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PATCH(1)		    General Commands Manual		      PATCH(1)

       patch - apply a diff file to an original

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

       but usually just

       patch patchfile

       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 filenames), or as specified  by  the  -b,
       -B,  or	-V  switches.	The extension used for making backup files may
       also be specified in  the  SIMPLE_BACKUP_SUFFIX	environment  variable,
       which is	overridden by above switches.

       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

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

       If  no  patchfile  argument  is	specified using	the -i option, and the
       patchfile argument 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, -e,	-n,  or	 -u  switch.   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-

       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  filenames).
       (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 filename 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
       filename	from that line.	 The context diff header takes precedence over
       an  Index  line.	  If  no  filename  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

       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 filenames and	revision level,	as mentioned previously.  You can give
       switches	(and another original file name) for the second	and subsequent
       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 switches:

       -B or --prefix
	    causes the next argument to	be interpreted	as  a  prefix  to  the
	    backup file	name.  If this argument	is specified any argument from
	    -b will be ignored.

       -b or --suffix
	    causes the next argument to	be interpreted as  the	backup	exten-
	    sion, to be	used in	place of ".orig" or "~".

       -C or --dry-run
	    causes  patch  to  report  what would be done, but not to actually
	    modify any files or	create any rejects.

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

       -D or --ifdef
	    causes patch  to  use  the	"#ifdef...#endif"  construct  to  mark
	    changes.  The argument following will be used as the differentiat-
	    ing	symbol.	 Note that, unlike the C compiler,  there  must	 be  a
	    space between the -D and the argument.

       -d or --directory
	    causes patch to interpret the next argument	as a directory,	and cd
	    to it before doing anything	else.

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

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

       -Fnumber	or --fuzz number
	    sets the maximum fuzz factor.  This	switch 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.

       -f or --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.

       -i patchfile or --patchfile patchfile
	    Read the patch to be applied from the specified file.

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

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

       -o or --output
	    causes  the	 next  argument	 to  be	interpreted as the output file

       -pnumber	or --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 filename	in the patch file was


	    setting -p or -p0 gives the	entire pathname	unmodified, -p1	gives


	    without the	leading	slash, -p4 gives


	    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

       -R or --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 switch will	not work with ed diff scripts  because
	    there  is too little information to	reconstruct the	reverse	opera-

	    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 switch 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.)

       -r or --reject-file
	    causes  the	 next  argument	 to  be	interpreted as the reject file

       -S or --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.

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

       -t or --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.

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

       -V or --version-control
	    causes the next argument to	be interpreted as a method for	creat-
	    ing	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
	    values 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.

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

       -xnumber	or --debug number
	    sets  internal  debugging  flags, and is of	interest only to patch

       Larry Wall
       with many other contributors.

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

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

	      Selects when numbered backup files are made.



       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
       filenames  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 switch 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-

       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.

       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.

       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.



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