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.TH PATCH 1 \*(Dt GNU

.ta 3n

.SH NAME

patch \- apply a diff file to an original

.SH SYNOPSIS

.B patch

.RI [ options ]

.RI [ originalfile

.RI [ patchfile ]]

.Sp

but usually just

.Sp

.BI "patch \-p" "num"

.BI < patchfile

.SH DESCRIPTION

.B patch

takes a patch file

.I patchfile

containing a difference listing produced by the

.B 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 \-b

or

.B \*=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 specified on the

command line as

.IR originalfile .

.PP

Upon startup, patch attempts to determine the type of the diff listing,

unless overruled by a

\fB\-c\fP (\fB\*=context\fP),

\fB\-e\fP (\fB\*=ed\fP),

\fB\-n\fP (\fB\*=normal\fP),

or

\fB\-u\fP (\fB\*=unified\fP)

option.

Context diffs (old-style, new-style, and unified) and

normal diffs are applied by the

.B patch

program itself, while

.B ed

diffs are simply fed to the

.BR ed (1)

editor via a pipe.

.PP

.B 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

.BR patch ,

and it should work.

If the entire diff is indented by a consistent amount,

or if a context diff is encapsulated one or more times by prepending

"\fB\- \fP" to lines starting with "\fB\-\fP" as specified by Internet RFC 934,

this is taken into account.

.PP

With context diffs, and to a lesser extent with normal diffs,

.B 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,

.B patch

scans both forwards and backwards for a set of lines matching the context

given in the hunk.

First

.B 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.)

If

.B 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

.B \&.rej

suffix, or

.B #

if

.B \&.rej

would generate a file name that is too long

(if even appending the single character

.B #

makes the file name too long, then

.B #

replaces the file name's last character).

(The rejected hunk comes out in ordinary context diff form regardless of

the input patch's form.

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.

.PP

As each hunk is completed, you are told if the hunk

failed, and if so which line (in the new file)

.B 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

.I 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

.B \*=verbose

option is given, you are also told about hunks that match exactly.

.PP

If no original file

.I origfile

is specified on the command line,

.B patch

tries to figure out from the leading garbage what the name of the file

to edit is, using the following rules.

.TP 3

.B " \(bu"

If the header is that of a context diff,

.B patch

takes the old and new file names in the header.

Any

.B /dev/null

names are ignored.

.TP

.B " \(bu"

If there is an

.B Index:\&

line in the leading garbage

and if either the old and new names are both absent or the

.B POSIXLY_CORRECT

environment variable is set,

.B patch

takes the name in the

.B Index:\&

line.

.TP

.B " \(bu"

For the purpose of the following rules,

the names are considered to be in the order (old, new, index),

regardless of the order that they appear in the header.

.TP

.B " \(bu"

If some of the named files exist,

.B patch

uses the first name if the

.B POSIXLY_CORRECT

environment variable is set, and the best name otherwise.

.TP

.B " \(bu"

If

.B patch

is not ignoring \s-1RCS\s0 and \s-1SCCS\s0 (see the

.BI "\-g\ " num

or

.BI \*=get= num

option), and no named files exist

but an \s-1RCS\s0 or \s-1SCCS\s0 master is found,

.B patch

uses the first named file with an \s-1RCS\s0 or \s-1SCCS\s0 master.

.TP

.B " \(bu"

If no named files exist, no \s-1RCS\s0 or \s-1SCCS\s0 master was found,

some names are given,

.B POSIXLY_CORRECT

is not set, and the patch appears to create a file,

.B patch

uses the best name requiring the creation of the fewest directories.

.TP

.B " \(bu"

If no file name results from the above heuristics, you are asked

for the name of the file to patch.

.LP

To determine the

.I best

of a nonempty list of file names,

.B 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.

.PP

Additionally, if the leading garbage contains a

.B Prereq:\&

line,

.B 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,

.B patch

asks for confirmation before proceeding.

.PP

The upshot of all this is that you should be able to say, while in a news

interface, something like the following:

.Sp

	\fB| patch \-d /usr/src/local/blurfl\fP

.Sp

and patch a file in the

.B blurfl

directory directly from the article containing

the patch.

.PP

If the patch file contains more than one patch,

.B 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.

.SH OPTIONS

.TP 3

\fB\-b\fP  or  \fB\*=backup\fP

Make backup files.

That is, when patching a file,

rename or copy the original instead of removing it.

When backing up a file that does not exist,

an empty, unreadable backup file is created

as a placeholder to represent the nonexistent file.

