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PATCH(1)		    General Commands Manual		      PATCH(1)

NAME
       patch - apply a diff file to an original

SYNOPSIS
       patch [options] [origfile [patchfile]] [+ [options] [origfile]]...

       but usually just

       patch <patchfile

DESCRIPTION
       Patch  will  take a patch file containing any of	the four forms of dif-
       ference listing produced	by the diff program and	 apply	those  differ-
       ences  to  an  original file, producing a patched version.  By default,
       the patched version is put in place of the original, with the  original
       file backed up to the same name with the	extension ".orig" ("~" on sys-
       tems that do not	support	long file names), or as	specified  by  the  -b
       (--suffix),  -B (--prefix), or -V (--version-control) options.  The ex-
       tension used for	making backup files may	also be	specified in the  SIM-
       PLE_BACKUP_SUFFIX  environment  variable,  which	 is  overridden	by the
       above options.

       If the backup file already exists, patch	creates	a new backup file name
       by  changing  the  first	 lowercase letter in the last component	of the
       file's name into	uppercase.  If there are no more lowercase letters  in
       the  name,  it  removes	the first character from the name.  It repeats
       this process until it comes up with a backup file that does not already
       exist.

       You  may	also specify where you want the	output to go with a -o (--out-
       put) option; if that file already exists, it is backed up first.

       If patchfile is omitted,	or is a	hyphen,	the patch will	be  read  from
       standard	input.

       Upon  startup,  patch  will  attempt  to	determine the type of the diff
       listing,	unless over-ruled by a -c (--context), -e (--ed),  -n  (--nor-
       mal),  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 editor via a pipe.

       Patch  will  try	 to skip any leading garbage, apply the	diff, and then
       skip any	trailing garbage.  Thus	you could feed an article  or  message
       containing  a diff listing to patch, and	it should work.	 If the	entire
       diff is indented	by a consistent	amount,	this will be  taken  into  ac-
       count.

       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
       will attempt 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	will scan 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  an-
       other  scan is made.  (The default maximum fuzz factor is 2.)  If patch
       cannot find a place to install that hunk	of the patch, it will put  the
       hunk  out  to  a	 reject	file, which normally is	the name of the	output
       file plus ".rej"	("#" on	systems	that do	not support long file  names).
       (Note that the rejected hunk will come out in context diff form whether
       the input patch was a context diff or a normal diff.  If	the input  was
       a  normal  diff,	 many  of the contexts will simply be 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 will be told whether the hunk  succeeded
       or  failed,  and	 which	line  (in the new file)	patch thought the hunk
       should go on.  If this is different from	the line number	 specified  in
       the  diff you will be told the offset.  A single	large offset MAY be an
       indication that a hunk was installed in the wrong place.	 You will also
       be  told	if a fuzz factor was used to make the match, in	which case you
       should also be slightly suspicious.

       If no original file is specified	on the command line, patch will	try to
       figure  out  from the leading garbage what the name of the file to edit
       is.  In the header of a context diff, the file name is found from lines
       beginning  with	"***"  or "---", with the shortest name	of an existing
       file winning.  Only context diffs have lines like that, but if there is
       an "Index:" line	in the leading garbage,	patch will try to use the file
       name from that line.  The context diff header takes precedence over  an
       Index  line.  If	no file	name can be intuited from the leading garbage,
       you will	be asked for the name of the file to patch.

       If the original file cannot be found or is read-only,  but  a  suitable
       SCCS  or	 RCS file is handy, patch will attempt to get or check out the
       file.

       Additionally, if	the leading garbage contains a "Prereq:	" line,	 patch
       will  take  the first word from the prerequisites line (normally	a ver-
       sion number) and	check the input	file to	see if that word can be	found.
       If not, patch will ask for confirmation before proceeding.

       The  upshot  of	all this is that you should be able to say, while in a
       news interface, 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 will try 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 will be examined for interesting things such
       as file names and revision level, as  mentioned	previously.   You  can
       give options (and another original file name) for the second and	subse-
       quent patches by	separating the corresponding argument lists by a  '+'.
       (The  argument  list for	a second or subsequent patch may not specify a
       new patch file, however.)

