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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       patch — apply changes to files

SYNOPSIS

       patch [−blNR] [−c|−e|−n|−u] [−d dir] [−D define] [−i patchfile]
           [−o outfile] [−p num] [−r rejectfile] [file]

DESCRIPTION

       The  patch  utility  shall  read  a  source  (patch)  file containing any of four forms of
       difference (diff) listings produced by the diff utility (normal, copied  context,  unified
       context,  or  in the style of ed) and apply those differences to a file. By default, patch
       shall read from the standard input.

       The patch utility shall attempt  to  determine  the  type  of  the  diff  listing,  unless
       overruled by a −c, −e, −n, or −u option.

       If  the patch file contains more than one patch, patch shall attempt to apply each of them
       as if they came from separate patch files. (In this case,  the  application  shall  ensure
       that the name of the patch file is determinable for each diff listing.)

OPTIONS

The patch utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section
12.2, Utility Syntax Guidelines.

The following options shall be supported:

−b Save a copy of the original contents of each modified file, before the
differences are applied, in a file of the same name with the suffix .orig
appended to it. If the file already exists, it shall be overwritten; if multiple
patches are applied to the same file, the .orig file shall be written only for
the first patch. When the −o outfile option is also specified, file.orig shall
not be created but, if outfile already exists, outfile.orig shall be created.

−c Interpret the patch file as a copied context difference (the output of the
utility diff when the −c or −C options are specified).

−d dir Change the current directory to dir before processing as described in the
EXTENDED DESCRIPTION section.

−D define Mark changes with one of the following C preprocessor constructs:

#ifdef define
...
#endif

#ifndef define
...
#endif

optionally combined with the C preprocessor construct #else. If the patched
file is processed with the C preprocessor, where the macro define is defined,
the output shall contain the changes from the patch file; otherwise, the output
shall not contain the patches specified in the patch file.

−e Interpret the patch file as an ed script, rather than a diff script.

−i patchfile
Read the patch information from the file named by the pathname patchfile, rather
than the standard input.

−l (The letter ell.) Cause any sequence of <blank> characters in the difference
script to match any sequence of <blank> characters in the input file. Other
characters shall be matched exactly.

−n Interpret the script as a normal difference.

−N Ignore patches where the differences have already been applied to the file; by
default, already-applied patches shall be rejected.

−o outfile
Instead of modifying the files (specified by the file operand or the difference
listings) directly, write a copy of the file referenced by each patch, with the
appropriate differences applied, to outfile. Multiple patches for a single file
shall be applied to the intermediate versions of the file created by any
previous patches, and shall result in multiple, concatenated versions of the
file being written to outfile.

−p num For all pathnames in the patch file that indicate the names of files to be
patched, delete num pathname components from the beginning of each pathname. If
the pathname in the patch file is absolute, any leading <slash> characters shall
be considered the first component (that is, −p 1 shall remove the leading
<slash> characters). Specifying −p 0 shall cause the full pathname to be used.
If −p is not specified, only the basename (the final pathname component) shall
be used.

−R Reverse the sense of the patch script; that is, assume that the difference
script was created from the new version to the old version. The −R option
cannot be used with ed scripts. The patch utility shall attempt to reverse each
portion of the script before applying it. Rejected differences shall be saved in
swapped format. If this option is not specified, and until a portion of the
patch file is successfully applied, patch attempts to apply each portion in its
reversed sense as well as in its normal sense. If the attempt is successful, the
user shall be prompted to determine whether the −R option should be set.

−r rejectfile
Override the default reject filename. In the default case, the reject file shall
have the same name as the output file, with the suffix .rej appended to it; see
Patch Application.

−u Interpret the patch file as a unified context difference (the output of the diff
utility when the −u or −U options are specified).

OPERANDS

       The following operand shall be supported:

       file      A pathname of a file to patch.

STDIN

       See the INPUT FILES section.

INPUT FILES

       Input files shall be text files.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of patch:

       LANG      Provide a default value for the internationalization variables that are unset or
                 null.  (See  the  Base  Definitions  volume  of   POSIX.1‐2008,   Section   8.2,
                 Internationalization  Variables the precedence of internationalization variables
                 used to determine the values of locale categories.)

       LC_ALL    If set to a non-empty string  value,  override  the  values  of  all  the  other
                 internationalization variables.