See the

.B \-V

or

.B \*=version\-control

option for details about how backup file names are determined.

.TP

.B \*=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 the

.B POSIXLY_CORRECT

environment variable is set.

.TP

.B \*=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 the

.B POSIXLY_CORRECT

environment variable is set.

.TP

\fB\-B\fP \fIpref\fP  or  \fB\*=prefix=\fP\fIpref\fP

Prefix

.I pref

to a file name when generating its simple backup file name.

For example, with

.B "\-B\ /junk/"

the simple backup file name for

.B src/patch/util.c

is

.BR /junk/src/patch/util.c .

.TP

\fB\*=binary\fP

Read and write all files in binary mode,

except for standard output and

.BR /dev/tty .

This option has no effect on \s-1POSIX\s0-compliant systems.

On systems like \s-1DOS\s0 where this option makes a difference,

the patch should be generated by

.BR "diff\ \-a\ \*=binary" .

.TP

\fB\-c\fP  or  \fB\*=context\fP

Interpret the patch file as a ordinary context diff.

.TP

\fB\-d\fP \fIdir\fP  or  \fB\*=directory=\fP\fIdir\fP

Change to the directory

.I dir

immediately, before doing

anything else.

.TP

\fB\-D\fP \fIdefine\fP  or  \fB\*=ifdef=\fP\fIdefine\fP

Use the

.BR #ifdef " .\|.\|. " #endif

construct to mark changes, with

.I define

as the differentiating symbol.

.TP

.B "\*=dry\-run"

Print the results of applying the patches without actually changing any files.

.TP

\fB\-e\fP  or  \fB\*=ed\fP

Interpret the patch file as an

.B ed

script.

.TP

\fB\-E\fP  or  \fB\*=remove\-empty\-files\fP

Remove output files that are empty after the patches have been applied.

Normally this option is unnecessary, since

.B 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 the

.B POSIXLY_CORRECT

environment variable is set,

.B patch

does not remove empty patched files unless this option is given.

When

.B patch

removes a file, it also attempts to remove any empty ancestor directories.

.TP

\fB\-f\fP  or  \fB\*=force\fP

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

.B 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

.B \-s

for that.

.TP

\fB\-F\fP \fInum\fP  or  \fB\*=fuzz=\fP\fInum\fP

Set the maximum fuzz factor.

This option only applies to diffs that have context, and causes

.B patch

to ignore up to that many lines 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, and it may not be set to more than

the number of lines of context in the context diff, ordinarily 3.

.TP

\fB\-g\fP \fInum\fP  or  \fB\*=get=\fP\fInum\fP

This option controls

.BR patch 's

actions when a file is under \s-1RCS\s0 or \s-1SCCS\s0 control,

and does not exist or is read-only and matches the default version.

If

.I num

is positive,

.B patch

gets (or checks out) the file from the revision control system; if zero,

.B patch

ignores \s-1RCS\s0 and \s-1SCCS\s0 and does not get the file; and if negative,

.B patch

asks the user whether to get the file.

The default value of this option is given by the value of the

.B PATCH_GET

environment variable if it is set; if not, the default value is zero if 

.B POSIXLY_CORRECT

is set, negative otherwise.

.TP

.B "\*=help"

Print a summary of options and exit.

.TP

\fB\-i\fP \fIpatchfile\fP  or  \fB\*=input=\fP\fIpatchfile\fP

Read the patch from

.IR patchfile .

If

.I patchfile

is

.BR \- ,

read from standard input, the default.

.TP

\fB\-l\fP  or  \fB\*=ignore\-whitespace\fP

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.

.TP

\fB\-n\fP  or  \fB\*=normal\fP

Interpret the patch file as a normal diff.

.TP

\fB\-N\fP  or  \fB\*=forward\fP

Ignore patches that seem to be reversed or already applied.

See also

.BR \-R .

.TP

\fB\-o\fP \fIoutfile\fP  or  \fB\*=output=\fP\fIoutfile\fP

Send output to

.I outfile

instead of patching files in place.

.TP

\fB\-p\fP\fInum\fP  or  \fB\*=strip\fP\fB=\fP\fInum\fP

Strip the smallest prefix containing

.I 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

.Sp

	\fB/u/howard/src/blurfl/blurfl.c\fP

.Sp

setting

.B \-p0

gives the entire file name unmodified,

.B \-p1

gives

.Sp

	\fBu/howard/src/blurfl/blurfl.c\fP

.Sp

without the leading slash,

.B \-p4

gives

.Sp

	\fBblurfl/blurfl.c\fP

.Sp

and not specifying

.B \-p

at all just gives you \fBblurfl.c\fP.

