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 PATCH(1)                            GNU                            PATCH(1)

      patch - apply a diff file to an original

      patch [options] [originalfile [patchfile]]

      but usually just

      patch -pnum <patchfile

      patch takes a patch file patchfile containing a difference listing
      produced by the diff program and applies those differences to one or
      more original files, producing patched versions.  Normally the patched
      versions are put in place of the originals.  Backups can be made; see
      the -b or --backup option.  The names of the files to be patched are
      usually taken from the patch file, but if there's just one file to be
      patched it can be specified on the command line as originalfile.

      Upon startup, patch attempts to determine the type of the diff
      listing, unless overruled by a -c (--context), -e (--ed), -n
      (--normal), 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(1) editor via a pipe.

      patch tries 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, if lines end in CRLF, or if a
      diff is encapsulated one or more times by prepending "- " to lines
      starting with "-" as specified by Internet RFC 934, this is taken into
      account.  After removing indenting or encapsulation, lines beginning
      with # are ignored, as they are considered to be comments.

      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 attempts 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 scans 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.)

      Hunks with less prefix context than suffix context (after applying
      fuzz) must apply at the start of the file if their first line number

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 PATCH(1)                            GNU                            PATCH(1)

      is 1.  Hunks with more prefix context than suffix context (after
      applying fuzz) must apply at the end of the file.

      If patch cannot find a place to install that hunk of the patch, it
      puts the hunk out to a reject file, which normally is the name of the
      output file plus a .rej suffix, or # if .rej would generate a file
      name that is too long (if even appending the single character # makes
      the file name too long, then # replaces the file name's last

      The rejected hunk comes out in unified or context diff format.  If the
      input was a normal diff, many of the contexts are simply 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 are told if the hunk failed, and if so
      which line (in the new file) patch thought the hunk should go on.  If
      the hunk is installed at a different line from the line number
      specified in the diff, you are told the offset.  A single large offset
      may indicate that a hunk was installed in the wrong place.  You are
      also told if a fuzz factor was used to make the match, in which case
      you should also be slightly suspicious.  If the --verbose option is
      given, you are also told about hunks that match exactly.

      If no original file origfile is specified on the command line, patch
      tries to figure out from the leading garbage what the name of the file
      to edit is, using the following rules.  First, patch takes an ordered
      list of candidate file names as follows:

       + If the header is that of a context diff, patch takes the old and
         new file names in the header.  A name is ignored if it does not
         have enough slashes to satisfy the -pnum or --strip=num option.
         The name /dev/null is also ignored.

       + If there is an Index: line in the leading garbage and if either the
         old and new names are both absent or if patch is conforming to
         POSIX, patch takes the name in the Index: line.

       + For the purpose of the following rules, the candidate file names
         are considered to be in the order (old, new, index), regardless of
         the order that they appear in the header.  Then patch selects a
         file name from the candidate list as follows:

       + If some of the named files exist, patch selects the first name if
         conforming to POSIX, and the best name otherwise.

       + If patch is not ignoring RCS, ClearCase, Perforce, and SCCS (see
         the -g num or --get=num option), and no named files exist but an
         RCS, ClearCase, Perforce, or SCCS master is found, patch selects
         the first named file with an RCS, ClearCase, Perforce, or SCCS

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 PATCH(1)                            GNU                            PATCH(1)


       + If no named files exist, no RCS, ClearCase, Perforce, or SCCS
         master was found, some names are given, patch is not conforming to
         POSIX, and the patch appears to create a file, patch selects the
         best name requiring the creation of the fewest directories.

       + If no file name results from the above heuristics, you are asked
         for the name of the file to patch, and patch selects that name.  To
         determine the best of a nonempty list of file names, patch first
         takes all the names with the fewest path name components; of those,
         it then takes all the names with the shortest basename; of those,
         it then takes all the shortest names; finally, it takes the first
         remaining name.

