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M4(1)											    M4(1)

       m4 - macro processor

       m4 [ files ]

       M4  is a macro processor intended as a front end for Ratfor, C, and other languages.  Each
       of the argument files is processed in order; if there are no arguments, or if an  argument
       is `-', the standard input is read.  The processed text is written on the standard output.

       Macro calls have the form

	    name(arg1,arg2, . . . , argn)

       The  `('  must  immediately  follow the name of the macro.  If a defined macro name is not
       followed by a `(', it is deemed to have no arguments.  Leading unquoted blanks, tabs,  and
       newlines  are ignored while collecting arguments.  Potential macro names consist of alpha-
       betic letters, digits, and underscore `_', where the first character is not a digit.

       Left and right single quotes (`') are used to quote strings.  The value of a quoted string
       is the string stripped of the quotes.

       When  a	macro name is recognized, its arguments are collected by searching for a matching
       right parenthesis.  Macro evaluation proceeds normally during the collection of the  argu-
       ments,  and  any commas or right parentheses which happen to turn up within the value of a
       nested call are as effective as those in the original input text.  After argument  collec-
       tion, the value of the macro is pushed back onto the input stream and rescanned.

       M4 makes available the following built-in macros.  They may be redefined, but once this is
       done the original meaning is lost.  Their values are null unless otherwise stated.

       define	 The second argument is installed as the value of the macro  whose  name  is  the
		 first	argument.   Each  occurrence  of $n in the replacement text, where n is a
		 digit, is replaced by the n-th argument.  Argument 0 is the name of  the  macro;
		 missing arguments are replaced by the null string.

       undefine  removes the definition of the macro named in its argument.

       ifdef	 If  the  first  argument is defined, the value is the second argument, otherwise
		 the third.  If there is no third argument, the value is null.	The word unix  is
		 predefined on UNIX versions of m4.

		 Change  quote characters to the first and second arguments.  Changequote without
		 arguments restores the original values (i.e., `').

       divert	 M4 maintains 10 output streams, numbered 0-9.	The final output is the  concate-
		 nation  of  the  streams  in  numerical order; initially stream 0 is the current
		 stream.  The divert macro changes the	current  output  stream  to  its  (digit-
		 string)  argument.   Output  diverted to a stream other than 0 through 9 is dis-

       undivert  causes immediate output of text from  diversions  named  as  arguments,  or  all
		 diversions  if  no  argument.	 Text  may  be undiverted into another diversion.
		 Undiverting discards the diverted text.

       divnum	 returns the value of the current output stream.

       dnl	 reads and discards characters up to and including the next newline.

       ifelse	 has three or more arguments.  If the first argument is the same  string  as  the
		 second,  then	the  value  is the third argument.  If not, and if there are more
		 than four arguments, the process is repeated with arguments 4, 5, 6 and 7.  Oth-
		 erwise, the value is either the fourth string, or, if it is not present, null.

       incr	 returns  the  value of its argument incremented by 1.	The value of the argument
		 is calculated by interpreting an initial digit-string as a decimal number.

       eval	 evaluates its argument as an arithmetic  expression,  using  32-bit  arithmetic.
		 Operators include +, -, *, /, %, ^ (exponentiation); relationals; parentheses.

       len	 returns the number of characters in its argument.

       index	 returns  the  position  in  its  first argument where the second argument begins
		 (zero origin), or -1 if the second argument does not occur.

       substr	 returns a substring of its first argument.  The second argument is a zero origin
		 number selecting the first character; the third argument indicates the length of
		 the substring.  A missing third argument is taken to be large enough  to  extend
		 to the end of the first string.

       translit  transliterates  the  characters  in its first argument from the set given by the
		 second argument to the set given by the third.  No abbreviations are permitted.

       include	 returns the contents of the file named in the argument.

       sinclude  is identical to include, except that it says nothing if the file  is  inaccessi-

       syscmd	 executes the UNIX command given in the first argument.  No value is returned.

       maketemp  fills in a string of XXXXX in its argument with the current process id.

       errprint  prints its argument on the diagnostic output file.

       dumpdef	 prints  current  names  and  definitions,  for the named items, or for all if no
		 arguments are given.

       B. W. Kernighan and D. M. Ritchie, The M4 Macro Processor

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