Whatever you end up with is looked for either in the current directory,

or the directory specified by the

.B \-d

option.

.TP

\fB\-r\fP \fIrejectfile\fP  or  \fB\*=reject\-file=\fP\fIrejectfile\fP

Put rejects into

.I rejectfile

instead of the default

.B \&.rej

file.

.TP

\fB\-R\fP  or  \fB\*=reverse\fP

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.)

.B patch

attempts to swap each hunk around before applying it.

Rejects come out in the swapped format.

The

.B \-R

option does not work with

.B ed

diff scripts because there is too little

information to reconstruct the reverse operation.

.Sp

If the first hunk of a patch fails,

.B 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

.B \-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.)

.TP

\fB\-s\fP  or  \fB\*=silent\fP  or  \fB\*=quiet\fP

Work silently, unless an error occurs.

.TP

\fB\-t\fP  or  \fB\*=batch\fP

Suppress questions like

.BR \-f ,

but make some different assumptions:

skip patches whose headers do not contain file names (the same as \fB\-f\fP);

skip patches for which the file has the wrong version for the

.B Prereq:\&

line

in the patch; and assume that patches are reversed if they look like

they are.

.TP

\fB\-T\fP  or  \fB\*=set\-time\fP

Set the modification and access times of patched files from time stamps

given in context diff headers, assuming that the context diff headers

use local time.  This option 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.  Instead of using this option,

generate patches with \s-1UTC\s0 and use the

.B \-Z

or

.B \*=set\-utc

option instead.

.TP

\fB\-u\fP  or  \fB\*=unified\fP

Interpret the patch file as a unified context diff.

.TP

\fB\-v\fP  or  \fB\*=version\fP

Print out

.BR patch 's

revision header and patch level, and exit.

.TP

\fB\-V\fP \fImethod\fP  or  \fB\*=version\-control=\fP\fImethod\fP

Use

.I method

to determine

backup file names.  The method can also be given by the

.B PATCH_VERSION_CONTROL

(or, if that's not set, the

.BR 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.

.Sp

The value of

.I method

is like the \s-1GNU\s0

Emacs `version-control' variable;

.B patch

also recognizes synonyms that

are more descriptive.  The valid values for

.I method

are (unique abbreviations are

accepted):

.RS

.TP 3

\fBexisting\fP  or  \fBnil\fP

Make numbered backups of files that already have them,

otherwise simple backups.

This is the default.

.TP

\fBnumbered\fP  or  \fBt\fP

Make numbered backups.  The numbered backup file name for

.I F

is

.IB F .~ N ~

where

.I N

is the version number.

.TP

\fBsimple\fP  or  \fBnever\fP

Make simple backups.

The

.B \-B

or

.BR \*=prefix ,

.B \-Y

or

.BR \*=basename\-prefix ,

and

.B \-z

or

.BR \*=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

.B SIMPLE_BACKUP_SUFFIX

environment variable if set, and is

.B \&.orig

otherwise.

.PP

With numbered or simple backups,

if the backup file name is too long, the backup suffix

.B ~

is used instead; if even appending

.B ~

would make the name too long, then

.B ~

replaces the last character of the file name.

.RE

.TP

\fB\*=verbose\fP

Output extra information about the work being done.

.TP

\fB\-x\fP \fInum\fP  or  \fB\*=debug=\fP\fInum\fP

Set internal debugging flags of interest only to

.B patch

patchers.

.TP

\fB\-Y\fP \fIpref\fP  or  \fB\*=basename\-prefix=\fP\fIpref\fP

Prefix

.I pref

to the basename of a file name when generating its simple backup file name.

For example, with

.B "\-Y\ .del/"

the simple backup file name for

.B src/patch/util.c

is

.BR src/patch/.del/util.c .

.TP

\fB\-z\fP \fIsuffix\fP  or  \fB\*=suffix=\fP\fIsuffix\fP

Use

.I suffix

as the simple backup suffix.

For example, with

.B "\-z\ -"

the simple backup file name for

.B src/patch/util.c

is

.BR src/patch/util.c- .

The backup suffix may also be specified by the

.B SIMPLE_BACKUP_SUFFIX

environment variable, which is overridden by this option.

