfile  or  --input=patchfile
      Read  the  patch  from  patchfile.   If  patchfile  is  -, read from
      standard input, the default.

   -l  or  --ignore-whitespace
      Match patterns loosely, in case tabs or spaces have been  munged  in
      your  files.   Any  sequence of one or more blanks in the patch file
      matches any sequence in the original file, and sequences  of  blanks
      at  the  ends  of  lines  are ignored.  Normal characters must still
      match exactly.  Each line of the context must still match a line  in
      the original file.

   --merge or --merge=merge or --merge=diff3
      Merge  a  patch  file into the original files similar to diff3(1) or
      merge(1).  If a conflict is  found,  patch  outputs  a  warning  and
      brackets  the  conflict  with  <<<<<<< and >>>>>>> lines.  A typical
      conflict will look like this:

          lines from the original file
          original lines from the patch
          new lines from the patch

      The optional argument of --merge determines the  output  format  for
      conflicts:  the  diff3  format  shows  the  ||||||| section with the
      original lines from the patch; in the merge format, this section  is
      missing.  The merge format is the default.

      This  option  implies  --forward  and  does  not take the --fuzz=num
      option into account.

   -n  or  --normal
      Interpret the patch file as a normal diff.

   -N  or  --forward
      When a patch does not apply, patch usually checks if the patch looks
      like it has been reversed.  The --forward option prevents that.  See
      also -R.

   -o outfile  or  --output=outfile
      Send output to outfile instead of patching files in place.   Do  not
      use  this option if outfile is one of the files to be patched.  When
      outfile is -, send output to standard output, and send any  messages
      that would usually go to standard output to standard error.

   -pnum  or  --strip=num
      Strip  the  smallest prefix containing num leading slashes from each
      file name found in the patch  file.   A  sequence  of  one  or  more
      adjacent  slashes  is  counted as a single slash.  This controls how
      file names found in the patch file are treated,  in  case  you  keep
      your files in a different directory than the person who sent out the
      patch.  For example, supposing the file name in the patch file was


   setting -p0 gives the entire file name 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 option.

      Conform more strictly to the POSIX standard, as follows.

       * Take the first existing file from the list (old, new, index) when
         intuiting file names from diff headers.

       * Do not remove files that are empty after patching.

       * Do not ask whether to get files from RCS, ClearCase, Perforce, or

       * Require that all options precede the files in the command line.

       * Do not backup files when there is a mismatch.

      Use style word to quote output names.  The word should be one of the

             Output names as-is.

      shell  Quote   names   for   the   shell   if   they  contain  shell
             metacharacters or would cause ambiguous output.

             Quote names for the shell, even if they  would  normally  not
             require quoting.

      c      Quote names as for a C language string.

      escape Quote  as  with  c  except  omit the surrounding double-quote

      You can specify the default value of the --quoting-style option with
      the   environment   variable  QUOTING_STYLE.   If  that  environment
      variable is not set, the default value is shell.

   -r rejectfile  or  --reject-file=rejectfile
      Put rejects into rejectfile instead of the default .rej file.   When
      rejectfile is -, discard rejects.

   -R  or  --reverse
      Assume  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 attempts to swap each hunk around
      before applying it.  Rejects come out in the swapped format.  The -R
      option  does  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 reverses the hunk  to  see
      if it can be applied that way.  If it can, you are asked if you want
      to have the -R option set.  If it can't, the patch continues  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  matches  anywhere.   Luckily,  most
      patches  add  or  change  lines  rather  than  delete  them, so most
      reversed normal diffs begin with a delete, which  fails,  triggering
      the heuristic.)

      Behave  as  requested when trying to modify a read-only file: ignore
      the potential problem, warn about it (the default), or fail.

      Produce reject files in the  specified  format  (either  context  or
      unified).   Without  this option, rejected hunks come out in unified
      diff format if the input patch was  of  that  format,  otherwise  in
      ordinary context diff form.

   -s  or  --silent  or  --quiet
      Work silently, unless an error occurs.

      When  looking  for input files, follow symbolic links.  Replaces the
      symbolic links, instead of modifying the files  the  symbolic  links
      point to.  Git-style patches to symbolic links will no longer apply.
      This  option  exists  for  backwards  compatibility  with   previous
      versions of patch; its use is discouraged.

