man(1) Manual page archive

     M4(1)                                                       M4(1)

          m4 - macro processor

          m4 [ options ] [ 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 files, or if a file name is
          -, the standard input is read.  The processed text is writ-
          ten 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

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

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

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

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

          To be effective, these flags must appear before any file
          names and before any -D or -U flags:

               Defines name to val or to null in val's absence.

               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

          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 arguments are replaced by the null
                      string; $# is replaced by the number of argu-
                      ments; $* is replaced by a list of all the argu-
                      ments separated by commas; $@ is like $*, but
                      each argument is quoted (with the current

          undefine    removes the definition of the macro named in its

          defn        returns the quoted definition of its
                      argument(s).  It is useful for renaming macros,
                      especially built-ins.

          pushdef     like define, but saves any previous definition.

          popdef      removes current definition of its 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

          shift       returns all but its first argument.  The other
                      arguments are quoted and pushed back with commas
                      in between.  The quoting nullifies the effect of
                      the extra scan that will subsequently be per-

          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

          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 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 discarded.

          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

          divnum      returns the value of the current output stream.

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

          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.  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

     M4(1)                                                       M4(1)

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

          decr        returns the value of its argument decremented by

          eval        evaluates its argument as an arithmetic expres-
                      sion, using 32-bit arithmetic.  Operators
                      include +, -, *, /, %, ^ (exponentiation), bit-
                      wise &, |, ^, and ~; relationals; parentheses.
                      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 minimum number of
                      digits in the result.

          len         returns the number of characters in its argu-

          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 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    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 permitted.

          include     returns the contents of the file named in the

          sinclude    is identical to include, except that it says
                      nothing if the file is inaccessible.

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

          sysval      is the return code from the last call to syscmd.

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

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

     M4(1)                                                       M4(1)

          m4wrap      argument 1 will be pushed back at final EOF;
                      example: m4wrap(`cleanup()')

          errprint    prints its argument on the diagnostic output

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

          traceon     with no arguments, turns on tracing for all mac-
                      ros (including built-ins).  Otherwise, turns on
                      tracing for named macros.

          traceoff    turns off trace globally and for any macros
                      specified.  Macros specifically traced by
                      traceon can be untraced only by specific calls
                      to traceoff.

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