.TP

\fB\-Z\fP  or  \fB\*=set\-utc\fP

Set the modification and access times of patched files from time stamps

given in context diff headers, assuming that the context diff headers

use Coordinated Universal Time (\s-1UTC\s0, often known as \s-1GMT\s0).

Also see the

.B \-T

or

.B \*=set\-time

option.

.Sp

The

.B \-Z

or

.B \*=set\-utc

and

.B \-T

or

.B \*=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

.B \-f

or

.B \*=force

option is given, the file time is set regardless.

.Sp

Due to the limitations of

.B 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

.BR "make\ clean" )

all files that depend on the patched files, so that later invocations of

.B make

do not get confused by the patched files' times.

.SH ENVIRONMENT

.TP 3

\fBPATCH_GET\fP

This specifies whether

.B patch

gets missing or read-only files from \s-1RCS\s0 or \s-1SCCS\s0

by default; see the

.B \-g

or

.B \*=get

option.

.TP

.B POSIXLY_CORRECT

If set,

.B patch

conforms more strictly to the \s-1POSIX\s0 standard:

it takes the first existing file from the list (old, new, index)

when intuiting file names from diff headers,

it does not remove files that are empty after patching,

it does not ask whether to get files from \s-1RCS\s0 or \s-1SCCS\s0,

it requires that all options precede the files in the command line,

and it does not backup files when there is a mismatch.

.TP

.B SIMPLE_BACKUP_SUFFIX

Extension to use for simple backup file names instead of

.BR \&.orig .

.TP

\fBTMPDIR\fP, \fBTMP\fP, \fBTEMP\fP

Directory to put temporary files in;

.B patch

uses the first environment variable in this list that is set.

If none are set, the default is system-dependent;

it is normally

.B /tmp

on Unix hosts.

.TP

\fBVERSION_CONTROL\fP or \fBPATCH_VERSION_CONTROL\fP

Selects version control style; see the

.B \-v

or

.B \*=version\-control

option.

.SH FILES

.TP 3

.IB $TMPDIR "/p\(**"

temporary files

.TP

.B /dev/tty

controlling terminal; used to get answers to questions asked of the user

.SH "SEE ALSO"

.BR diff (1),

.BR ed (1)

.Sp

Marshall T. Rose and Einar A. Stefferud,

Proposed Standard for Message Encapsulation,

Internet RFC 934 <URL:ftp://ftp.isi.edu/in-notes/rfc934.txt> (1985-01).

.SH "NOTES FOR PATCH SENDERS"

There are several things you should bear in mind if you are going to

be sending out patches.

.PP

Create your patch systematically.

A good method is the command

.BI "diff\ \-Naur\ " "old\ new"

where

.I old

and

.I new

identify the old and new directories.

The names

.I old

and

.I new

should not contain any slashes.

The

.B diff

command's headers should have dates

and times in Universal Time using traditional Unix format,

so that patch recipients can use the

.B \-Z

or

.B \*=set\-utc

option.

Here is an example command, using Bourne shell syntax:

.Sp

	\fBLC_ALL=C TZ=UTC0 diff \-Naur gcc\-2.7 gcc\-2.8\fP

.PP

Tell your recipients how to apply the patch

by telling them which directory to

.B cd

to, and which

.B patch

options to use.  The option string

.B "\-Np1"

is recommended.

Test your procedure by pretending to be a recipient and applying

your patch to a copy of the original files.

.PP

You can save people a lot of grief by keeping a

.B patchlevel.h

file which is patched to increment the patch level

as the first diff in the patch file you send out.

If you put a

.B Prereq:\&

line in with the patch, it won't let them apply

patches out of order without some warning.

.PP

You can create a file by sending out a diff that compares

.B /dev/null

or an empty file dated the Epoch (1970-01-01 00:00:00 \s-1UTC\s0)

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 unless the

.B POSIXLY_CORRECT

environment variable is set and the

.B \-E

or

.B \*=remove\-empty\-files

option is not given.

An easy way to generate patches that create and remove files

is to use \s-1GNU\s0

.BR diff 's

.B \-N

or

.B \*=new\-file

option.

.PP

If the recipient is supposed to use the

.BI \-p N

option, do not send output that looks like this:

.Sp

.ft B

.ne 3

	diff \-Naur v2.0.29/prog/README prog/README

.br

	\-\^\-\^\- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997

.br

	+\^+\^+ prog/README   Mon Mar 17 14:58:22 1997

.ft

.Sp

because the two file names have different numbers of slashes,

and different versions of

.B patch

interpret the file names differently.

