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NetBSD 6.1.5 - man page for patch (netbsd section 1)

PATCH(1)			   BSD General Commands Manual				 PATCH(1)

     patch -- apply a diff file to an original

     patch [-bCcEeflNnRstuv] [-B backup-prefix] [-D symbol] [-d directory] [-F max-fuzz]
	   [-i patchfile] [-o out-file] [-p strip-count] [-r rej-name] [-V t | nil | never]
	   [-x number] [-z backup-ext] [--posix] [origfile [patchfile]]
     patch <patchfile

     patch will take a patch file containing any of the four forms of difference listing produced
     by the diff(1) program and apply those differences to an original file, producing a patched
     version.  If patchfile is omitted, or is a hyphen, the patch will be read from the standard

     patch will attempt to determine the type of the diff listing, unless over-ruled by a -c, -e,
     -n, or -u option.	Context diffs (old-style, new-style, and unified) and normal diffs are
     applied directly by the patch program itself, whereas ed diffs are simply fed to the ed(1)
     editor via a pipe.

     If the patchfile 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 (see the section on Filename Determination below).

     The options are as follows:

     -B backup-prefix, --prefix backup-prefix
	     Causes the next argument to be interpreted as a prefix to the backup file name.  If
	     this argument is specified, any argument to -z will be ignored.

     -b, --backup
	     Save a backup copy of the file before it is modified.  By default the original file
	     is saved with a backup extension of ".orig" unless the file already has a numbered
	     backup, in which case a numbered backup is made.  This is equivalent to specifying
	     "-V existing".  This option is currently the default, unless --posix is specified.

     -C, --check
	     Checks that the patch would apply cleanly, but does not modify anything.

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

     -D symbol, --ifdef symbol
	     Causes patch to use the "#ifdef...#endif" construct to mark changes.  The argument
	     following will be used as the differentiating symbol.  Note that, unlike the C com-
	     piler, there must be a space between the -D and the argument.

     -d directory, --directory directory
	     Causes patch to interpret the next argument as a directory, and change the working
	     directory to it before doing anything else.

     -E, --remove-empty-files
	     Causes patch to remove output files that are empty after the patches have been
	     applied.  This option is useful when applying patches that create or remove files.

     -e, --ed
	     Forces patch to interpret the patch file as an ed(1) script.

     -F max-fuzz, --fuzz max-fuzz
	     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.

     -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.

     -i patchfile, --input patchfile
	     Causes the next argument to be interpreted as the input file name (i.e. a patch-
	     file).  This option may be specified multiple times.

     -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, --forward
	     Causes patch to ignore patches that it thinks are reversed or already applied.  See
	     also -R.

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

     -o out-file, --output out-file
	     Causes the next argument to be interpreted as the output file name.

     -p strip-count, --strip strip-count
	     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

	     Setting -p0 gives the entire pathname unmodified.

	     -p1 gives


	     without the leading slash.

	     -p4 gives


	     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 option.

     -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 com-
	     mand 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.)

     -r rej-name, --reject-file rej-name
	     Causes the next argument to be interpreted as the reject file name.

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

     -t, --batch
	     Similar to -f, in that it suppresses questions, but makes some different assump-
	     tions: 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, --unified
	     Forces patch to interpret the patch file as a unified context diff (a unidiff).

     -V t | nil | never, --version-control t | nil | never
	     Causes the next argument to be interpreted as a method for creating backup file
	     names.  The type of backups made can also be given in the PATCH_VERSION_CONTROL or
	     VERSION_CONTROL environment variables, which are overridden by this option.  The -B
	     option overrides this option, causing the prefix to always be used for making backup
	     file names.  The values of the PATCH_VERSION_CONTROL and VERSION_CONTROL environment
	     variables and the argument to the -V option are like the GNU Emacs
	     ``version-control'' variable; they also recognize synonyms that are more descrip-
	     tive.  The valid values are (unique abbreviations are accepted):

		   t, numbered
			   Always make numbered backups.

		   nil, existing
			   Make numbered backups of files that already have them, simple backups
			   of the others.

		   never, simple
			   Always make simple backups.

