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M4(1)			FreeBSD	General	Commands Manual			 M4(1)

     m4	-- macro language processor

     m4	[-EgPs]	[-Dname[=value]] [-d flags] [-I	dirname] [-o filename]
	[-t macro] [-Uname] [file ...]

     The m4 utility is a macro processor that can be used as a front end to
     any language (e.g., C, ratfor, fortran, lex, and yacc).  If no input
     files are given, m4 reads from the	standard input,	otherwise files	speci-
     fied on the command line are processed in the given order.	 Input files
     can be regular files, files in the	m4 include paths, or a single dash
     (`-'), denoting standard input.  m4 writes	the processed text to the
     standard output, unless told otherwise.

     Macro calls have the form name(argument1[,	argument2, ...,	argumentN]).

     There cannot be any space following the macro name	and the	open parenthe-
     sis (`(').	 If the	macro name is not followed by an open parenthesis it
     is	processed with no arguments.

     Macro names consist of a leading alphabetic or underscore possibly	fol-
     lowed by alphanumeric or underscore characters, e.g., valid macro names
     match the pattern "[a-zA-Z_][a-zA-Z0-9_]*".

     In	arguments to macros, leading unquoted space, tab, and newline (`\n')
     characters	are ignored.  To quote strings,	use left and right single
     quotes (e.g., ` this is a string with a leading space').  You can change
     the quote characters with the changequote built-in	macro.

     Most built-ins do not make	any sense without arguments, and hence are not
     recognized	as special when	not followed by	an open	parenthesis.

     The options are as	follows:

	     Define the	symbol name to have some value (or NULL).

     -d	flags
	     Set trace flags.  flags may hold the following:

	     a	     print macro arguments.

	     c	     print macro expansion over	several	lines.

	     e	     print result of macro expansion.

	     f	     print filename location.

	     l	     print line	number.

	     q	     quote arguments and expansion with	the current quotes.

	     t	     start with	all macros traced.

	     x	     number macro expansions.

	     V	     turn on all options.

	     By	default, trace is set to "eq".

     -E	     Set warnings to be	fatal.	When a single -E flag is specified, if
	     warnings are issued, execution continues but m4 will exit with a
	     non-zero exit status.  When multiple -E flags are specified, exe-
	     cution will halt upon issuing the first warning and m4 will exit
	     with a non-zero exit status.  This	behaviour matches GNU-m4 1.4.9
	     and later.

     -g	     Activate GNU-m4 compatibility mode.  In this mode,	translit han-
	     dles simple character ranges (e.g., a-z), regular expressions
	     mimic emacs behavior, multiple m4wrap calls are handled as	a
	     stack, the	number of diversions is	unlimited, empty names for
	     macro definitions are allowed, and	eval understands
	     `0rbase:value' numbers.

     -I	dirname
	     Add directory dirname to the include path.

     -o	filename
	     Send trace	output to filename.

     -P	     Prefix all	built-in macros	with `m4_'.  For example, instead of
	     writing define, use m4_define.

     -s	     Output line synchronization directives, suitable for cpp(1).

     -t	macro
	     Turn tracing on for macro.

     -Uname  Undefine the symbol name.

     m4	provides the following built-in	macros.	 They may be redefined,	losing
     their original meaning.  Return values are	null unless otherwise stated.

		  Calls	a built-in by its name,	overriding possible redefini-

     changecom(startcomment, endcomment)
		  Changes the start comment and	end comment sequences.	Com-
		  ment sequences may be	up to five characters long.  The de-
		  fault	values are the hash sign and the newline character.

			# This is a comment

		  With no arguments, comments are turned off.  With one	single
		  argument, the	end comment sequence is	set to the newline

     changequote(beginquote, endquote)
		  Defines the open quote and close quote sequences.  Quote se-
		  quences may be up to five characters long.  The default val-
		  ues are the backquote	character and the quote	character.

