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 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

          When a macro name is recognized, its arguments are collected
          by searching for a matching right parenthesis.  Macro evalu-
          ation 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 argu-
                    ments are replaced by the null string.

          undefine  removes the definition of the macro named in its

     M4(1)                                                       M4(1)

          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 concatenation of the streams
                    in numerical order; initially stream 0 is the cur-
                    rent 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 discarded.

          undivert  causes 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.

          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 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.

          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

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

          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.

     M4(1)                                                       M4(1)

          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 argu-
                    ment from the set given by the second argument to
                    the set given by the third.  No abbreviations are

          include   returns the contents of the file named in the

          sinclude  is identical to include, except that it says noth-
                    ing if the file is inaccessible.

          syscmd    executes the UNIX command given in the first argu-
                    ment.  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