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patch - apply a diff file to an original

 

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*
        diff(1)
        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)
 

Sections

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FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.