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.	When backing up	 a  file  that
	  does	not  exist,  an	 empty, unreadable backup file is created as a
	  placeholder to represent the nonexistent file.  See the -V or --ver-
	  sion-control	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
	  Ignore patches that seem to be reversed or already  applied.	It  is
	  only checked if the first hunk of a patch can be reversed.  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)