			`Here is a quoted string'

		  With no arguments, the default quotes	are restored.  With
		  one single argument, the close quote sequence	is set to the
		  newline character.

     decr(arg)	  Decrements the argument arg by 1.  The argument arg must be
		  a valid numeric string.

     define(name, value)
		  Define a new macro named by the first	argument name to have
		  the value of the second argument value.  Each	occurrence of
		  `$n' (where n	is 0 through 9)	is replaced by the n'th	argu-
		  ment.	 `$0' is the name of the calling macro.	 Undefined ar-
		  guments are replaced by a null string.  `$#' is replaced by
		  the number of	arguments; `$*'	is replaced by all arguments
		  comma	separated; `$@'	is the same as `$*' but	all arguments
		  are quoted against further expansion.

     defn(name,	...)
		  Returns the quoted definition	for each argument.  This can
		  be used to rename macro definitions (even for	built-in

     divert(num)  There	are 10 output queues (numbered 0-9).  At the end of
		  processing m4	concatenates all the queues in numerical order
		  to produce the final output.	Initially the output queue is
		  0.  The divert macro allows you to select a new output queue
		  (an invalid argument passed to divert	causes output to be

     divnum	  Returns the current output queue number.

     dnl	  Discard input	characters up to and including the next	new-

     dumpdef(name, ...)
		  Prints the names and definitions for the named items,	or for
		  everything if	no arguments are passed.

		  Prints the first argument on the standard error output

		  Passes its first argument to a shell and returns the shell's
		  standard output.  Note that the shell	shares its standard
		  input	and standard error with	m4.

		  Computes the first argument as an arithmetic expression us-
		  ing 32-bit arithmetic.  Operators are	the standard C
		  ternary, arithmetic, logical,	shift, relational, bitwise,
		  and parentheses operators.  You can specify octal, decimal,
		  and hexadecimal numbers as in	C.  The	optional second	argu-
		  ment radix specifies the radix for the result	and the	op-
		  tional third argument	minimum	specifies the minimum number
		  of digits in the result.

     expr(expr)	  This is an alias for eval.

     format(formatstring, arg1,	...)
		  Returns formatstring with escape sequences substituted with
		  arg1 and following arguments,	in a way similar to printf(3).
		  This built-in	is only	available in GNU-m4 compatibility
		  mode,	and the	only parameters	implemented are	there for au-
		  toconf compatibility:	left-padding flag, an optional field
		  width, a maximum field width,	*-specified field widths, and
		  the %s and %c	data type.

     ifdef(name, yes, no)
		  If the macro named by	the first argument is defined then re-
		  turn the second argument, otherwise the third.  If there is
		  no third argument, the value is NULL.	 The word "unix" is

     ifelse(a, b, yes, ...)
		  If the first argument	a matches the second argument b	then
		  ifelse() returns the third argument yes.  If the match fails
		  the three arguments are discarded and	the next three argu-
		  ments	are used until there is	zero or	one arguments left,
		  either this last argument or NULL is returned	if no other
		  matches were found.

		  Returns the contents of the file specified in	the first ar-
		  gument.  If the file is not found as is, look	through	the
		  include path:	first the directories specified	with -I	on the
		  command line,	then the environment variable M4PATH, as a
		  colon-separated list of directories.	Include	aborts with an
		  error	message	if the file cannot be included.

     incr(arg)	  Increments the argument by 1.	 The argument must be a	valid
		  numeric string.

     index(string, substring)
		  Returns the index of the second argument in the first	argu-
		  ment (e.g., index(the	quick brown fox	jumped,	fox) returns
		  16).	If the second argument is not found index returns -1.

     indir(macro, arg1,	...)
		  Indirectly calls the macro whose name	is passed as the first
		  argument, with the remaining arguments passed	as first, ...

     len(arg)	  Returns the number of	characters in the first	argument.  Ex-
		  tra arguments	are ignored.

		  Immediately exits with the return value specified by the
		  first	argument, 0 if none.

		  Allows you to	define what happens at the final EOF, usually
		  for cleanup purposes (e.g., m4wrap("cleanup(tempfile)")
		  causes the macro cleanup to be invoked after all other pro-
		  cessing is done).

		  Multiple calls to m4wrap() get inserted in sequence at the
		  final	EOF.

		  Like mkstemp.

