Category : OS/2 Files
Archive   : PATCH2U6.ZIP
Filename : PATCH.MAN

.rn '' }`
''' $Header: patch.man,v 2.0.1.2 88/06/22 20:47:18 lwall Locked $
'''
''' $Log: patch.man,v $
''' Revision 2.0.1.2 88/06/22 20:47:18 lwall
''' patch12: now avoids Bell System Logo
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''' Revision 2.0.1.1 88/06/03 15:12:51 lwall
''' patch10: -B switch was contributed.
'''
''' Revision 2.0 86/09/17 15:39:09 lwall
''' Baseline for netwide release.
'''
''' Revision 1.4 86/08/01 19:23:22 lwall
''' Documented -v, -p, -F.
''' Added notes to patch senders.
'''
''' Revision 1.3 85/03/26 15:11:06 lwall
''' Frozen.
'''
''' Revision 1.2.1.4 85/03/12 16:14:27 lwall
''' Documented -p.
'''
''' Revision 1.2.1.3 85/03/12 16:09:41 lwall
''' Documented -D.
'''
''' Revision 1.2.1.2 84/12/05 11:06:55 lwall
''' Added -l switch, and noted bistability bug.
'''
''' Revision 1.2.1.1 84/12/04 17:23:39 lwall
''' Branch for sdcrdcf changes.
'''
''' Revision 1.2 84/12/04 17:22:02 lwall
''' Baseline version.
'''
.de Sh
.br
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp

.if t .sp .5v
.if n .sp
..
'''
''' Set up \*(-- to give an unbreakable dash;
''' string Tr holds user defined translation string.
''' Bell System Logo is used as a dummy character.
'''
.ie n \{\
.tr \(*W-\*(Tr
.ds -- \(*W-
.if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
.ds L" ""
.ds R" ""
.ds L' '
.ds R' '
'br \}
.el \{\
.ds -- \(em\|
.tr \*(Tr
.ds L" ``
.ds R" ''
.ds L' `
.ds R' '
'br\}
.TH PATCH 1 LOCAL
.SH NAME
patch - a program for applying a diff file to an original
.SH SYNOPSIS
.B patch
[options] orig patchfile [+ [options] orig]
.sp
but usually just
.sp
.B patch
.SH DESCRIPTION
.I Patch
will take a patch file containing any of the four 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" (\*(L"~\*(R" on systems that do not
support long filenames), or as specified by the
.BR -b ,
.BR -B ,
or
.B -V
switches.
The extension used for making backup files may also be specified in the
.B SIMPLE_BACKUP_SUFFIX
environment variable, which is overridden by above switches.
.PP
If the backup file already exists,
.B patch
creates a new backup file name by changing the first lowercase letter
in the last component of the file's name into uppercase. If there are
no more lowercase letters in the name, it removes the first character
from the name. It repeats this process until it comes up with a
backup file that does not already exist.
.PP
You may also specify where you want the output to go with a
.B -o
switch; if that file already exists, it is backed up first.
If
.I patchfile
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 listing,
unless over-ruled by a
.BR -c ,
.BR -e ,
.BR -n ,
or
.B -u
switch.
Context diffs (old-style, new-style, and unified) 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
diff listing 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.
First
.I 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
.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" (\*(L"#\*(R" on systems that do not support
long filenames).
(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.)
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 will be told whether the hunk succeeded or
failed, and which line (in the new file)
.I patch
thought the hunk should go on.
If this is different from the line number specified in the diff you will
be told the offset.
A single large offset MAY be an indication that a hunk was installed in the
wrong place.
You will also be told if a fuzz factor was used to make the match, in which
case you should also be slightly suspicious.
.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 the name of the file
to patch must be determined for each diff listing,
and that the garbage before each diff listing 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" or \*(L"~\*(R".
.TP 5
.B \-B
causes the next argument to be interpreted as a prefix to the backup file
name. If this argument is specified any argument from -b will be ignored.
.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 \-E
causes
.I patch
to remove output files that are empty after the patches have been applied.
.TP 5
.B \-f
forces
.I patch
to assume that the user knows exactly what he or she is doing, and to not
ask any questions.
It does not suppress commentary, however.
Use
.B \-s
for that.
.TP 5
.B \-F
sets the maximum fuzz factor.
This switch only applies to context diffs, and causes
.I 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 5
.B \-l
causes the pattern matching to be done loosely, in case the tabs and
spaces have been munged in your 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
causes
.I patch
to ignore patches that it thinks are reversed or already applied.
See also
.B \-R .
.TP 5
.B \-o
causes the next argument to be interpreted as the output file name.
.TP 5
.B \-p
sets the pathname strip count,
which controls how pathnames found in the patch file are treated, in case
the you keep your files in a different directory than the person who sent
out the patch.
The strip count specifies how many slashes are to be stripped from
the front of the pathname.
(Any intervening directory names also go away.)
For example, supposing the filename in the patch file was
.sp
/u/howard/src/blurfl/blurfl.c
.sp
setting
.B \-p
or
.B \-p0
gives the entire pathname unmodified,
.B \-p1
gives
.sp
u/howard/src/blurfl/blurfl.c
.sp
without the leading slash,
.B \-p4
gives
.sp
blurfl/blurfl.c
.sp
and not specifying
.B \-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
.B \-d
switch.
.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.
If it can, you will be asked if you want to have the
.B \-R
switch set.
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, due to the fact that a null context will match
anywhere.
Luckily, most patches add or change 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 \-S
causes
.I patch
to ignore this patch from the patch file, but continue on looking
for the next patch in the file.
Thus
.sp
patch -S + -S + .sp
will ignore the first and second of three patches.
.TP 5
.B \-u
forces
.I patch
to interpret the patch file as a unified context diff (a unidiff).
.TP 5
.B \-v
causes
.I patch
to print out its revision header and patch level.
.TP 5
.B \-V
causes the next argument to be interpreted as a method for creating
backup file names. The type of backups made can also be given in the
.B VERSION_CONTROL
environment variable, which is overridden by this option.
The
.B -B
option overrides this option, causing the prefix to always be used for
making backup file names.
The value of the
.B VERSION_CONTROL
environment variable and the argument to the
.B -V
option are like the GNU
Emacs `version-control' variable; they also recognize synonyms that
are more descriptive. The valid values are (unique abbreviations are
accepted):
.RS
.TP
`t' or `numbered'
Always make numbered backups.
.TP
`nil' or `existing'
Make numbered backups of files that already
have them, simple backups of the others.
This is the default.
.TP
`never' or `simple'
Always make simple backups.
.RE
.TP 5
.B \-x
sets internal debugging flags, and is of interest only to
.I patch
patchers.
.SH AUTHOR
Larry Wall
.br
with many other contributors.
.SH ENVIRONMENT
.TP
.B TMPDIR
Directory to put temporary files in; default is /tmp.
.TP
.B SIMPLE_BACKUP_SUFFIX
Extension to use for backup file names instead of \*(L".orig\*(R" or
\*(L"~\*(R".
.TP
.B VERSION_CONTROL
Selects when numbered backup files are made.
.SH FILES
$TMPDIR/patch*
.SH SEE ALSO
diff(1)
.SH NOTES FOR PATCH SENDERS
There are several things you should bear in mind if you are going to
be sending out patches.
First, you can save people a lot of grief by keeping a 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 Prereq: line in with the patch, it won't let them apply
patches out of order without some warning.
Second, make sure you've specified the filenames right, either in a
context diff header, or with an Index: line.
If you are patching something in a subdirectory, be sure to tell the patch
user to specify a
.B \-p
switch as needed.
Third, you can create a file by sending out a diff that compares a
null file to the file you want to create.
This will only work if the file you want to create doesn't exist already in
the target directory.
Fourth, take care not to send out reversed patches, since it makes people wonder
whether they already applied the patch.
Fifth, while you may be able to get away with putting 582 diff listings into
one file, it is probably wiser to group related patches into separate files in
case something goes haywire.
.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.
.PP
.I Patch
will exit with a non-zero status if any reject files were created.
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
.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" or
a \*(L"delete\*(R" command.
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
.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 that it succeeded to boot.
.PP
If you apply a patch you've already applied,
.I patch
will think it is a reversed patch, and offer to un-apply the patch.
This could be construed as a feature.
.rn }` ''
NAME
patch - a program for applying a diff file to an original