      Additionally, if the leading garbage contains a Prereq: line, patch
      takes the first word from the prerequisites line (normally a version
      number) and checks the original file to see if that word can be found.
      If not, patch asks for confirmation before proceeding.

      The upshot of all this is that you should be able to say, while in a
      news interface, something like 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 tries 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 contains interesting things such as file
      names and revision level, as mentioned previously.

      -b  or  --backup
         Make backup files.  That is, when patching a file, rename or copy
         the original instead of removing it.  When backing up a file that
         does not exist, an empty, unreadable backup file is created as a
         placeholder to represent the nonexistent file.  See the -V or
         --version-control option for details about how backup file names
         are determined.

         Back up a file if the patch does not match the file exactly and if
         backups are not otherwise requested.  This is the default unless
         patch is conforming to POSIX.

         Do not back up a file if the patch does not match the file exactly

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 PATCH(1)                            GNU                            PATCH(1)

         and if backups are not otherwise requested.  This is the default if
         patch is conforming to POSIX.

      -B pref  or  --prefix=pref
         Use the simple method to determine backup file names (see the -V
         method or --version-control method option), and append pref to a
         file name when generating its backup file name.  For example, with
         -B /junk/ the simple backup file name for src/patch/util.c is

         Write all files in binary mode, except for standard output and
         /dev/tty.  When reading, disable the heuristic for transforming
         CRLF line endings into LF line endings.  This option is needed on
         POSIX systems when applying patches generated on non-POSIX systems
         to non-POSIX files.  (On POSIX systems, file reads and writes never
         transform line endings. On Windows, reads and writes do transform
         line endings by default, and patches should be generated by
         diff --binary when line endings are significant.)

      -c  or  --context
         Interpret the patch file as a ordinary context diff.

      -d dir  or  --directory=dir
         Change to the directory dir immediately, before doing anything

      -D define  or  --ifdef=define
         Use the #ifdef ... #endif construct to mark changes, with define as
         the differentiating symbol.

         Print the results of applying the patches without actually changing
         any files.

      -e  or  --ed
         Interpret the patch file as an ed script.

      -E  or  --remove-empty-files
         Remove output files that are empty after the patches have been
         applied.  Normally this option is unnecessary, since patch can
         examine the time stamps on the header to determine whether a file
         should exist after patching.  However, if the input is not a
         context diff or if patch is conforming to POSIX, patch does not
         remove empty patched files unless this option is given.  When patch
         removes a file, it also attempts to remove any empty ancestor

      -f  or  --force
         Assume that the user knows exactly what he or she is doing, and do
         not ask any questions.  Skip patches whose headers do not say which

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 PATCH(1)                            GNU                            PATCH(1)

         file is to be patched; 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 num  or  --fuzz=num
         Set the maximum fuzz factor.  This option only applies to diffs
         that have context, and causes patch to ignore up to that many lines
         of context 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.  A fuzz factor greater than or equal to
         the number of lines of context in the context diff, ordinarily 3,
         ignores all context.

      -g num  or  --get=num
         This option controls patch's actions when a file is under RCS or
         SCCS control, and does not exist or is read-only and matches the
         default version, or when a file is under ClearCase or Perforce
         control and does not exist.  If num is positive, patch gets (or
         checks out) the file from the revision control system; if zero,
         patch ignores RCS, ClearCase, Perforce, and SCCS and does not get
         the file; and if negative, patch asks the user whether to get the
         file.  The default value of this option is given by the value of
         the PATCH_GET environment variable if it is set; if not, the
         default value is zero.

         Print a summary of options and exit.

      -i patchfile  or  --input=patchfile
         Read the patch from patchfile.  If patchfile is -, read from
         standard input, the default.

      -l  or  --ignore-whitespace
         Match patterns loosely, in case tabs or spaces have been munged in
         your files.  Any sequence of one or more blanks in the patch file
         matches any sequence in the original file, and sequences of blanks
         at the ends of lines are ignored.  Normal characters must still
         match exactly.  Each line of the context must still match a line in
         the original file.

