''' $Header: patch.man,v 1.3 85/03/26 15:11:06 lwall Exp $
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''' $Log:	patch.man,v $
''' Revision 1.3  85/03/26  15:11:06  lwall
''' Frozen.
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''' Revision 1.2.1.4  85/03/12  16:14:27  lwall
''' Documented -p.
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''' Revision 1.2.1.3  85/03/12  16:09:41  lwall
''' Documented -D.
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''' Revision 1.2.1.2  84/12/05  11:06:55  lwall
''' Added -l switch, and noted bistability bug.
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''' Revision 1.2.1.1  84/12/04  17:23:39  lwall
''' Branch for sdcrdcf changes.
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''' Revision 1.2  84/12/04  17:22:02  lwall
''' Baseline version.
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.PP
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.PP
..
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.if t .sp .5v
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'''
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'''     Bell System Logo is used as a dummy character.
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.TH PATCH 1 "May 10, 1986" "Systems Development Corp"
.SH NAME
patch \- a program for applying a diff file to an original
.SH SYNOPSIS
.B patch
[options] orig diff [+ [options] orig]
.SH DESCRIPTION
.I Patch
will take a patch file containing any of the three forms of difference
listing produced by the
.I diff
program and apply those differences to an original file, producing a patched
version.
By default, the patched version is put in place of the original, with
the original file backed up to the same name with the
extension \*(L".orig\*(R", or as specified by the
.B -b
switch.
You may also specify where you want the output to go with a
.B -o
switch.
If
.I diff
is omitted, or is a hyphen, the patch will be read from standard input.
.PP
Upon startup, patch will attempt to determine the type of the diff file,
unless over-ruled by a
.BR -c ,
.BR -e ,
or
.B -n
switch.
Context diffs and normal diffs are applied by the
.I patch
program itself, while ed diffs are simply fed to the
.I ed
editor via a pipe.
.PP
.I Patch
will try to skip any leading garbage, apply the diff,
and then skip any trailing garbage.
Thus you could feed an article or message containing a context or normal
diff to
.IR patch ,
and it should work.
If the entire diff is indented by a consistent amount,
this will be taken into account.
.PP
With context diffs, and to a lesser extent with normal diffs,
.I patch
can detect when the line numbers mentioned in the patch are incorrect,
and will attempt 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,
.I patch
will scan both forwards and backwards for a set of lines matching the context
given in the hunk.
All lines of the context must match.
If
.I patch
cannot find a place to install that hunk of the patch, it will put the
hunk out to a reject file, which normally is the name of the output file
plus \*(L".rej\*(R".
(Note that the rejected hunk will come out in context diff form whether the
input patch was a context diff or a normal diff.
If the input was a normal diff, many of the contexts will simply be null.)
.PP
If no original file is specified on the command line,
.I patch
will try to figure out from the leading garbage what the name of the file
to edit is.
In the header of a context diff, the filename is found from lines beginning
with \*(L"***\*(R" or \*(L"---\*(R", with the shortest name of an existing
file winning.
Only context diffs have lines like that, but if there is an \*(L"Index:\*(R"
line in the leading garbage,
.I patch
will try to use the filename from that line.
The context diff header takes precedence over an Index line.
If no filename can be intuited from the leading garbage, you will be asked
for the name of the file to patch.
.PP
(If the original file cannot be found, but a suitable SCCS or RCS file is
handy,
.I patch
will attempt to get or check out the file.)
.PP
Additionally, if the leading garbage contains a \*(L"Prereq: \*(R" line,
.I patch
will take the first word from the prerequisites line (normally a version
number) and check the input file to see if that word can be found.
If not,
.I patch
will ask for confirmation before proceeding.
.PP
The upshot of all this is that you should be able to say, while in a news
interface, the following:
.Sp
	| patch -d /usr/src/local/blurfl
.Sp
and patch a file in the blurfl directory directly from the article containing
the patch.
.PP
If the patch file contains more than one patch,
.I patch
will try to apply each of them as if they came from separate patch files.
