patch(1)



PATCH(1)                    General Commands Manual                   PATCH(1)

NAME
       patch - apply a diff file to an original

SYNOPSIS
       patch [options] [originalfile [patchfile]]

       but usually just

       patch -pnum <patchfile

DESCRIPTION
       patch takes a patch file patchfile containing a difference listing pro-
       duced by the diff program and applies those differences to one or  more
       original  files, producing patched versions.  Normally the patched ver-
       sions 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 usu-
       ally 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  con-
       taining  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 apply-
       ing 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 speci-
       fied 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:

        o 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.

        o 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.

        o 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:

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

        o 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.

        o 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.

        o 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
       name.

       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 con-
       taining 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.

OPTIONS
       -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-con-
          trol option for details about how backup file names are determined.

       --backup-if-mismatch
          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.

       --no-backup-if-mismatch
          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
          /junk/src/patch/util.c.

       --binary
          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 trans-
          form 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.

       --dry-run
          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 exam-
          ine 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 con-
          text.

       -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 con-
          trol 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.

       --help
          Print a summary of options and exit.

       -i patchfile  or  --input=patchfile
          Read the patch from patchfile.  If patchfile is -, read  from  stan-
          dard 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 orig-
          inal  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 adja-
          cent 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

          /u/howard/src/blurfl/blurfl.c

       setting -p0 gives the entire file name 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 option.

       --posix
          Conform more strictly to the POSIX standard, as follows.

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

           o Do not remove files that are empty after patching.

           o Do not ask whether to get files from RCS, ClearCase, Perforce, or
             SCCS.

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

           o Do not backup files when there is a mismatch.

       --quoting-style=word
          Use style word to quote output names.  The word should be one of the
          following:

          literal
                 Output names as-is.

          shell  Quote names for the shell if they contain  shell  metacharac-
                 ters or would cause ambiguous output.

          shell-always
                 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
                 characters.

          You can specify the default value of the --quoting-style option with
          the environment variable QUOTING_STYLE.  If that  environment  vari-
          able 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  lit-
          tle 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.)

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

       --reject-format=format
          Produce reject files in the specified format (either context or uni-
          fied).  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.

       --follow-symlinks
          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 ver-
          sions 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-sav-
          ing 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 VER-
          SION_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'  vari-
          able; 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-pre-
             fix,  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 envi-
             ronment variable if set, and is .orig otherwise.

          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.

       --verbose
          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 Univer-
          sal  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.

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

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

       QUOTING_STYLE
          Default value of the --quoting-style option.

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

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

       VERSION_CONTROL or PATCH_VERSION_CONTROL
          Selects  version  control  style;  see  the  -v or --version-control
          option.

FILES
       $TMPDIR/p*
          temporary files

       /dev/tty
          controlling terminal; used to get answers to questions asked of  the
          user

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

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

NOTES FOR PATCH SENDERS
       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 directo-
       ries.  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 syn-
       tax:

              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 recipi-
       ent 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 dif-
       ferent 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  won-
       der whether they already applied the patch.

       Try  not to have your patch modify derived files (e.g. the file config-
       ure where there is a line configure: configure.in  in  your  makefile),
       since the recipient should be able to regenerate the derived files any-
       way.  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
       Diagnostics  generally  indicate  that  patch couldn't parse your patch
       file.

       If the --verbose option is given, the  message  Hmm...  indicates  that
       there  is unprocessed text in the patch file and that patch is attempt-
       ing 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.

CAVEATS
       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  prob-
       lem.   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.

COMPATIBILITY ISSUES
       The POSIX standard specifies behavior that differs from patch's  tradi-
       tional  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.

        o In  traditional  patch,  the -p option's operand was optional, and a
          bare -p was equivalent to -p0.  The -p option now requires an  oper-
          and,  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
          names.

        o In traditional patch, backups were enabled by default.  This  behav-
          ior 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  vari-
          able.

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

        o 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 bet-
          ter 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 identi-
          cal  after  prefix-stripping.   Your patch is normally compatible if
          each header's file names all contain the same number of slashes.

        o When traditional patch asked the user a question, it sent the  ques-
          tion  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.

        o 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.

        o 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.

             -c
             -d dir
             -D define
             -e
             -l
             -n
             -N
             -o outfile
             -pnum
             -R
             -r rejectfile

BUGS
       Please report bugs via email to <bug-patch@gnu.org>.

       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  con-
       strued 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
       down.

COPYING
       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 per-
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man-
       ual into another language, under the above conditions for modified ver-
       sions, except that this permission notice may be included  in  transla-
       tions approved by the copyright holders instead of in the original Eng-
       lish.

AUTHORS
       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
       Grunbacher added support for merging.

GNU                                                                   PATCH(1)

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