<software> 1. A temporary addition to a piece of code, usually
	as a {quick-and-dirty} remedy to an existing {bug} or
	{misfeature}.  A patch may or may not work, and may or may not
	eventually be incorporated permanently into the program.
	Distinguished from a {diff} or {mod} by the fact that a patch
	is generated by more primitive means than the rest of the
	program; the classical examples are instructions modified by
	using the front panel switches, and changes made directly to
	the binary executable of a program originally written in an
	{HLL}.  Compare {one-line fix}.

	2. To insert a patch into a piece of code.

	3. [in the Unix world] A {diff}.

	4. A set of modifications to binaries to be applied by a
	patching program.  {IBM} systems often receive updates to the
	{operating system} in the form of absolute {hexadecimal}
	patches.  If you have modified your OS, you have to
	disassemble these back to the {source code}.  The patches
	might later be corrected by other patches on top of them
	(patches were said to "grow scar tissue").  The result was
	often a convoluted {patch space} and headaches galore.

	There is a classic story of a {tiger team} penetrating a
	secure military computer that illustrates the danger inherent
	in binary patches (or, indeed, any patches that you can't - or
	don't - inspect and examine before installing).  They couldn't
	find any {trap doors} or any way to penetrate security of
	IBM's OS, so they made a site visit to an IBM office
	(remember, these were official military types who were
	purportedly on official business), swiped some IBM stationery,
	and created a fake patch.  The patch was actually the trapdoor
	they needed.  The patch was distributed at about the right
	time for an IBM patch, had official stationery and all
	accompanying documentation, and was dutifully installed.  The
	installation manager very shortly thereafter learned something
	about proper procedures.

	5. {Larry Wall}'s "patch" utility, which automatically applies
	a patch to a set of {source code} or other text files.  Patch
	accepts input in any of the four forms output by the {Unix}
	{diff} utility.  When the files being patched are not
	identical to those on which the diffs were based, patch uses
	{heuristics} to determine how to proceed.

	Diff and patch are the standard way of producing and applying
	updates under {Unix}.  Both have been ported to other
	{operating systems}.

	{Patch Home (http://www.gnu.org/software/patch/patch.html)}.

	[{Jargon File}]

	(2005-05-16)