SYNOPSIS
patch [options] orig patchfile [+ [options] orig]

but usually just

patch
DESCRIPTION
Patch will take a patch file containing any of the four forms of
difference listing produced by the 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 ".orig"
("~" on systems that do not support long filenames), or as specified
by the -b, -B, or -V switches. The extension used for making backup
files may also be specified in the SIMPLE_BACKUP_SUFFIX environment
variable, which is overridden by above switches.

If the backup file already exists, patch creates a new backup file
name by changing the first lowercase letter in the last component of
the file's name into uppercase. If there are no more lowercase
letters in the name, it removes the first character from the name. It
repeats this process until it comes up with a backup file that does
not already exist.

You may also specify where you want the output to go with a -o switch;
if that file already exists, it is backed up first. If patchfile is
omitted, or is a hyphen, the patch will be read from standard input.

Upon startup, patch will attempt to determine the type of the diff
listing, unless over-ruled by a -c, -e, -n, or -u switch. Context
diffs (old-style, new-style, and unified) and normal diffs are applied
by the patch program itself, while ed diffs are simply fe entire diff
is indented by a consistent amount, this will be taken into account.

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 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, patch will scan 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.) If 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 ".rej" ("#" on
systems that do not support long filenames). (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.) 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 will be told whether the hunk succeeded
or failed, and which line (in the new file) patch thought the hunk
should go on. If this is different from the line number specified in
the diff you will be told the offset. A single large offset MAY be an
indication that a hunk was installed in the wrong place. You will
also be told if a fuzz factor was used to make the match, in which
case you should also be slightly suspicious.

If no original file is specified on the command line, 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 "***" or "---", with the shortest name of an
existing file winning. Only context diffs have lines like that, but
if there is an "Index:" line in the leading garbage, 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.