       Patch recognizes	the following options:

       -b suff,	--suffix=suff
	    causes suff	to be interpreted as the backup	extension, to be  used
	    in place of	".orig"	or "~".

       -B pref,	--prefix=pref
	    causes pref	to be interpreted as a prefix to the backup file name.
	    If this argument is	specified, any argument	from -b	 will  be  ig-
	    nored.

       -c, --context
	    forces patch to interpret the patch	file as	a context diff.

       -d dir, --directory=dir
	    causes  patch to interpret dir as a	directory, and cd to it	before
	    doing anything else.

       -D sym, --ifdef=sym
	    causes patch  to  use  the	"#ifdef...#endif"  construct  to  mark
	    changes.  sym will be used as the differentiating symbol.

       -e, --ed
	    forces patch to interpret the patch	file as	an ed script.

       -E, --remove-empty-files
	    causes  patch  to  remove  output  files  that are empty after the
	    patches have been applied.

       -f, --force
	    forces patch to assume that	the user knows exactly what he or  she
	    is doing, and to not ask any questions.  It	assumes	the following:
	    skip patches for which a file to patch can't be found; 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 commen-
	    tary; use -s for that.

       -t, --batch
	    similar to -f, in that it suppresses  questions,  but  makes  some
	    different  assumptions:  skip  patches  for	 which a file to patch
	    can't be found (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.

       -F number, --fuzz=number
	    sets the maximum fuzz factor.  This	option only applies to context
	    diffs, and causes patch to ignore up to that many lines in looking
	    for	places to install a hunk.  Note	that a larger fuzz factor  in-
	    creases 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  context
	    in the context diff, ordinarily 3.

       -l, --ignore-whitespace
	    causes  the	 pattern matching to be	done loosely, in case the tabs
	    and	spaces have been munged	in your	input file.  Any  sequence  of
	    whitespace	in the pattern line will match any sequence in the in-
	    put	file.  Normal characters must still match exactly.  Each  line
	    of the context must	still match a line in the input	file.

       -n, --normal
	    forces patch to interpret the patch	file as	a normal diff.

       -N, --forward
	    causes  patch to ignore patches that it thinks are reversed	or al-
	    ready applied.  See	also -R	.

       -o file,	--output=file
	    causes file	to be interpreted as the output	file name.

       -p[number], --strip[=number]
	    sets the pathname strip count, which controls how pathnames	 found
	    in	the patch file are treated, in case the	you keep your files in
	    a different	directory than the person who sent out the patch.  The
	    strip count	specifies how many slashes are to be stripped from the
	    front of the pathname.  (Any intervening directory names  also  go
	    away.)  For	example, supposing the file name in the	patch file was

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

	    setting -p or -p0 gives the	entire pathname	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", unless all
	    of the directories in the leading path (u/howard/src/blurfl) exist
	    and	 that path is relative,	in which case you get the entire path-
	    name unmodified.  Whatever you end up with is looked for either in
	    the	 current  directory,  or the directory specified by the	-d op-
	    tion.

       -r file,	--reject-file=file
	    causes file	to be interpreted as the reject	file name.

       -R, --reverse
	    tells patch	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 will attempt to  swap  each  hunk
	    around  before  applying it.  Rejects will come out	in the swapped
	    format.  The -R option will	not work with ed diff scripts  because
	    there  is too little information to	reconstruct the	reverse	opera-
	    tion.

	    If the first hunk of a patch fails,	patch will reverse the hunk to
	    see	 if  it	can be applied that way.  If it	can, you will be asked
	    if you want	to have	the -R option set.  If	it  can't,  the	 patch
	    will  continue  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 ap-
	    pends always succeed, due to the fact that	a  null	 context  will
	    match  anywhere.  Luckily, most patches add	or change lines	rather
	    than delete	them, so most reversed normal diffs will begin with  a
	    delete, which will fail, triggering	the heuristic.)

