patch - Online in the Cloud

PROGRAM:

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
When a patch does not apply, patch usually checks if the patch looks like it has been
reversed. The --forward option prevents that. 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.)

--read-only=behavior
Behave as requested when trying to modify a read-only file: ignore the potential
problem, warn about it (the default), or fail.

--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.

--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.

-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. Unless specified in the time stamps, assume that the context
diff headers use local time.

Use of this option with time stamps 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 time stamps are ambiguous when local clocks move backwards during
daylight-saving time adjustments. Make sure that time stamps include time zones, or
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. Unless specified in the time stamps, assume 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.

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