       LC_COLLATE
                 Determine the locale for the behavior of ranges, equivalence classes, and multi-
                 character collating elements used in the extended regular expression defined for
                 the yesexpr locale keyword in the LC_MESSAGES category.

       LC_CTYPE  Determine  the  locale for the interpretation of sequences of bytes of text data
                 as characters (for example, single-byte as opposed to multi-byte  characters  in
                 arguments  and  input  files), and the behavior of character classes used in the
                 extended regular expression defined  for  the  yesexpr  locale  keyword  in  the
                 LC_MESSAGES category.

       LC_MESSAGES
                 Determine  the locale used to process affirmative responses, and the locale used
                 to affect the format and contents of diagnostic messages and prompts written  to
                 standard error.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

       LC_TIME   Determine  the  locale  for recognizing the format of file timestamps written by
                 the diff utility in a context-difference input file.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used for diagnostic and informational messages.

OUTPUT FILES

       The output of the patch utility, the save files (.orig suffixes),  and  the  reject  files
       (.rej suffixes) shall be text files.

EXTENDED DESCRIPTION

A patch file may contain patching instructions for more than one file; filenames shall be
determined as specified in Filename Determination. When the −b option is specified, for
each patched file, the original shall be saved in a file of the same name with the suffix
.orig appended to it.

For each patched file, a reject file may also be created as noted in Patch Application.
In the absence of a −r option, the name of this file shall be formed by appending the
suffix .rej to the original filename.

Patch File Format
The patch file shall contain zero or more lines of header information followed by one or
more patches. Each patch shall contain zero or more lines of filename identification in
the format produced by the −c, −C, −u, or −U options of the diff utility, and one or more
sets of diff output, which are customarily called hunks.

The patch utility shall recognize the following expression in the header information:

Index: pathname
The file to be patched is named pathname.

If all lines (including headers) within a patch begin with the same leading sequence of
<blank> characters, the patch utility shall remove this sequence before proceeding. Within
each patch, if the type of difference is common context, the patch utility shall recognize
the following expressions:

*** filename timestamp
The patches arose from filename.

−−− filename timestamp
The patches should be applied to filename.

If the type of difference is unified context, the patch utility shall recognize the
following expressions:

−−− filename timestamp
The patches arose from filename.

+++ filename timestamp
The patches should be applied to filename.

Each hunk within a patch shall be the diff output to change a line range within the
original file. The line numbers for successive hunks within a patch shall occur in
ascending order.

Filename Determination
If no file operand is specified, patch shall perform the following steps to determine the
filename to use:

1. If the type of diff is context, the patch utility shall delete pathname components (as
specified by the −p option) from the filename on the line beginning with "***" (if
copied context) or "−−−" (if unified context), then test for the existence of this
file relative to the current directory (or the directory specified with the −d
option). If the file exists, the patch utility shall use this filename.

2. If the type of diff is context, the patch utility shall delete the pathname components
(as specified by the −p option) from the filename on the line beginning with "−−−" (if
copied context) or "+++" (if unified context), then test for the existence of this
file relative to the current directory (or the directory specified with the −d
option). If the file exists, the patch utility shall use this filename.

3. If the header information contains a line beginning with the string Index:, the patch
utility shall delete pathname components (as specified by the −p option) from this
line, then test for the existence of this file relative to the current directory (or
the directory specified with the −d option). If the file exists, the patch utility
shall use this filename.

4. If an SCCS directory exists in the current directory, patch shall attempt to perform a
get −e SCCS/s.filename command to retrieve an editable version of the file. If the
file exists, the patch utility shall use this filename.

5. The patch utility shall write a prompt to standard output and request a filename
interactively from the controlling terminal (for example, /dev/tty).

Patch Application
If the −c, −e, −n, or −u option is present, the patch utility shall interpret information
within each hunk as a copied context difference, an ed difference, a normal difference, or
a unified context difference, respectively. In the absence of any of these options, the
patch utility shall determine the type of difference based on the format of information
within the hunk.

For each hunk, the patch utility shall begin to search for the place to apply the patch at
the line number at the beginning of the hunk, plus or minus any offset used in applying
the previous hunk. If lines matching the hunk context are not found, patch shall scan both
forwards and backwards at least 1000 bytes for a set of lines that match the hunk context.

If no such place is found and it is a context difference, then another scan shall take
place, ignoring the first and last line of context. If that fails, the first two and last
two lines of context shall be ignored and another scan shall be made. Implementations may
search more extensively for installation locations.

