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PATCH(1)							      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
       extension used for making backup	files may also	be  specified  in  the
       SIMPLE_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.	 If a -i argument is specified,	the filename following
       it will be used,	instead	of standard input. You may specify only	one -i
       directive.

       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
       account.

       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
       another	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
	    ignored.

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

       -C, --check
	    see	what would happen, but don't do	it.

       -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
	    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.

       -i patchfile
	    tells patch	to apply patchfile instead of stdin.

       -I, --index-first
	    forces  patch to take ``Index:'' line precedence over context diff
	    header.  The same effect have PATCH_INDEX_FIRST environment	 vari-
	    able if present.

       -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
	    input 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
	    already 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 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
	    option.

       -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
	    appends  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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