Like all of Larry Wall's widely used programs (including
a software configuration script called
betrays a whimsical
intelligence of its own.
Feed it any kind of
an editing script produced with the
figures out what it needs to do to apply the diff,
and updates the file, supplying all the while a breezy commentary
on what it's doing:
patch &lt; testfile.diff
Hmm... Looks like a normal diff to me...
File to patch:
Patching file testfile using Plan A...
Hunk #1 succeeded at 2.
As Larry once noted,
has done an awful lot to "change the
culture of computing."
Almost all free software is now updated by
means of patches rather than complete new releases.
smart enough to discard any leading or trailing garbage (such as mail
headers or signatures) so that a program source file can be updated by
piping a mail message containing a diff listing between old and new
versions directly to
Here are a few of the other things
is smart enough to
Figure out the name of the file to be updated and do it without
asking (usually only if the diff file is a
context diff (
Look for a suitable
SCCS or RCS (
file and check it out, if the filename itself can't be found.
Handle diff listings that don't quite match.
it possible for
to update a file that the recipient has
already changed from the one that the diff was based on.
Save any pieces of the diff file that don't end up being used, in a
file named by adding
(reject) to the name of the file being
Back up the file that is being patched, appending the
to the name of the file being patched.
Recognize that its input may actually apply to several files, and
patch each of them separately.
So, for example, a whole directory
might be updated by a "patch" file that contained diff listings for
each of the files in the directory.
(By the way, the
tells it to
to a specified directory before
Recognize (or at least speculate) that a patch might have been created
incorrectly, with the old and new files swapped.
"Yes, I'm afraid that does happen
occasionally, human nature being what it is."
option will force
to reverse the sense of the patch; what's
really amusing is to see
suggest that this might be the
thing to do, when things seem out of sync.
If you are a programmer,
is worth studying just to see
how much a program can do to anticipate errors, deal with fuzzy
input, and in general "make the computer do the dirty work."
you're a programmer, you doubtless already know about
One last note:
is so useful that it's been added to many
Check to see if your system has it before installing
it from the CD-ROM.
[I've seen buggy or crippled versions from software vendors, though.
The one on the disc is worth comparing to yours.