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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,	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 are read-only or
	  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.)

       --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.

       -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
       English.

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)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | FILES | SEE ALSO | NOTES FOR PATCH SENDERS | DIAGNOSTICS | CAVEATS | COMPATIBILITY ISSUES | BUGS | COPYING | AUTHORS

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