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     M4(1)                                                       M4(1)

     NAME
          m4 - macro processor

     SYNOPSIS
          m4 [ option ... ] [ file ... ]

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

          The options and their effects are as follows:

          -e   Operate interactively.  Interrupts are ignored and the
               output is unbuffered.  Using this mode requires a spe-
               cial state of mind.

          -s   Enable line sync output for the C preprocessor, (#line
               ...)

          -Bint
               Change the size of the push-back and argument collec-
               tion buffers from the default of 4,096.

          -Hint
               Change the size of the symbol table hash array from the
               default of 199.  The size should be prime.

          -Sint
               Change the size of the call stack from the default of
               100 slots.  Macros take three slots, and non-macro
               arguments take one.

          -Tint
               Change the size of the token buffer from the default of
               512 bytes.

          The preceding options must appear before any file names or
          -D or -U options.

          -Dname[=val]
               Defines name to val or to null if val is missing.

          -Uname
               undefines name.

          Macro calls have the form:

     M4(1)                                                       M4(1)

               `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 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.

          The value of a macro is obtained by replacing each occur-
          rence of $n in the replacement text, where n is a digit,
          with the n-th argument.  Argument 0 is the name of the
          macro; missing arguments are replaced by the null string; $#
          is replaced by the number of arguments; $* is replaced by a
          list of all the arguments separated by commas; $@ is like
          $*, but each argument is quoted (with the current quotes).

          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 replace-
                      ment text of the macro whose name is the first
                      argument.

          undefine    Remove the definition of the macro named in the
                      argument.

          defn        Return the quoted definition of the argument(s);
                      useful for renaming macros, especially built-
                      ins.

          pushdef     Like define, but save any previous definition.

          popdef      Remove current definition of the argument(s),
                      exposing the previous one if any.

          ifdef       If the first argument is defined, the value is
                      the second argument, otherwise the third.  If

     M4(1)                                                       M4(1)

                      there is no third argument, the value is null.
                      The word `unix' is predefined on UNIX versions
                      of m4.

          shift       Return all but the first argument.  The other
                      arguments pushed back with commas in between and
                      quoted to nullify the effect of the extra scan.

          changequote Change quote symbols to the first and second
                      arguments.  The symbols may be up to five char-
                      acters long.  Changequote without arguments
                      restores the original values (i.e., ``'').

          changecom   Change left and right comment markers from the
                      default # and new-line.  With no arguments, the
                      comment mechanism is effectively disabled.  With
                      one argument, the left marker becomes the argu-
                      ment and the right marker becomes new-line.
                      With two arguments, both markers are affected.
                      Comment markers may be up to five characters
                      long.

          divert      m4 Switch output to one of 10 streams, numbered
                      0-9 designated by the argument.  The final out-
                      put is the concatenation of the streams in
                      numerical order; stream 0 is the current ini-
                      tially.  Output to a stream other than 0 through
                      9 is discarded.

          undivert    Cause immediate output of text from diversions
                      named as arguments, or all diversions if no
                      argument.  Text may be undiverted into another
                      diversion.  Once undiverted, the diverted text
                      is no longer contained in that diversion.

          divnum      Return the name of the current output stream.

          dnl         reads and discards characters up to and includ-
                      ing the next new-line.

          ifelse      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 argu-
                      ments, the process is repeated with arguments 4,
                      5, 6 and 7.  Otherwise, the value is either the
                      fourth string, or, if that is not present, null.

          incr        Return the value of the argument incremented by
                      1.  The value of the argument is calculated by
                      interpreting an initial digit-string as a deci-
                      mal number.

     M4(1)                                                       M4(1)

          decr        Return the value of the argument decremented by
                      1.

          eval        Evaluate the argument as an arithmetic expres-
                      sion, using 32-bit arithmetic.  C-like operators
                      include +-*/%, bitwise &|^~; relationals; paren-
                      theses.  Octal and hex numbers may be specified
                      as in C.  The second argument specifies the
                      radix for the result; the default is 10.  The
                      third argument may be used to specify the mini-
                      mum number of digits in the result.

          len         Returns the number of characters in the argu-
                      ment.

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

          substr      Return a substring of the first argument.  The
                      second argument is a zero origin number select-
                      ing the first character; the third argument
                      indicates the length of the substring.  A miss-
                      ing third argument is taken to be large enough
                      to extend to the end of the first string.

          translit    Transliterate the characters in the first argu-
                      ment from the set given by the second argument
                      to the set given by the third, deleting charac-
                      ters that lack a correspondent in the third set.
                      There is no character-range notation.

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

          sinclude    Same, but give no diagnostic if the file is
                      inaccessible.

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

          sysval      The return code from the last call to syscmd.

          maketemp    Fill in a string of `X' characters in the argu-
                      ment with the current process id.

          m4exit      Exit immediately from m4. Argument 1, if given,
                      is the exit code; the default is 0.

          m4wrap      Push the argument back at the end of the input.
                      Example: `m4wrap(`cleanup()')'

     M4(1)                                                       M4(1)

          errprint    Prints the argument on the standard error file.

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

          traceon     If there are no arguments, turn on tracing for
                      all macros (including built-ins).  Otherwise,
                      turn on tracing for named macros.

          traceoff    Turn off trace globally and for any macros spec-
                      ified.  Macros specifically traced by traceon
                      can be untraced only by specific calls to
                      traceoff.

     EXAMPLES
          define(fib,`ifelse(define(`n',eval($1))n,0,1,n,1,1,dnl()
          `eval(fib(n-1)+fib($1-2))')')dnl()
          fib(2*3)
               Recursively evaluate a Fibonacci number.  The inner
               define avoids some reevaluations.