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M4(1)		    UNIX Programmer's Manual		    M4(1)



[1mNAME
     [0mm4 - macro processor

[1mSYNOPSIS
     m4 [0m[ files ]

[1mDESCRIPTION
     [0m_M_4 is a macro processor intended as a front end for Ratfor,
     C, and other languages.  Each of the argument files is pro-
     cessed in order; if there are no arguments, or if an argu-
     ment 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 new-
     lines are ignored while collecting arguments.  Potential
     macro names consist of alphabetic 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
     arguments, and any commas or right parentheses which happen
     to turn up within the value of a nested call are as effec-
     tive as those in the original input text.	After argument
     collection, the value of the macro is pushed back onto the
     input stream and rescanned.

     _M_4 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.

     [1mdefine    [0mThe 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 argu-
	       ments are replaced by the null string.

     [1mundefine  [0mremoves the definition of the macro named in its
	       argument.

     [1mifdef     [0mIf the first argument is defined, the value is the



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M4(1)		    UNIX Programmer's Manual		    M4(1)



	       second argument, otherwise the third.  If there is
	       no third argument, the value is null.  The word
	       _u_n_i_x is predefined on UNIX versions of _m_4.

     [1mchangequote
	       [0mChange quote characters to the first and second
	       arguments.  _C_h_a_n_g_e_q_u_o_t_e without arguments restores
	       the original values (i.e., `').

     [1mdivert    [0m_M_4 maintains 10 output streams, numbered 0-9.  The
	       final output is the concatenation of the streams
	       in numerical order; initially stream 0 is the
	       current stream.	The _d_i_v_e_r_t macro changes the
	       current output stream to its (digit-string) argu-
	       ment.  Output diverted to a stream other than 0
	       through 9 is discarded.

     [1mundivert  [0mcauses immediate output of text from diversions
	       named as arguments, or all diversions if no argu-
	       ment.  Text may be undiverted into another diver-
	       sion.  Undiverting discards the diverted text.

     [1mdivnum    [0mreturns the value of the current output stream.

     [1mdnl       [0mreads and discards characters up to and including
	       the next newline.

     [1mifelse    [0mhas three or more arguments.  If the first argu-
	       ment 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.  Otherwise,
	       the value is either the fourth string, or, if it
	       is not present, null.

     [1mincr      [0mreturns 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.

     [1meval      [0mevaluates its argument as an arithmetic expres-
	       sion, using 32-bit arithmetic.  Operators include
	       +, -, *, /, %, ^ (exponentiation); relationals;
	       parentheses.

     [1mlen       [0mreturns the number of characters in its argument.

     [1mindex     [0mreturns the position in its first argument where
	       the second argument begins (zero origin), or -1 if
	       the second argument does not occur.

     [1msubstr    [0mreturns a substring of its first argument.  The



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M4(1)		    UNIX Programmer's Manual		    M4(1)



	       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.

     [1mtranslit  [0mtransliterates the characters in its first argu-
	       ment from the set given by the second argument to
	       the set given by the third.  No abbreviations are
	       permitted.

     [1minclude   [0mreturns the contents of the file named in the
	       argument.

     [1msinclude  [0mis identical to _i_n_c_l_u_d_e, except that it says noth-
	       ing if the file is inaccessible.

     [1msyscmd    [0mexecutes the UNIX command given in the first argu-
	       ment.  No value is returned.

     [1mmaketemp  [0mfills in a string of XXXXX in its argument with
	       the current process id.

     [1merrprint  [0mprints its argument on the diagnostic output file.

     [1mdumpdef   [0mprints current names and definitions, for the
	       named items, or for all if no arguments are given.

[1mSEE ALSO
     [0mB. W. Kernighan and D. M. Ritchie, _T_h_e _M_4 _M_a_c_r_o _P_r_o_c_e_s_s_o_r

























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