		  Invokes mkstemp(3) on	the first argument, and	returns	the
		  modified string.  This can be	used to	create unique tempo-
		  rary file names.

     paste(file)  Includes the contents	of the file specified by the first ar-
		  gument without any macro processing.	Aborts with an error
		  message if the file cannot be	included.

     patsubst(string, regexp, replacement)
		  Substitutes a	regular	expression in a	string with a replace-
		  ment string.	Usual substitution patterns apply: an amper-
		  sand (`&') is	replaced by the	string matching	the regular
		  expression.  The string `\#',	where `#' is a digit, is re-
		  placed by the	corresponding back-reference.

     popdef(arg, ...)
		  Restores the pushdefed definition for	each argument.

     pushdef(macro, def)
		  Takes	the same arguments as define, but it saves the defini-
		  tion on a stack for later retrieval by popdef().

     regexp(string, regexp, replacement)
		  Finds	a regular expression in	a string.  If no further argu-
		  ments	are given, it returns the first	match position or -1
		  if no	match.	If a third argument is provided, it returns
		  the replacement string, with sub-patterns replaced.

     shift(arg1, ...)
		  Returns all but the first argument, the remaining arguments
		  are quoted and pushed	back with commas in between.  The
		  quoting nullifies the	effect of the extra scan that will
		  subsequently be performed.

		  Similar to include, except it	ignores	any errors.

		  Similar to paste(), except it	ignores	any errors.

     substr(string, offset, length)
		  Returns a substring of the first argument starting at	the
		  offset specified by the second argument and the length spec-
		  ified	by the third argument.	If no third argument is
		  present it returns the rest of the string.

     syscmd(cmd)  Passes the first argument to the shell.  Nothing is re-

     sysval	  Returns the return value from	the last syscmd.

     traceon(arg, ...)
		  Enables tracing of macro expansions for the given arguments,
		  or for all macros if no argument is given.

     traceoff(arg, ...)
		  Disables tracing of macro expansions for the given argu-
		  ments, or for	all macros if no argument is given.

     translit(string, mapfrom, mapto)
		  Transliterate	the characters in the first argument from the
		  set given by the second argument to the set given by the
		  third.  You cannot use tr(1) style abbreviations.

     undefine(name1, ...)
		  Removes the definition for the macros	specified by its argu-

     undivert(arg, ...)
		  Flushes the named output queues (or all queues if no argu-

     unix	  A pre-defined	macro for testing the OS platform.

     __line__	  Returns the current file's line number.

     __file__	  Returns the current file's name.

     The m4 utility exits 0 on success,	and >0 if an error occurs.

     But note that the m4exit macro can	modify the exit	status,	as can the -E

     B.	W. Kernighan and D. M. Ritchie,	The M4 Macro Processor,	AT_T Bell
     Laboratories, Computing Science Technical Report, 59, July	1977.

     The m4 utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1")

     The flags [-dEgIPot] and the macros builtin, esyscmd, expr, format,
     indir, paste, patsubst, regexp, spaste, unix, __line__, and __file__ are
     extensions	to that	specification.

     maketemp is not supposed to be a synonym for mkstemp, but instead to be
     an	insecure temporary file	name creation function.	 It is marked by IEEE
     Std 1003.1-2008 ("POSIX.1") as being obsolescent and should not be	used
     if	portability is a concern.

     The output	format of traceon and dumpdef are not specified	in any stan-
     dard, are likely to change	and should not be relied upon.	The current
     format of tracing is closely modelled on gnu-m4, to allow autoconf	to

     The built-ins pushdef and popdef handle macro definitions as a stack.
     However, define interacts with the	stack in an undefined way.  In this
     implementation, define replaces the top-most definition only.  Other im-
     plementations may erase all definitions on	the stack instead.

     All built-ins do expand without arguments in many other m4.

     Many other	m4 have	dire size limitations with respect to buffer sizes.

     Ozan Yigit	<> and Richard A. O'Keefe

     GNU-m4 compatibility extensions by	Marc Espie <>.

FreeBSD	13.0			 April 8, 2021			  FreeBSD 13.0


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