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m4 is a pure Javascript implementation of an m4 macro language processor. You can use it with Node.js or in the browser, via browserify. A command-line version is provided, usable as a drop-in replacement for a native version (such as GNU M4).


npm install m4

Example usage

$ node example.js
// example.js 
'use strict';
var M4 = require('m4');
var input = new M4();
input.write("define(`beep', `boop')dnl\nbeep\n");


Class: M4

Inherit stream.Transform. As such this is a duplex stream you can pipe, write and read.

new M4(opts)

  • opts Object Options:

Event: 'error'

Signal a non-recuperable error. The stream will not produce further output in the case of an error.

Event: 'warning'

Signal a warning. The steam continues to produce output normally, but there may be some unwanted behavior.

m4.define(name, {fn|str})

  • name String Identifier.
  • fn Fonction Called with (name, [arg1, arg2 ... ]), must return the macro expansion result as a string. name is the macro defined name itself.
  • str String Macro content, just like you were defining the macro in M4.

Define a M4 macro as a Javascript function.


  • index Number Diversion index.

Change how the output is processed. If the index is zero, output is directly emitted by the stream. If the index is a positive integer, the output is stored in an internal buffer — a "diversion" — instead.


  • diversions Number Diversion indices.

Output the content of the specified diversions. They are emptied. If no diversion is specified, all of them are undiverted, in numerical order.


Put the stream into a special mode where all the tokens are ignored until the next newline.