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NAME |SYNOPSIS |DESCRIPTION |OPTIONS |ENVIRONMENT |FILES |SEE ALSO |NOTES FOR PATCH SENDERS |DIAGNOSTICS |CAVEATS |COMPATIBILITY ISSUES |BUGS |COPYING |AUTHORS |COLOPHON | |
PATCH(1) General Commands ManualPATCH(1)patch - apply a diff file to an original
patch[options] [originalfile [patchfile]] but usually justpatch -pnum<patchfile
patchtakes a patch filepatchfile containing a difference listing produced by thediffprogram 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-bor--backupoption. 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 asoriginalfile. 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 thepatch program itself, whileeddiffs are simply fed to theed(1) editor via a pipe.patchtries to skip any leading garbage, apply the diff, and then skip any trailing garbage. Thus you could feed an email message containing a diff listing topatch, 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,patchcan 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,patchscans both forwards and backwards for a set of lines matching the context given in the hunk. Firstpatchlooks 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. Ifpatchcannot 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.rejsuffix, or#if.rejwould 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)patchthought 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 offsetmay 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--verboseoption is given, you are also told about hunks that match exactly. If no original fileorigfile is specified on the command line,patchtries to figure out from the leading garbage what the name of the file to edit is, using the following rules. First,patchtakes an ordered list of candidate file names as follows: • If the header is that of a context diff,patchtakes 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/nullis also ignored. • If there is anIndex:line in the leading garbage and if either the old and new names are both absent or ifpatchis conforming to POSIX,patchtakes the name in theIndex: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. Thenpatchselects a file name from the candidate list as follows: • If some of the named files exist,patchselects the first name if conforming to POSIX, and the best name otherwise. • Ifpatchis not ignoring RCS, ClearCase, Perforce, and SCCS (see the-gnum or--get=num option), and no named files exist but an RCS, ClearCase, Perforce, or SCCS master is found,patchselects 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,patchis not conforming to POSIX, and the patch appears to create a file,patchselects 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, andpatchselects that name. To determine thebest 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 aPrereq:line,patchtakes 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,patchasks for confirmation before proceeding. The upshot of all this is that you should be able to run something like the following shell command:patch -d /usr/src/local/blurfl and patch a file in theblurfldirectory directly from a patch that is read from standard input. If the patch file contains more than one patch,patchtries 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.
-bor--backup Make backup files. That is, when patching a file, rename or copy the original instead of removing it. See the-Vor--version-controloption 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 unlesspatchis 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 ifpatchis conforming to POSIX.-Bpref or--prefix=pref Use thesimplemethod to determine backup file names (see the-Vmethod or--version-controlmethod option), and appendpref to a file name when generating its backup file name. For example, with-B /junk/the simple backup file name forsrc/patch/util.cis/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 bydiff --binarywhen line endings are significant.)-cor--context Interpret the patch file as a ordinary context diff.-ddir or--directory=dir Change to the directorydir immediately, before doing anything else.-Ddefine or--ifdef=define Use the#ifdef...#endifconstruct to mark changes, withdefine as the differentiating symbol.--dry-run Print the results of applying the patches without actually changing any files.-eor--ed Interpret the patch file as anedscript.-Eor--remove-empty-files Remove output files that are empty after the patches have been applied. Normally this option is unnecessary, sincepatchcan examine the timestamps on the header to determine whether a file should exist after patching. However, if the input is not a context diff or ifpatchis conforming to POSIX,patchdoes not remove empty patched files unless this option is given. Whenpatchremoves a file, it also attempts to remove any empty ancestor directories.-for--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 thePrereq: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-sfor that.-Fnum or--fuzz=num Set the maximum fuzz factor. This option only applies to diffs that have context, and causespatchto 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.-gnum or--get=num This option controlspatch'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. Ifnum is positive,patch gets (or checks out) the file from the revision control system; if zero,patchignores RCS, ClearCase, Perforce, and SCCS and does not get the file; and if negative,patchasks the user whether to get the file. The default value of this option is given by the value of thePATCH_GETenvironment variable if it is set; if not, the default value is zero.--help Print a summary of options and exit.-ipatchfile or--input=patchfile Read the patch frompatchfile. Ifpatchfile is-, read from standard input, the default.