This means, among other things, that it is assumed that separate patches
will apply to separate files, and that the garbage before each patch will
be examined for interesting things such as filenames and revision level, as
mentioned previously.
You can give switches (and another original file name) for the second and
subsequent patches by separating the corresponding argument lists
by a \*(L'+\*(R'.
The argument list for a second or subsequent patch may not specify a new
patch file, however.
.PP
.I Patch
recognizes the following switches:
.TP 5
.B \-b
causes the next argument to be interpreted as the backup extension, to be
used in place of \*(L".orig\*(R".
.TP 5
.B \-c
forces
.I patch
to interpret the patch file as a context diff.
.TP 5
.B \-d
causes
.I patch
to interpret the next argument as a directory, and cd to it before doing
anything else.
.TP 5
.B \-D
causes
.I patch
to use the "#ifdef...#endif" construct to mark changes.
The argument following will be used as the differentiating symbol.
Note that, unlike the C compiler, there must be a space between the
.B \-D
and the argument.
.TP 5
.B \-e
forces
.I patch
to interpret the patch file as an ed script.
.TP 5
.B \-l
causes the pattern matching to be done loosely, in case the tabs and
spaces have been munged in you input file.
Any sequence of whitespace in the pattern line will match any sequence
in the input file.
Normal characters must still match exactly.
Each line of the context must still match a line in the input file.
.TP 5
.B \-n
forces
.I patch
to interpret the patch file as a normal diff.
.TP 5
.B \-N
forces patch to not try and reverse the diffs if it thinks that they may have
been swapped.  See the
.B \-R
option below.
.TP 5
.B \-o
causes the next argument to be interpreted as the output file name.
.TP 5
.B \-p
causes leading pathnames to be kept.
If the diff is of the file \*(lqb/a.c\*(rq, patch will look for \*(lqa.c\*(rq
in the \*(lqb\*(rq directory, instead of the current directory.
This probably won't work if the diff has rooted pathnames.
.TP 5
.B \-r
causes the next argument to be interpreted as the reject file name.
.TP 5
.B \-R
tells
.I patch
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.)
.I Patch
will attempt to swap each hunk around before applying it.
Rejects will come out in the swapped format.
The
.B \-R
switch will not work with ed diff scripts because there is too little
information to reconstruct the reverse operation.
.Sp
If the first hunk of a patch fails,
.I patch
will reverse the hunk to see if it can be applied that way unless the
.B \-N
option is supplied.
If it can, the
.B \-R
switch will be set automatically.
If it can't, the patch will continue 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.
Luckily, most patches add lines rather than delete them, so most reversed
normal diffs will begin with a delete, which will fail, triggering the
heuristic.)
.TP 5
.B \-s
makes
.I patch
do its work silently, unless an error occurs.
.TP 5
.B \-x<number>
sets internal debugging flags, and is of interest only to
.I patch
patchers.
.SH ENVIRONMENT
No environment variables are used by
.IR patch .
.SH FILES
/tmp/patch*
.SH SEE ALSO
diff(1)
.SH DIAGNOSTICS
Too many to list here, but generally indicative that
.I patch
couldn't parse your patch file.
.PP
The message \*(L"Hmm...\*(R" indicates that there is unprocessed text in
the patch file and that
.I patch
is attempting to intuit whether there is a patch in that text and, if so,
what kind of patch it is.
.SH CAVEATS
.I Patch
cannot tell if the line numbers are off in an ed script, and can only detect
bad line numbers in a normal diff when it finds a \*(L"change\*(R" command.
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 it
worked, but not always.
.PP
.I 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 BUGS
Could be smarter about partial matches, excessively \&deviant offsets and
swapped code, but that would take an extra pass.
.PP
If code has been duplicated (for instance with #ifdef OLDCODE ... #else ...
#endif),
.I patch
is incapable of patching both versions, and, if it works at all, will likely
patch the wrong one, and tell you it succeeded to boot.
.PP
If you apply a patch you've already applied,
.I patch
will think it is a reversed patch, and un-apply the patch.
This could be construed as a feature.