completion.js

var fs = require('fs'),
  path = require('path');

// add bash completions to your
//  yargs-powered applications.
module.exports = function (yargs, usage) {
  var self = {
    completionKey: 'get-yargs-completions'
  };

  // get a list of completion commands.
  self.getCompletion = function (done) {
    var completions = [],
      current = process.argv[process.argv.length - 1],
      previous = process.argv.slice(process.argv.indexOf('--' + self.completionKey) + 1),
      argv = yargs.parse(previous);

    // a custom completion function can be provided
    // to completion().
    if (completionFunction) {
      if (completionFunction.length < 3) {
        // synchronous completion function.
        return done(completionFunction(current, argv));
      } else {
        // asynchronous completion function
        return completionFunction(current, argv, function(completions) {
          done(completions);
        });
      }
    }

    if (!current.match(/^-/)) {
      usage.getCommands().forEach(function(command) {
        completions.push(command[0]);
      });
    }

    if (current.match(/^-/)) {
      Object.keys(yargs.getOptions().key).forEach(function(key) {
        completions.push('--' + key);
      });
    }

    done(completions);
  };

  // generate the completion script to add to your .bashrc.
  self.generateCompletionScript = function ($0) {
    var script = fs.readFileSync(
        path.resolve(__dirname, '../completion.sh.hbs'),
        'utf-8'
      ),
      name = path.basename($0);

    // add ./to applications not yet installed as bin.
    if ($0.match(/\.js$/)) $0 = './' + $0;

    script = script.replace(/{{app_name}}/g, name);
    return script.replace(/{{app_path}}/g, $0);
  };

  // register a function to perform your own custom
  // completions., this function can be either
  // synchrnous or asynchronous.
  var completionFunction = null;
  self.registerFunction = function (fn) {
      completionFunction = fn;
  }

  return self;
};