       -s, --silent, --quiet
	    makes patch	do its work silently, unless an	error occurs.

       -S, --skip
	    causes  patch  to  ignore this patch from the patch	file, but con-
	    tinue on looking for the next patch	in the file.  Thus

		 patch -S + -S + <patchfile

	    will ignore	the first and second of	three patches.

       -u, --unified
	    forces patch to interpret the patch	file as	a unified context diff
	    (a unidiff).

       -v, --version
	    causes patch to print out its revision header and patch level.

       -V method, --version--control=method
	    causes  method  to	be interpreted as a method for creating	backup
	    file names.	 The type of backups made can also  be	given  in  the
	    VERSION_CONTROL  environment variable, which is overridden by this
	    option.  The -B option overrides this option, causing  the	prefix
	    to	always be used for making backup file names.  The value	of the
	    VERSION_CONTROL environment	variable and the argument  to  the  -V
	    option  are	 like  the  GNU	Emacs `version-control'	variable; they
	    also recognize synonyms that are more descriptive.	The valid val-
	    ues	are (unique abbreviations are accepted):

	    `t'	or `numbered'
		   Always make numbered	backups.

	    `nil' or `existing'
		   Make	numbered backups of files that already have them, sim-
		   ple backups of the others.  This is the default.

	    `never' or `simple'
		   Always make simple backups.

       -x number, --debug=number
	    sets internal debugging flags, and is of interest  only  to	 patch
	    patchers.

AUTHOR
       Larry Wall <lwall@netlabs.com>
       with many other contributors.

ENVIRONMENT
       TMPDIR Directory	to put temporary files in; default is /tmp.

       SIMPLE_BACKUP_SUFFIX
	      Extension	 to  use  for  backup file names instead of ".orig" or
	      "~".

       VERSION_CONTROL
	      Selects when numbered backup files are made.

FILES
       $TMPDIR/patch*

SEE ALSO
       diff(1)

NOTES FOR PATCH	SENDERS
       There are several things	you should bear	in mind	if you are going to be
       sending	out  patches.	First,	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.	Second,	make sure you've specified the
       file names right, either	in a context diff header, or  with  an	Index:
       line.  If you are patching something in a subdirectory, be sure to tell
       the patch user to specify a -p option as	needed.	 Third,	you can	create
       a  file by sending out a	diff that compares a null file to the file you
       want to create.	This will only work if the file	 you  want  to	create
       doesn't	exist  already in the target directory.	 Fourth, take care not
       to send out reversed patches, since it makes people wonder whether they
       already	applied	 the  patch.  Fifth, while you may be able to get away
       with putting 582	diff listings into one file, it	is probably  wiser  to
       group  related  patches into separate files in case something goes hay-
       wire.

DIAGNOSTICS
       Too many	to list	here, but generally  indicative	 that  patch  couldn't
       parse your patch	file.

       The  message  "Hmm..."  indicates that there is unprocessed text	in the
       patch file and that patch is attempting to intuit whether  there	 is  a
       patch in	that text and, if so, what kind	of patch it is.

       Patch  will  exit  with a non-zero status if any	reject files were cre-
       ated.  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
       Patch cannot tell if the	line numbers are off in	an ed script, and  can
       only  detect bad	line numbers in	a normal diff when it finds a "change"
       or a "delete" command.  A context diff using fuzz factor	3 may have the
       same  problem.	Until  a  suitable interactive interface is added, 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 indi-
       cation 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.

BUGS
       Could be	smarter	about partial matches, excessively deviant offsets and
       swapped code, but that would take an extra pass.

       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 will think it is a
       reversed	patch, and offer to un-apply the patch.	 This  could  be  con-
       strued as a feature.

				     LOCAL			      PATCH(1)

NAME | SYNOPSIS | DESCRIPTION | AUTHOR | ENVIRONMENT | FILES | SEE ALSO | NOTES FOR PATCH SENDERS | DIAGNOSTICS | CAVEATS | BUGS

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