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

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

     -z backup-ext, --suffix backup-ext
	     Causes the next argument to be interpreted as the backup extension, to be used in
	     place of ".orig".

	     Enables strict IEEE Std 1003.1-2004 (``POSIX.1'') conformance, specifically:

	     1.   Backup files are not created unless the -b option is specified.

	     2.   If unspecified, the file name used is the first of the old, new and index files
		  that exists.

   Patch Application
     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 cor-
     rect place, patch will scan both forwards and backwards for a set of lines matching the con-
     text 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".	(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 suspi-

   Filename Determination
     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.  When checking a prospective file
     name, pathname components are stripped as specified by the -p option and the file's exis-
     tence and writability are checked relative to the current working directory (or the direc-
     tory specified by the -d option).

     If the diff is a context or unified diff, patch is able to determine the old and new file
     names from the diff header.  For context diffs, the ``old'' file is specified in the line
     beginning with "***" and the ``new'' file is specified in the line beginning with "---".
     For a unified diff, the ``old'' file is specified in the line beginning with "---" and the
     ``new'' file is specified in the line beginning with "+++".  If there is an "Index:" line in
     the leading garbage (regardless of the diff type), patch will use the file name from that
     line as the ``index'' file.

     patch will choose the file name by performing the following steps, with the first match

     1.   If patch is operating in strict IEEE Std 1003.1-2004 (``POSIX.1'') mode, the first of
	  the ``old'', ``new'' and ``index'' file names that exist is used.  Otherwise, patch
	  will examine either the ``old'' and ``new'' file names or, for a non-context diff, the
	  ``index'' file name, and choose the file name with the fewest path components, the
	  shortest basename, and the shortest total file name length (in that order).

     2.   If no file exists, patch checks for the existence of the files in an SCCS or RCS direc-
	  tory (using the appropriate prefix or suffix) using the criteria specified above.  If
	  found, patch will attempt to get or check out the file.

     3.   If no suitable file was found to patch, the patch file is a context or unified diff,
	  and the old file was zero length, the new file name is created and used.

     4.   If the file name still cannot be determined, patch will prompt the user for the file
	  name to use.

     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

	   | patch -d /usr/src/local/blurfl

     and patch a file in the blurfl directory directly from the article containing the patch.

   Backup Files
     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", or as specified by the -B, -V, or -z
     options.  The extension used for making backup files may also be specified in the
     SIMPLE_BACKUP_SUFFIX environment variable, which is overridden by the options above.

     If the backup file is a symbolic or hard link to the original file, 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 or is not linked to the original file.

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

   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

     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.

     POSIXLY_CORRECT	    When set, patch behaves as if the --posix option has been specified.
     SIMPLE_BACKUP_SUFFIX   Extension to use for backup file names instead of ".orig".
     TMPDIR		    Directory to put temporary files in; default is /tmp.
     PATCH_VERSION_CONTROL  Selects when numbered backup files are made.

     $TMPDIR/patch*  patch temporary files
     /dev/tty	     used to read input when patch prompts the user

     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.

     The patch utility exits with one of the following values:

	   0	   Successful completion.
	   1	   One or more lines were written to a reject file.
	   >1	   An error occurred.

     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.


     The patch utility is compliant with the IEEE Std 1003.1-2004 (``POSIX.1'') specification
     (except as detailed above for the --posix option), though the presence of patch itself is

     The flags [-CEfstuvBFVxz] and [--posix] are extensions to that specification.

     Larry Wall with many other contributors.

     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.  How-
     ever, 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.

     Check patch mode (-C) will fail if you try to check several patches in succession that build
     on each other.  The entire patch code would have to be restructured to keep temporary files
     around so that it can handle this situation.

     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.

BSD					 August 18, 2008				      BSD

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