The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


patch - apply changes to files


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


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

The patch utility attempts to determine the type of the diff listing, unless overruled by a -c, -e or -n option.

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


The patch utility supports the XBD specification, Utility Syntax Guidelines  .

The following options are supported:

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 will be overwritten; if multiple patches are applied to the same file, the .orig file will be written only for the first patch. When the -o outfile option is also specified, file.orig will not be created but, if outfile already exists, outfile.orig will be created.
Interpret the patch file as a 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 the C preprocessor construct:

#ifdef define

The option-argument define will be used as the differentiating symbol.
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.
(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 will be matched exactly.
Interpret the script as a normal difference.
Ignore patches where the differences have already been applied to the file; by default, already-applied patches are 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 will be applied to the intermediate versions of the file created by any previous patches, and will 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 slashes are considered the first component (that is, -p 1 removes the leading slashes). Specifying -p 0 causes the full pathname to be used. If -p is not specified, only the basename (the final pathname component) is used.
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 attempts to reverse each portion of the script before applying it. Rejected differences will 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 will be prompted to determine if the -R option should be set.
-r rejectfile
Override the default reject filename. In the default case, the reject file will have the same name as the output file, with the suffix .rej appended to it. See Patch Application .


The following operand is supported:
A pathname of a file to patch.


See the INPUT FILES section.


Input files must be text files.


The following environment variables affect the execution of patch:
Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
If set to a non-empty string value, override the values of all the other internationalisation variables.
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- as opposed to multi-byte characters in arguments and input files).
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informative messages written to standard output.
Determine the location of message catalogues for the processing of LC_MESSAGES .
Determine the locale for recognising the format of file timestamps written by the diff utility in a context-difference input file.




Not used.


Used for diagnostic and informational messages.


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


A patchfile may contain patching instructions for more than one file; filenames are determined as specified in Filename Determination . When the -b option is specified, for each patched file, the original will 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 will be formed by appending the suffix .rej to the original filename.

 Patchfile Format
The patch file must contain zero or more lines of header information followed by one or more patches. Each patch must contain zero or more lines of filename identification in the format produced by diff -c, and one or more sets of diff output, which are customarily called hunks.

The patch utility recognises 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 will remove this sequence before proceeding. Within each patch, if the type of difference is context, the patch utility recognises the following expressions:

*** filename timestamp
The patches arose from filename.
--- filename timestamp
The patches should be applied to filename.

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

 Filename Determination
If no file operand is specified, patch performs the following steps to obtain a pathname:

  1. If the patch contains the strings *** and ---, the patch utility strips components from the beginning of each pathname (depending on the presence or value of the -p option), then tests for the existence of both files in the current directory (or directory specified with the -d option). If both files exist, patch assumes that no pathname can be obtained from this step.

  2. If the header information contains a line with the string Index:, patch utility strips components from the beginning of the pathname (depending on -p), then tests for the existence of this file in the current directory (or directory specified with the -d option).

  3. If an SCCS directory exists in the current directory, patch will attempt to perform a get -e SCCS/s.filename command to retrieve an editable version of the file.

  4. If no pathname can be obtained by applying the previous steps, or if the pathnames obtained do not exist, patch will write a prompt to standard output and request a filename interactively from standard input.

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

For each hunk, the patch utility begins 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 scans 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 will take place, ignoring the first and last line of context. If that fails, the first two and last two lines of context will be ignored and another scan will be made. Implementations may search more extensively for installation locations.

If no location can be found, the patch utility will append the hunk to the reject file. The rejected hunk will be written in context-difference format regardless of the format of the patch file. 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 will 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.


The following exit values are returned:
Successful completion.
One or more lines were written to a reject file.
An error occurred.


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


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

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


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


without the leading slash, -p 4 gives:


and not specifying -p at all gives:

blurfl.c .

When using -b 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 will overwrite the new file.




The IEEE PASC 1003.2 Interpretations Committee has forwarded concerns about parts of this interface definition to the IEEE PASC Shell and Utilities Working Group which is identifying the corrections. A future revision of this specification will align with IEEE Std. 1003.2b when finalised.


ed, diff.

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Copyright © 1997 The Open Group
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