   -t  or  --batch
      Suppress  questions  like  -f,  but make some different assumptions:
      skip patches whose headers do not contain file names  (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.

   -T  or  --set-time
      Set  the  modification  and  access times of patched files from time
      stamps given in context diff headers.  Unless specified in the  time
      stamps, assume that the context diff headers use local time.

      Use  of  this option with time stamps that do not include time zones
      is not recommended, because patches using local time  cannot  easily
      be used by people in other time zones, and because local time stamps
      are ambiguous when local  clocks  move  backwards  during  daylight-
      saving  time  adjustments.   Make sure that time stamps include time
      zones, or generate patches with UTC and  use  the  -Z  or  --set-utc
      option instead.

   -u  or  --unified
      Interpret the patch file as a unified context diff.

   -v  or  --version
      Print out patch's revision header and patch level, and exit.

   -V method  or  --version-control=method
      Use  method  to determine backup file names.  The method can also be
      given by the PATCH_VERSION_CONTROL  (or,  if  that's  not  set,  the
      VERSION_CONTROL)  environment  variable, which is overridden by this
      option.  The method does not affect whether backup files  are  made;
      it affects only the names of any backup files that are made.

      The  value  of  method  is  like  the  GNU  Emacs  `version-control'
      variable; patch also recognizes synonyms that are more  descriptive.
      The valid values for method are (unique abbreviations are accepted):

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

      numbered  or  t
         Make numbered backups.  The numbered backup file name  for  F  is
         F.~N~ where N is the version number.

      simple  or  never
         Make    simple    backups.    The   -B   or   --prefix,   -Y   or
         --basename-prefix, and -z or --suffix options specify the  simple
         backup  file  name.   If  none of these options are given, then a
         simple  backup  suffix  is  used;  it  is  the   value   of   the
         SIMPLE_BACKUP_SUFFIX  environment  variable  if set, and is .orig

      With numbered or simple backups, if the  backup  file  name  is  too
      long, the backup suffix ~ is used instead; if even appending ~ would
      make the name too long, then ~ replaces the last  character  of  the
      file name.

      Output extra information about the work being done.

   -x num  or  --debug=num
      Set internal debugging flags of interest only to patch patchers.

   -Y pref  or  --basename-prefix=pref
      Use  the  simple  method  to determine backup file names (see the -V
      method or --version-control method option), and prefix pref  to  the
      basename  of  a file name when generating its backup file name.  For
      example,  with  -Y .del/   the   simple   backup   file   name   for
      src/patch/util.c is src/patch/.del/util.c.

   -z suffix  or  --suffix=suffix
      Use  the  simple  method  to determine backup file names (see the -V
      method or --version-control method option), and use  suffix  as  the
      suffix.    For   example,   with  -z -  the  backup  file  name  for
      src/patch/util.c is src/patch/util.c-.

   -Z  or  --set-utc
      Set the modification and access times of  patched  files  from  time
      stamps  given  in context diff headers. Unless specified in the time
      stamps,  assume  that  the  context  diff  headers  use  Coordinated
      Universal  Time  (UTC,  often  known  as  GMT).   Also see the -T or
      --set-time option.

      The -Z or --set-utc and -T or --set-time  options  normally  refrain
      from  setting  a  file's  time  if the file's original time does not
      match the time given in the patch header, or if its contents do  not
      match  the  patch  exactly.  However, if the -f or --force option is
      given, the file time is set regardless.

      Due to the limitations of diff output format, these  options  cannot
      update the times of files whose contents have not changed.  Also, if
      you use these options, you should remove (e.g. with make clean)  all
      files that depend on the patched files, so that later invocations of
      make do not get confused by the patched files' times.


      This specifies whether patch gets missing or  read-only  files  from
      RCS,  ClearCase,  Perforce,  or SCCS by default; see the -g or --get

      If set, patch conforms  more  strictly  to  the  POSIX  standard  by
      default: see the --posix option.

      Default value of the --quoting-style option.

      Extension to use for simple backup file names instead of .orig.

      Directory   to   put  temporary  files  in;  patch  uses  the  first
      environment variable in this list that is set.  If none are set, the
      default is system-dependent; it is normally /tmp on Unix hosts.

