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PROLOG

       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 .