-lor--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.--mergeor--merge=mergeor--merge=diff3 Merge a patch file into the original files similar todiff3(1) ormerge(1). If a conflict is found,patchoutputs 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--mergedetermines 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--forwardand does not take the--fuzz=num option into account.-nor--normal Interpret the patch file as a normal diff.-Nor--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--forwardoption prevents that. See also-R.-ooutfile or--output=outfile Send output tooutfile instead of patching files in place. Do not use this option ifoutfile is one of the files to be patched. Whenoutfile 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 containingnum 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-p0gives the entire file name unmodified,-p1givesu/howard/src/blurfl/blurfl.c without the leading slash,-p4givesblurfl/blurfl.c and not specifying-pat all just gives youblurfl.c. Whatever you end up with is looked for either in the current directory, or the directory specified by the-doption.--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 styleword to quote output names. Theword should be one of the following:literal Output names as-is.shellQuote 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.cQuote names as for a C language string.escapeQuote as withcexcept omit the surrounding double-quote characters. You can specify the default value of the--quoting-styleoption with the environment variableQUOTING_STYLE. If that environment variable is not set, the default value isshell.-rrejectfile or--reject-file=rejectfile Put rejects intorejectfile instead of the default.rejfile. Whenrejectfile is-, discard rejects.-Ror--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.)patchattempts to swap each hunk around before applying it. Rejects come out in the swapped format. The-Roption does not work witheddiff scripts because there is too little information to reconstruct the reverse operation. If the first hunk of a patch fails,patchreverses the hunk to see if it can be applied that way. If it can, you are asked if you want to have the-Roption 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.)--read-only=behavior Behave as requested when trying to modify a read-only file:ignorethe potential problem,warnabout it (the default), orfail.--reject-format=format Produce reject files in the specifiedformat (eithercontextorunified). 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.-sor--silentor--quiet Work silently, unless an error occurs.--follow-symlinks 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.-tor--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 thePrereq:line in the patch; and assume that patches are reversed if they look like they are.-Tor--set-time Set the modification and access times of patched files from timestamps given in context diff headers. Unless specified in the timestamps, assume that the context diff headers use local time. Use of this option with timestamps 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 timestamps are ambiguous when local clocks move backwards during daylight-saving time adjustments. Make sure that timestamps include time zones, or generate patches with UTC and use the-Zor--set-utcoption instead.-uor--unified Interpret the patch file as a unified context diff.-vor--version Print outpatch's revision header and patch level, and exit.-Vmethod or--version-control=method Usemethod to determine backup file names. The method can also be given by thePATCH_VERSION_CONTROL(or, if that's not set, theVERSION_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 ofmethod is like the GNU Emacs version-control variable;patchalso recognizes synonyms that are more descriptive. The valid values formethod are (unique abbreviations are accepted):existingornil Make numbered backups of files that already have them, otherwise simple backups. This is the default.numberedort Make numbered backups. The numbered backup file name forF isF.~N~whereN is the version number.simpleornever Make simple backups. The-Bor--prefix,-Yor--basename-prefix, and-zor--suffixoptions 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 theSIMPLE_BACKUP_SUFFIXenvironment variable if set, and is.origotherwise. 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.-xnum or--debug=num Set internal debugging flags of interest only topatch patchers.-Ypref or--basename-prefix=pref Use thesimplemethod to determine backup file names (see the-Vmethod or--version-controlmethod option), and prefixpref to the basename of a file name when generating its backup file name. For example, with-Y .del/the simple backup file name forsrc/patch/util.cissrc/patch/.del/util.c.-zsuffix or--suffix=suffix Use thesimplemethod to determine backup file names (see the-Vmethod or--version-controlmethod option), and usesuffix as the suffix. For example, with-z -the backup file name forsrc/patch/util.cissrc/patch/util.c-.-Zor--set-utc Set the modification and access times of patched files from timestamps given in context diff headers. Unless specified in the timestamps, assume that the context diff headers use Coordinated Universal Time (UTC, often known as GMT). Also see the-Tor--set-timeoption. The-Zor--set-utcand-Tor--set-timeoptions 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-for--forceoption is given, the file time is set regardless. Due to the limitations ofdiffoutput 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. withmake clean) all files that depend on the patched files, so that later invocations ofmakedo not get confused by the patched files' times.