      Selects  version  control  style;  see  the  -v or --version-control


      temporary files

      controlling terminal; used to get answers to questions asked of  the


   diff(1), ed(1), merge(1).

   Marshall  T. Rose and Einar A. Stefferud, Proposed Standard for Message
   Encapsulation,    Internet    RFC    934     <URL:
   notes/rfc934.txt> (1985-01).


   There are several things you should bear in mind if you are going to be
   sending out patches.

   Create your  patch  systematically.   A  good  method  is  the  command
   diff -Naur old new   where  old  and  new  identify  the  old  and  new
   directories.  The names old and new should  not  contain  any  slashes.
   The  diff  command's  headers  should have dates and times in Universal
   Time using traditional Unix format, so that patch  recipients  can  use
   the  -Z  or --set-utc option.  Here is an example command, using Bourne
   shell syntax:

          LC_ALL=C TZ=UTC0 diff -Naur gcc-2.7 gcc-2.8

   Tell your recipients how to apply  the  patch  by  telling  them  which
   directory  to cd to, and which patch options to use.  The option string
   -Np1 is recommended.   Test  your  procedure  by  pretending  to  be  a
   recipient and applying your patch to a copy of the original files.

   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.

   You can create a file by sending out a diff that compares /dev/null  or
   an empty file dated the Epoch (1970-01-01 00:00:00 UTC) to the file you
   want to create.  This only works if the file you want to create doesn't
   exist  already  in  the target directory.  Conversely, you can remove a
   file by sending out a context diff that compares the file to be deleted
   with  an  empty  file dated the Epoch.  The file will be removed unless
   patch is conforming to POSIX and the -E or --remove-empty-files  option
   is  not  given.  An easy way to generate patches that create and remove
   files is to use GNU diff's -N or --new-file option.

   If the recipient is supposed to use the -pN option, do not send  output
   that looks like this:

          diff -Naur v2.0.29/prog/README prog/README
          --- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997
          +++ prog/README   Mon Mar 17 14:58:22 1997

   because  the  two  file  names  have  different numbers of slashes, and
   different versions of patch interpret the file names  differently.   To
   avoid confusion, send output that looks like this instead:

          diff -Naur v2.0.29/prog/README v2.0.30/prog/README
          --- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997
          +++ v2.0.30/prog/README   Mon Mar 17 14:58:22 1997

   Avoid  sending patches that compare backup file names like README.orig,
   since this might confuse patch into patching a backup file  instead  of
   the  real  file.  Instead, send patches that compare the same base file
   names in different directories, e.g. old/README and new/README.

   Take care not to send out  reversed  patches,  since  it  makes  people
   wonder whether they already applied the patch.

   Try  not  to  have  your  patch  modify  derived  files  (e.g. the file
   configure where  there  is  a  line  configure:  in  your
   makefile), since the recipient should be able to regenerate the derived
   files anyway.  If you must send diffs of derived  files,  generate  the
   diffs  using  UTC,  have  the recipients apply the patch with the -Z or
   --set-utc option, and have them remove any unpatched files that  depend
   on patched files (e.g. with make clean).

   While  you  may be able to get away with putting 582 diff listings into
   one file, it may be wiser to group related patches into separate  files
   in case something goes haywire.


   Diagnostics  generally  indicate  that  patch couldn't parse your patch

   If the --verbose option is given, 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's  exit  status  is 0 if all hunks are applied successfully, 1 if
   some hunks cannot be applied or there were merge conflicts,  and  2  if
   there  is  more  serious  trouble.  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.


   Context  diffs  cannot  reliably  represent the creation or deletion of
   empty files, empty directories,  or  special  files  such  as  symbolic
   links.  Nor can they represent changes to file metadata like ownership,
   permissions, or whether one file is a hard link to another.  If changes
   like  these  are  also  required,  separate  instructions (e.g. a shell
   script) to accomplish them should accompany the patch.

   patch cannot tell if the line numbers are off in an ed script, and  can
   detect bad line numbers in a normal diff only when it finds a change or
   deletion.  A context diff  using  fuzz  factor  3  may  have  the  same
   problem.   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  POSIX  standard  specifies  behavior  that  differs  from  patch's
   traditional  behavior.  You should be aware of these differences if you
   must interoperate with patch versions 2.1 and  earlier,  which  do  not
   conform to POSIX.

