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NAME    [Toc]    [Back]

       patch - apply a diff file to an original

SYNOPSIS    [Toc]    [Back]

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

       but usually just

       patch <patchfile

DESCRIPTION    [Toc]    [Back]

       Patch  will  take a patch file containing any of the four forms of difference
 listing produced by the diff program and  apply	those  differences
  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 systems
 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

       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

       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

       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

       Additionally, if the leading garbage contains a "Prereq: " line,  patch
       will  take  the first word from the prerequisites line (normally a version
 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 containing
 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 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 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

       -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 commentary;
 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  context
 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  variable
 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 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


	    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  pathname
 unmodified.  Whatever you end up with is looked for either in
	    the current directory,  or	the  directory	specified  by  the  -d

       -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	operation.

	    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  continue
 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 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, simple
 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

AUTHOR    [Toc]    [Back]

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

ENVIRONMENT    [Toc]    [Back]

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

       SIMPLE_BACKUP_SUFFIX    [Toc]    [Back]
	      Extension to use for backup file names  instead  of  ".orig"  or

       VERSION_CONTROL    [Toc]    [Back]
	      Selects when numbered backup files are made.

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]



       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  haywire.

DIAGNOSTICS    [Toc]    [Back]

       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  created.
   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    [Toc]    [Back]

       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 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.

BUGS    [Toc]    [Back]

       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 construed
 as a feature.

				     LOCAL			      PATCH(1)
[ Back ]
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