      --merge or --merge=merge or --merge=diff3
         Merge a patch file into the original files similar to diff3(1) or
         merge(1).  If a conflict is found, patch outputs a warning and
         brackets the conflict with <<<<<<< and >>>>>>> lines.  A typical
         conflict will look like this:
         lines from the original file
         original lines from the patch

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 PATCH(1)                            GNU                            PATCH(1)

         new lines from the patch

         The optional argument of --merge determines the output format for
         conflicts: the diff3 format shows the ||||||| section with the
         original lines from the patch; in the merge format, this section is
         missing.  The merge format is the default.

         This option implies --forward and does not take the --fuzz=num
         option into account.

      -n  or  --normal
         Interpret the patch file as a normal diff.

      -N  or  --forward
         When a patch does not apply, patch usually checks if the patch
         looks like it has been applied already by trying to reverse-apply
         the first hunk.  The --forward option prevents that.  See also -R.

      -o outfile  or  --output=outfile
         Send output to outfile instead of patching files in place.  Do not
         use this option if outfile is one of the files to be patched.  When
         outfile is -, send output to standard output, and send any messages
         that would usually go to standard output to standard error.

      -pnum  or  --strip=num
         Strip the smallest prefix containing num leading slashes from each
         file name found in the patch file.  A sequence of one or more
         adjacent slashes is counted as a single slash.  This controls how
         file names 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.  For example, supposing the file name in the patch file


      setting -p0 gives the entire file name unmodified, -p1 gives


      without the leading slash, -p4 gives


      and not specifying -p at all just gives you blurfl.c.  Whatever you
      end up with is looked for either in the current directory, or the
      directory specified by the -d option.

         Conform more strictly to the POSIX standard, as follows.

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 PATCH(1)                            GNU                            PATCH(1)

          + Take the first existing file from the list (old, new, index)
            when intuiting file names from diff headers.

          + Do not remove files that are empty after patching.

          + Do not ask whether to get files from RCS, ClearCase, Perforce,
            or SCCS.

          + Require that all options precede the files in the command line.

          + Do not backup files when there is a mismatch.

         Use style word to quote output names.  The word should be one of
         the following:

              Output names as-is.

              Quote names for the shell if they contain shell metacharacters
              or would cause ambiguous output.

              Quote names for the shell, even if they would normally not
              require quoting.

         c    Quote names as for a C language string.

              Quote as with c except omit the surrounding double-quote
              characters.  You can specify the default value of the
              --quoting-style option with the environment variable
              QUOTING_STYLE.  If that environment variable is not set, the
              default value is shell.

      -r rejectfile  or  --reject-file=rejectfile
         Put rejects into rejectfile instead of the default .rej file.  When
         rejectfile is -, discard rejects.

      -R  or  --reverse
         Assume 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 attempts to swap each hunk around
         before applying it.  Rejects come out in the swapped format.  The
         -R option does 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 reverses the hunk to see
         if it can be applied that way.  If it can, you are asked if you
         want to have the -R option set.  If it can't, the patch continues

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 PATCH(1)                            GNU                            PATCH(1)

         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 matches anywhere.
         Luckily, most patches add or change lines rather than delete them,
         so most reversed normal diffs begin with a delete, which fails,
         triggering the heuristic.)

         Behave as requested when trying to modify a read-only file: ignore
         the potential problem, warn about it (the default), or fail.

         Produce reject files in the specified format (either context or
         unified).  Without this option, rejected hunks come out in unified
         diff format if the input patch was of that format, otherwise in
         ordinary context diff form.

      -s  or  --silent  or  --quiet
         Work silently, unless an error occurs.

         When looking for input files, follow symbolic links.  Replaces the
         symbolic links, instead of modifying the files the symbolic links
         point to.  Git-style patches to symbolic links will no longer
         apply.  This option exists for backwards compatibility with
         previous versions of patch; its use is discouraged.

      -t  or  --batch
         Suppress questions like -f, but make some different assumptions:
         skip patches whose headers do not contain file names (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.

      -T  or  --set-time
         Set the modification and access times of patched files from time
         stamps given in context diff headers.  Unless specified in the time
         stamps, assume that the context diff headers use local time.

         Use of this option with time stamps that do not include time zones
         is not recommended, because patches using local time cannot easily
         be used by people in other time zones, and because local time
         stamps are ambiguous when local clocks move backwards during
         daylight-saving time adjustments.  Make sure that time stamps
         include time zones, or generate patches with UTC and use the -Z or
         --set-utc option instead.

      -u  or  --unified
         Interpret the patch file as a unified context diff.

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 PATCH(1)                            GNU                            PATCH(1)

      -v  or  --version
         Print out patch's revision header and patch level, and exit.

      -V method  or  --version-control=method
         Use method to determine backup file names.  The method can also be
         given by the PATCH_VERSION_CONTROL (or, if that's not set, the
         VERSION_CONTROL) environment variable, which is overridden by this
         option.  The method does not affect whether backup files are made;
         it affects only the names of any backup files that are made.

         The value of method is like the GNU Emacs `version-control'
         variable; patch also recognizes synonyms that are more descriptive.
         The valid values for method are (unique abbreviations are

         existing  or  nil
            Make numbered backups of files that already have them, otherwise
            simple backups.  This is the default.

         numbered  or  t
            Make numbered backups.  The numbered backup file name for F is
            F.~N~ where N is the version number.

         simple  or  never
            Make simple backups.  The -B or --prefix, -Y or
            --basename-prefix, and -z or --suffix options specify the simple
            backup file name.  If none of these options are given, then a
            simple backup suffix is used; it is the value of the
            SIMPLE_BACKUP_SUFFIX environment variable if set, and is .orig

         With numbered or simple backups, if the backup file name is too
         long, the backup suffix ~ is used instead; if even appending ~
         would make the name too long, then ~ replaces the last character of
         the file name.

         Output extra information about the work being done.

      -x num  or  --debug=num
         Set internal debugging flags of interest only to patch patchers.

      -Y pref  or  --basename-prefix=pref
         Use the simple method to determine backup file names (see the -V
         method or --version-control method option), and prefix pref to the
         basename of a file name when generating its backup file name.  For
         example, with -Y .del/ the simple backup file name for
         src/patch/util.c is src/patch/.del/util.c.

      -z suffix  or  --suffix=suffix
         Use the simple method to determine backup file names (see the -V

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 PATCH(1)                            GNU                            PATCH(1)

         method or --version-control method option), and use suffix as the
         suffix.  For example, with -z - the backup file name for
         src/patch/util.c is src/patch/util.c-.

      -Z  or  --set-utc
         Set the modification and access times of patched files from time
         stamps given in context diff headers. Unless specified in the time
         stamps, assume that the context diff headers use Coordinated
         Universal Time (UTC, often known as GMT).  Also see the -T or
         --set-time option.

         The -Z or --set-utc and -T or --set-time options normally refrain
         from setting a file's time if the file's original time does not
         match the time given in the patch header, or if its contents do not
         match the patch exactly.  However, if the -f or --force option is
         given, the file time is set regardless.

         Due to the limitations of diff output format, these options cannot
         update the times of files whose contents have not changed.  Also,
         if you use these options, you should remove (e.g. with make clean)
         all files that depend on the patched files, so that later
         invocations of make do not get confused by the patched files'

         This specifies whether patch gets missing or read-only files from
         RCS, ClearCase, Perforce, or SCCS by default; see the -g or --get

         If set, patch conforms more strictly to the POSIX standard by
         default: see the --posix option.

         Default value of the --quoting-style option.

         Extension to use for simple backup file names instead of .orig.

         Directory to put temporary files in; patch uses the first
         environment variable in this list that is set.  If none are set,
         the default is system-dependent; it is normally /tmp on Unix hosts.