(If the original file cannot be found, but a suitable SCCS or RCS file
is handy, patch will attempt to get or check out the file.)

Additionally, if the leading garbage contains a "Prereq: " line, 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, patch will ask for confirmation before proceeding.

The upshot of all this is that you should be able to say, while in a
news interface, 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 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 the name of the
file to patch must be determined for each diff listing, and that the
garbage before each diff listing 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 '+'. (The argument list for a second or subsequent patch may not
specify a new patch file, however.)

Patch recognizes the following switches:

-b causes the next argument to be interpreted as the backup
extension, to be used in place of ".orig" or "~".

-B causes the next argument to be interpreted as a prefix to the
backup file name. If this argument is specified any argument from
-b will be ignored.

-c forces patch to interpret the patch file as a context diff.

-d causes patch to interpret the next argument as a directory, and
cd to it before doing anything else.

-D causes patch to use the "#ifdef...#endif" construct to mark
changes. The argument following will output files that are
empty after the patches have been applied.

-f forces patch to assume that the user knows exactly what he or she
is doing, and to not ask any questions. It does not suppress
commentary, however. Use -s for that.

-F
sets the maximum fuzz factor. This switch only applies to
context diffs, and causes 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.

-l causes the pattern matching to be done loosely, in case the tabs
and spaces have been munged in your 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.

-n forces patch to interpret the patch file as a normal diff.

-N causes patch to ignore patches that it thinks are reversed or
already applied. See also -R .

-o causes the next argument to be interpreted as the output file

-p
sets the pathname strip count, which controls how pathnames found
in the patch file are treated, in case the you keep your files in
a different directory than the person who sent out the patch.
The strip count specifies how many slashes are to be stripped
from the front of the pathname. (Any intervening directory names
also go away.) For example, supposing the filename in the patch
file was

/u/howard/src/blurfl/blurfl.c

setting -p or -p0 gives the entire pathname 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 switch.

-r causes the next argument to be interpreted as the reject file

name.

-R tells 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.) Patch will attempt to swap each
hunk around before applying it. Rejects will come out in the
swapped format. The -R switch will 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 will reverse the hunk
to see if it can be applied that way. If it can, you will be
asked if you want to have the -R switch set. 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, due to the fact that a null context
will match anywhere. Luckily, most patches add or change lines
rather than delete them, so most reversed normal diffs will begin
with a delete, which will fail, triggering the heuristic.)

-s makes patch do its work silently, unless an error occurs.

-S causes patch to ignore this patch from the patch file, but
continue on looking for the next patch in the file. Thus

patch -S + -S +
will ignore the first and second of three patches.

-backup file names. The type of
VERSION_CONTROL environment variable, which is overridden by this
option. The -B option overrides this option, causing the prefix
to always be used for making backup file names. The value of the
VERSION_CONTROL environment variable and the argument to the -V
option are like the GNU Emacs `version-control' variable; they
also recognize synonyms that are more descriptive. The valid
values are (unique abbreviations are accepted):

`t' or `numbered'
Always make numbered backups.

`nil' or `existing'
Make numbered backups of files that already have them,
simple backups of the others. This is the default.

`never' or `simple'
Always make simple backups.

-x
sets internal debugging flags, and is of interest only to patch
patchers.

AUTHOR
Larry Wall
with many other contributors.

ENVIRONMENT
TMPDIR
Directory to put temporary files in; default is /tmp.

SIMPLE_BACKUP_SUFFIX
Extension to use for backup file names instead of ".orig" or "~".

VERSION_CONTROL
Selects when numbered backup files are made.

FILES
$TMPDIR/patch*

SEE ALSO
diff(1)

NOTES FOR PATCH SENDERS
There are several things you should bear in mind if you are going to

be sending out patches. First, you can save people a lot of grief by
keeping a 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
Prereq: line in with the patch, it won't let them apply patches out of
order without some warning. Second, make sure you've specified the
filenames right, either in a context diff header, or with an Index:
line. If you are patching something in a subdirectory, be sure to
tell the patch user to specify a -p switch as needed. Third, you can
create a file by sending out a diff that compares a null file to the
file you want to create. This will only work if the file you want to
create doesn't exist already in the target directory. Fourth, take
care not to send out reversed patches, since it makes people wonder
whether they already applied the patch. Fifth, while you may be able
to get away with putting 582 diff listings into one file, it is
probably wiser to group related patches into separate files in case
something goes haywire.

DIAGNOSTICS
Too many to list here, but generally indicative that patch couldn't
parse your patch file.

The message "Hmm..." indicates that there is unprocessed text in the
patch file and that patch is attempting to intuit whether there is a
patch in that text and, if so, what kind of patch it is.

Patch will exit with a non-zero status if any reject files were
created. 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.

CAVEATS
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 "change"
or a "delete" command. 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.

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.

BUGS
Could be smarter about partial matches, excessively deviant offsets
and swapped code, but that would take an extra pass.

If code has been duplicated (for instance with #ifdef OLDCODE ...
#else ... #endif), patch is 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, patch will think it is a
reversed patch, and offer to un-apply the patch. This could be
construed as a feature.