To avoid confusion, send output that looks like this instead:

.Sp

.ft B

.ne 3

	diff \-Naur v2.0.29/prog/README v2.0.30/prog/README

.br

	\-\^\-\^\- v2.0.29/prog/README   Mon Mar 10 15:13:12 1997

.br

	+\^+\^+ v2.0.30/prog/README   Mon Mar 17 14:58:22 1997

.ft

.Sp

.PP

Avoid sending patches that compare backup file names like

.BR README.orig ,

since this might confuse

.B patch

into patching a backup file instead of the real file.

Instead, send patches that compare the same base file names

in different directories, e.g.\&

.B old/README

and

.BR new/README .

.PP

Take care not to send out reversed patches, since it makes people wonder

whether they already applied the patch.

.PP

Try not to have your patch modify derived files

(e.g. the file

.B configure

where there is a line

.B "configure: configure.in"

in 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 \s-1UTC\s0,

have the recipients apply the patch with the

.B \-Z

or

.B \*=set\-utc

option, and have them remove any unpatched files that depend on patched files

(e.g. with

.BR "make\ clean" ).

.PP

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.

.SH DIAGNOSTICS

Diagnostics generally indicate that

.B patch

couldn't parse your patch file.

.PP

If the

.B \*=verbose

option is given, the message

.B Hmm.\|.\|.\&

indicates that there is unprocessed text in

the patch file and that

.B patch

is attempting to intuit whether there is a patch in that text and, if so,

what kind of patch it is.

.PP

.BR patch 's

exit status is

1 if some hunks cannot be applied,

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.

.SH CAVEATS

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.

.PP

.B patch

cannot tell if the line numbers are off in an

.B ed

script, 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.

Until a suitable interactive interface is added, 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.

.PP

.B patch

usually 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.

.SH "COMPATIBILITY ISSUES"

The \s-1POSIX\s0 standard specifies behavior that differs from

.BR patch 's

traditional behavior.

You should be aware of these differences if you must interoperate with

.B patch

versions 2.1 and earlier, which are not \s-1POSIX\s0-compliant.

.TP 3

.B " \(bu"

In traditional

.BR patch ,

the

.B \-p

option's operand was optional, and a bare

.B \-p

was equivalent to

.BR \-p0.

The

.B \-p

option now requires an operand, and

.B "\-p\ 0"

is now equivalent to

.BR \-p0 .

For maximum compatibility, use options like

.B \-p0

and

.BR \-p1 .

.Sp

Also,

traditional

.B patch

simply counted slashes when stripping path prefixes;

.B patch

now counts pathname components.

That is, a sequence of one or more adjacent slashes

now counts as a single slash.

For maximum portability, avoid sending patches containing

.B //

in file names.

.TP

.B " \(bu"

In traditional

.BR patch ,

backups were enabled by default.

This behavior is now enabled with the

.B \-b

or

.B \*=backup

option.

.Sp

Conversely, in \s-1POSIX\s0

.BR patch ,

backups are never made, even when there is a mismatch.

In \s-1GNU\s0

.BR patch ,

this behavior is enabled with the

.B \*=no\-backup\-if\-mismatch

option or by setting the

.B POSIXLY_CORRECT

environment variable.

.Sp

The

.BI \-b "\ suffix"

option

of traditional

.B patch

is equivalent to the

.BI "\-b\ \-z" "\ suffix"

options of \s-1GNU\s0

.BR patch .

.TP

.B " \(bu"

Traditional

.B patch

used a complicated (and incompletely documented) method

to intuit the name of the file to be patched from the patch header.

This method was not \s-1POSIX\s0-compliant, and had a few gotchas.

Now

.B patch

uses a different, equally complicated (but better documented) method

that is optionally \s-1POSIX\s0-compliant; we hope it has

fewer gotchas.  The two methods are compatible if the

file names in the context diff header and the

.B Index:\&

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.

.TP

.B " \(bu"

When traditional

.B patch

asked the user a question, it sent the question to standard error

and looked for an answer from

the first file in the following list that was a terminal:

standard error, standard output,

.BR /dev/tty ,

and standard input.

Now

.B patch

sends questions to standard output and gets answers from

.BR /dev/tty .

Defaults for some answers have been changed so that

.B patch

never goes into an infinite loop when using default answers.

.TP

.B " \(bu"

Traditional

.B patch

exited with a status value that counted the number of bad hunks,

or with status 1 if there was real trouble.

Now

.B patch