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NAME    [Toc]    [Back]

     patch - apply a diff file to an original

SYNOPSIS    [Toc]    [Back]

     patch [options] [origfile [patchfile]]
     patch <patchfile

DESCRIPTION    [Toc]    [Back]

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

     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, newstyle,
 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

     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
             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 but
that will
             change in a future release.

     -B, --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.

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

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

     -d, --directory
             Causes patch to interpret the next argument as a directory, and
             cd(1) to it before doing anything else.

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

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

     -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.

     -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.

     -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, --input
             Causes the next argument to be  interpreted  as  the
input file name
             (i.e.  a  patchfile).   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

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

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

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

     -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 -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

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

     -R, --reverse
             Tells patch that this patch was created with the old
and new
             files  swapped.   (Yes,  I'm afraid that does happen
             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

             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

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

     -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.

     -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, --version-control
             Causes the next argument  to  be  interpreted  as  a
method for creating
 backup file names.  The type of backups made can
also be given
             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
             ``version-control''  variable;  they  also recognize
synonyms that
             are more descriptive.  The valid values are  (unique
             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.

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

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

             Enables strict IEEE Std 1003.2 (``POSIX.2'') 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    [Toc]    [Back]
     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".   (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
     patch thinks the failed hunks belong in the new file  rather
than the old

     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.

   Filename Determination    [Toc]    [Back]
     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  existence  and
     are  checked  relative  to the current working directory (or
the directory
     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 used:

     1.    If  patch  is  operating  in  strict  IEEE  Std 1003.2
(``POSIX.2'') 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

     2.    If  no  file exists, patch checks for the existence of
the files in an
          SCCS or RCS directory (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 following:

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

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

   Backup Files    [Toc]    [Back]
     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

     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    [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

     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.

ENVIRONMENT    [Toc]    [Back]

     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
     TMPDIR                  Directory to put temporary files in;
default is
     PATCH_VERSION_CONTROL  Selects when  numbered  backup  files
are made.

FILES    [Toc]    [Back]

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

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.

     The patch utility exits with one of the following values:

           0       Successful completion.
           1        One  or  more  lines were written to a reject
           >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.

SEE ALSO    [Toc]    [Back]


AUTHORS    [Toc]    [Back]

     Larry Wall with many other contributors.

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
     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.

     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

     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.

OpenBSD     3.6                           July      23,      2003
[ Back ]
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