    * In  traditional  patch,  the -p option's operand was optional, and a
      bare -p was equivalent to  -p0.   The  -p  option  now  requires  an
      operand,   and   -p 0   is  now  equivalent  to  -p0.   For  maximum
      compatibility, use options like -p0 and -p1.

      Also, traditional patch simply counted slashes when  stripping  path
      prefixes; patch now counts pathname components.  That is, a sequence
      of one or more adjacent slashes now counts as a single  slash.   For
      maximum  portability,  avoid  sending  patches containing // in file

    * In  traditional  patch,  backups  were  enabled  by  default.   This
      behavior is now enabled with the -b or --backup option.

      Conversely,  in POSIX patch, backups are never made, even when there
      is a mismatch.  In GNU patch, this  behavior  is  enabled  with  the
      --no-backup-if-mismatch  option,  or by conforming to POSIX with the
      --posix  option  or  by  setting  the  POSIXLY_CORRECT   environment

      The  -b suffix  option  of  traditional  patch  is equivalent to the
      -b -z suffix options of GNU patch.

    * Traditional patch used a complicated (and  incompletely  documented)
      method  to  intuit the name of the file to be patched from the patch
      header.  This method did  not  conform  to  POSIX,  and  had  a  few
      gotchas.   Now  patch  uses  a  different,  equally complicated (but
      better documented) method that is  optionally  POSIX-conforming;  we
      hope  it  has  fewer gotchas.  The two methods are compatible if the
      file names in the context diff header and the Index:  line  are  all
      identical after prefix-stripping.  Your patch is normally compatible
      if each header's file names all contain the same number of slashes.

    * When traditional patch asked  the  user  a  question,  it  sent  the
      question  to  standard error and looked for an answer from the first
      file in the following list that  was  a  terminal:  standard  error,
      standard  output,  /dev/tty,  and  standard  input.  Now patch sends
      questions  to  standard  output  and  gets  answers  from  /dev/tty.
      Defaults for some answers have been changed so that patch never goes
      into an infinite loop when using default answers.

    * Traditional patch exited with a status value that counted the number
      of bad hunks, or with status 1 if there was real trouble.  Now patch
      exits with status 1 if some hunks failed, or with  2  if  there  was
      real trouble.

    * Limit  yourself  to  the following options when sending instructions
      meant to be executed by anyone running GNU patch, traditional patch,
      or  a  patch  that conforms to POSIX.  Spaces are significant in the
      following list, and operands are required.

         -d dir
         -D define
         -o outfile
         -r rejectfile


   Please report bugs via email to <>.

   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 thinks it is a
   reversed patch, and offers  to  un-apply  the  patch.   This  could  be
   construed as a feature.

   Computing  how  to  merge a hunk is significantly harder than using the
   standard fuzzy algorithm.  Bigger hunks, more context, a bigger  offset
   from  the  original  location, and a worse match all slow the algorithm


   Copyright (C) 1984, 1985, 1986, 1988 Larry Wall.
   Copyright (C) 1989, 1990, 1991, 1992, 1993,  1994,  1995,  1996,  1997,
   1998, 1999, 2000, 2001, 2002, 2009 Free Software Foundation, Inc.

   Permission  is  granted  to make and distribute verbatim copies of this
   manual provided the copyright notice and  this  permission  notice  are
   preserved on all copies.

   Permission  is granted to copy and distribute modified versions of this
   manual under the conditions for verbatim  copying,  provided  that  the
   entire  resulting  derived  work  is  distributed  under the terms of a
   permission notice identical to this one.

   Permission is granted to  copy  and  distribute  translations  of  this
   manual  into  another language, under the above conditions for modified
   versions, except  that  this  permission  notice  may  be  included  in
   translations  approved  by  the  copyright  holders  instead  of in the
   original English.


   Larry Wall wrote the original version of patch.   Paul  Eggert  removed
   patch's  arbitrary limits; added support for binary files, setting file
   times, and deleting files; and made it conform better to POSIX.   Other
   contributors  include  Wayne  Davison,  who  added unidiff support, and
   David MacKenzie, who added configuration and backup  support.   Andreas
   Grnbacher added support for merging.


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