         Selects version control style; see the -v or --version-control


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 PATCH(1)                            GNU                            PATCH(1)

         temporary files

         controlling terminal; used to get answers to questions asked of the

      diff(1), ed(1), merge(1).

      Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message
      Encapsulation, Internet RFC 934 <URL:
      notes/rfc934.txt> (1985-01).

      There are several things you should bear in mind if you are going to
      be sending out patches.

      Create your patch systematically.  A good method is the command
      diff -Naur old new where old and new identify the old and new
      directories.  The names old and new should not contain any slashes.
      The diff command's headers should have dates and times in Universal
      Time using traditional Unix format, so that patch recipients can use
      the -Z or --set-utc option.  Here is an example command, using Bourne
      shell syntax:

           LC_ALL=C TZ=UTC0 diff -Naur gcc-2.7 gcc-2.8

      Tell your recipients how to apply the patch by telling them which
      directory to cd to, and which patch options to use.  The option string
      -Np1 is recommended.  Test your procedure by pretending to be a
      recipient and applying your patch to a copy of the original files.

      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.

      You can create a file by sending out a diff that compares /dev/null or
      an empty file dated the Epoch (1970-01-01 00:00:00 UTC) to the file
      you want to create.  This only works if the file you want to create
      doesn't exist already in the target directory.  Conversely, you can
      remove a file by sending out a context diff that compares the file to
      be deleted with an empty file dated the Epoch.  The file will be
      removed unless patch is conforming to POSIX and the -E or
      --remove-empty-files option is not given.  An easy way to generate
      patches that create and remove files is to use GNU diff's -N or
      --new-file option.

      If the recipient is supposed to use the -pN option, do not send output
      that looks like this:

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 PATCH(1)                            GNU                            PATCH(1)

           diff -Naur v2.0.29/prog/README prog/README
           --- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997
           +++ prog/README   Mon Mar 17 14:58:22 1997

      because the two file names have different numbers of slashes, and
      different versions of patch interpret the file names differently.  To
      avoid confusion, send output that looks like this instead:

           diff -Naur v2.0.29/prog/README v2.0.30/prog/README
           --- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997
           +++ v2.0.30/prog/README   Mon Mar 17 14:58:22 1997

      Avoid sending patches that compare backup file names like README.orig,
      since this might confuse patch into patching a backup file instead of
      the real file.  Instead, send patches that compare the same base file
      names in different directories, e.g. old/README and new/README.

      Take care not to send out reversed patches, since it makes people
      wonder whether they already applied the patch.

      Try not to have your patch modify derived files (e.g. the file
      configure where there is a line configure: in your
      makefile), since the recipient should be able to regenerate the
      derived files anyway.  If you must send diffs of derived files,
      generate the diffs using UTC, have the recipients apply the patch with
      the -Z or --set-utc option, and have them remove any unpatched files
      that depend on patched files (e.g. with make clean).

      While you may be able to get away with putting 582 diff listings into
      one file, it may be wiser to group related patches into separate files
      in case something goes haywire.

      Diagnostics generally indicate that patch couldn't parse your patch

      If the --verbose option is given, 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's exit status is 0 if all hunks are applied successfully, 1 if
      some hunks cannot be applied or there were merge conflicts, and 2 if
      there is more serious trouble.  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.

      Context diffs cannot reliably represent the creation or deletion of
      empty files, empty directories, or special files such as symbolic

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 PATCH(1)                            GNU                            PATCH(1)

      links.  Nor can they represent changes to file metadata like
      ownership, permissions, or whether one file is a hard link to another.
      If changes like these are also required, separate instructions (e.g. a
      shell script) to accomplish them should accompany the patch.

      patch cannot tell if the line numbers are off in an ed script, and can
      detect bad line numbers in a normal diff only when it finds a change
      or deletion.  A context diff using fuzz factor 3 may have the same
      problem.  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.

      The POSIX standard specifies behavior that differs from patch's
      traditional behavior.  You should be aware of these differences if you
      must interoperate with patch versions 2.1 and earlier, which do not
      conform to POSIX.

       + In traditional patch, the -p option's operand was optional, and a
         bare -p was equivalent to -p0.  The -p option now requires an
         operand, and -p 0 is now equivalent to -p0.  For maximum
         compatibility, use options like -p0 and -p1.

         Also, traditional patch simply counted slashes when stripping path
         prefixes; patch now counts pathname components.  That is, a
         sequence of one or more adjacent slashes now counts as a single
         slash.  For maximum portability, avoid sending patches containing
         // in file names.

       + In traditional patch, backups were enabled by default.  This
         behavior is now enabled with the -b or --backup option.

         Conversely, in POSIX patch, backups are never made, even when there
         is a mismatch.  In GNU patch, this behavior is enabled with the
         --no-backup-if-mismatch option, or by conforming to POSIX with the
         --posix option or by setting the POSIXLY_CORRECT environment

         The -b suffix option of traditional patch is equivalent to the
         -b -z suffix options of GNU patch.

       + Traditional patch used a complicated (and incompletely documented)
         method to intuit the name of the file to be patched from the patch
         header.  This method did not conform to POSIX, and had a few
         gotchas.  Now patch uses a different, equally complicated (but
         better documented) method that is optionally POSIX-conforming; we

                                   - 13 -          Formatted:  June 12, 2024

 PATCH(1)                            GNU                            PATCH(1)

         hope it has fewer gotchas.  The two methods are compatible if the
         file names in the context diff header and the Index: line are all
         identical after prefix-stripping.  Your patch is normally
         compatible if each header's file names all contain the same number
         of slashes.

       + When traditional patch asked the user a question, it sent the
         question to standard error and looked for an answer from the first
         file in the following list that was a terminal: standard error,
         standard output, /dev/tty, and standard input.  Now patch sends
         questions to standard output and gets answers from /dev/tty.
         Defaults for some answers have been changed so that patch never
         goes into an infinite loop when using default answers.

       + Traditional patch exited with a status value that counted the
         number of bad hunks, or with status 1 if there was real trouble.
         Now patch exits with status 1 if some hunks failed, or with 2 if
         there was real trouble.

       + Limit yourself to the following options when sending instructions
         meant to be executed by anyone running GNU patch, traditional
         patch, or a patch that conforms to POSIX.  Spaces are significant
         in the following list, and operands are required.

            -d dir
            -D define
            -o outfile
            -r rejectfile

      Please report bugs via email to <>.

      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 thinks it is a
      reversed patch, and offers to un-apply the patch.  This could be
      construed as a feature.

      Computing how to merge a hunk is significantly harder than using the
      standard fuzzy algorithm.  Bigger hunks, more context, a bigger offset
      from the original location, and a worse match all slow the algorithm

                                   - 14 -          Formatted:  June 12, 2024

 PATCH(1)                            GNU                            PATCH(1)


      Copyright (C) 1984, 1985, 1986, 1988 Larry Wall.
      Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
      1998, 1999, 2000, 2001, 2002, 2009 Free Software Foundation, Inc.

      Permission is granted to make and distribute verbatim copies of this
      manual provided the copyright notice and this permission notice are
      preserved on all copies.

      Permission is granted to copy and distribute modified versions of this
      manual under the conditions for verbatim copying, provided that the
      entire resulting derived work is distributed under the terms of a
      permission notice identical to this one.

      Permission is granted to copy and distribute translations of this
      manual into another language, under the above conditions for modified
      versions, except that this permission notice may be included in
      translations approved by the copyright holders instead of in the
      original English.

      Larry Wall wrote the original version of patch.  Paul Eggert removed
      patch's arbitrary limits; added support for binary files, setting file
      times, and deleting files; and made it conform better to POSIX.  Other
      contributors include Wayne Davison, who added unidiff support, and
      David MacKenzie, who added configuration and backup support.  Andreas
      Gr[:u]nbacher added support for merging.

                                   - 15 -          Formatted:  June 12, 2024