PATCH_GET This specifies whetherpatchgets missing or read-only files from RCS, ClearCase, Perforce, or SCCS by default; see the-g or--getoption.POSIXLY_CORRECT If set,patchconforms more strictly to the POSIX standard by default: see the--posixoption.QUOTING_STYLE Default value of the--quoting-styleoption.SIMPLE_BACKUP_SUFFIX Extension to use for simple backup file names instead of.orig.TMPDIR,TMP,TEMP Directory to put temporary files in;patchuses the first environment variable in this list that is set. If none are set, the default is system-dependent; it is normally/tmpon Unix hosts.VERSION_CONTROLorPATCH_VERSION_CONTROL Selects version control style; see the-vor--version-control option.
$TMPDIR/p* temporary files/dev/tty controlling terminal; used to get answers to questions asked of the user
diff(1),ed(1),merge(1). Marshall T. Rose and Einar A. Stefferud, Proposed Standard for Message Encapsulation, Internet RFC 934 <https://datatracker.ietf.org/doc/html/rfc934> (1985-01).
There are several things you should bear in mind if you are going to be sending out patches. Create your patch systematically. When using a version control system this should be easy; for example, with Git you can usegitdiff. Otherwise, a good method is the commanddiff -Naurold new whereold andnew identify the old and new directories. The namesold andnew should not contain any slashes. If the patch should communicate file timestamps as well as file contents, itsdiffcommands' headers should have dates and times in Universal Time using traditional Unix format, so that patch recipients can use the-Zor--set-utcoption. Here is an example command to generate such headers, using Bourne shell syntax:LC_ALL=C TZ=UTC0 diff -Naur myprog-2.7 myprog-2.8 Tell your recipients how to apply the patch by telling them which directory tocdto, and whichpatchoptions to use. The option string-Np1is 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 apatchlevel.hfile which is patched to increment the patch level as the first diff in the patch file you send out. If you put aPrereq: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/nullor 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 unlesspatchis conforming to POSIX and the-Eor--remove-empty-filesoption is not given. An easy way to generate patches that create and remove files is to use GNUdiff's-Nor--new-fileoption. 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 2024 +++ prog/README Mon Mar 17 14:58:22 2024 because the two file names have different numbers of slashes, and different versions ofpatchinterpret 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 2024 +++ v2.0.30/prog/README Mon Mar 17 14:58:22 2024 Avoid sending patches that compare backup file names likeREADME.orig, since this might confusepatchinto 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 andnew/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 fileconfigurewhere there is a lineconfigure: configure.acin 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-Zor--set-utcoption, and have them remove any unpatched files that depend on patched files (e.g. withmake 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 thatpatchcouldn't parse your patch file. If the--verboseoption is given, the messageHmm...indicates that there is unprocessed text in the patch file and thatpatchis 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 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.patchcannot tell if the line numbers are off in anedscript, 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.patchusually 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 GNUpatch. • In POSIXpatchwhen-bis not used, backups are not made even when there is a mismatch. In GNUpatch, this behavior is enabled with the--no-backup-if-mismatchoption, or by conforming to POSIX with the--posixoption or by setting thePOSIXLY_CORRECTenvironment variable. • When intuiting the name of the file to be patched from the patch header,patchuses a complicated method that is optionally POSIX-conforming. The method is equivalent to POSIX if the file names in the context diff header and theIndex: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. • Limit yourself to the following options when sending instructions meant to be executed by anyone running GNUpatch or apatchthat conforms to POSIX. Spaces are optional in the following list.-b-c-ddir-Ddefine-e-ipatchfile-l-n-N-ooutfile-pnum-R-rrejectfile-u
Please report bugs via email to<bug-patch@gnu.org>. If code has been duplicated (for instance with#ifdef OLDCODE...#else ... #endif),patchis 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,patchthinks 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.
Copyright © 1989–2025 Free Software Foundation, Inc. Copyright © 1984–1986, 1988 Larry Wall. 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 ofpatch. Paul Eggert removedpatch'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 Gruenbacher added support for merging.
This page is part of thepatch (GNU patch) project. Information about the project can be found at ⟨http://savannah.gnu.org/projects/patch/⟩. If you have a bug report for this manual page, see ⟨http://savannah.gnu.org/bugs/?group=patch⟩. This page was obtained from the project's upstream Git repository ⟨git://git.savannah.gnu.org/patch.git⟩ on 2026-01-16. (At that time, the date of the most recent commit that was found in the repository was 2025-05-01.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgGNUPATCH(1)Pages that refer to this page:diff(1), dpkg-source(1), gendiff(1), quilt(1), rpmuncompress(1), rpmbuild-config(5), suffixes(7)
HTML rendering created 2026-01-16 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |