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DIFF(7)		     BSD Miscellaneous Information Manual	       DIFF(7)

NAME
     diff -- Comparing and Merging Files

Comparing and Merging Files
Overview
     Computer users often find occasion	to ask how two files differ. Perhaps
     one file is a newer version of the	other file. Or maybe the two files
     started out as identical copies but were changed by different people.

     You can use the diff command to show differences between two files, or
     each corresponding	file in	two directories.  diff outputs differences be-
     tween files line by line in any of	several	formats, selectable by command
     line options. This	set of differences is often called a diff or patch.
     For files that are	identical, diff	normally produces no output; for bi-
     nary (non-text) files, diff normally reports only that they are differ-
     ent.

     You can use the cmp command to show the byte and line numbers where two
     files differ.  cmp	can also show all the bytes that differ	between	the
     two files,	side by	side.  A way to	compare	two files character by charac-
     ter is the	Emacs command M-x compare-windows.  See	Section.Dq Other Win-
     dow , for more information	on that	command.

     You can use the diff3 command to show differences among three files. When
     two people	have made independent changes to a common original, diff3 can
     report the	differences between the	original and the two changed versions,
     and can produce a merged file that	contains both persons' changes to-
     gether with warnings about	conflicts.

     You can use the sdiff command to merge two	files interactively.

     You can use the set of differences	produced by diff to distribute updates
     to	text files (such as program source code) to other people. This method
     is	especially useful when the differences are small compared to the com-
     plete files. Given	diff output, you can use the patch program to update,
     or	patch, a copy of the file. If you think	of diff	as subtracting one
     file from another to produce their	difference, you	can think of patch as
     adding the	difference to one file to reproduce the	other.

     This manual first concentrates on making diffs, and later shows how to
     use diffs to update files.

     GNU diff was written by Paul Eggert, Mike Haertel,	David Hayes, Richard
     Stallman, and Len Tower. Wayne Davison designed and implemented the uni-
     fied output format.  The basic algorithm is described by Eugene W.	Myers
     in	"An O(ND) Difference Algorithm and its Variations", Algorithmica Vol.
     1 No. 2, 1986, pp.	251--266; and in "A File Comparison Program", Webb
     Miller and	Eugene W. Myers, Software---Practice and Experience Vol. 15
     No. 11, 1985, pp. 1025--1040. The algorithm was independently discovered
     as	described by E.	Ukkonen	in "Algorithms for Approximate String Match-
     ing", Information and Control Vol.	64, 1985, pp. 100--118.	Unless the
     [--minimal] option	is used, diff uses a heuristic by Paul Eggert that
     limits the	cost to	O(N^1.5	log N) at the price of producing suboptimal
     output for	large inputs with many differences.  Related algorithms	are
     surveyed by Alfred	V. Aho in section 6.3 of "Algorithms for Finding Pat-
     terns in Strings",	Handbook of Theoretical	Computer Science (Jan Van
     Leeuwen, ed.), Vol. A, Algorithms and Complexity, Elsevier/MIT Press,
     1990, pp. 255--300.

     GNU diff3 was written by Randy Smith. GNU sdiff was written by Thomas
     Lord. GNU cmp was written by Torbjorn Granlund and	David MacKenzie.

     GNU patch was written mainly by Larry Wall	and Paul Eggert; several GNU
     enhancements were contributed by Wayne Davison and	David MacKenzie. Parts
     of	this manual are	adapted	from a manual page written by Larry Wall, with
     his permission.

What Comparison	Means
     There are several ways to think about the differences between two files.
     One way to	think of the differences is as a series	of lines that were
     deleted from, inserted in,	or changed in one file to produce the other
     file.  diff compares two files line by line, finds	groups of lines	that
     differ, and reports each group of differing lines.	It can report the dif-
     fering lines in several formats, which have different purposes.

     GNU diff can show whether files are different without detailing the dif-
     ferences. It also provides	ways to	suppress certain kinds of differences
     that are not important to you. Most commonly, such	differences are
     changes in	the amount of white space between words	or lines.  diff	also
     provides ways to suppress differences in alphabetic case or in lines that
     match a regular expression	that you provide. These	options	can accumu-
     late; for example,	you can	ignore changes in both white space and alpha-
     betic case.

     Another way to think of the differences between two files is as a se-
     quence of pairs of	bytes that can be either identical or different.  cmp
     reports the differences between two files byte by byte, instead of	line
     by	line. As a result, it is often more useful than	diff for comparing bi-
     nary files. For text files, cmp is	useful mainly when you want to know
     only whether two files are	identical, or whether one file is a prefix of
     the other.

     To	illustrate the effect that considering changes byte by byte can	have
     compared with considering them line by line, think	of what	happens	if a
     single newline character is added to the beginning	of a file. If that
     file is then compared with	an otherwise identical file that lacks the
     newline at	the beginning, diff will report	that a blank line has been
     added to the file,	while cmp will report that almost every	byte of	the
     two files differs.

     diff3 normally compares three input files line by line, finds groups of
     lines that	differ,	and reports each group of differing lines. Its output
     is	designed to make it easy to inspect two	different sets of changes to
     the same file.

   Hunks
     When comparing two	files, diff finds sequences of lines common to both
     files, interspersed with groups of	differing lines	called hunks.  Compar-
     ing two identical files yields one	sequence of common lines and no	hunks,
     because no	lines differ. Comparing	two entirely different files yields no
     common lines and one large	hunk that contains all lines of	both files. In
     general, there are	many ways to match up lines between two	given files.
     diff tries	to minimize the	total hunk size	by finding large sequences of
     common lines interspersed with small hunks	of differing lines.

     For example, suppose the file F contains the three	lines a, b, c, and the
     file G contains the same three lines in reverse order c, b, a.  If	diff
     finds the line c as common, then the command diff F G produces this out-
     put:

	   1,2d0
	   < a
	   < b
	   3a2,3
	   > b
	   > a

     But if diff notices the common line b instead, it produces	this output:

	   1c1
	   < a
	   ---
	   > c
	   3c3
	   < c
	   ---
	   > a

     It	is also	possible to find a as the common line.	diff does not always
     find an optimal matching between the files; it takes shortcuts to run
     faster. But its output is usually close to	the shortest possible. You can
     adjust this tradeoff with the [-d]	or [--minimal] option (see Section
     "diff Performance").

   Suppressing Differences in Blank and	Tab Spacing
     The [-E] or [--ignore-tab-expansion] option ignores the distinction be-
     tween tabs	and spaces on input. A tab is considered to be equivalent to
     the number	of spaces to the next tab stop (see Section "Tabs").

     The [-b] or [--ignore-space-change] option	is stronger. It	ignores	white
     space at line end,	and considers all other	sequences of one or more white
     space characters within a line to be equivalent. With this	option,	diff
     considers the following two lines to be equivalent, where $ denotes the
     line end:

	   Here	lyeth  muche rychnesse	in lytell space.   -- John Heywood$
	   Here	lyeth muche rychnesse in lytell	space. -- John Heywood	 $

     The [-w] or [--ignore-all-space] option is	stronger still.	It ignores
     differences even if one line has white space where	the other line has
     none.  White space	characters include tab,	newline, vertical tab, form
     feed, carriage return, and	space; some locales may	define additional
     characters	to be white space.  With this option, diff considers the fol-
     lowing two	lines to be equivalent,	where $	denotes	the line end and ^M
     denotes a carriage	return:

	   Here	lyeth  muche  rychnesse	in lytell space.--  John Heywood$
	     He	relyeth	much erychnes  seinly tells pace.  --John Heywood   ^M$

   Suppressing Differences Whose Lines Are All Blank
     The [-B] or [--ignore-blank-lines]	option ignores changes that consist
     entirely of blank lines. With this	option,	for example, a file containing

	   1.  A point is that which has no part.

	   2.  A line is breadthless length.
	   -- Euclid, The Elements, I
     is	considered identical to	a file containing

	   1.  A point is that which has no part.
	   2.  A line is breadthless length.

	   -- Euclid, The Elements, I

     Normally this option affects only lines that are completely empty,	but if
     you also specify the [-b] or [--ignore-space-change] option, or the [-w]
     or	[--ignore-all-space] option, lines are also affected if	they look
     empty but contain white space.  In	other words, [-B] is equivalent	to -I
     '^$' by default, but it is	equivalent to [-I '^[[:space:]]*$'] if [-b] or
     [-w] is also specified.

   Suppressing Differences Whose Lines All Match a Regular Expression
     To	ignore insertions and deletions	of lines that match a grep -style reg-
     ular expression, use the [-I regexp] or [--ignore-matching-lines= regexp]
     option. You should	escape regular expressions that	contain	shell
     metacharacters to prevent the shell from expanding	them. For example,
     diff -I '^[[:digit:]]' ignores all	changes	to lines beginning with	a
     digit.

     However, [-I] only	ignores	the insertion or deletion of lines that	con-
     tain the regular expression if every changed line in the hunk---every in-
     sertion and every deletion---matches the regular expression. In other
     words, for	each nonignorable change, diff prints the complete set of
     changes in	its vicinity, including	the ignorable ones.

     You can specify more than one regular expression for lines	to ignore by
     using more	than one [-I] option.  diff tries to match each	line against
     each regular expression.

   Suppressing Case Differences
     GNU diff can treat	lower case letters as equivalent to their upper	case
     counterparts, so that, for	example, it considers Funky Stuff, funky
     STUFF, and	fUNKy stuFf to all be the same.	To request this, use the [-i]
     or	[--ignore-case]	option.

   Summarizing Which Files Differ
     When you only want	to find	out whether files are different, and you don't
     care what the differences are, you	can use	the summary output format. In
     this format, instead of showing the differences between the files,	diff
     simply reports whether files differ. The [-q] or [--brief]	option selects
     this output format.

     This format is especially useful when comparing the contents of two di-
     rectories.	 It is also much faster	than doing the normal line by line
     comparisons, because diff can stop	analyzing the files as soon as it
     knows that	there are any differences.

     You can also get a	brief indication of whether two	files differ by	using
     cmp.  For files that are identical, cmp produces no output. When the
     files differ, by default, cmp outputs the byte and	line number where the
     first difference occurs, or reports that one file is a prefix of the
     other. You	can use	the [-s], [--quiet], or	[--silent] option to suppress
     that information, so that cmp produces no output and reports whether the
     files differ using	only its exit status (see Section "Invoking cmp").

     Unlike diff, cmp cannot compare directories; it can only compare two
     files.

   Binary Files	and Forcing Text Comparisons
     If	diff thinks that either	of the two files it is comparing is binary (a
     non-text file), it	normally treats	that pair of files much	as if the sum-
     mary output format	had been selected (see Section "Brief"), and reports
     only that the binary files	are different. This is because line by line
     comparisons are usually not meaningful for	binary files.

     diff determines whether a file is text or binary by checking the first
     few bytes in the file; the	exact number of	bytes is system	dependent, but
     it	is typically several thousand. If every	byte in	that part of the file
     is	non-null, diff considers the file to be	text; otherwise	it considers
     the file to be binary.

     Sometimes you might want to force diff to consider	files to be text. For
     example, you might	be comparing text files	that contain null characters;
     diff would	erroneously decide that	those are non-text files. Or you might
     be	comparing documents that are in	a format used by a word	processing
     system that uses null characters to indicate special formatting. You can
     force diff	to consider all	files to be text files,	and compare them line
     by	line, by using the [-a]	or [--text] option. If the files you compare
     using this	option do not in fact contain text, they will probably contain
     few newline characters, and the diff output will consist of hunks showing
     differences between long lines of whatever	characters the files contain.

     You can also force	diff to	report only whether files differ (but not
     how). Use the [-q]	or [--brief] option for	this.

     Normally, differing binary	files count as trouble because the resulting
     diff output does not capture all the differences. This trouble causes
     diff to exit with status 2. However, this trouble cannot occur with the
     [-a] or [--text] option, or with the [-q] or [--brief] option, as these
     options both cause	diff to	generate a form	of output that represents dif-
     ferences as requested.

     In	operating systems that distinguish between text	and binary files, diff
     normally reads and	writes all data	as text. Use the [--binary] option to
     force diff	to read	and write binary data instead. This option has no ef-
     fect on a POSIX-compliant system like GNU or traditional Unix. However,
     many personal computer operating systems represent	the end	of a line with
     a carriage	return followed	by a newline.  On such systems,	diff normally
     ignores these carriage returns on input and generates them	at the end of
     each output line, but with	the [--binary] option diff treats each car-
     riage return as just another input	character, and does not	generate a
     carriage return at	the end	of each	output line. This can be useful	when
     dealing with non-text files that are meant	to be interchanged with	POSIX-
     compliant systems.

     The [--strip-trailing-cr] causes diff to treat input lines	that end in
     carriage return followed by newline as if they end	in plain newline. This
     can be useful when	comparing text that is imperfectly imported from many
     personal computer operating systems. This option affects how lines	are
     read, which in turn affects how they are compared and output.

     If	you want to compare two	files byte by byte, you	can use	the cmp	pro-
     gram with the [-l]	or [--verbose] option to show the values of each dif-
     fering byte in the	two files. With	GNU cmp, you can also use the [-b] or
     [--print-bytes] option to show the	ASCII representation of	those
     bytes.See Section "Invoking cmp", for more	information.

     If	diff3 thinks that any of the files it is comparing is binary (a	non-
     text file), it normally reports an	error, because such comparisons	are
     usually not useful.  diff3	uses the same test as diff to decide whether a
     file is binary. As	with diff, if the input	files contain a	few non-text
     bytes but otherwise are like text files, you can force diff3 to consider
     all files to be text files	and compare them line by line by using the
     [-a] or [--text] option.

diff(Output) Formats
     diff has several mutually exclusive options for output format. The	fol-
     lowing sections describe each format, illustrating	how diff reports the
     differences between two sample input files.

   Two Sample Input Files
     Here are two sample files that we will use	in numerous examples to	illus-
     trate the output of diff and how various options can change it.

     This is the file lao:

	   The Way that	can be told of is not the eternal Way;
	   The name that can be	named is not the eternal name.
	   The Nameless	is the origin of Heaven	and Earth;
	   The Named is	the mother of all things.
	   Therefore let there always be non-being,
	     so	we may see their subtlety,
	   And let there always	be being,
	     so	we may see their outcome.
	   The two are the same,
	   But after they are produced,
	     they have different names.

     This is the file tzu:

	   The Nameless	is the origin of Heaven	and Earth;
	   The named is	the mother of all things.

	   Therefore let there always be non-being,
	     so	we may see their subtlety,
	   And let there always	be being,
	     so	we may see their outcome.
	   The two are the same,
	   But after they are produced,
	     they have different names.
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!

     In	this example, the first	hunk contains just the first two lines of lao,
     the second	hunk contains the fourth line of lao opposing the second and
     third lines of tzu, and the last hunk contains just the last three	lines
     of	tzu.

   Showing Differences in Their	Context
     Usually, when you are looking at the differences between files, you will
     also want to see the parts	of the files near the lines that differ, to
     help you understand exactly what has changed. These nearby	parts of the
     files are called the context.

     GNU diff provides two output formats that show context around the differ-
     ing lines:	context	format and unified format.  It can optionally show in
     which function or section of the file the differing lines are found.

     If	you are	distributing new versions of files to other people in the form
     of	diff output, you should	use one	of the output formats that show	con-
     text so that they can apply the diffs even	if they	have made small
     changes of	their own to the files.	 patch can apply the diffs in this
     case by searching in the files for	the lines of context around the	dif-
     fering lines; if those lines are actually a few lines away	from where the
     diff says they are, patch can adjust the line numbers accordingly and
     still apply the diff correctly.See	Section	"Imperfect", for more informa-
     tion on using patch to apply imperfect diffs.

     Context Format

     The context output	format shows several lines of context around the lines
     that differ. It is	the standard format for	distributing updates to	source
     code.

     To	select this output format, use the [-C lines], [--context[= lines]],
     or	[-c] option. The argument lines	that some of these options take	is the
     number of lines of	context	to show.  If you do not	specify	lines, it de-
     faults to three. For proper operation, patch typically needs at least two
     lines of context.

     Example of	Context	Format

     Here is the output	of diff	-c lao tzu (see	Section	"Sample	diff Input",
     for the complete contents of the two files). Notice that up to three
     lines that	are not	different are shown around each	line that is differ-
     ent; they are the context lines. Also notice that the first two hunks
     have run together,	because	their contents overlap.

	   *** lao 2002-02-21 23:30:39.942229878 -0800
	   --- tzu 2002-02-21 23:30:50.442260588 -0800
	   ***************
	   *** 1,7 ****
	   - The Way that can be told of is not	the eternal Way;
	   - The name that can be named	is not the eternal name.
	     The Nameless is the origin	of Heaven and Earth;
	   ! The Named is the mother of	all things.
	     Therefore let there always	be non-being,
	       so we may see their subtlety,
	     And let there always be being,
	   --- 1,6 ----
	     The Nameless is the origin	of Heaven and Earth;
	   ! The named is the mother of	all things.
	   !
	     Therefore let there always	be non-being,
	       so we may see their subtlety,
	     And let there always be being,
	   ***************
	   *** 9,11 ****
	   --- 8,13 ----
	     The two are the same,
	     But after they are	produced,
	       they have different names.
	   + They both may be called deep and profound.
	   + Deeper and	more profound,
	   + The door of all subtleties!

     Example of	Context	Format with Less Context

     Here is the output	of diff	-C 1 lao tzu (see Section "Sample diff Input",
     for the complete contents of the two files). Notice that at most one con-
     text line is reported here.

	   *** lao 2002-02-21 23:30:39.942229878 -0800
	   --- tzu 2002-02-21 23:30:50.442260588 -0800
	   ***************
	   *** 1,5 ****
	   - The Way that can be told of is not	the eternal Way;
	   - The name that can be named	is not the eternal name.
	     The Nameless is the origin	of Heaven and Earth;
	   ! The Named is the mother of	all things.
	     Therefore let there always	be non-being,
	   --- 1,4 ----
	     The Nameless is the origin	of Heaven and Earth;
	   ! The named is the mother of	all things.
	   !
	     Therefore let there always	be non-being,
	   ***************
	   *** 11 ****
	   --- 10,13 ----
	       they have different names.
	   + They both may be called deep and profound.
	   + Deeper and	more profound,
	   + The door of all subtleties!

     Detailed Description of Context Format

     The context output	format starts with a two-line header, which looks like
     this:

	   *** from-file from-file-modification-time
	   --- to-file to-file-modification time

     The time stamp normally looks like	2002-02-21 23:30:39.942229878 -0800 to
     indicate the date,	time with fractional seconds, and time zone in
     ftp://ftp.isi.edu/in-notes/rfc2822.txt (The fractional seconds are	omit-
     ted on hosts that do not support fractional time stamps.) However,	a tra-
     ditional time stamp like Thu Feb 21 23:30:39 2002 is used if the LC_TIME
     locale category is	either C or POSIX.

     You can change the	header's content with the [--label= label] option; see
     Alternate Names.

     Next come one or more hunks of differences; each hunk shows one area
     where the files differ. Context format hunks look like this:

	   ***************
	   *** from-file-line-numbers ****
	     from-file-line
	     from-file-line...
	   --- to-file-line-numbers ----
	     to-file-line
	     to-file-line...

     If	a hunk contains	two or more lines, its line numbers look like start,
     end.  Otherwise only its end line number appears. An empty	hunk is	con-
     sidered to	end at the line	that precedes the hunk.

     The lines of context around the lines that	differ start with two space
     characters.  The lines that differ	between	the two	files start with one
     of	the following indicator	characters, followed by	a space	character:

     !	     A line that is part of a group of one or more lines that changed
	     between the two files. There is a corresponding group of lines
	     marked with !  in the part	of this	hunk for the other file.

     +	     An	"inserted" line	in the second file that	corresponds to nothing
	     in	the first file.

     -	     A "deleted" line in the first file	that corresponds to nothing in
	     the second	file.

     If	all of the changes in a	hunk are insertions, the lines of from-file
     are omitted. If all of the	changes	are deletions, the lines of to-file
     are omitted.

     Unified Format

     The unified output	format is a variation on the context format that is
     more compact because it omits redundant context lines. To select this
     output format, use	the [-U	lines],	[--unified[= lines]], or [-u] option.
     The argument lines	is the number of lines of context to show. When	it is
     not given,	it defaults to three.

     At	present, only GNU diff can produce this	format and only	GNU patch can
     automatically apply diffs in this format. For proper operation, patch
     typically needs at	least three lines of context.

     Example of	Unified	Format

     Here is the output	of the command diff -u lao tzu (see Section "Sample
     diff Input", for the complete contents of the two files):

	   --- lao 2002-02-21 23:30:39.942229878 -0800
	   +++ tzu 2002-02-21 23:30:50.442260588 -0800
	   @@ -1,7 +1,6	@@
	   -The	Way that can be	told of	is not the eternal Way;
	   -The	name that can be named is not the eternal name.
	    The	Nameless is the	origin of Heaven and Earth;
	   -The	Named is the mother of all things.
	   +The	named is the mother of all things.
	   +
	    Therefore let there	always be non-being,
	      so we may	see their subtlety,
	    And	let there always be being,
	   @@ -9,3 +8,6	@@
	    The	two are	the same,
	    But	after they are produced,
	      they have	different names.
	   +They both may be called deep and profound.
	   +Deeper and more profound,
	   +The	door of	all subtleties!

     Detailed Description of Unified Format

     The unified output	format starts with a two-line header, which looks like
     this:

	   --- from-file from-file-modification-time
	   +++ to-file to-file-modification-time

     The time stamp looks like 2002-02-21 23:30:39.942229878 -0800 to indicate
     the date, time with fractional seconds, and time zone. The	fractional
     seconds are omitted on hosts that do not support fractional time stamps.

     You can change the	header's content with the [--label= label] option;
     seeSee Section "Alternate Names".

     Next come one or more hunks of differences; each hunk shows one area
     where the files differ. Unified format hunks look like this:

	   @@ from-file-line-numbers to-file-line-numbers @@
	    line-from-either-file
	    line-from-either-file...

     If	a hunk contains	just one line, only its	start line number appears.
     Otherwise its line	numbers	look like start, count.	 An empty hunk is con-
     sidered to	start at the line that follows the hunk.

     If	a hunk and its context contain two or more lines, its line numbers
     look like start, count.  Otherwise	only its end line number appears. An
     empty hunk	is considered to end at	the line that precedes the hunk.

     The lines common to both files begin with a space character. The lines
     that actually differ between the two files	have one of the	following in-
     dicator characters	in the left print column:

     +	     A line was	added here to the first	file.

     -	     A line was	removed	here from the first file.

     Showing Which Sections Differences	Are in

     Sometimes you might want to know which part of the	files each change
     falls in. If the files are	source code, this could	mean which function
     was changed.  If the files	are documents, it could	mean which chapter or
     appendix was changed.  GNU	diff can show this by displaying the nearest
     section heading line that precedes	the differing lines. Which lines are
     "section headings"	is determined by a regular expression.

     Showing Lines That	Match Regular Expressions

     To	show in	which sections differences occur for files that	are not	source
     code for C	or similar languages, use the [-F regexp] or
     [--show-function-line= regexp] option.  diff considers lines that match
     the grep -style regular expression	regexp to be the beginning of a	sec-
     tion of the file. Here are	suggested regular expressions for some common
     languages:

     ^[[:alpha:]$_]
	     C,	C++, Prolog

     ^(	     Lisp

     ^@node  Texinfo

     This option does not automatically	select an output format; in order to
     use it, you must select the context format	(see Section "Context Format")
     or	unified	format (see Section "Unified Format").	In other output	for-
     mats it has no effect.

     The [-F] or [--show-function-line]	option finds the nearest unchanged
     line that precedes	each hunk of differences and matches the given regular
     expression. Then it adds that line	to the end of the line of asterisks in
     the context format, or to the @@ line in unified format. If no matching
     line exists, this option leaves the output	for that hunk unchanged. If
     that line is more than 40 characters long,	it outputs only	the first 40
     characters. You can specify more than one regular expression for such
     lines; diff tries to match	each line against each regular expression,
     starting with the last one	given. This means that you can use [-p]	and
     [-F] together, if you wish.

     Showing C Function	Headings

     To	show in	which functions	differences occur for C	and similar languages,
     you can use the [-p] or [--show-c-function] option. This option automati-
     cally defaults to the context output format (see Section "Context
     Format"), with the	default	number of lines	of context. You	can override
     that number with [-C lines] elsewhere in the command line.	You can	over-
     ride both the format and the number with [-U lines] elsewhere in the com-
     mand line.

     The [-p] or [--show-c-function] option is equivalent to [-F
     '^[[:alpha:]$_]'] if the unified format is	specified, otherwise [-c -F
     '^[[:alpha:]$_]'] (see Section "Specified Headings").  GNU	diff provides
     this option for the sake of convenience.

     Showing Alternate File Names

     If	you are	comparing two files that have meaningless or uninformative
     names, you	might want diff	to show	alternate names	in the header of the
     context and unified output	formats.  To do	this, use the [--label=	label]
     option. The first time you	give this option, its argument replaces	the
     name and date of the first	file in	the header; the	second time, its argu-
     ment replaces the name and	date of	the second file. If you	give this op-
     tion more than twice, diff	reports	an error. The [--label]	option does
     not affect	the file names in the pr header	when the [-l] or [--paginate]
     option is used (see Section "Pagination").

     Here are the first	two lines of the output	from diff -C 2
     --label=original --label=modified lao tzu:

	   *** original
	   --- modified

   Showing Differences Side by Side
     diff can produce a	side by	side difference	listing	of two files. The
     files are listed in two columns with a gutter between them. The gutter
     contains one of the following markers:

     white space
	     The corresponding lines are in common. That is, either the	lines
	     are identical, or the difference is ignored because of one	of the
	     [--ignore]	options	(see Section "White Space").

     |	     The corresponding lines differ, and they are either both complete
	     or	both incomplete.

     <	     The files differ and only the first file contains the line.

     >	     The files differ and only the second file contains	the line.

     (	     Only the first file contains the line, but	the difference is ig-
	     nored.

     )	     Only the second file contains the line, but the difference	is ig-
	     nored.

     \	     The corresponding lines differ, and only the first	line is	incom-
	     plete.

     /	     The corresponding lines differ, and only the second line is in-
	     complete.

     Normally, an output line is incomplete if and only	if the lines that it
     contains are incomplete;See Section "Incomplete Lines".  However, when an
     output line represents two	differing lines, one might be incomplete while
     the other is not. In this case, the output	line is	complete, but its the
     gutter is marked \	if the first line is incomplete, / if the second line
     is.

     Side by side format is sometimes easiest to read, but it has limitations.
     It	generates much wider output than usual,	and truncates lines that are
     too long to fit. Also, it relies on lining	up output more heavily than
     usual, so its output looks	particularly bad if you	use varying width
     fonts, nonstandard	tab stops, or nonprinting characters.

     You can use the sdiff command to interactively merge side by side differ-
     ences.See Section "Interactive Merging", for more information on merging
     files.

     Controlling Side by Side Format

     The [-y] or [--side-by-side] option selects side by side format. Because
     side by side output lines contain two input lines,	the output is wider
     than usual: normally 130 print columns, which can fit onto	a traditional
     printer line. You can set the width of the	output with the	[-W columns]
     or	[--width= columns] option. The output is split into two	halves of
     equal width, separated by a small gutter to mark differences; the right
     half is aligned to	a tab stop so that tabs	line up. Input lines that are
     too long to fit in	half of	an output line are truncated for output.

     The [--left-column] option	prints only the	left column of two common
     lines. The	[--suppress-common-lines] option suppresses common lines en-
     tirely.

     Example of	Side by	Side Format

     Here is the output	of the command diff -y -W 72 lao tzu (see Section
     "Sample diff Input", for the complete contents of the two files).

	   The Way that	can be told of is n   <
	   The name that can be	named is no   <
	   The Nameless	is the origin of He	   The Nameless	is the origin of He
	   The Named is	the mother of all t   |	   The named is	the mother of all t
					      >
	   Therefore let there always be no	   Therefore let there always be no
	     so	we may see their subtlety,	     so	we may see their subtlety,
	   And let there always	be being,	   And let there always	be being,
	     so	we may see their outcome.	     so	we may see their outcome.
	   The two are the same,		   The two are the same,
	   But after they are produced,		   But after they are produced,
	     they have different names.		     they have different names.
					      >	   They	both may be called deep	and
					      >	   Deeper and more profound,
					      >	   The door of all subtleties!

   Showing Differences Without Context
     The "normal" diff output format shows each	hunk of	differences without
     any surrounding context.  Sometimes such output is	the clearest way to
     see how lines have	changed, without the clutter of	nearby unchanged lines
     (although you can get similar results with	the context or unified formats
     by	using 0	lines of context). However, this format	is no longer widely
     used for sending out patches; for that purpose, the context format	(see
     Section "Context Format") and the unified format (see Section "Unified
     Format") are superior. Normal format is the default for compatibility
     with older	versions of diff and the POSIX standard. Use the [--normal]
     option to select this output format explicitly.

     Example of	Normal Format

     Here is the output	of the command diff lao	tzu (see Section "Sample diff
     Input", for the complete contents of the two files). Notice that it shows
     only the lines that are different between the two files.

	   1,2d0
	   < The Way that can be told of is not	the eternal Way;
	   < The name that can be named	is not the eternal name.
	   4c2,3
	   < The Named is the mother of	all things.
	   ---
	   > The named is the mother of	all things.
	   >
	   11a11,13
	   > They both may be called deep and profound.
	   > Deeper and	more profound,
	   > The door of all subtleties!

     Detailed Description of Normal Format

     The normal	output format consists of one or more hunks of differences;
     each hunk shows one area where the	files differ. Normal format hunks look
     like this:

	   change-command
	   < from-file-line
	   < from-file-line...
	   ---
	   > to-file-line
	   > to-file-line...

     There are three types of change commands. Each consists of	a line number
     or	comma-separated	range of lines in the first file, a single character
     indicating	the kind of change to make, and	a line number or comma-sepa-
     rated range of lines in the second	file. All line numbers are the origi-
     nal line numbers in each file. The	types of change	commands are:

     la	r    Add the lines in range r of the second file after line l of the
	     first file. For example, 8a12,15 means append lines 12--15	of
	     file 2 after line 8 of file 1; or,	if changing file 2 into	file
	     1,	delete lines 12--15 of file 2.

     fc	t    Replace the lines in range	f of the first file with lines in
	     range t of	the second file. This is like a	combined add and
	     delete, but more compact.	For example, 5,7c8,10 means change
	     lines 5--7	of file	1 to read as lines 8--10 of file 2; or,	if
	     changing file 2 into file 1, change lines 8--10 of	file 2 to read
	     as	lines 5--7 of file 1.

     rd	l    Delete the	lines in range r from the first	file; line l is	where
	     they would	have appeared in the second file had they not been
	     deleted.  For example, 5,7d3 means	delete lines 5--7 of file 1;
	     or, if changing file 2 into file 1, append	lines 5--7 of file 1
	     after line	3 of file 2.

   Making Edit Scripts
     Several output modes produce command scripts for editing from-file	to
     produce to-file.

     ed(Scripts)

     diff can produce commands that direct the ed text editor to change	the
     first file	into the second	file. Long ago,	this was the only output mode
     that was suitable for editing one file into another automatically;	today,
     with patch, it is almost obsolete.	Use the	[-e] or	[--ed] option to se-
     lect this output format.

     Like the normal format (see Section "Normal"), this output	format does
     not show any context; unlike the normal format, it	does not include the
     information necessary to apply the	diff in	reverse	(to produce the	first
     file if all you have is the second	file and the diff).

     If	the file d contains the	output of diff -e old new, then	the command
     (cat d && echo w) | ed - old edits	old to make it a copy of new.  More
     generally,	if d1, d2, ...,	dN contain the outputs of diff -e old new1,
     diff -e new1 new2,	..., diff -e newN-1 newN, respectively,	then the com-
     mand (cat d1 d2 ... dN && echo w) | ed - old edits	old to make it a copy
     of	newN.

     Example ed(Script)

     Here is the output	of diff	-e lao tzu (see	Section	"Sample	diff Input",
     for the complete contents of the two files):

	   11a
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!
	   .
	   4c
	   The named is	the mother of all things.

	   .
	   1,2d

     Detailed Description of ed(Format)

     The ed output format consists of one or more hunks	of differences.	The
     changes closest to	the ends of the	files come first so that commands that
     change the	number of lines	do not affect how ed interprets	line numbers
     in	succeeding commands.  ed format	hunks look like	this:

	   change-command
	   to-file-line
	   to-file-line...
	   .

     Because ed	uses a single period on	a line to indicate the end of input,
     GNU diff protects lines of	changes	that contain a single period on	a line
     by	writing	two periods instead, then writing a subsequent ed command to
     change the	two periods into one. The ed format cannot represent an	incom-
     plete line, so if the second file ends in a changed incomplete line, diff
     reports an	error and then pretends	that a newline was appended.

     There are three types of change commands. Each consists of	a line number
     or	comma-separated	range of lines in the first file and a single charac-
     ter indicating the	kind of	change to make.	All line numbers are the orig-
     inal line numbers in the file. The	types of change	commands are:

     la	     Add text from the second file after line l	in the first file. For
	     example, 8a means to add the following lines after	line 8 of file
	     1.

     rc	     Replace the lines in range	r in the first file with the following
	     lines. Like a combined add	and delete, but	more compact. For ex-
	     ample, 5,7c means change lines 5--7 of file 1 to read as the text
	     file 2.

     rd	     Delete the	lines in range r from the first	file. For example,
	     5,7d means	delete lines 5--7 of file 1.

     Forward ed(Scripts)

     diff can produce output that is like an ed	script,	but with hunks in for-
     ward (front to back) order. The format of the commands is also changed
     slightly: command characters precede the lines they modify, spaces	sepa-
     rate line numbers in ranges, and no attempt is made to disambiguate hunk
     lines consisting of a single period. Like ed format, forward ed format
     cannot represent incomplete lines.

     Forward ed	format is not very useful, because neither ed nor patch	can
     apply diffs in this format. It exists mainly for compatibility with older
     versions of diff.	Use the	[-f] or	[--forward-ed] option to select	it.

     RCS Scripts

     The RCS output format is designed specifically for	use by the Revision
     Control System, which is a	set of free programs used for organizing dif-
     ferent versions and systems of files. Use the [-n]	or [--rcs] option to
     select this output	format.	It is like the forward ed format (see Section
     "Forward ed"), but	it can represent arbitrary changes to the contents of
     a file because it avoids the forward ed format's problems with lines con-
     sisting of	a single period	and with incomplete lines. Instead of ending
     text sections with	a line consisting of a single period, each command
     specifies the number of lines it affects; a combination of	the a and d
     commands are used instead of c.  Also, if the second file ends in a
     changed incomplete	line, then the output also ends	in an incomplete line.

     Here is the output	of diff	-n lao tzu (see	Section	"Sample	diff Input",
     for the complete contents of the two files):

	   d1 2
	   d4 1
	   a4 2
	   The named is	the mother of all things.

	   a11 3
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!

   Merging Files with If-then-else
     You can use diff to merge two files of C source code. The output of diff
     in	this format contains all the lines of both files. Lines	common to both
     files are output just once; the differing parts are separated by the C
     preprocessor directives #ifdef name or #ifndef name, #else, and #endif.
     When compiling the	output,	you select which version to use	by either
     defining or leaving undefined the macro name.

     To	merge two files, use diff with the [-D name] or	[--ifdef= name]	op-
     tion. The argument	name is	the C preprocessor identifier to use in	the
     #ifdef and	#ifndef	directives.

     For example, if you change	an instance of wait (&s) to waitpid (-1, &s,
     0)	and then merge the old and new files with the [--ifdef=HAVE_WAITPID]
     option, then the affected part of your code might look like this:

	       do {
	   #ifndef HAVE_WAITPID
		   if ((w = wait (&s)) < 0  &&	errno != EINTR)
	   #else /* HAVE_WAITPID */
		   if ((w = waitpid (-1, &s, 0)) < 0  &&  errno	!= EINTR)
	   #endif /* HAVE_WAITPID */
		       return w;
	       } while (w != child);

     You can specify formats for languages other than C	by using line group
     formats and line formats, as described in the next	sections.

     Line Group	Formats

     Line group	formats	let you	specify	formats	suitable for many applications
     that allow	if-then-else input, including programming languages and	text
     formatting	languages. A line group	format specifies the output format for
     a contiguous group	of similar lines.

     For example, the following	command	compares the TeX files old and new,
     and outputs a merged file in which	old regions are	surrounded by
     \begin{em}	- \end{em} lines, and new regions are surrounded by \begin{bf}
     - \end{bf}	lines.

	   diff	\
	      --old-group-format='\begin{em}
	   %<\end{em}
	   ' \
	      --new-group-format='\begin{bf}
	   %>\end{bf}
	   ' \
	      old new

     The following command is equivalent to the	above example, but it is a
     little more verbose, because it spells out	the default line group for-
     mats.

	   diff	\
	      --old-group-format='\begin{em}
	   %<\end{em}
	   ' \
	      --new-group-format='\begin{bf}
	   %>\end{bf}
	   ' \
	      --unchanged-group-format='%=' \
	      --changed-group-format='\begin{em}
	   %<\end{em}
	   \begin{bf}
	   %>\end{bf}
	   ' \
	      old new

     Here is a more advanced example, which outputs a diff listing with	head-
     ers containing line numbers in a "plain English" style.

	   diff	\
	      --unchanged-group-format=" \
	      --old-group-format='-------- %dn line%(n=1?:s) deleted at	%df:
	   %<' \
	      --new-group-format='-------- %dN line%(N=1?:s) added after %de:
	   %>' \
	      --changed-group-format='-------- %dn line%(n=1?:s) changed at %df:
	   %<-------- to:
	   %>' \
	      old new

     To	specify	a line group format, use diff with one of the options listed
     below. You	can specify up to four line group formats, one for each	kind
     of	line group. You	should quote format, because it	typically contains
     shell metacharacters.

     --old-group-format= format
	     These line	groups are hunks containing only lines from the	first
	     file. The default old group format	is the same as the changed
	     group format if it	is specified; otherwise	it is a	format that
	     outputs the line group as-is.

     --new-group-format= format
	     These line	groups are hunks containing only lines from the	second
	     file. The default new group format	is same	as the changed group
	     format if it is specified;	otherwise it is	a format that outputs
	     the line group as-is.

     --changed-group-format= format
	     These line	groups are hunks containing lines from both files. The
	     default changed group format is the concatenation of the old and
	     new group formats.

     --unchanged-group-format= format
	     These line	groups contain lines common to both files. The default
	     unchanged group format is a format	that outputs the line group
	     as-is.

     In	a line group format, ordinary characters represent themselves; conver-
     sion specifications start with % and have one of the following forms.

     %<	     stands for	the lines from the first file, including the trailing
	     newline.  Each line is formatted according	to the old line	format
	     (see Section "Line	Formats").

     %>	     stands for	the lines from the second file,	including the trailing
	     newline.  Each line is formatted according	to the new line	for-
	     mat.

     %=	     stands for	the lines common to both files,	including the trailing
	     newline.  Each line is formatted according	to the unchanged line
	     format.

     %%	     stands for	%.

     %c' C'  where C is	a single character, stands for C.  C may not be	a
	     backslash or an apostrophe. For example, %c':' stands for a
	     colon, even inside	the then-part of an if-then-else format, which
	     a colon would normally terminate.

     %c'\ O'
	     where O is	a string of 1, 2, or 3 octal digits, stands for	the
	     character with octal code O.  For example,	%c'\0' stands for a
	     null character.

     F n     where F is	a printf conversion specification and n	is one of the
	     following letters,	stands for n 's	value formatted	with F.

	     e	     The line number of	the line just before the group in the
		     old file.

	     f	     The line number of	the first line in the group in the old
		     file; equals e + 1.

	     l	     The line number of	the last line in the group in the old
		     file.

	     m	     The line number of	the line just after the	group in the
		     old file; equals l	+ 1.

	     n	     The number	of lines in the	group in the old file; equals
		     l - f + 1.

	     E,	F, L, M, N
		     Likewise, for lines in the	new file.

	     The printf	conversion specification can be	%d, %o,	%x, or %X,
	     specifying	decimal, octal,	lower case hexadecimal,	or upper case
	     hexadecimal output	respectively. After the	% the following	op-
	     tions can appear in sequence: a series of zero or more flags; an
	     integer specifying	the minimum field width; and a period followed
	     by	an optional integer specifying the minimum number of digits.
	     The flags are - for left-justification, ' for separating the
	     digit into	groups as specified by the LC_NUMERIC locale category,
	     and 0 for padding with zeros instead of spaces. For example, %5dN
	     prints the	number of new lines in the group in a field of width 5
	     characters, using the printf format %5d.

     (A= B? T: E)
	     If	A equals B then	T else E.  A and B are each either a decimal
	     constant or a single letter interpreted as	above.	This format
	     spec is equivalent	to T if	A 's value equals B 's;	otherwise it
	     is	equivalent to E.

	     For example, %(N=0?no:%dN)	line%(N=1?:s) is equivalent to no
	     lines if N	(the number of lines in	the group in the new file) is
	     0,	to 1 line if N is 1, and to %dN	lines otherwise.

     Line Formats

     Line formats control how each line	taken from an input file is output as
     part of a line group in if-then-else format.

     For example, the following	command	outputs	text with a one-character
     change indicator to the left of the text. The first character of output
     is	- for deleted lines, | for added lines,	and a space for	unchanged
     lines. The	formats	contain	newline	characters where newlines are desired
     on	output.

	   diff	\
	      --old-line-format='-%l
	   ' \
	      --new-line-format='|%l
	   ' \
	      --unchanged-line-format='	%l
	   ' \
	      old new

     To	specify	a line format, use one of the following	options. You should
     quote format, since it often contains shell metacharacters.

     --old-line-format=	format
	     formats lines just	from the first file.

     --new-line-format=	format
	     formats lines just	from the second	file.

     --unchanged-line-format= format
	     formats lines common to both files.

     --line-format= format
	     formats all lines;	in effect, it sets all three above options si-
	     multaneously.

     In	a line format, ordinary	characters represent themselves; conversion
     specifications start with % and have one of the following forms.

     %l	     stands for	the contents of	the line, not counting its trailing
	     newline (if any). This format ignores whether the line is incom-
	     plete;See Section "Incomplete Lines".

     %L	     stands for	the contents of	the line, including its	trailing new-
	     line (if any).  If	a line is incomplete, this format preserves
	     its incompleteness.

     %%	     stands for	%.

     %c' C'  where C is	a single character, stands for C.  C may not be	a
	     backslash or an apostrophe. For example, %c':' stands for a
	     colon.

     %c'\ O'
	     where O is	a string of 1, 2, or 3 octal digits, stands for	the
	     character with octal code O.  For example,	%c'\0' stands for a
	     null character.

	     where F is	a printf conversion specification, stands for the line
	     number formatted with F.  For example, %.5dn prints the line num-
	     ber using the printf format %.5d.	See Section.Dq Line Group For-
	     mats , for	more about printf conversion specifications.

     The default line format is	%l followed by a newline character.

     If	the input contains tab characters and it is important that they	line
     up	on output, you should ensure that %l or	%L in a	line format is just
     after a tab stop (e.g. by preceding %l or %L with a tab character), or
     you should	use the	[-t] or	[--expand-tabs]	option.

     Taken together, the line and line group formats let you specify many dif-
     ferent formats. For example, the following	command	uses a format similar
     to	normal diff format. You	can tailor this	command	to get fine control
     over diff output.

	   diff	\
	      --old-line-format='< %l
	   ' \
	      --new-line-format='> %l
	   ' \
	      --old-group-format='%df%(f=l?:,%dl)d%dE
	   %<' \
	      --new-group-format='%dea%dF%(F=L?:,%dL)
	   %>' \
	      --changed-group-format='%df%(f=l?:,%dl)c%dF%(F=L?:,%dL)
	   %<---
	   %>' \
	      --unchanged-group-format=" \
	      old new

     Example of	If-then-else Format

     Here is the output	of diff	-DTWO lao tzu (see Section "Sample diff
     Input", for the complete contents of the two files):

	   #ifndef TWO
	   The Way that	can be told of is not the eternal Way;
	   The name that can be	named is not the eternal name.
	   #endif /* ! TWO */
	   The Nameless	is the origin of Heaven	and Earth;
	   #ifndef TWO
	   The Named is	the mother of all things.
	   #else /* TWO	*/
	   The named is	the mother of all things.

	   #endif /* TWO */
	   Therefore let there always be non-being,
	     so	we may see their subtlety,
	   And let there always	be being,
	     so	we may see their outcome.
	   The two are the same,
	   But after they are produced,
	     they have different names.
	   #ifdef TWO
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!
	   #endif /* TWO */

     Detailed Description of If-then-else Format

     For lines common to both files, diff uses the unchanged line group	for-
     mat. For each hunk	of differences in the merged output format, if the
     hunk contains only	lines from the first file, diff	uses the old line
     group format; if the hunk contains	only lines from	the second file, diff
     uses the new group	format;	otherwise, diff	uses the changed group format.

     The old, new, and unchanged line formats specify the output format	of
     lines from	the first file,	lines from the second file, and	lines common
     to	both files, respectively.

     The option	[--ifdef= name]	is equivalent to the following sequence	of op-
     tions using shell syntax:

	   --old-group-format='#ifndef name
	   %<#endif /* ! name */
	   ' \
	   --new-group-format='#ifdef name
	   %>#endif /* name */
	   ' \
	   --unchanged-group-format='%=' \
	   --changed-group-format='#ifndef name
	   %<#else /* name */
	   %>#endif /* name */
	   '

     You should	carefully check	the diff output	for proper nesting. For	exam-
     ple, when using the [-D name] or [--ifdef=	name] option, you should check
     that if the differing lines contain any of	the C preprocessor directives
     #ifdef, #ifndef, #else, #elif, or #endif, they are	nested properly	and
     match. If they don't, you must make corrections manually. It is a good
     idea to carefully check the resulting code	anyway to make sure that it
     really does what you want it to; depending	on how the input files were
     produced, the output might	contain	duplicate or otherwise incorrect code.

     The patch [-D name] option	behaves	like the diff [-D name]	option,	except
     it	operates on a file and a diff to produce a merged file;See Section
     "patch Options".

Incomplete Lines
     When an input file	ends in	a non-newline character, its last line is
     called an incomplete line because its last	character is not a newline.
     All other lines are called	full lines and end in a	newline	character. In-
     complete lines do not match full lines unless differences in white	space
     are ignored (see Section "White Space").

     An	incomplete line	is normally distinguished on output from a full	line
     by	a following line that starts with \.  However, the RCS format (see
     Section "RCS") outputs the	incomplete line	as-is, without any trailing
     newline or	following line.	The side by side format	normally represents
     incomplete	lines as-is, but in some cases uses a \	or / gutter marker;See
     Section "Side by Side".  The if-then-else line format preserves a line's
     incompleteness with %L, and discards the newline with %l ;See Section
     "Line Formats".  Finally, with the	ed and forward ed output formats (see
     Section "Output Formats") diff cannot represent an	incomplete line, so it
     pretends there was	a newline and reports an error.

     For example, suppose F and	G are one-byte files that contain just f and
     g,	respectively. Then diff	F G outputs

	   1c1
	   < f
	   \ No	newline	at end of file
	   ---
	   > g
	   \ No	newline	at end of file

     (The exact	message	may differ in non-English locales.)  diff -n F G out-
     puts the following	without	a trailing newline:

	   d1 1
	   a1 1
	   g

     diff -e F G reports two errors and	outputs	the following:

	   1c
	   g
	   .

Comparing Directories
     You can use diff to compare some or all of	the files in two directory
     trees. When both file name	arguments to diff are directories, it compares
     each file that is contained in both directories, examining	file names in
     alphabetical order	as specified by	the LC_COLLATE locale category.	Nor-
     mally diff	is silent about	pairs of files that contain no differences,
     but if you	use the	[-s] or	[--report-identical-files] option, it reports
     pairs of identical	files. Normally	diff reports subdirectories common to
     both directories without comparing	subdirectories'	files, but if you use
     the [-r] or [--recursive] option, it compares every corresponding pair of
     files in the directory trees, as many levels deep as they go.

     For file names that are in	only one of the	directories, diff normally
     does not show the contents	of the file that exists; it reports only that
     the file exists in	that directory and not in the other. You can make diff
     act as though the file existed but	was empty in the other directory, so
     that it outputs the entire	contents of the	file that actually exists. (It
     is	output as either an insertion or a deletion, depending on whether it
     is	in the first or	the second directory given.) To	do this, use the [-N]
     or	[--new-file] option.

     If	the older directory contains one or more large files that are not in
     the newer directory, you can make the patch smaller by using the
     [--unidirectional-new-file] option	instead	of [-N].  This option is like
     [-N] except that it only inserts the contents of files that appear	in the
     second directory but not the first	(that is, files	that were added). At
     the top of	the patch, write instructions for the user applying the	patch
     to	remove the files that were deleted before applying the patch.See Sec-
     tion "Making Patches", for	more discussion	of making patches for distri-
     bution.

     To	ignore some files while	comparing directories, use the [-x pattern] or
     [--exclude= pattern] option. This option ignores any files	or subdirecto-
     ries whose	base names match the shell pattern pattern.  Unlike in the
     shell, a period at	the start of the base of a file	name matches a wild-
     card at the start of a pattern. You should	enclose	pattern	in quotes so
     that the shell does not expand it.	For example, the option	[-x '*.[ao]']
     ignores any file whose name ends with .a or .o.

     This option accumulates if	you specify it more than once. For example,
     using the options [-x 'RCS' -x '*,v'] ignores any file or subdirectory
     whose base	name is	RCS or ends with ,v.

     If	you need to give this option many times, you can instead put the pat-
     terns in a	file, one pattern per line, and	use the	[-X file] or
     [--exclude-from= file] option. Trailing white space and empty lines are
     ignored in	the pattern file.

     If	you have been comparing	two directories	and stopped partway through,
     later you might want to continue where you	left off. You can do this by
     using the [-S file] or [--starting-file= file] option. This compares only
     the file file and all alphabetically later	files in the topmost directory
     level.

     If	two directories	differ only in that file names are lower case in one
     directory and upper case in the upper, diff normally reports many differ-
     ences because it compares file names in a case sensitive way. With	the
     [--ignore-file-name-case] option, diff ignores case differences in	file
     names, so that for	example	the contents of	the file Tao in	one directory
     are compared to the contents of the file TAO in the other.	The
     [--no-ignore-file-name-case] option cancels the effect of the
     [--ignore-file-name-case] option, reverting to the	default	behavior.

     If	an [-x pattern]	or [--exclude= pattern]	option,	or an [-X file]	or
     [--exclude-from= file] option, is specified while the
     [--ignore-file-name-case] option is in effect, case is ignored when ex-
     cluding file names	matching the specified patterns.

Making diff(Output) Prettier
     diff provides several ways	to adjust the appearance of its	output.	These
     adjustments can be	applied	to any output format.

   Preserving Tab Stop Alignment
     The lines of text in some of the diff output formats are preceded by one
     or	two characters that indicate whether the text is inserted, deleted, or
     changed. The addition of those characters can cause tabs to move to the
     next tab stop, throwing off the alignment of columns in the line. GNU
     diff provides two ways to make tab-aligned	columns	line up	correctly.

     The first way is to have diff convert all tabs into the correct number of
     spaces before outputting them; select this	method with the	[-t] or
     [--expand-tabs] option. To	use this form of output	with patch, you	must
     give patch	the [-l] or [--ignore-white-space] option (see Section
     "Changed White Space", for	more information).  diff normally assumes that
     tab stops are set every 8 print columns, but this can be altered by the
     [--tabsize= columns] option.

     The other method for making tabs line up correctly	is to add a tab	char-
     acter instead of a	space after the	indicator character at the beginning
     of	the line.  This	ensures	that all following tab characters are in the
     same position relative to tab stops that they were	in the original	files,
     so	that the output	is aligned correctly. Its disadvantage is that it can
     make long lines too long to fit on	one line of the	screen or the paper.
     It	also does not work with	the unified output format, which does not have
     a space character after the change	type indicator character. Select this
     method with the [-T] or [--initial-tab] option.

   Paginating diff(Output)
     It	can be convenient to have long output page-numbered and	time-stamped.
     The [-l] or [--paginate] option does this by sending the diff output
     through the pr program. Here is what the page header might	look like for
     diff -lc lao tzu:

	   2002-02-22 14:20		    diff -lc lao tzu		     Page 1

diff(Performance) Tradeoffs
     GNU diff runs quite efficiently; however, in some circumstances you can
     cause it to run faster or produce a more compact set of changes.

     One way to	improve	diff performance is to use hard	or symbolic links to
     files instead of copies. This improves performance	because	diff normally
     does not need to read two hard or symbolic	links to the same file,	since
     their contents must be identical. For example, suppose you	copy a large
     directory hierarchy, make a few changes to	the copy, and then often use
     diff -r to	compare	the original to	the copy. If the original files	are
     read-only,	you can	greatly	improve	performance by creating	the copy using
     hard or symbolic links (e.g., with	GNU cp -lR or cp -sR).	Before editing
     a file in the copy	for the	first time, you	should break the link and re-
     place it with a regular copy.

     You can also affect the performance of GNU	diff by	giving it options that
     change the	way it compares	files. Performance has more than one dimen-
     sion. These options improve one aspect of performance at the cost of an-
     other, or they improve performance	in some	cases while hurting it in oth-
     ers.

     The way that GNU diff determines which lines have changed always comes up
     with a near-minimal set of	differences. Usually it	is good	enough for
     practical purposes. If the	diff output is large, you might	want diff to
     use a modified algorithm that sometimes produces a	smaller	set of differ-
     ences.  The [-d] or [--minimal] option does this; however,	it can also
     cause diff	to run more slowly than	usual, so it is	not the	default	behav-
     ior.

     When the files you	are comparing are large	and have small groups of
     changes scattered throughout them,	you can	use the	[--speed-large-files]
     option to make a different	modification to	the algorithm that diff	uses.
     If	the input files	have a constant	small density of changes, this option
     speeds up the comparisons without changing	the output. If not, diff might
     produce a larger set of differences; however, the output will still be
     correct.

     Normally diff discards the	prefix and suffix that is common to both files
     before it attempts	to find	a minimal set of differences. This makes diff
     run faster, but occasionally it may produce non-minimal output. The
     [--horizon-lines= lines] option prevents diff from	discarding the last
     lines lines of the	prefix and the first lines lines of the	suffix.	This
     gives diff	further	opportunities to find a	minimal	output.

     Suppose a run of changed lines includes a sequence	of lines at one	end
     and there is an identical sequence	of lines just outside the other	end.
     The diff command is free to choose	which identical	sequence is included
     in	the hunk.  In this case, diff normally shifts the hunk's boundaries
     when this merges adjacent hunks, or shifts	a hunk's lines towards the end
     of	the file. Merging hunks	can make the output look nicer in some cases.

Comparing Three	Files
     Use the program diff3 to compare three files and show any differences
     among them. ( diff3 can also merge	files; see diff3 Merging).

     The "normal" diff3	output format shows each hunk of differences without
     surrounding context.  Hunks are labeled depending on whether they are
     two-way or	three-way, and lines are annotated by their location in	the
     input files.

     See Section.Dq Invoking diff3 , for more information on how to run	diff3.

   A Third Sample Input	File
     Here is a third sample file that will be used in examples to illustrate
     the output	of diff3 and how various options can change it.	The first two
     files are the same	that we	used for diff (see Section "Sample diff
     Input").  This is the third sample	file, called tao:

	   The Way that	can be told of is not the eternal Way;
	   The name that can be	named is not the eternal name.
	   The Nameless	is the origin of Heaven	and Earth;
	   The named is	the mother of all things.

	   Therefore let there always be non-being,
	     so	we may see their subtlety,
	   And let there always	be being,
	     so	we may see their result.
	   The two are the same,
	   But after they are produced,
	     they have different names.

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan

   Example of diff3(Normal) Format
     Here is the output	of the command diff3 lao tzu tao (see Section "Sample
     diff3 Input", for the complete contents of	the files). Notice that	it
     shows only	the lines that are different among the three files.

	   ====2
	   1:1,2c
	   3:1,2c
	     The Way that can be told of is not	the eternal Way;
	     The name that can be named	is not the eternal name.
	   2:0a
	   ====1
	   1:4c
	     The Named is the mother of	all things.
	   2:2,3c
	   3:4,5c
	     The named is the mother of	all things.

	   ====3
	   1:8c
	   2:7c
	       so we may see their outcome.
	   3:9c
	       so we may see their result.
	   ====
	   1:11a
	   2:11,13c
	     They both may be called deep and profound.
	     Deeper and	more profound,
	     The door of all subtleties!
	   3:13,14c

	       -- The Way of Lao-Tzu, tr. Wing-tsit Chan

   Detailed Description	of diff3(Normal) Format
     Each hunk begins with a line marked ====.	Three-way hunks	have plain
     ==== lines, and two-way hunks have	1, 2, or 3 appended to specify which
     of	the three input	files differ in	that hunk. The hunks contain copies of
     two or three sets of input	lines each preceded by one or two commands
     identifying where the lines came from.

     Normally, two spaces precede each copy of an input	line to	distinguish it
     from the commands.	But with the [-T] or [--initial-tab] option, diff3
     uses a tab	instead	of two spaces; this lines up tabs correctly.See	Sec-
     tion "Tabs", for more information.

     Commands take the following forms:

     file: la
	     This hunk appears after line l of file file, and contains no
	     lines in that file. To edit this file to yield the	other files,
	     one must append hunk lines	taken from the other files. For	exam-
	     ple, 1:11a	means that the hunk follows line 11 in the first file
	     and contains no lines from	that file.

     file: rc
	     This hunk contains	the lines in the range r of file file.	The
	     range r is	a comma-separated pair of line numbers,	or just	one
	     number if the range is a singleton. To edit this file to yield
	     the other files, one must change the specified lines to be	the
	     lines taken from the other	files. For example, 2:11,13c means
	     that the hunk contains lines 11 through 13	from the second	file.

     If	the last line in a set of input	lines is incomplete (see Section
     "Incomplete Lines"), it is	distinguished on output	from a full line by a
     following line that starts	with \.

   diff3(Hunks)
     Groups of lines that differ in two	or three of the	input files are	called
     diff3 hunks, by analogy with diff hunks (see Section "Hunks").  If	all
     three input files differ in a diff3 hunk, the hunk	is called a three-way
     hunk ; if just two	input files differ, it is a two-way hunk.

     As	with diff, several solutions are possible. When	comparing the files A,
     B,	and C, diff3 normally finds diff3 hunks	by merging the two-way hunks
     output by the two commands	diff A B and diff A C.	This does not neces-
     sarily minimize the size of the output, but exceptions should be rare.

     For example, suppose F contains the three lines a,	b, f, G	contains the
     lines g, b, g, and	H contains the lines a,	b, h.  diff3 F G H might out-
     put the following:

	   ====2
	   1:1c
	   3:1c
	     a
	   2:1c
	     g
	   ====
	   1:3c
	     f
	   2:3c
	     g
	   3:3c
	     h

     because it	found a	two-way	hunk containing	a in the first and third files
     and g in the second file, then the	single line b common to	all three
     files, then a three-way hunk containing the last line of each file.

Merging	From a Common Ancestor
     When two people have made changes to copies of the	same file, diff3 can
     produce a merged output that contains both	sets of	changes	together with
     warnings about conflicts.

     One might imagine programs	with names like	diff4 and diff5	to compare
     more than three files simultaneously, but in practice the need rarely
     arises. You can use diff3 to merge	three or more sets of changes to a
     file by merging two change	sets at	a time.

     diff3 can incorporate changes from	two modified versions into a common
     preceding version.	This lets you merge the	sets of	changes	represented by
     the two newer files. Specify the common ancestor version as the second
     argument and the two newer	versions as the	first and third	arguments,
     like this:

	   diff3 mine older yours

     You can remember the order	of the arguments by noting that	they are in
     alphabetical order.

     You can think of this as subtracting older	from yours and adding the re-
     sult to mine, or as merging into mine the changes that would turn older
     into yours.  This merging is well-defined as long as mine and older match
     in	the neighborhood of each such change. This fails to be true when all
     three input files differ or when only older differs; we call this a
     conflict.	When all three input files differ, we call the conflict	an
     overlap.

     diff3 gives you several ways to handle overlaps and conflicts. You	can
     omit overlaps or conflicts, or select only	overlaps, or mark conflicts
     with special <<<<<<< and >>>>>>> lines.

     diff3 can output the merge	results	as an ed script	that that can be ap-
     plied to the first	file to	yield the merged output.  However, it is usu-
     ally better to have diff3 generate	the merged output directly; this by-
     passes some problems with ed.

   Selecting Which Changes to Incorporate
     You can select all	unmerged changes from older to yours for merging into
     mine with the [-e]	or [--ed] option. You can select only the nonoverlap-
     ping unmerged changes with	[-3] or	[--easy-only], and you can select only
     the overlapping changes with [-x] or [--overlap-only].

     The [-e], [-3] and	[-x] options select only unmerged changes, i.e.
     changes where mine	and yours differ; they ignore changes from older to
     yours where mine and yours	are identical, because they assume that	such
     changes have already been merged.	If this	assumption is not a safe one,
     you can use the [-A] or [--show-all] option (see Section "Marking
     Conflicts").

     Here is the output	of the command diff3 with each of these	three options
     (see Section "Sample diff3	Input",	for the	complete contents of the
     files). Notice that [-e] outputs the union	of the disjoint	sets of
     changes output by [-3] and	[-x].

     Output of diff3 -e	lao tzu	tao:

	   11a

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan
	   .
	   8c
	     so	we may see their result.
	   .

     Output of diff3 -3	lao tzu	tao:

	   8c
	     so	we may see their result.
	   .

     Output of diff3 -x	lao tzu	tao:

	   11a

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan
	   .

   Marking Conflicts
     diff3 can mark conflicts in the merged output by bracketing them with
     special marker lines. A conflict that comes from two files	A and B	is
     marked as follows:

	   <<<<<<< A
	   lines from A
	   =======
	   lines from B
	   >>>>>>> B

     A conflict	that comes from	three files A, B and C is marked as follows:

	   <<<<<<< A
	   lines from A
	   ||||||| B
	   lines from B
	   =======
	   lines from C
	   >>>>>>> C

     The [-A] or [--show-all] option acts like the [-e]	option,	except that it
     brackets conflicts, and it	outputs	all changes from older to yours, not
     just the unmerged changes.	Thus, given the	sample input files (see	Sec-
     tion "Sample diff3	Input"), diff3 -A lao tzu tao puts brackets around the
     conflict where only tzu differs:

	   <<<<<<< tzu
	   =======
	   The Way that	can be told of is not the eternal Way;
	   The name that can be	named is not the eternal name.
	   >>>>>>> tao

     And it outputs the	three-way conflict as follows:

	   <<<<<<< lao
	   ||||||| tzu
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!
	   =======

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan
	   >>>>>>> tao

     The [-E] or [--show-overlap] option outputs less information than the
     [-A] or [--show-all] option, because it outputs only unmerged changes,
     and it never outputs the contents of the second file. Thus	the [-E] op-
     tion acts like the	[-e] option, except that it brackets the first and
     third files from three-way	overlapping changes. Similarly,	[-X] acts like
     [-x], except it brackets all its (necessarily overlapping)	changes. For
     example, for the three-way	overlapping change above, the [-E] and [-X]
     options output the	following:

	   <<<<<<< lao
	   =======

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan
	   >>>>>>> tao

     If	you are	comparing files	that have meaningless or uninformative names,
     you can use the [--label= label] option to	show alternate names in	the
     <<<<<<<, ||||||| and >>>>>>> brackets. This option	can be given up	to
     three times, once for each	input file. Thus diff3 -A --label X --label Y
     --label Z A B C acts like diff3 -A	A B C, except that the output looks
     like it came from files named X, Y	and Z rather than from files named A,
     B and C.

   Generating the Merged Output	Directly
     With the [-m] or [--merge]	option,	diff3 outputs the merged file di-
     rectly. This is more efficient than using ed to generate it, and works
     even with non-text	files that ed would reject. If you specify [-m]	with-
     out an ed script option, [-A] is assumed.

     For example, the command diff3 -m lao tzu tao (see	Section	"Sample	diff3
     Input" for	a copy of the input files) would output	the following:

	   <<<<<<< tzu
	   =======
	   The Way that	can be told of is not the eternal Way;
	   The name that can be	named is not the eternal name.
	   >>>>>>> tao
	   The Nameless	is the origin of Heaven	and Earth;
	   The Named is	the mother of all things.
	   Therefore let there always be non-being,
	     so	we may see their subtlety,
	   And let there always	be being,
	     so	we may see their result.
	   The two are the same,
	   But after they are produced,
	     they have different names.
	   <<<<<<< lao
	   ||||||| tzu
	   They	both may be called deep	and profound.
	   Deeper and more profound,
	   The door of all subtleties!
	   =======

	     --	The Way	of Lao-Tzu, tr.	Wing-tsit Chan
	   >>>>>>> tao

   How diff3(Merges) Incomplete	Lines
     With [-m],	incomplete lines (see Section "Incomplete Lines") are simply
     copied to the output as they are found; if	the merged output ends in an
     conflict and one of the input files ends in an incomplete line, succeed-
     ing |||||||, ======= or >>>>>>> brackets appear somewhere other than the
     start of a	line because they are appended to the incomplete line.

     Without [-m], if an ed script option is specified and an incomplete line
     is	found, diff3 generates a warning and acts as if	a newline had been
     present.

   Saving the Changed File
     Traditional Unix diff3 generates an ed script without the trailing	w and
     q commands	that save the changes. System V	diff3 generates	these extra
     commands. GNU diff3 normally behaves like traditional Unix	diff3, but
     with the [-i] option it behaves like System V diff3 and appends the w and
     q commands.

     The [-i] option requires one of the ed script options [-AeExX3], and is
     incompatible with the merged output option	[-m].

Interactive Merging with sdiff
     With sdiff, you can merge two files interactively based on	a side-by-side
     [-y] format comparison (see Section "Side by Side").  Use [-o file] or
     [--output=	file] to specify where to put the merged text.See Section
     "Invoking sdiff", for more	details	on the options to sdiff.

     Another way to merge files	interactively is to use	the Emacs Lisp package
     emerge.  See Section.Dq emerge , for more information.

   Specifying diff(Options) to sdiff
     The following sdiff options have the same meaning as for diff.  See Sec-
     tion.Dq diff Options , for	the use	of these options.

	   -a -b -d -i -t -v
	   -B -E -I regexp

	   --expand-tabs
	   --ignore-blank-lines	 --ignore-case
	   --ignore-matching-lines=regexp  --ignore-space-change
	   --ignore-tab-expansion
	   --left-column  --minimal  --speed-large-files
	   --strip-trailing-cr	--suppress-common-lines
	   --tabsize=columns  --text  --version	 --width=columns

     For historical reasons, sdiff has alternate names for some	options. The
     [-l] option is equivalent to the [--left-column] option, and similarly
     [-s] is equivalent	to [--suppress-common-lines].  The meaning of the
     sdiff [-w]	and [-W] options is interchanged from that of diff: with
     sdiff, [-w	columns] is equivalent to [--width= columns], and [-W] is
     equivalent	to [--ignore-all-space].  sdiff	without	the [-o] option	is
     equivalent	to diff	with the [-y] or [--side-by-side] option (see Section
     "Side by Side").

   Merge Commands
     Groups of common lines, with a blank gutter, are copied from the first
     file to the output. After each group of differing lines, sdiff prompts
     with % and	pauses,	waiting	for one	of the following commands. Follow each
     command with RET.

     e	     Discard both versions. Invoke a text editor on an empty temporary
	     file, then	copy the resulting file	to the output.

     eb	     Concatenate the two versions, edit	the result in a	temporary
	     file, then	copy the edited	result to the output.

     ed	     Like eb, except precede each version with a header	that shows
	     what file and lines the version came from.

     el

     e1	     Edit a copy of the	left version, then copy	the result to the out-
	     put.

     er

     e2	     Edit a copy of the	right version, then copy the result to the
	     output.

     l

     1	     Copy the left version to the output.

     q	     Quit.

     r

     2	     Copy the right version to the output.

     s	     Silently copy common lines.

     v	     Verbosely copy common lines. This is the default.

     The text editor invoked is	specified by the EDITOR	environment variable
     if	it is set. The default is system-dependent.

Merging	with patch
     patch takes comparison output produced by diff and	applies	the differ-
     ences to a	copy of	the original file, producing a patched version.	With
     patch, you	can distribute just the	changes	to a set of files instead of
     distributing the entire file set; your correspondents can apply patch to
     update their copy of the files with your changes.	patch automatically
     determines	the diff format, skips any leading or trailing headers,	and
     uses the headers to determine which file to patch.	This lets your corre-
     spondents feed a mail message containing a	difference listing directly to
     patch.

     patch detects and warns about common problems like	forward	patches. It
     saves any patches that it could not apply.	It can also maintain a
     patchlevel.h file to ensure that your correspondents apply	diffs in the
     proper order.

     patch accepts a series of diffs in	its standard input, usually separated
     by	headers	that specify which file	to patch. It applies diff hunks	(see
     Section "Hunks") one by one. If a hunk does not exactly match the origi-
     nal file, patch uses heuristics to	try to patch the file as well as it
     can. If no	approximate match can be found,	patch rejects the hunk and
     skips to the next hunk.  patch normally replaces each file	f with its new
     version, putting reject hunks (if any) into f.rej.

     See Section.Dq Invoking patch , for detailed information on the options
     to	patch.

   Selecting the patch(Input) Format
     patch normally determines which diff format the patch file	uses by	exam-
     ining its contents. For patch files that contain particularly confusing
     leading text, you might need to use one of	the following options to force
     patch to interpret	the patch file as a certain format of diff. The	output
     formats listed here are the only ones that	patch can understand.

     -c

     --context
	     context diff.

     -e

     --ed    ed	script.

     -n

     --normal
	     normal diff.

     -u

     --unified
	     unified diff.

   Revision Control
     If	a nonexistent input file is under a revision control system supported
     by	patch, patch normally asks the user whether to get (or check out) the
     file from the revision control system. Patch currently supports RCS,
     ClearCase and SCCS. Under RCS and SCCS, patch also	asks when the input
     file is read-only and matches the default version in the revision control
     system.

     The [-g num] or [--get= num] option affects access	to files under sup-
     ported revision control systems. If num is	positive, patch	gets the file
     without asking the	user; if zero, patch neither asks the user nor gets
     the file; and if negative,	patch asks the user before getting the file.
     The default value of num is given by the value of the PATCH_GET environ-
     ment variable if it is set; if not, the default value is zero if patch is
     conforming	to POSIX, negative otherwise.See Section "patch	and POSIX".

     The choice	of revision control system is unaffected by the
     VERSION_CONTROL environment variable (see Section "Backup Names").

   Applying Imperfect Patches
     patch tries to skip any leading text in the patch file, apply the diff,
     and then skip any trailing	text. Thus you can feed	a mail message di-
     rectly to patch, and it should work. If the entire	diff is	indented by a
     constant amount of	white space, patch automatically ignores the indenta-
     tion. If a	context	diff contains trailing carriage	return on each line,
     patch automatically ignores the carriage return. If a context diff	has
     been encapsulated by prepending - to lines	beginning with - as per
     ftp://ftp.isi.edu/in-notes/rfc934.txt, patch automatically	unencapsulates
     the input.

     However, certain other types of imperfect input require user intervention
     or	testing.

     Applying Patches with Changed White Space

     Sometimes mailers,	editors, or other programs change spaces into tabs, or
     vice versa. If this happens to a patch file or an input file, the files
     might look	the same, but patch will not be	able to	match them properly.
     If	this problem occurs, use the [-l] or [--ignore-white-space] option,
     which makes patch compare blank characters	(i.e. spaces and tabs) loosely
     so	that any nonempty sequence of blanks in	the patch file matches any
     nonempty sequence of blanks in the	input files. Non-blank characters must
     still match exactly. Each line of the context must	still match a line in
     the input file.

     Applying Reversed Patches

     Sometimes people run diff with the	new file first instead of second. This
     creates a diff that is "reversed".	 To apply such patches,	give patch the
     [-R] or [--reverse] option.  patch	then attempts to swap each hunk	around
     before applying it. Rejects come out in the swapped format.

     Often patch can guess that	the patch is reversed. If the first hunk of a
     patch fails, patch	reverses the hunk to see if it can apply it that way.
     If	it can,	patch asks you if you want to have the [-R] option set;	if it
     can't, patch continues to apply the patch normally. This method cannot
     detect a reversed patch if	it is a	normal diff and	the first command is
     an	append (which should have been a delete) since appends always succeed,
     because a null context matches anywhere. But most patches add or change
     lines rather than delete them, so most reversed normal diffs begin	with a
     delete, which fails, and patch notices.

     If	you apply a patch that you have	already	applied, patch thinks it is a
     reversed patch and	offers to un-apply the patch. This could be construed
     as	a feature. If you did this inadvertently and you don't want to un-ap-
     ply the patch, just answer	n to this offer	and to the subsequent "apply
     anyway" question---or type	C-c to kill the	patch process.

     Helping patch(Find) Inexact Matches

     For context diffs,	and to a lesser	extent normal diffs, patch can detect
     when the line numbers mentioned in	the patch are incorrect, and it	at-
     tempts to find the	correct	place to apply each hunk of the	patch. As a
     first guess, it takes the line number mentioned in	the hunk, plus or mi-
     nus any offset used in applying the previous hunk.	If that	is not the
     correct place, patch scans	both forward and backward 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 it
     cannot find such a	place, and it is reading a context or unified diff,
     and the maximum fuzz factor is set	to 1 or	more, then patch makes another
     scan, ignoring the	first and last line of context.	If that	fails, and the
     maximum fuzz factor is set	to 2 or	more, it makes another scan, ignoring
     the first two and last two	lines of context are ignored. It continues
     similarly if the maximum fuzz factor is larger.

     The [-F lines] or [--fuzz=	lines] option sets the maximum fuzz factor to
     lines.  This option only applies to context and unified diffs; it ignores
     up	to lines lines while looking for the place to install a	hunk. Note
     that a larger fuzz	factor increases the odds of making a faulty patch.
     The default fuzz factor is	2; there is no point to	setting	it to more
     than the number of	lines of context in the	diff, ordinarily 3.

     If	patch cannot find a place to install a hunk of the patch, it writes
     the hunk out to a reject file (see	Section	"Reject	Names",	for informa-
     tion on how reject	files are named). It writes out	rejected hunks in con-
     text format no matter what	form the input patch is	in. If the input is a
     normal or ed diff,	many of	the contexts are simply	null. The line numbers
     on	the hunks in the reject	file may be different from those in the	patch
     file: they	show the approximate location where patch thinks the failed
     hunks belong in the new file rather than in the old one.

     If	the [--verbose]	option is given, then as it completes each hunk	patch
     tells you whether the hunk	succeeded or failed, and if it failed, on
     which line	(in the	new file) patch	thinks the hunk	should go. If this is
     different from the	line number specified in the diff, it tells you	the
     offset. A single large offset may indicate	that patch installed a hunk in
     the wrong place.  patch also tells	you if it used a fuzz factor to	make
     the match,	in which case you should also be slightly suspicious.

     patch cannot tell if the line numbers are off in an ed script, and	can
     only detect wrong line numbers in a normal	diff when it finds a change or
     delete command. It	may have the same problem with a context diff using a
     fuzz factor equal to or greater than the number of	lines of context shown
     in	the diff (typically 3).	In these cases,	you should probably look at a
     context diff between your original	and patched input files	to see if the
     changes make sense. Compiling without errors is a pretty good indication
     that the patch worked, but	not a guarantee.

     A patch against an	empty file applies to a	nonexistent file, and vice
     versa.See Section "Creating and Removing".

     patch usually produces the	correct	results, even when it must make	many
     guesses.  However,	the results are	guaranteed only	when the patch is ap-
     plied to an exact copy of the file	that the patch was generated from.

     Predicting	what patch(will) do

     It	may not	be obvious in advance what patch will do with a	complicated or
     poorly formatted patch. If	you are	concerned that the input might cause
     patch to modify the wrong files, you can use the [--dry-run] option,
     which causes patch	to print the results of	applying patches without actu-
     ally changing any files.  You can then inspect the	diagnostics generated
     by	the dry	run to see whether patch will modify the files that you	ex-
     pect. If the patch	does not do what you want, you can modify the patch
     (or the other options to patch) and try another dry run. Once you are
     satisfied with the	proposed patch you can apply it	by invoking patch as
     before, but this time without the [--dry-run] option.

   Creating and	Removing Files
     Sometimes when comparing two directories, a file may exist	in one direc-
     tory but not the other. If	you give diff the [-N] or [--new-file] option,
     or	if you supply an old or	new file that is named /dev/null or is empty
     and is dated the Epoch (1970-01-01	00:00:00 UTC), diff outputs a patch
     that adds or deletes the contents of this file. When given	such a patch,
     patch normally creates a new file or removes the old file.	However, when
     conforming	to POSIX (see Section "patch and POSIX"), patch	does not re-
     move the old file,	but leaves it empty. The [-E] or
     [--remove-empty-files] option causes patch	to remove output files that
     are empty after applying a	patch, even if the patch does not appear to be
     one that removed the file.

     If	the patch appears to create a file that	already	exists,	patch asks for
     confirmation before applying the patch.

   Updating Time Stamps	on Patched Files
     When patch	updates	a file,	it normally sets the file's last-modified time
     stamp to the current time of day. If you are using	patch to track a soft-
     ware distribution,	this can cause make to incorrectly conclude that a
     patched file is out of date. For example, if syntax.c depends on
     syntax.y, and patch updates syntax.c and then syntax.y, then syntax.c
     will normally appear to be	out of date with respect to syntax.y even
     though its	contents are actually up to date.

     The [-Z] or [--set-utc] option causes patch to set	a patched file's modi-
     fication and access times to the time stamps given	in context diff	head-
     ers. If the context diff headers do not specify a time zone, they are as-
     sumed to use Coordinated Universal	Time (UTC, often known as GMT).

     The [-T] or [--set-time] option acts like [-Z] or [--set-utc], except
     that it assumes that the context diff headers' time stamps	use local time
     instead of	UTC. This option is not	recommended, because patches using lo-
     cal 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. If the context diff headers specify a
     time zone,	this option is equivalent to [-Z] or [--set-utc].

     patch normally refrains from setting a file's time	stamps if the file's
     original last-modified time stamp does not	match the time given in	the
     diff header, of if	the file's contents do not exactly match the patch.
     However, if the [-f] or [--force] option is given,	the file's time	stamps
     are set regardless.

     Due to the	limitations of the current diff	format,	patch cannot update
     the times of files	whose contents have not	changed. Also, if you set file
     time stamps to values other than the current time of day, you should also
     remove (e.g., with	make clean) all	files that depend on the patched
     files, so that later invocations of make do not get confused by the
     patched files' times.

   Multiple Patches in a File
     If	the patch file contains	more than one patch, and if you	do not specify
     an	input file on the command line,	patch tries to apply each patch	as if
     they came from separate patch files. This means that it determines	the
     name of the file to patch for each	patch, and that	it examines the	lead-
     ing text before each patch	for file names and prerequisite	revision level
     (see Section "Making Patches", for	more on	that topic).

     patch uses	the following rules to intuit a	file name from the leading
     text before a patch. First, patch takes an	ordered	list of	candidate file
     names as follows:

     +o	 If the	header is that of a context diff, patch	takes the old and new
	 file names in the header. A name is ignored if	it does	not have
	 enough	slashes	to satisfy the [-p num]	or [--strip= num] option. The
	 name /dev/null	is also	ignored.

     +o	 If there is an	Index: line in the leading garbage and if either the
	 old and new names are both absent or if patch is conforming to	POSIX,
	 patch takes the name in the Index: line.

     +o	 For the purpose of the	following rules, the candidate file names are
	 considered to be in the order (old, new, index), regardless of	the
	 order that they appear	in the header.

     Then patch	selects	a file name from the candidate list as follows:

     +o	 If some of the	named files exist, patch selects the first name	if
	 conforming to POSIX, and the best name	otherwise.

     +o	 If patch is not ignoring RCS, ClearCase, and SCCS (see	Section
	 "Revision Control"), and no named files exist but an RCS, ClearCase,
	 or SCCS master	is found, patch	selects	the first named	file with an
	 RCS, ClearCase, or SCCS master.

     +o	 If no named files exist, no RCS, ClearCase, or	SCCS master was	found,
	 some names are	given, patch is	not conforming to POSIX, and the patch
	 appears to create a file, patch selects the best name requiring the
	 creation of the fewest	directories.

     +o	 If no file name results from the above	heuristics, you	are asked for
	 the name of the file to patch,	and patch selects that name.

     To	determine the best of a	nonempty list of file names, 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.

     See Section.Dq patch and POSIX , to see whether patch is conforming to
     POSIX.

   Applying Patches in Other Directories
     The [-d directory]	or [--directory= directory] option to patch makes di-
     rectory directory the current directory for interpreting both file	names
     in	the patch file,	and file names given as	arguments to other options
     (such as [-B] and [-o]).  For example, while in a mail reading program,
     you can patch a file in the /usr/src/emacs	directory directly from	a mes-
     sage containing the patch like this:

	   | patch -d /usr/src/emacs

     Sometimes the file	names given in a patch contain leading directories,
     but you keep your files in	a directory different from the one given in
     the patch.	 In those cases, you can use the [-p number] or	[--strip=
     number] option to set the file name strip count to	number.	 The strip
     count tells patch how many	slashes, along with the	directory names	be-
     tween them, to strip from the front of file names.	A sequence of one or
     more adjacent slashes is counted as a single slash. By default, patch
     strips off	all leading directories, leaving just the base file names.

     For example, suppose the file name	in the patch file is
     /gnu/src/emacs/etc/NEWS.  Using [-p0] gives the entire file name unmodi-
     fied, [-p1] gives gnu/src/emacs/etc/NEWS (no leading slash), [-p4]	gives
     etc/NEWS, and not specifying [-p] at all gives NEWS.

     patch looks for each file (after any slashes have been stripped) in the
     current directory,	or if you used the [-d directory] option, in that di-
     rectory.

   Backup Files
     Normally, patch creates a backup file if the patch	does not exactly match
     the original input	file, because in that case the original	data might not
     be	recovered if you undo the patch	with patch -R (see Section "Reversed
     Patches").	 However, when conforming to POSIX, patch does not create
     backup files by default.See Section "patch	and POSIX".

     The [-b] or [--backup] option causes patch	to make	a backup file regard-
     less of whether the patch matches the original input. The
     [--backup-if-mismatch] option causes patch	to create backup files for
     mismatches	files; this is the default when	not conforming to POSIX. The
     [--no-backup-if-mismatch] option causes patch to not create backup	files,
     even for mismatched patches; this is the default when conforming to
     POSIX.

     When backing up a file that does not exist, an empty, unreadable backup
     file is created as	a placeholder to represent the nonexistent file.

   Backup File Names
     Normally, patch renames an	original input file into a backup file by ap-
     pending to	its name the extension .orig, or ~ if using .orig would	make
     the backup	file name too long. The	[-z backup-suffix] or [--suffix=
     backup-suffix] option causes patch	to use backup-suffix as	the backup ex-
     tension instead.

     Alternately, you can specify the extension	for backup files with the
     SIMPLE_BACKUP_SUFFIX environment variable,	which the options override.

     patch can also create numbered backup files the way GNU Emacs does. With
     this method, instead of having a single backup of each file, patch	makes
     a new backup file name each time it patches a file. For example, the
     backups of	a file named sink would	be called, successively, sink.~1~,
     sink.~2~, sink.~3~, etc.

     The [-V backup-style] or [--version-control= backup-style]	option takes
     as	an argument a method for creating backup file names. You can alter-
     nately control the	type of	backups	that patch makes with the
     PATCH_VERSION_CONTROL environment variable, which the [-V]	option over-
     rides. If PATCH_VERSION_CONTROL is	not set, the VERSION_CONTROL environ-
     ment variable is used instead. Please note	that these options and vari-
     ables control backup file names; they do not affect the choice of revi-
     sion control system (see Section "Revision	Control").

     The values	of these environment variables and the argument	to the [-V]
     option are	like the GNU Emacs version-control variable (see Section
     "Backup Names", for more information on backup versions in	Emacs).	They
     also recognize synonyms that are more descriptive.	The valid values are
     listed below; unique abbreviations	are acceptable.

     t

     numbered
	     Always make numbered backups.

     nil

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

     never

     simple  Always make simple	backups.

     You can also tell patch to	prepend	a prefix, such as a directory name, to
     produce backup file names.	 The [-B prefix] or [--prefix= prefix] option
     makes backup files	by prepending prefix to	them. The [-Y prefix] or
     [--basename-prefix= prefix] prepends prefix to the	last file name compo-
     nent of backup file names instead;	for example, [-Y ~] causes the backup
     name for dir/file.c to be dir/~file.c.  If	you use	either of these	prefix
     options, the suffix-based options are ignored.

     If	you specify the	output file with the [-o] option, that file is the one
     that is backed up,	not the	input file.

     Options that affect the names of backup files do not affect whether back-
     ups are made. For example,	if you specify the [--no-backup-if-mismatch]
     option, none of the options described in this section have	any affect,
     because no	backups	are made.

   Reject File Names
     The names for reject files	(files containing patches that patch could not
     find a place to apply) are	normally the name of the output	file with .rej
     appended (or # if using .rej would	make the backup	file name too long).

     Alternatively, you	can tell patch to place	all of the rejected patches in
     a single file. The	[-r reject-file] or [--reject-file= reject-file] op-
     tion uses reject-file as the reject file name.

   Messages and	Questions from patch
     patch can produce a variety of messages, especially if it has trouble de-
     coding its	input. In a few	situations where it's not sure how to proceed,
     patch normally prompts you	for more information from the keyboard.	There
     are options to produce more or fewer messages, to have it not ask for
     keyboard input, and to affect the way that	file names are quoted in mes-
     sages.

     patch exits with status 0 if all hunks are	applied	successfully, 1	if
     some hunks	cannot be applied, and 2 if there is more serious trouble.
     When applying a set of patches in a loop, you should check	the exit sta-
     tus, so you don't apply a later patch to a	partially patched file.

     Controlling the Verbosity of patch

     You can cause patch to produce more messages by using the [--verbose] op-
     tion. For example,	when you give this option, the message Hmm... indi-
     cates that	patch is reading text in the patch file, attempting to deter-
     mine whether there	is a patch in that text, and if	so, what kind of patch
     it	is.

     You can inhibit all terminal output from patch, unless an error occurs,
     by	using the [-s],	[--quiet], or [--silent] option.

     Inhibiting	Keyboard Input

     There are two ways	you can	prevent	patch from asking you any questions.
     The [-f] or [--force] option assumes that you know	what you are doing. It
     causes patch to do	the following:

     +o	 Skip patches that do not contain file names in	their headers.

     +o	 Patch files even though they have the wrong version for the Prereq:
	 line in the patch;

     +o	 Assume	that patches are not reversed even if they look	like they are.

     The [-t] or [--batch] option is similar to	[-f], in that it suppresses
     questions,	but it makes somewhat different	assumptions:

     +o	 Skip patches that do not contain file names in	their headers (the
	 same as [-f]).

     +o	 Skip patches for which	the file has the wrong version for the Prereq:
	 line in the patch;

     +o	 Assume	that patches are reversed if they look like they are.

     patch(Quoting) Style

     When patch	outputs	a file name in a diagnostic message, it	can format the
     name in any of several ways. This can be useful to	output file names un-
     ambiguously, even if they contain punctuation or special characters like
     newlines. The [--quoting-style= word] option controls how names are out-
     put. The word should be one of the	following:

     literal
	     Output names as-is.

     shell   Quote names for the shell if they contain shell metacharacters or
	     would cause ambiguous output.

     shell-always
	     Quote names for the shell,	even if	they would normally not	re-
	     quire quoting.

     c	     Quote names as for	a C language string.

     escape  Quote as with c except omit the surrounding double-quote charac-
	     ters.

     You can specify the default value of the [--quoting-style]	option with
     the environment variable QUOTING_STYLE.  If that environment variable is
     not set, the default value	is shell, but this default may change in a fu-
     ture version of patch.

   patch(and) the POSIX	Standard
     If	you specify the	[--posix] option, or set the POSIXLY_CORRECT environ-
     ment variable, patch conforms more	strictly to the	POSIX standard,	as
     follows:

     +o	 Take the first	existing file from the list (old, new, index) when in-
	 tuiting file names from diff headers.See Section "Multiple Patches".

     +o	 Do not	remove files that are removed by a diff.See Section "Creating
	 and Removing".

     +o	 Do not	ask whether to get files from RCS, ClearCase, or SCCS.See Sec-
	 tion "Revision	Control".

     +o	 Require that all options precede the files in the command line.

     +o	 Do not	backup files, even when	there is a mismatch.See	Section
	 "Backups".

   GNU patch(and) Traditional patch
     The current version of GNU	patch normally follows the POSIX standard.See
     Section "patch and	POSIX",	for the	few exceptions to this general rule.

     Unfortunately, POSIX redefined the	behavior of patch in several important
     ways. You should be aware of the following	differences if you must	inter-
     operate with traditional patch, or	with GNU patch version 2.1 and ear-
     lier.

     +o	 In traditional	patch, the [-p]	option's operand was optional, and a
	 bare [-p] was equivalent to [-p0].  The [-p] option now requires an
	 operand, and [-p 0] is	now equivalent to [-p0].  For maximum compati-
	 bility, use options like [-p0]	and [-p1].

	 Also, traditional patch simply	counted	slashes	when stripping path
	 prefixes; 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 // in file
	 names.

     +o	 In traditional	patch, backups were enabled by default.	This behavior
	 is now	enabled	with the [-b] or [--backup] option.

	 Conversely, in	POSIX patch, backups are never made, even when there
	 is a mismatch.	In GNU patch, this behavior is enabled with the
	 [--no-backup-if-mismatch] option, or by conforming to POSIX.

	 The [-b suffix] option	of traditional patch is	equivalent to the -b
	 -z suffix options of GNU patch.

     +o	 Traditional patch used	a complicated (and incompletely	documented)
	 method	to intuit the name of the file to be patched from the patch
	 header. This method did not conform to	POSIX, and had a few gotchas.
	 Now patch uses	a different, equally complicated (but better docu-
	 mented) method	that is	optionally POSIX-conforming; we	hope it	has
	 fewer gotchas.	The two	methods	are compatible if the file names in
	 the context diff header and the 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.

     +o	 When traditional patch	asked the user a question, it sent the ques-
	 tion to standard error	and looked for an answer from the first	file
	 in the	following list that was	a terminal: standard error, standard
	 output, /dev/tty, and standard	input. Now patch sends questions to
	 standard output and gets answers from /dev/tty.  Defaults for some
	 answers have been changed so that patch never goes into an infinite
	 loop when using default answers.

     +o	 Traditional patch exited with a status	value that counted the number
	 of bad	hunks, or with status 1	if there was real trouble. Now patch
	 exits with status 1 if	some hunks failed, or with 2 if	there was real
	 trouble.

     +o	 Limit yourself	to the following options when sending instructions
	 meant to be executed by anyone	running	GNU patch, traditional patch,
	 or a patch that conforms to POSIX. Spaces are significant in the fol-
	 lowing	list, and operands are required.

	       -c
	       -d dir
	       -D define
	       -e
	       -l
	       -n
	       -N
	       -o outfile
	       -pnum
	       -R
	       -r rejectfile

Tips for Making	and Using Patches
     Use some common sense when	making and using patches. For example, when
     sending bug fixes to a program's maintainer, send several small patches,
     one per independent subject, instead of one large,	harder-to-digest patch
     that covers all the subjects.

     Here are some other things	you should keep	in mind	if you are going to
     distribute	patches	for updating a software	package.

   Tips	for Patch Producers
     To	create a patch that changes an older version of	a package into a newer
     version, first make a copy	of the older and newer versions	in adjacent
     subdirectories.  It is common to do that by unpacking tar archives	of the
     two versions.

     To	generate the patch, use	the command diff -Naur old new where old and
     new identify the old and new directories. The names old and new should
     not contain any slashes. The [-N] option lets the patch create and	remove
     files; [-a] lets the patch	update non-text	files; [-u] generates useful
     time stamps and enough context; and [-r] lets the patch update subdirec-
     tories. Here is an	example	command, using Bourne shell syntax:

	   diff	-Naur gcc-3.0.3	gcc-3.0.4

     Tell your recipients how to apply the patches. This should	include	which
     working directory to use, and which patch options to use; the option -p1
     is	recommended. Test your procedure by pretending to be a recipient and
     applying your patches to a	copy of	the original files.

     See Section.Dq Avoiding Common Mistakes , for how to avoid	common mis-
     takes when	generating a patch.

   Tips	for Patch Consumers
     A patch producer should tell recipients how to apply the patches, so the
     first rule	of thumb for a patch consumer is to follow the instructions
     supplied with the patch.

     GNU diff can analyze files	with arbitrarily long lines and	files that end
     in	incomplete lines. However, older versions of patch cannot patch	such
     files. If you are having trouble applying such patches, try upgrading to
     a recent version of GNU patch.

   Avoiding Common Mistakes
     When producing a patch for	multiple files,	apply diff to directories
     whose names do not	have slashes. This reduces confusion when the patch
     consumer specifies	the [-p	number]	option,	since this option can have
     surprising	results	when the old and new file names	have different numbers
     of	slashes. For example, do not send a patch with a header	that looks
     like this:

	   diff	-Naur v2.0.29/prog/README prog/README
	   --- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800
	   +++ prog/README 2002-03-17 20:49:32.442260588 -0800

     because the two file names	have different numbers of slashes, and differ-
     ent versions of patch interpret the file names differently. To avoid con-
     fusion, send output that looks like this instead:

	   diff	-Naur v2.0.29/prog/README v2.0.30/prog/README
	   --- v2.0.29/prog/README 2002-03-10 23:30:39.942229878 -0800
	   +++ v2.0.30/prog/README 2002-03-17 20:49:32.442260588 -0800

     Make sure you have	specified the file names correctly, either in a	con-
     text diff header or with an Index:	line. Take care	to not send out	re-
     versed patches, since these make people wonder whether they have already
     applied the patch.

     Avoid sending patches that	compare	backup file names like README.orig or
     README~, since this might confuse patch into patching a backup file in-
     stead of the real file. Instead, send patches that	compare	the same base
     file names	in different directories, e.g.	old/README and new/README.

     To	save people from partially applying a patch before other patches that
     should have gone before it, you can make the first	patch in the patch
     file update a file	with a name like patchlevel.h or version.c, which con-
     tains a patch level or version number. If the input file contains the
     wrong version number, patch will complain immediately.

     An	even clearer way to prevent this problem is to put a Prereq: line be-
     fore the patch. If	the leading text in the	patch file contains a line
     that starts with Prereq:, patch takes the next word from that line	(nor-
     mally a version number) and checks	whether	the next input file contains
     that word,	preceded and followed by either	white space or a newline. If
     not, patch	prompts	you for	confirmation before proceeding.	This makes it
     difficult to accidentally apply patches in	the wrong order.

   Generating Smaller Patches
     The simplest way to generate a patch is to	use diff -Naur (see Section
     "Tips for Patch Producers"), but you might	be able	to reduce the size of
     the patch by renaming or removing some files before making	the patch. If
     the older version of the package contains any files that the newer	ver-
     sion does not, or if any files have been renamed between the two ver-
     sions, make a list	of rm and mv commands for the user to execute in the
     old version directory before applying the patch. Then run those commands
     yourself in the scratch directory.

     If	there are any files that you don't need	to include in the patch	be-
     cause they	can easily be rebuilt from other files (for example, TAGS and
     output from yacc and makeinfo), exclude them from the patch by giving
     diff the [-x pattern] option (see Section "Comparing Directories").  If
     you want your patch to modify a derived file because your recipients lack
     tools to build it,	make sure that the patch for the derived file follows
     any patches for files that	it depends on, so that the recipients' time
     stamps will not confuse make.

     Now you can create	the patch using	diff -Naur.  Make sure to specify the
     scratch directory first and the newer directory second.

     Add to the	top of the patch a note	telling	the user any rm	and mv com-
     mands to run before applying the patch. Then you can remove the scratch
     directory.

     You can also shrink the patch size	by using fewer lines of	context, but
     bear in mind that patch typically needs at	least two lines	for proper op-
     eration when patches do not exactly match the input files.

Invoking cmp
     The cmp command compares two files, and if	they differ, tells the first
     byte and line number where	they differ or reports that one	file is	a pre-
     fix of the	other.	Bytes and lines	are numbered starting with 1. The ar-
     guments of	cmp are	as follows:

	   cmp options... from-file [to-file [from-skip	[to-skip]]]

     The file name - is	always the standard input.  cmp	also uses the standard
     input if one file name is omitted.	The from-skip and to-skip operands
     specify how many bytes to ignore at the start of each file; they are
     equivalent	to the [--ignore-initial= from-skip: to-skip] option.

     By	default, cmp outputs nothing if	the two	files have the same contents.
     If	one file is a prefix of	the other, cmp prints to standard error	a mes-
     sage of the following form:

	   cmp:	EOF on shorter-file

     Otherwise,	cmp prints to standard output a	message	of the following form:

	   from-file to-file differ: char byte-number, line line-number

     The message formats can differ outside the	POSIX locale. Also, POSIX al-
     lows the EOF message to be	followed by a blank and	some additional	infor-
     mation.

     An	exit status of 0 means no differences were found, 1 means some differ-
     ences were	found, and 2 means trouble.

   Options to cmp
     Below is a	summary	of all of the options that GNU cmp accepts. Most op-
     tions have	two equivalent names, one of which is a	single letter preceded
     by	-, and the other of which is a long name preceded by --.  Multiple
     single letter options (unless they	take an	argument) can be combined into
     a single command line word: [-bl] is equivalent to	[-b -l].

     -b

     --print-bytes
	     Print the differing bytes.	Display	control	bytes as a ^ followed
	     by	a letter of the	alphabet and precede bytes that	have the high
	     bit set with M- (which stands for "meta").

     --help  Output a summary of usage and then	exit.

     -i	skip

     --ignore-initial= skip
	     Ignore any	differences in the first skip bytes of the input
	     files. Treat files	with fewer than	skip bytes as if they are
	     empty. If skip is of the form [from-skip: to-skip], skip the
	     first from-skip bytes of the first	input file and the first
	     to-skip bytes of the second.

     -l

     --verbose
	     Output the	(decimal) byte numbers and (octal) values of all dif-
	     fering bytes, instead of the default standard output.

     -n	count

     --bytes= count
	     Compare at	most count input bytes.

     -s

     --quiet

     --silent
	     Do	not print anything; only return	an exit	status indicating
	     whether the files differ.

     -v

     --version
	     Output version information	and then exit.

     In	the above table, operands that are byte	counts are normally decimal,
     but may be	preceded by 0 for octal	and 0x for hexadecimal.

     A byte count can be followed by a suffix to specify a multiple of that
     count; in this case an omitted integer is understood to be	1. A bare size
     letter, or	one followed by	iB, specifies a	multiple using powers of 1024.
     A size letter followed by B specifies powers of 1000 instead. For exam-
     ple, [-n 4M] and [-n 4MiB]	are equivalent to [-n 4194304],	whereas	[-n
     4MB] is equivalent	to [-n 4000000].  This notation	is upward compatible
     with the http://www.bipm.fr/enus/3_SI/si-prefixes.html for	decimal	multi-
     ples and with the http://physics.nist.gov/cuu/Units/binary.html

     The following suffixes are	defined. Large sizes like 1Y may be rejected
     by	your computer due to limitations of its	arithmetic.

     kB	     kilobyte: 10^3 = 1000.

     k

     K

     KiB     kibibyte: 2^10 = 1024.  K is special: the SI prefix is k and the
	     IEC 60027-2 prefix	is Ki, but tradition and POSIX use k to	mean
	     KiB.

     MB	     megabyte: 10^6 = 1,000,000.

     M

     MiB     mebibyte: 2^20 = 1,048,576.

     GB	     gigabyte: 10^9 = 1,000,000,000.

     G

     GiB     gibibyte: 2^30 = 1,073,741,824.

     TB	     terabyte: 10^12 = 1,000,000,000,000.

     T

     TiB     tebibyte: 2^40 = 1,099,511,627,776.

     PB	     petabyte: 10^15 = 1,000,000,000,000,000.

     P

     PiB     pebibyte: 2^50 = 1,125,899,906,842,624.

     EB	     exabyte: 10^18 = 1,000,000,000,000,000,000.

     E

     EiB     exbibyte: 2^60 = 1,152,921,504,606,846,976.

     ZB	     zettabyte:	10^21 =	1,000,000,000,000,000,000,000

     Z

     ZiB     2^70 = 1,180,591,620,717,411,303,424. ( Zi	is a GNU extension to
	     IEC 60027-2.)

     YB	     yottabyte:	10^24 =	1,000,000,000,000,000,000,000,000.

     Y

     YiB     2^80 = 1,208,925,819,614,629,174,706,176. ( Yi is a GNU extension
	     to	IEC 60027-2.)

Invoking diff
     The format	for running the	diff command is:

	   diff	options... files...

     In	the simplest case, two file names from-file and	to-file	are given, and
     diff compares the contents	of from-file and to-file.  A file name of -
     stands for	text read from the standard input. As a	special	case, diff - -
     compares a	copy of	standard input to itself.

     If	one file is a directory	and the	other is not, diff compares the	file
     in	the directory whose name is that of the	non-directory.	The non-direc-
     tory file must not	be -.

     If	two file names are given and both are directories, diff	compares cor-
     responding	files in both directories, in alphabetical order; this compar-
     ison is not recursive unless the [-r] or [--recursive] option is given.
     diff never	compares the actual contents of	a directory as if it were a
     file. The file that is fully specified may	not be standard	input, because
     standard input is nameless	and the	notion of "file	with the same name"
     does not apply.

     If	the [--from-file= file]	option is given, the number of file names is
     arbitrary,	and file is compared to	each named file. Similarly, if the
     [--to-file= file] option is given,	each named file	is compared to file.

     diff options begin	with -,	so normally file names may not begin with -.
     However, [--] as an argument by itself treats the remaining arguments as
     file names	even if	they begin with	-.

     An	exit status of 0 means no differences were found, 1 means some differ-
     ences were	found, and 2 means trouble. Normally, differing	binary files
     count as trouble, but this	can be altered by using	the [-a] or [--text]
     option, or	the [-q] or [--brief] option.

   Options to diff
     Below is a	summary	of all of the options that GNU diff accepts. Most op-
     tions have	two equivalent names, one of which is a	single letter preceded
     by	-, and the other of which is a long name preceded by --.  Multiple
     single letter options (unless they	take an	argument) can be combined into
     a single command line word: [-ac] is equivalent to	[-a -c].  Long named
     options can be abbreviated	to any unique prefix of	their name.  Brackets
     ([	and ]) indicate	that an	option takes an	optional argument.

     -a

     --text  Treat all files as	text and compare them line-by-line, even if
	     they do not seem to be text.See Section "Binary".

     -b

     --ignore-space-change
	     Ignore changes in amount of white space.See Section "White
	     Space".

     -B

     --ignore-blank-lines
	     Ignore changes that just insert or	delete blank lines.See Section
	     "Blank Lines".

     --binary
	     Read and write data in binary mode.See Section "Binary".

     -c	     Use the context output format, showing three lines	of context.See
	     Section "Context Format".

     -C	lines

     --context[= lines]
	     Use the context output format, showing lines (an integer) lines
	     of	context, or three if lines is not given.See Section "Context
	     Format".  For proper operation, patch typically needs at least
	     two lines of context.

	     On	older systems, diff supports an	obsolete option	[- lines] that
	     has effect	when combined with [-c]	or [-p].  POSIX	1003.1-2001
	     (see Section "Standards conformance") does	not allow this;	use
	     [-C lines]	instead.

     --changed-group-format= format
	     Use format	to output a line group containing differing lines from
	     both files	in if-then-else	format.See Section "Line Group
	     Formats".

     -d

     --minimal
	     Change the	algorithm perhaps find a smaller set of	changes. This
	     makes diff	slower (sometimes much slower).See Section "diff
	     Performance".

     -D	name

     --ifdef= name
	     Make merged #ifdef	format output, conditional on the preprocessor
	     macro name.  See Section.Dq If-then-else .

     -e

     --ed    Make output that is a valid ed script.See Section "ed Scripts".

     -E

     --ignore-tab-expansion
	     Ignore changes due	to tab expansion.See Section "White Space".

     -f

     --forward-ed
	     Make output that looks vaguely like an ed script but has changes
	     in	the order they appear in the file.See Section "Forward ed".

     -F	regexp

     --show-function-line= regexp
	     In	context	and unified format, for	each hunk of differences, show
	     some of the last preceding	line that matches regexp.  See Sec-
	     tion.Dq Specified Headings	.

     --from-file= file
	     Compare file to each operand; file	may be a directory.

     --help  Output a summary of usage and then	exit.

     --horizon-lines= lines
	     Do	not discard the	last lines lines of the	common prefix and the
	     first lines lines of the common suffix.See	Section	"diff
	     Performance".

     -i

     --ignore-case
	     Ignore changes in case; consider upper- and lower-case letters
	     equivalent.See Section "Case Folding".

     -I	regexp

     --ignore-matching-lines= regexp
	     Ignore changes that just insert or	delete lines that match
	     regexp.  See Section.Dq Specified Lines .

     --ignore-file-name-case
	     Ignore case when comparing	file names during recursive compari-
	     son.See Section "Comparing	Directories".

     -l

     --paginate
	     Pass the output through pr	to paginate it.See Section
	     "Pagination".

     --label= label
	     Use label instead of the file name	in the context format (see
	     Section "Context Format") and unified format (see Section
	     "Unified Format") headers.See Section "RCS".

     --left-column
	     Print only	the left column	of two common lines in side by side
	     format.See	Section	"Side by Side Format".

     --line-format= format
	     Use format	to output all input lines in if-then-else format.See
	     Section "Line Formats".

     -n

     --rcs   Output RCS-format diffs; like [-f]	except that each command spec-
	     ifies the number of lines affected.See Section "RCS".

     -N

     --new-file
	     In	directory comparison, if a file	is found in only one direc-
	     tory, treat it as present but empty in the	other directory.See
	     Section "Comparing	Directories".

     --new-group-format= format
	     Use format	to output a group of lines taken from just the second
	     file in if-then-else format.See Section "Line Group Formats".

     --new-line-format=	format
	     Use format	to output a line taken from just the second file in
	     if-then-else format.See Section "Line Formats".

     --old-group-format= format
	     Use format	to output a group of lines taken from just the first
	     file in if-then-else format.See Section "Line Group Formats".

     --old-line-format=	format
	     Use format	to output a line taken from just the first file	in if-
	     then-else format.See Section "Line	Formats".

     -p

     --show-c-function
	     Show which	C function each	change is in.See Section "C Function
	     Headings".

     -q

     --brief
	     Report only whether the files differ, not the details of the dif-
	     ferences.See Section "Brief".

     -r

     --recursive
	     When comparing directories, recursively compare any subdirecto-
	     ries found.See Section "Comparing Directories".

     -s

     --report-identical-files
	     Report when two files are the same.See Section "Comparing
	     Directories".

     -S	file

     --starting-file= file
	     When comparing directories, start with the	file file.  This is
	     used for resuming an aborted comparison.See Section "Comparing
	     Directories".

     --speed-large-files
	     Use heuristics to speed handling of large files that have numer-
	     ous scattered small changes.See Section "diff Performance".

     --strip-trailing-cr
	     Strip any trailing	carriage return	at the end of an input
	     line.See Section "Binary".

     --suppress-common-lines
	     Do	not print common lines in side by side format.See Section
	     "Side by Side Format".

     -t

     --expand-tabs
	     Expand tabs to spaces in the output, to preserve the alignment of
	     tabs in the input files.See Section "Tabs".

     -T

     --initial-tab
	     Output a tab rather than a	space before the text of a line	in
	     normal or context format. This causes the alignment of tabs in
	     the line to look normal.See Section "Tabs".

     --tabsize=	columns
	     Assume that tab stops are set every columns (default 8) print
	     columns.See Section "Tabs".

     --to-file=	file
	     Compare each operand to file ; file may be	a directory.

     -u	     Use the unified output format, showing three lines	of context.See
	     Section "Unified Format".

     --unchanged-group-format= format
	     Use format	to output a group of common lines taken	from both
	     files in if-then-else format.See Section "Line Group Formats".

     --unchanged-line-format= format
	     Use format	to output a line common	to both	files in if-then-else
	     format.See	Section	"Line Formats".

     --unidirectional-new-file
	     When comparing directories, if a file appears only	in the second
	     directory of the two, treat it as present but empty in the
	     other.See Section "Comparing Directories".

     -U	lines

     --unified[= lines]
	     Use the unified output format, showing lines (an integer) lines
	     of	context, or three if lines is not given.See Section "Unified
	     Format".  For proper operation, patch typically needs at least
	     two lines of context.

	     On	older systems, diff supports an	obsolete option	[- lines] that
	     has effect	when combined with [-u].  POSIX	1003.1-2001 (see Sec-
	     tion "Standards conformance") does	not allow this;	use [-U	lines]
	     instead.

     -v

     --version
	     Output version information	and then exit.

     -w

     --ignore-all-space
	     Ignore white space	when comparing lines.See Section "White
	     Space".

     -W	columns

     --width= columns
	     Output at most columns (default 130) print	columns	per line in
	     side by side format.See Section "Side by Side Format".

     -x	pattern

     --exclude=	pattern
	     When comparing directories, ignore	files and subdirectories whose
	     basenames match pattern.  See Section.Dq Comparing	Directories .

     -X	file

     --exclude-from= file
	     When comparing directories, ignore	files and subdirectories whose
	     basenames match any pattern contained in file.  See Section.Dq
	     Comparing Directories .

     -y

     --side-by-side
	     Use the side by side output format.See Section "Side by Side
	     Format".

Invoking diff3
     The diff3 command compares	three files and	outputs	descriptions of	their
     differences.  Its arguments are as	follows:

	   diff3 options... mine older yours

     The files to compare are mine, older, and yours.  At most one of these
     three file	names may be -,	which tells diff3 to read the standard input
     for that file.

     An	exit status of 0 means diff3 was successful, 1 means some conflicts
     were found, and 2 means trouble.

   Options to diff3
     Below is a	summary	of all of the options that GNU diff3 accepts. Multiple
     single letter options (unless they	take an	argument) can be combined into
     a single command line argument.

     -a

     --text  Treat all files as	text and compare them line-by-line, even if
	     they do not appear	to be text.See Section "Binary".

     -A

     --show-all
	     Incorporate all unmerged changes from older to yours into mine,
	     surrounding conflicts with	bracket	lines.See Section "Marking
	     Conflicts".

     --diff-program= program
	     Use the compatible	comparison program program to compare files
	     instead of	diff.

     -e

     --ed    Generate an ed script that	incorporates all the changes from
	     older to yours into mine.	See Section.Dq Which Changes .

     -E

     --show-overlap
	     Like [-e],	except bracket lines from overlapping changes' first
	     and third files.See Section "Marking Conflicts".  With [-E], an
	     overlapping change	looks like this:

		   <<<<<<< mine
		   lines from mine
		   =======
		   lines from yours
		   >>>>>>> yours

     --help  Output a summary of usage and then	exit.

     -i	     Generate w	and q commands at the end of the ed script for System
	     V compatibility. This option must be combined with	one of the
	     [-AeExX3] options,	and may	not be combined	with [-m].  See	Sec-
	     tion.Dq Saving the	Changed	File .

     --label= label
	     Use the label label for the brackets output by the	[-A], [-E] and
	     [-X] options. This	option may be given up to three	times, one for
	     each input	file.  The default labels are the names	of the input
	     files. Thus diff3 --label X --label Y --label Z -m	A B C acts
	     like diff3	-m A B C, except that the output looks like it came
	     from files	named X, Y and Z rather	than from files	named A, B and
	     C.	 See Section.Dq	Marking	Conflicts .

     -m

     --merge
	     Apply the edit script to the first	file and send the result to
	     standard output.  Unlike piping the output	from diff3 to ed, this
	     works even	for binary files and incomplete	lines.	[-A] is	as-
	     sumed if no edit script option is specified.See Section
	     "Bypassing	ed".

     --strip-trailing-cr
	     Strip any trailing	carriage return	at the end of an input
	     line.See Section "Binary".

     -T

     --initial-tab
	     Output a tab rather than two spaces before	the text of a line in
	     normal format.  This causes the alignment of tabs in the line to
	     look normal.See Section "Tabs".

     -v

     --version
	     Output version information	and then exit.

     -x

     --overlap-only
	     Like [-e],	except output only the overlapping changes.See Section
	     "Which Changes".

     -X	     Like [-E],	except output only the overlapping changes. In other
	     words, like [-x], except bracket changes as in [-E].  See Sec-
	     tion.Dq Marking Conflicts .

     -3

     --easy-only
	     Like [-e],	except output only the nonoverlapping changes.See Sec-
	     tion "Which Changes".

Invoking patch
     Normally patch is invoked like this:

	   patch <patchfile

     The full format for invoking patch	is:

	   patch options... [origfile [patchfile]]

     You can also specify where	to read	the patch from with the	[-i patchfile]
     or	[--input= patchfile] option. If	you do not specify patchfile, or if
     patchfile is -, patch reads the patch (that is, the diff output) from the
     standard input.

     If	you do not specify an input file on the	command	line, patch tries to
     intuit from the leading text (any text in the patch that comes before the
     diff output) which	file to	edit.See Section "Multiple Patches".

     By	default, patch replaces	the original input file	with the patched ver-
     sion, possibly after renaming the original	file into a backup file	(see
     Section "Backup Names", for a description of how patch names backup
     files). You can also specify where	to put the output with the [-o file]
     or	[--output= file] option; however, do not use this option if file is
     one of the	input files.

   Options to patch
     Here is a summary of all of the options that GNU patch accepts.See	Sec-
     tion "patch and Tradition", for which of these options are	safe to	use in
     older versions of patch.

     Multiple single-letter options that do not	take an	argument can be	com-
     bined into	a single command line argument with only one dash.

     -b

     --backup
	     Back up the original contents of each file, even if backups would
	     normally not be made.See Section "Backups".

     -B	prefix

     --prefix= prefix
	     Prepend prefix to backup file names.See Section "Backup Names".

     --backup-if-mismatch
	     Back up the original contents of each file	if the patch does not
	     exactly match the file. This is the default behavior when not
	     conforming	to POSIX.See Section "Backups".

     --binary
	     Read and write all	files in binary	mode, except for standard out-
	     put and /dev/tty.	This option has	no effect on POSIX-conforming
	     systems like GNU/Linux. On	systems	where this option makes	a dif-
	     ference, the patch	should be generated by diff -a --binary.  See
	     Section.Dq	Binary .

     -c

     --context
	     Interpret the patch file as a context diff.See Section "patch
	     Input".

     -d	directory

     --directory= directory
	     Make directory directory the current directory for	interpreting
	     both file names in	the patch file,	and file names given as	argu-
	     ments to other options.See	Section	"patch Directories".

     -D	name

     --ifdef= name
	     Make merged if-then-else output using name.  See Section.Dq If-
	     then-else .

     --dry-run
	     Print the results of applying the patches without actually	chang-
	     ing any files.See Section "Dry Runs".

     -e

     --ed    Interpret the patch file as an ed script.See Section "patch
	     Input".

     -E

     --remove-empty-files
	     Remove output files that are empty	after the patches have been
	     applied.See Section "Creating and Removing".

     -f

     --force
	     Assume that the user knows	exactly	what he	or she is doing, and
	     do	not ask	any questions.See Section "patch Messages".

     -F	lines

     --fuzz= lines
	     Set the maximum fuzz factor to lines.  See	Section.Dq Inexact .

     -g	num

     --get= num
	     If	num is positive, get input files from a	revision control sys-
	     tem as necessary; if zero,	do not get the files; if negative, ask
	     the user whether to get the files.See Section "Revision Control".

     --help  Output a summary of usage and then	exit.

     -i	patchfile

     --input= patchfile
	     Read the patch from patchfile rather than from standard input.See
	     Section "patch Options".

     -l

     --ignore-white-space
	     Let any sequence of blanks	(spaces	or tabs) in the	patch file
	     match any sequence	of blanks in the input file.See	Section
	     "Changed White Space".

     -n

     --normal
	     Interpret the patch file as a normal diff.See Section "patch
	     Input".

     -N

     --forward
	     Ignore patches that patch thinks are reversed or already applied.
	     See also [-R].  See Section.Dq Reversed Patches .

     --no-backup-if-mismatch
	     Do	not back up the	original contents of files. This is the	de-
	     fault behavior when conforming to POSIX.See Section "Backups".

     -o	file

     --output= file
	     Use file as the output file name.See Section "patch Options".

     -p	number

     --strip= number
	     Set the file name strip count to number.  See Section.Dq patch
	     Directories .

     --posix
	     Conform to	POSIX, as if the POSIXLY_CORRECT environment variable
	     had been set.See Section "patch and POSIX".

     --quoting-style= word
	     Use style word to quote names in diagnostics, as if the
	     QUOTING_STYLE environment variable	had been set to	word.  See
	     Section.Dq	patch Quoting Style .

     -r	reject-file

     --reject-file= reject-file
	     Use reject-file as	the reject file	name.See Section "Reject
	     Names".

     -R

     --reverse
	     Assume that this patch was	created	with the old and new files
	     swapped.See Section "Reversed Patches".

     -s

     --quiet

     --silent
	     Work silently unless an error occurs.See Section "patch
	     Messages".

     -t

     --batch
	     Do	not ask	any questions.See Section "patch Messages".

     -T

     --set-time
	     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.See Section "Patching Time Stamps".

     -u

     --unified
	     Interpret the patch file as a unified diff.See Section "patch
	     Input".

     -v

     --version
	     Output version information	and then exit.

     -V	backup-style

     --version=control=	backup-style
	     Select the	naming convention for backup file names.See Section
	     "Backup Names".

     --verbose
	     Print more	diagnostics than usual.See Section "patch Messages".

     -x	number

     --debug= number
	     Set internal debugging flags. Of interest only to patch patchers.

     -Y	prefix

     --basename-prefix=	prefix
	     Prepend prefix to base names of backup files.See Section "Backup
	     Names".

     -z	suffix

     --suffix= suffix
	     Use suffix	as the backup extension	instead	of .orig or ~.	See
	     Section.Dq	Backup Names .

     -Z

     --set-utc
	     Set the modification and access times of patched files from time
	     stamps given in context diff headers, assuming that the context
	     diff headers use UTC.See Section "Patching	Time Stamps".

Invoking sdiff
     The sdiff command merges two files	and interactively outputs the results.
     Its arguments are as follows:

	   sdiff -o outfile options... from-file to-file

     This merges from-file with	to-file, with output to	outfile.  If from-file
     is	a directory and	to-file	is not,	sdiff compares the file	in from-file
     whose file	name is	that of	to-file, and vice versa.  from-file and
     to-file may not both be directories.

     sdiff options begin with -, so normally from-file and to-file may not be-
     gin with -.  However, [--]	as an argument by itself treats	the remaining
     arguments as file names even if they begin	with -.	 You may not use - as
     an	input file.

     sdiff without [-o]	(or [--output])	produces a side-by-side	difference.
     This usage	is obsolete; use the [-y] or [--side-by-side] option of	diff
     instead.

     An	exit status of 0 means no differences were found, 1 means some differ-
     ences were	found, and 2 means trouble.

   Options to sdiff
     Below is a	summary	of all of the options that GNU sdiff accepts. Each op-
     tion has two equivalent names, one	of which is a single letter preceded
     by	-, and the other of which is a long name preceded by --.  Multiple
     single letter options (unless they	take an	argument) can be combined into
     a single command line argument. Long named	options	can be abbreviated to
     any unique	prefix of their	name.

     -a

     --text  Treat all files as	text and compare them line-by-line, even if
	     they do not appear	to be text.See Section "Binary".

     -b

     --ignore-space-change
	     Ignore changes in amount of white space.See Section "White
	     Space".

     -B

     --ignore-blank-lines
	     Ignore changes that just insert or	delete blank lines.See Section
	     "Blank Lines".

     -d

     --minimal
	     Change the	algorithm to perhaps find a smaller set	of changes.
	     This makes	sdiff slower (sometimes	much slower).See Section "diff
	     Performance".

     --diff-program= program
	     Use the compatible	comparison program program to compare files
	     instead of	diff.

     -E

     --ignore-tab-expansion
	     Ignore changes due	to tab expansion.See Section "White Space".

     --help  Output a summary of usage and then	exit.

     -i

     --ignore-case
	     Ignore changes in case; consider upper- and lower-case to be the
	     same.See Section "Case Folding".

     -I	regexp

     --ignore-matching-lines= regexp
	     Ignore changes that just insert or	delete lines that match
	     regexp.  See Section.Dq Specified Lines .

     -l

     --left-column
	     Print only	the left column	of two common lines.See	Section	"Side
	     by	Side Format".

     -o	file

     --output= file
	     Put merged	output into file.  This	option is required for merg-
	     ing.

     -s

     --suppress-common-lines
	     Do	not print common lines.See Section "Side by Side Format".

     --speed-large-files
	     Use heuristics to speed handling of large files that have numer-
	     ous scattered small changes.See Section "diff Performance".

     --strip-trailing-cr
	     Strip any trailing	carriage return	at the end of an input
	     line.See Section "Binary".

     -t

     --expand-tabs
	     Expand tabs to spaces in the output, to preserve the alignment of
	     tabs in the input files.See Section "Tabs".

     --tabsize=	columns
	     Assume that tab stops are set every columns (default 8) print
	     columns.See Section "Tabs".

     -v

     --version
	     Output version information	and then exit.

     -w	columns

     --width= columns
	     Output at most columns (default 130) print	columns	per line.See
	     Section "Side by Side Format".  Note that for historical reasons,
	     this option is [-W] in diff, [-w] in sdiff.

     -W

     --ignore-all-space
	     Ignore white space	when comparing lines.See Section "White
	     Space".  Note that	for historical reasons,	this option is [-w] in
	     diff, [-W]	in sdiff.

Standards conformance
     In	a few cases, the GNU utilities'	default	behavior is incompatible with
     the POSIX standard. To suppress these incompatibilities, define the
     POSIXLY_CORRECT environment variable. Unless you are checking for POSIX
     conformance, you probably do not need to define POSIXLY_CORRECT.

     Normally options and operands can appear in any order, and	programs act
     as	if all the options appear before any operands. For example, diff lao
     tzu -C 2 acts like	diff -C	2 lao tzu, since 2 is an option-argument of
     [-C].  However, if	the POSIXLY_CORRECT environment	variable is set, op-
     tions must	appear before operands,	unless otherwise specified for a par-
     ticular command.

     Newer versions of POSIX are occasionally incompatible with	older ver-
     sions.  For example, older	versions of POSIX allowed the command diff -c
     -10 to have the same meaning as diff -C 10, but POSIX 1003.1-2001 diff no
     longer allows digit-string	options	like [-10].

     The GNU utilities normally	conform	to the version of POSIX	that is	stan-
     dard for your system. To cause them to conform to a different version of
     POSIX, define the _POSIX2_VERSION environment variable to a value of the
     form yyyymm specifying the	year and month the standard was	adopted. Two
     values are	currently supported for	_POSIX2_VERSION: 199209	stands for
     POSIX 1003.2-1992,	and 200112 stands for POSIX 1003.1-2001. For example,
     if	you are	running	older software that assumes an older version of	POSIX
     and uses diff -c -10, you can work	around the compatibility problems by
     setting _POSIX2_VERSION=199209 in your environment.

Future Projects
     Here are some ideas for improving GNU diff	and patch.  The	GNU project
     has identified some improvements as potential programming projects	for
     volunteers. You can also help by reporting	any bugs that you find.

     If	you are	a programmer and would like to contribute something to the GNU
     project, please consider volunteering for one of these projects. If you
     are seriously contemplating work, please write to gvc@gnu.org to coordi-
     nate with other volunteers.

   Suggested Projects for Improving GNU	diff(and) patch
     One should	be able	to use GNU diff	to generate a patch from any pair of
     directory trees, and given	the patch and a	copy of	one such tree, use
     patch to generate a faithful copy of the other. Unfortunately, some
     changes to	directory trees	cannot be expressed using current patch	for-
     mats; also, patch does not	handle some of the existing formats. These
     shortcomings motivate the following suggested projects.

     Handling Multibyte	and Varying-Width Characters

     diff, diff3 and sdiff treat each line of input as a string	of unibyte
     characters. This can mishandle multibyte characters in some cases.	For
     example, when asked to ignore spaces, diff	does not properly ignore a
     multibyte space character.

     Also, diff	currently assumes that each byte is one	column wide, and this
     assumption	is incorrect in	some locales, e.g., locales that use UTF-8 en-
     coding. This causes problems with the [-y]	or [--side-by-side] option of
     diff.

     These problems need to be fixed without unduly affecting the performance
     of	the utilities in unibyte environments.

     The IBM GNU/Linux Technology Center Internationalization Team has pro-
     posed
     http://oss.software.ibm.com/developer/opensource/linux/patches/i18n/diffutils-2.7.2-i18n-0.1.patch.gz
     Unfortunately, these patches are incomplete and are to an older version
     of	diff, so more work needs to be done in this area.

     Handling Changes to the Directory Structure

     diff and patch do not handle some changes to directory structure. For ex-
     ample, suppose one	directory tree contains	a directory named D with some
     subsidiary	files, and another contains a file with	the same name D.  diff
     -r	does not output	enough information for patch to	transform the direc-
     tory subtree into the file.

     There should be a way to specify that a file has been removed without
     having to include its entire contents in the patch	file. There should
     also be a way to tell patch that a	file was renamed, even if there	is no
     way for diff to generate such information.	There should be	a way to tell
     patch that	a file's time stamp has	changed, even if its contents have not
     changed.

     These problems can	be fixed by extending the diff output format to	repre-
     sent changes in directory structure, and extending	patch to understand
     these extensions.

     Files that	are Neither Directories	Nor Regular Files

     Some files	are neither directories	nor regular files: they	are unusual
     files like	symbolic links,	device special files, named pipes, and sock-
     ets. Currently, diff treats symbolic links	as if they were	the pointed-to
     files, except that	a recursive diff reports an error if it	detects	infi-
     nite loops	of symbolic links (e.g., symbolic links	to ..).	 diff treats
     other special files like regular files if they are	specified at the top
     level, but	simply reports their presence when comparing directories. This
     means that	patch cannot represent changes to such files. For example, if
     you change	which file a symbolic link points to, diff outputs the differ-
     ence between the two files, instead of the	change to the symbolic link.

     diff should optionally report changes to special files specially, and
     patch should be extended to understand these extensions.

     File Names	that Contain Unusual Characters

     When a file name contains an unusual character like a newline or white
     space, diff -r generates a	patch that patch cannot	parse. The problem is
     with format of diff output, not just with patch, because with odd enough
     file names	one can	cause diff to generate a patch that is syntactically
     correct but patches the wrong files.  The format of diff output should be
     extended to handle	all possible file names.

     Outputting	Diffs in Time Stamp Order

     Applying patch to a multiple-file diff can	result in files	whose time
     stamps are	out of order.  GNU patch has options to	restore	the time
     stamps of the updated files (see Section "Patching	Time Stamps"), but
     sometimes it is useful to generate	a patch	that works even	if the recipi-
     ent does not have GNU patch, or does not use these	options. One way to do
     this would	be to implement	a diff option to output	diffs in time stamp
     order.

     Ignoring Certain Changes

     It	would be nice to have a	feature	for specifying two strings, one	in
     from-file and one in to-file, which should	be considered to match.	Thus,
     if	the two	strings	are foo	and bar, then if two lines differ only in that
     foo in file 1 corresponds to bar in file 2, the lines are treated as
     identical.

     It	is not clear how general this feature can or should be,	or what	syntax
     should be used for	it.

     A partial substitute is to	filter one or both files before	comparing,
     e.g.:

	   sed 's/foo/bar/g' file1 | diff - file2

     However, this outputs the filtered	text, not the original.

     Improving Performance

     When comparing two	large directory	structures, one	of which was origi-
     nally copied from the other with time stamps preserved (e.g., with	cp
     -pR), it would greatly improve performance	if an option told diff to as-
     sume that two files with the same size and	time stamps have the same con-
     tent.See Section "diff Performance".

   Reporting Bugs
     If	you think you have found a bug in GNU cmp, diff, diff3,	or sdiff,
     please report it by electronic mail to the
     http://mail.gnu.org/mailman/listinfo/bug-gnu-utils	bug-gnu-utils@gnu.org.
     Please send bug reports for GNU patch to bug-patch@gnu.org.  Send as pre-
     cise a description	of the problem as you can, including the output	of the
     [--version] option	and sample input files that produce the	bug, if	appli-
     cable. If you have	a nontrivial fix for the bug, please send it as	well.
     If	you have a patch, please send it too. It may simplify the maintainer's
     job if the	patch is relative to a recent test release, which you can find
     in	the directory ftp://alpha.gnu.org/gnu/diffutils/

Copying	This Manual
   GNU Free Documentation License
	   Copyright (C) 2000,2001,2002	Free Software Foundation, Inc. 59 Tem-
	   ple Place, Suite 330, Boston, MA 02111-1307,	USA

	   Everyone is permitted to copy and  distribute  verbatim  copies  of
	   this	license	document, but changing it is not allowed.

     1.	  PREAMBLE

	  The purpose of this License is to make a manual, textbook, or	other
	  functional and useful	document free in the sense of freedom: to as-
	  sure everyone	the effective freedom to copy and redistribute it,
	  with or without modifying it,	either commercially or noncommer-
	  cially. Secondarily, this License preserves for the author and pub-
	  lisher a way to get credit for their work, while not being consid-
	  ered responsible for modifications made by others.

	  This License is a kind of "copyleft",	which means that derivative
	  works	of the document	must themselves	be free	in the same sense. It
	  complements the GNU General Public License, which is a copyleft li-
	  cense	designed for free software.

	  We have designed this	License	in order to use	it for manuals for
	  free software, because free software needs free documentation: a
	  free program should come with	manuals	providing the same freedoms
	  that the software does. But this License is not limited to software
	  manuals; it can be used for any textual work,	regardless of subject
	  matter or whether it is published as a printed book. We recommend
	  this License principally for works whose purpose is instruction or
	  reference.

     2.	  APPLICABILITY	AND DEFINITIONS

	  This License applies to any manual or	other work, in any medium,
	  that contains	a notice placed	by the copyright holder	saying it can
	  be distributed under the terms of this License. Such a notice	grants
	  a world-wide,	royalty-free license, unlimited	in duration, to	use
	  that work under the conditions stated	herein.	The "Document",	below,
	  refers to any	such manual or work. Any member	of the public is a li-
	  censee, and is addressed as "you". You accept	the license if you
	  copy,	modify or distribute the work in a way requiring permission
	  under	copyright law.

	  A "Modified Version" of the Document means any work containing the
	  Document or a	portion	of it, either copied verbatim, or with modifi-
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	  A "Secondary Section"	is a named appendix or a front-matter section
	  of the Document that deals exclusively with the relationship of the
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	  ject (or to related matters) and contains nothing that could fall
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	  any mathematics.) The	relationship could be a	matter of historical
	  connection with the subject or with related matters, or of legal,
	  commercial, philosophical, ethical or	political position regarding
	  them.

	  The "Invariant Sections" are certain Secondary Sections whose	titles
	  are designated, as being those of Invariant Sections,	in the notice
	  that says that the Document is released under	this License. If a
	  section does not fit the above definition of Secondary then it is
	  not allowed to be designated as Invariant. The Document may contain
	  zero Invariant Sections. If the Document does	not identify any In-
	  variant Sections then	there are none.

	  The "Cover Texts" are	certain	short passages of text that are
	  listed, as Front-Cover Texts or Back-Cover Texts, in the notice that
	  says that the	Document is released under this	License. A Front-Cover
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	  A "Transparent" copy of the Document means a machine-readable	copy,
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	  text formatters. A copy made in an otherwise Transparent file	format
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	  discourage subsequent	modification by	readers	is not Transparent. An
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	  of text. A copy that is not "Transparent" is called "Opaque".

	  Examples of suitable formats for Transparent copies include plain
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	  output purposes only.

	  The "Title Page" means, for a	printed	book, the title	page itself,
	  plus such following pages as are needed to hold, legibly, the	mate-
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	  formats which	do not have any	title page as such, "Title Page" means
	  the text near	the most prominent appearance of the work's title,
	  preceding the	beginning of the body of the text.

	  A section "Entitled XYZ" means a named subunit of the	Document whose
	  title	either is precisely XYZ	or contains XYZ	in parentheses follow-
	  ing text that	translates XYZ in another language. (Here XYZ stands
	  for a	specific section name mentioned	below, such as "Acknowledge-
	  ments", "Dedications", "Endorsements", or "History".)	To "Preserve
	  the Title" of	such a section when you	modify the Document means that
	  it remains a section "Entitled XYZ" according	to this	definition.

	  The Document may include Warranty Disclaimers	next to	the notice
	  which	states that this License applies to the	Document. These	War-
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	  License, but only as regards disclaiming warranties: any other im-
	  plication that these Warranty	Disclaimers may	have is	void and has
	  no effect on the meaning of this License.

     3.	  VERBATIM COPYING

	  You may copy and distribute the Document in any medium, either com-
	  mercially or noncommercially,	provided that this License, the	copy-
	  right	notices, and the license notice	saying this License applies to
	  the Document are reproduced in all copies, and that you add no other
	  conditions whatsoever	to those of this License. You may not use
	  technical measures to	obstruct or control the	reading	or further
	  copying of the copies	you make or distribute.	However, you may ac-
	  cept compensation in exchange	for copies. If you distribute a	large
	  enough number	of copies you must also	follow the conditions in sec-
	  tion 3.

	  You may also lend copies, under the same conditions stated above,
	  and you may publicly display copies.

     4.	  COPYING IN QUANTITY

	  If you publish printed copies	(or copies in media that commonly have
	  printed covers) of the Document, numbering more than 100, and	the
	  Document's license notice requires Cover Texts, you must enclose the
	  copies in covers that	carry, clearly and legibly, all	these Cover
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	  the back cover. Both covers must also	clearly	and legibly identify
	  you as the publisher of these	copies.	The front cover	must present
	  the full title with all words	of the title equally prominent and
	  visible. You may add other material on the covers in addition. Copy-
	  ing with changes limited to the covers, as long as they preserve the
	  title	of the Document	and satisfy these conditions, can be treated
	  as verbatim copying in other respects.

	  If the required texts	for either cover are too voluminous to fit
	  legibly, you should put the first ones listed	(as many as fit	rea-
	  sonably) on the actual cover,	and continue the rest onto adjacent
	  pages.

	  If you publish or distribute Opaque copies of	the Document numbering
	  more than 100, you must either include a machine-readable Transpar-
	  ent copy along with each Opaque copy,	or state in or with each
	  Opaque copy a	computer-network location from which the general net-
	  work-using public has	access to download using public-standard net-
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	  ably prudent steps, when you begin distribution of Opaque copies in
	  quantity, to ensure that this	Transparent copy will remain thus ac-
	  cessible at the stated location until	at least one year after	the
	  last time you	distribute an Opaque copy (directly or through your
	  agents or retailers) of that edition to the public.

	  It is	requested, but not required, that you contact the authors of
	  the Document well before redistributing any large number of copies,
	  to give them a chance	to provide you with an updated version of the
	  Document.

     5.	  MODIFICATIONS

	  You may copy and distribute a	Modified Version of the	Document under
	  the conditions of sections 2 and 3 above, provided that you release
	  the Modified Version under precisely this License, with the Modified
	  Version filling the role of the Document, thus licensing distribu-
	  tion and modification	of the Modified	Version	to whoever possesses a
	  copy of it. In addition, you must do these things in the Modified
	  Version:

	  1.   Use in the Title	Page (and on the covers, if any) a title dis-
	       tinct from that of the Document,	and from those of previous
	       versions	(which should, if there	were any, be listed in the
	       History section of the Document). You may use the same title as
	       a previous version if the original publisher of that version
	       gives permission.

	  2.   List on the Title Page, as authors, one or more persons or en-
	       tities responsible for authorship of the	modifications in the
	       Modified	Version, together with at least	five of	the principal
	       authors of the Document (all of its principal authors, if it
	       has fewer than five), unless they release you from this re-
	       quirement.

	  3.   State on	the Title page the name	of the publisher of the	Modi-
	       fied Version, as	the publisher.

	  4.   Preserve	all the	copyright notices of the Document.

	  5.   Add an appropriate copyright notice for your modifications ad-
	       jacent to the other copyright notices.

	  6.   Include,	immediately after the copyright	notices, a license no-
	       tice giving the public permission to use	the Modified Version
	       under the terms of this License,	in the form shown in the Ad-
	       dendum below.

	  7.   Preserve	in that	license	notice the full	lists of Invariant
	       Sections	and required Cover Texts given in the Document's li-
	       cense notice.

	  8.   Include an unaltered copy of this License.

	  9.   Preserve	the section Entitled "History",	Preserve its Title,
	       and add to it an	item stating at	least the title, year, new au-
	       thors, and publisher of the Modified Version as given on	the
	       Title Page. If there is no section Entitled "History" in	the
	       Document, create	one stating the	title, year, authors, and pub-
	       lisher of the Document as given on its Title Page, then add an
	       item describing the Modified Version as stated in the previous
	       sentence.

	  10.  Preserve	the network location, if any, given in the Document
	       for public access to a Transparent copy of the Document,	and
	       likewise	the network locations given in the Document for	previ-
	       ous versions it was based on. These may be placed in the	"His-
	       tory" section. You may omit a network location for a work that
	       was published at	least four years before	the Document itself,
	       or if the original publisher of the version it refers to	gives
	       permission.

	  11.  For any section Entitled	"Acknowledgements" or "Dedications",
	       Preserve	the Title of the section, and preserve in the section
	       all the substance and tone of each of the contributor acknowl-
	       edgements and/or	dedications given therein.

	  12.  Preserve	all the	Invariant Sections of the Document, unaltered
	       in their	text and in their titles. Section numbers or the
	       equivalent are not considered part of the section titles.

	  13.  Delete any section Entitled "Endorsements". Such	a section may
	       not be included in the Modified Version.

	  14.  Do not retitle any existing section to be Entitled "Endorse-
	       ments" or to conflict in	title with any Invariant Section.

	  15.  Preserve	any Warranty Disclaimers.

	  If the Modified Version includes new front-matter sections or	appen-
	  dices	that qualify as	Secondary Sections and contain no material
	  copied from the Document, you	may at your option designate some or
	  all of these sections	as invariant.  To do this, add their titles to
	  the list of Invariant	Sections in the	Modified Version's license no-
	  tice.	These titles must be distinct from any other section titles.

	  You may add a	section	Entitled "Endorsements", provided it contains
	  nothing but endorsements of your Modified Version by various par-
	  ties---for example, statements of peer review	or that	the text has
	  been approved	by an organization as the authoritative	definition of
	  a standard.

	  You may add a	passage	of up to five words as a Front-Cover Text, and
	  a passage of up to 25	words as a Back-Cover Text, to the end of the
	  list of Cover	Texts in the Modified Version. Only one	passage	of
	  Front-Cover Text and one of Back-Cover Text may be added by (or
	  through arrangements made by)	any one	entity.	If the Document	al-
	  ready	includes a cover text for the same cover, previously added by
	  you or by arrangement	made by	the same entity	you are	acting on be-
	  half of, you may not add another; but	you may	replace	the old	one,
	  on explicit permission from the previous publisher that added	the
	  old one.

	  The author(s)	and publisher(s) of the	Document do not	by this	Li-
	  cense	give permission	to use their names for publicity for or	to as-
	  sert or imply	endorsement of any Modified Version.

     6.	  COMBINING DOCUMENTS

	  You may combine the Document with other documents released under
	  this License,	under the terms	defined	in section 4 above for modi-
	  fied versions, provided that you include in the combination all of
	  the Invariant	Sections of all	of the original	documents, unmodified,
	  and list them	all as Invariant Sections of your combined work	in its
	  license notice, and that you preserve	all their Warranty Dis-
	  claimers.

	  The combined work need only contain one copy of this License,	and
	  multiple identical Invariant Sections	may be replaced	with a single
	  copy.	If there are multiple Invariant	Sections with the same name
	  but different	contents, make the title of each such section unique
	  by adding at the end of it, in parentheses, the name of the original
	  author or publisher of that section if known,	or else	a unique num-
	  ber. Make the	same adjustment	to the section titles in the list of
	  Invariant Sections in	the license notice of the combined work.

	  In the combination, you must combine any sections Entitled "History"
	  in the various original documents, forming one section Entitled
	  "History"; likewise combine any sections Entitled "Acknowledge-
	  ments", and any sections Entitled "Dedications". You must delete all
	  sections Entitled "Endorsements."

     7.	  COLLECTIONS OF DOCUMENTS

	  You may make a collection consisting of the Document and other docu-
	  ments	released under this License, and replace the individual	copies
	  of this License in the various documents with	a single copy that is
	  included in the collection, provided that you	follow the rules of
	  this License for verbatim copying of each of the documents in	all
	  other	respects.

	  You may extract a single document from such a	collection, and	dis-
	  tribute it individually under	this License, provided you insert a
	  copy of this License into the	extracted document, and	follow this
	  License in all other respects	regarding verbatim copying of that
	  document.

     8.	  AGGREGATION WITH INDEPENDENT WORKS

	  A compilation	of the Document	or its derivatives with	other separate
	  and independent documents or works, in or on a volume	of a storage
	  or distribution medium, is called an "aggregate" if the copyright
	  resulting from the compilation is not	used to	limit the legal	rights
	  of the compilation's users beyond what the individual	works permit.
	  When the Document is included	in an aggregate, this License does not
	  apply	to the other works in the aggregate which are not themselves
	  derivative works of the Document.

	  If the Cover Text requirement	of section 3 is	applicable to these
	  copies of the	Document, then if the Document is less than one	half
	  of the entire	aggregate, the Document's Cover	Texts may be placed on
	  covers that bracket the Document within the aggregate, or the	elec-
	  tronic equivalent of covers if the Document is in electronic form.
	  Otherwise they must appear on	printed	covers that bracket the	whole
	  aggregate.

     9.	  TRANSLATION

	  Translation is considered a kind of modification, so you may dis-
	  tribute translations of the Document under the terms of section 4.
	  Replacing Invariant Sections with translations requires special per-
	  mission from their copyright holders,	but you	may include transla-
	  tions	of some	or all Invariant Sections in addition to the original
	  versions of these Invariant Sections.	You may	include	a translation
	  of this License, and all the license notices in the Document,	and
	  any Warranty Disclaimers, provided that you also include the origi-
	  nal English version of this License and the original versions	of
	  those	notices	and disclaimers. In case of a disagreement between the
	  translation and the original version of this License or a notice or
	  disclaimer, the original version will	prevail.

	  If a section in the Document is Entitled "Acknowledgements", "Dedi-
	  cations", or "History", the requirement (section 4) to Preserve its
	  Title	(section 1) will typically require changing the	actual title.

     10.  TERMINATION

	  You may not copy, modify, sublicense,	or distribute the Document ex-
	  cept as expressly provided for under this License. Any other attempt
	  to copy, modify, sublicense or distribute the	Document is void, and
	  will automatically terminate your rights under this License. How-
	  ever,	parties	who have received copies, or rights, from you under
	  this License will not	have their licenses terminated so long as such
	  parties remain in full compliance.

     11.  FUTURE REVISIONS OF THIS LICENSE

	  The Free Software Foundation may publish new,	revised	versions of
	  the GNU Free Documentation License from time to time.	Such new ver-
	  sions	will be	similar	in spirit to the present version, but may dif-
	  fer in detail	to address new problems	or concerns. See
	  http://www.gnu.org/copyleft/

	  Each version of the License is given a distinguishing	version	num-
	  ber. If the Document specifies that a	particular numbered version of
	  this License "or any later version" applies to it, you have the op-
	  tion of following the	terms and conditions either of that specified
	  version or of	any later version that has been	published (not as a
	  draft) by the	Free Software Foundation. If the Document does not
	  specify a version number of this License, you	may choose any version
	  ever published (not as a draft) by the Free Software Foundation.

     ADDENDUM: How to use this License for your	documents

     To	use this License in a document you have	written, include a copy	of the
     License in	the document and put the following copyright and license no-
     tices just	after the title	page:

	     Copyright (C)  year  your name.
	     Permission	is granted to copy, distribute and/or modify this document
	     under the terms of	the GNU	Free Documentation License, Version 1.2
	     or	any later version published by the Free	Software Foundation;
	     with no Invariant Sections, no Front-Cover	Texts, and no Back-Cover
	     Texts.  A copy of the license is included in the section entitled "GNU
	     Free Documentation	License".

     If	you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
     replace the "with...Texts." line with this:

	       with the	Invariant Sections being list their titles, with
	       the Front-Cover Texts being list, and with the Back-Cover Texts
	       being list.

     If	you have Invariant Sections without Cover Texts, or some other combi-
     nation of the three, merge	those two alternatives to suit the situation.

     If	your document contains nontrivial examples of program code, we recom-
     mend releasing these examples in parallel under your choice of free soft-
     ware license, such	as the GNU General Public License, to permit their use
     in	free software.

Translations of	This Manual
     Nishio Futoshi of the GNUjdoc project has prepared	a Japanese translation
     of	this manual. Its most recent version can be found at
     http://openlab.ring.gr.jp/gnujdoc/cvsweb/cvsweb.cgi/gnujdoc/

Index
BSD			       October 16, 2019				   BSD

NAME | Comparing and Merging Files | Overview | What Comparison Means | Incomplete Lines | Comparing Directories | Comparing Three Files | Merging From a Common Ancestor | Tips for Making and Using Patches | Standards conformance | Future Projects | Copying This Manual | Translations of This Manual | Index

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