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PATCH(1)							      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, or if a context diff  contains
       lines ending in CRLF or 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  com‐
       ments.

       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:

	· 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
       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.   (On  POSIX-conforming  systems,
	  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.

       --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 in
	  looking for places to install a hunk.	 Note that a larger fuzz  fac‐
	  tor  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 con‐
	  text in the context diff, ordinarily 3.

       -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
	  Merge a patch file into the original files similar to 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
	      =======
	      lines from the patch
	      >>>>>>>

	  If  there  are conflicts, the user should edit the result and delete
	  one of the alternatives.  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
	  Ignore  patches  that	 seem  to be reversed or already applied.  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.

	   · 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
	     SCCS.

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

	   · 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.

       --global-reject-file=rejectfile
	  Same	as --reject-file=rejectfile.  This option is deprecated and is
	  a Debian-specific  extension	that  will  be	removed	 in  a	future
	  release.

       -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.)

       --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.

       -U  or  --unified-reject-files
	  Produce unified reject files.	  This option is deprecated and	 is  a
	  Debian-specific  extension that will be removed in a future release.
	  Use --reject-format=format instead.

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

       -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, assuming that the context diff
	  headers use local time.  This option	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.
	  Instead of using this option, 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, assuming 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.

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.

	· 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.

	· 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.

	· 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.

	· 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.

	· 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.

	     -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
       Grünbacher added support for merging.

				      GNU			      PATCH(1)
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