If no location can be found, the patch utility shall append the hunk to the reject file. A
rejected hunk that is a copied context difference, an ed difference, or a normal
difference shall be written in copied-context-difference format regardless of the format
of the patch file. It is implementation-defined whether a rejected hunk that is a unified
context difference is written in copied-context-difference format or in unified-context-
difference format. If the input was a normal or ed-style difference, the reject file may
contain differences with zero lines of context. The line numbers on the hunks in the
reject file may be different from the line numbers in the patch file since they shall
reflect the approximate locations for the failed hunks in the new file rather than the old
one.

If the type of patch is an ed diff, the implementation may accomplish the patching by
invoking the ed utility.

EXIT STATUS

       The following exit values shall be returned:

        0    Successful completion.

        1    One or more lines were written to a reject file.

       >1    An error occurred.

CONSEQUENCES OF ERRORS

       Patches that cannot be correctly placed in the file shall be written to a reject file.

       The following sections are informative.

APPLICATION USAGE

       The  −R  option  does  not work with ed scripts because there is too little information to
       reconstruct the reverse operation.

       The −p option makes it possible  to  customize  a  patch  file  to  local  user  directory
       structures  without  manually  editing the patch file. For example, if the filename in the
       patch file was:

           /curds/whey/src/blurfl/blurfl.c

       Setting −p 0 gives the entire pathname unmodified; −p 1 gives:

           curds/whey/src/blurfl/blurfl.c

       without the leading <slash>, −p 4 gives:

           blurfl/blurfl.c

       and not specifying −p at all gives:

           blurfl.c .

EXAMPLES

       None.

RATIONALE

Some of the functionality in historical patch implementations was not specified. The
following documents those features present in historical implementations that have not
been specified.

A deleted piece of functionality was the '+' pseudo-option allowing an additional set of
options and a patch file operand to be given. This was seen as being insufficiently useful
to standardize.

In historical implementations, if the string "Prereq:" appeared in the header, the patch
utility would search for the corresponding version information (the string specified in
the header, delimited by <blank> characters or the beginning or end of a line or the file)
anywhere in the original file. This was deleted as too simplistic and insufficiently
trustworthy a mechanism to standardize. For example, if:

Prereq: 1.2

were in the header, the presence of a delimited 1.2 anywhere in the file would satisfy the
prerequisite.

The following options were dropped from historical implementations of patch as
insufficiently useful to standardize:

−b The −b option historically provided a method for changing the name extension of
the backup file from the default .orig. This option has been modified and
retained in this volume of POSIX.1‐2008.

−F The −F option specified the number of lines of a context diff to ignore when
searching for a place to install a patch.

−f The −f option historically caused patch not to request additional information
from the user.

−r The −r option historically provided a method of overriding the extension of the
reject file from the default .rej.

−s The −s option historically caused patch to work silently unless an error
occurred.

−x The −x option historically set internal debugging flags.

In some file system implementations, the saving of a .orig file may produce unwanted
results. In the case of 12, 13, or 14-character filenames (on file systems supporting
14-character maximum filenames), the .orig file overwrites the new file. The reject file
may also exceed this filename limit. It was suggested, due to some historical practice,
that a <tilde> ('~') suffix be used instead of .orig and some other character instead of
the .rej suffix. This was rejected because it is not obvious to the user which file is
which. The suffixes .orig and .rej are clearer and more understandable.

The −b option has the opposite sense in some historical implementations—do not save the
.orig file. The default case here is not to save the files, making patch behave more
consistently with the other standard utilities.

The −w option in early proposals was changed to −l to match historical practice.

The −N option was included because without it, a non-interactive application cannot reject
previously applied patches. For example, if a user is piping the output of diff into the
patch utility, and the user only wants to patch a file to a newer version non-
interactively, the −N option is required.

Changes to the −l option description were proposed to allow matching across <newline>
characters in addition to just <blank> characters. Since this is not historical practice,
and since some ambiguities could result, it is suggested that future developments in this
area utilize another option letter, such as −L.

The −u option of GNU patch has been added, along with support for unified context formats.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  In  the  event of any
       discrepancy between this version and the original IEEE and The Open  Group  Standard,  the
       original  IEEE  and The Open Group Standard is the referee document. The original Standard
       can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .