PATCH(1)                                                                                                                              PATCH(1)

NAME

       patch - apply a diff file to an original

SYNOPSIS

       patch [options] [originalfile [patchfile]]

       but usually just

       patch -pnum <patchfile

DESCRIPTION

       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
       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 character).

       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
          master.

        ·> 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.

OPTIONS

       -b  or  --backup
          Make backup files.  That is, when patching  a  file,  rename  or  copy  the  original  instead  of  removing  it.   See  the  -V  or
          --version-control option for details about how backup file names are determined.

       --backup-if-mismatch
          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.

       --no-backup-if-mismatch
          Do not back up a file if the patch does not match the file exactly 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
          /junk/src/patch/util.c.

       --binary
          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 else.

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

       --dry-run
          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 directories.

       -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 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.

       --help
          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
              =======
              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
          Ignore patches that seem to be reversed or already applied.  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
          was

             /u/howard/src/blurfl/blurfl.c

          setting -p0 gives the entire file name 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.  Whatever you end up with is looked for either in the  current  directory,  or
          the directory specified by the -d option.

       --posix
          Conform more strictly to the POSIX standard, as follows.

           ·> 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.

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

          literal
                 Output names as-is.

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

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

          c      Quote names as for a C language string.

          escape 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 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.)

       --reject-format=format
          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.

       -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, assuming that the context
          diff headers use local time.  This option 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.  Instead of using this option, 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.

       -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 accepted):

          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 otherwise.

          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.

       --verbose
          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 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, assuming 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' times.

ENVIRONMENT

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

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

       QUOTING_STYLE
          Default value of the --quoting-style option.

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

       TMPDIR, TMP, TEMP
          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.

       VERSION_CONTROL or PATCH_VERSION_CONTROL
          Selects version control style; see the -v or --version-control option.

FILES

       $TMPDIR/p*
          temporary files

       /dev/tty
          controlling terminal; used to get answers to questions asked of the user

SEE ALSO

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

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

NOTES FOR PATCH SENDERS

       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:

          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: configure.in 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

       Diagnostics generally indicate that patch couldn't parse your patch file.

       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.

CAVEATS

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

COMPATIBILITY ISSUES

       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
          variable.

          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 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.

             -c
             -d dir
             -D define
             -e
             -l
             -n
             -N
             -o outfile
             -pnum
             -R
             -r rejectfile

BUGS

       Please report bugs via email to <bug-patch@gnu.org>.

       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 down.

COPYING

       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.

AUTHORS

       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 Grünbacher added support for merging.

                                                                      GNU                                                             PATCH(1)
 

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