index.js

/**
 * Module dependencies.
 */

var EventEmitter = require('events').EventEmitter;
var spawn = require('child_process').spawn;
var path = require('path');
var dirname = path.dirname;
var basename = path.basename;
var fs = require('fs');

/**
 * Inherit `Command` from `EventEmitter.prototype`.
 */

require('util').inherits(Command, EventEmitter);

/**
 * Expose the root command.
 */

exports = module.exports = new Command();

/**
 * Expose `Command`.
 */

exports.Command = Command;

/**
 * Expose `Option`.
 */

exports.Option = Option;

/**
 * Initialize a new `Option` with the given `flags` and `description`.
 *
 * @param {String} flags
 * @param {String} description
 * @api public
 */

function Option(flags, description) {
  this.flags = flags;
  this.required = flags.indexOf('<') >= 0;
  this.optional = flags.indexOf('[') >= 0;
  this.bool = flags.indexOf('-no-') === -1;
  flags = flags.split(/[ ,|]+/);
  if (flags.length > 1 && !/^[[<]/.test(flags[1])) this.short = flags.shift();
  this.long = flags.shift();
  this.description = description || '';
}

/**
 * Return option name.
 *
 * @return {String}
 * @api private
 */

Option.prototype.name = function() {
  return this.long
    .replace('--', '')
    .replace('no-', '');
};

/**
 * Return option name, in a camelcase format that can be used
 * as a object attribute key.
 *
 * @return {String}
 * @api private
 */

Option.prototype.attributeName = function() {
  return camelcase(this.name());
};

/**
 * Check if `arg` matches the short or long flag.
 *
 * @param {String} arg
 * @return {Boolean}
 * @api private
 */

Option.prototype.is = function(arg) {
  return this.short === arg || this.long === arg;
};

/**
 * Initialize a new `Command`.
 *
 * @param {String} name
 * @api public
 */

function Command(name) {
  this.commands = [];
  this.options = [];
  this._execs = {};
  this._allowUnknownOption = false;
  this._args = [];
  this._name = name || '';
}

/**
 * Add command `name`.
 *
 * The `.action()` callback is invoked when the
 * command `name` is specified via __ARGV__,
 * and the remaining arguments are applied to the
 * function for access.
 *
 * When the `name` is "*" an un-matched command
 * will be passed as the first arg, followed by
 * the rest of __ARGV__ remaining.
 *
 * Examples:
 *
 *      program
 *        .version('0.0.1')
 *        .option('-C, --chdir <path>', 'change the working directory')
 *        .option('-c, --config <path>', 'set config path. defaults to ./deploy.conf')
 *        .option('-T, --no-tests', 'ignore test hook')
 *
 *      program
 *        .command('setup')
 *        .description('run remote setup commands')
 *        .action(function() {
 *          console.log('setup');
 *        });
 *
 *      program
 *        .command('exec <cmd>')
 *        .description('run the given remote command')
 *        .action(function(cmd) {
 *          console.log('exec "%s"', cmd);
 *        });
 *
 *      program
 *        .command('teardown <dir> [otherDirs...]')
 *        .description('run teardown commands')
 *        .action(function(dir, otherDirs) {
 *          console.log('dir "%s"', dir);
 *          if (otherDirs) {
 *            otherDirs.forEach(function (oDir) {
 *              console.log('dir "%s"', oDir);
 *            });
 *          }
 *        });
 *
 *      program
 *        .command('*')
 *        .description('deploy the given env')
 *        .action(function(env) {
 *          console.log('deploying "%s"', env);
 *        });
 *
 *      program.parse(process.argv);
  *
 * @param {String} name
 * @param {String} [desc] for git-style sub-commands
 * @return {Command} the new command
 * @api public
 */

Command.prototype.command = function(name, desc, opts) {
  if (typeof desc === 'object' && desc !== null) {
    opts = desc;
    desc = null;
  }
  opts = opts || {};
  var args = name.split(/ +/);
  var cmd = new Command(args.shift());

  if (desc) {
    cmd.description(desc);
    this.executables = true;
    this._execs[cmd._name] = true;
    if (opts.isDefault) this.defaultExecutable = cmd._name;
  }
  cmd._noHelp = !!opts.noHelp;
  this.commands.push(cmd);
  cmd.parseExpectedArgs(args);
  cmd.parent = this;

  if (desc) return this;
  return cmd;
};

/**
 * Define argument syntax for the top-level command.
 *
 * @api public
 */

Command.prototype.arguments = function(desc) {
  return this.parseExpectedArgs(desc.split(/ +/));
};

/**
 * Add an implicit `help [cmd]` subcommand
 * which invokes `--help` for the given command.
 *
 * @api private
 */

Command.prototype.addImplicitHelpCommand = function() {
  this.command('help [cmd]', 'display help for [cmd]');
};

/**
 * Parse expected `args`.
 *
 * For example `["[type]"]` becomes `[{ required: false, name: 'type' }]`.
 *
 * @param {Array} args
 * @return {Command} for chaining
 * @api public
 */

Command.prototype.parseExpectedArgs = function(args) {
  if (!args.length) return;
  var self = this;
  args.forEach(function(arg) {
    var argDetails = {
      required: false,
      name: '',
      variadic: false
    };

    switch (arg[0]) {
      case '<':
        argDetails.required = true;
        argDetails.name = arg.slice(1, -1);
        break;
      case '[':
        argDetails.name = arg.slice(1, -1);
        break;
    }

    if (argDetails.name.length > 3 && argDetails.name.slice(-3) === '...') {
      argDetails.variadic = true;
      argDetails.name = argDetails.name.slice(0, -3);
    }
    if (argDetails.name) {
      self._args.push(argDetails);
    }
  });
  return this;
};

/**
 * Register callback `fn` for the command.
 *
 * Examples:
 *
 *      program
 *        .command('help')
 *        .description('display verbose help')
 *        .action(function() {
 *           // output help here
 *        });
 *
 * @param {Function} fn
 * @return {Command} for chaining
 * @api public
 */

Command.prototype.action = function(fn) {
  var self = this;
  var listener = function(args, unknown) {
    // Parse any so-far unknown options
    args = args || [];
    unknown = unknown || [];

    var parsed = self.parseOptions(unknown);

    // Output help if necessary
    outputHelpIfNecessary(self, parsed.unknown);

    // If there are still any unknown options, then we simply
    // die, unless someone asked for help, in which case we give it
    // to them, and then we die.
    if (parsed.unknown.length > 0) {
      self.unknownOption(parsed.unknown[0]);
    }

    // Leftover arguments need to be pushed back. Fixes issue #56
    if (parsed.args.length) args = parsed.args.concat(args);

    self._args.forEach(function(arg, i) {
      if (arg.required && args[i] == null) {
        self.missingArgument(arg.name);
      } else if (arg.variadic) {
        if (i !== self._args.length - 1) {
          self.variadicArgNotLast(arg.name);
        }

        args[i] = args.splice(i);
      }
    });

    // Always append ourselves to the end of the arguments,
    // to make sure we match the number of arguments the user
    // expects
    if (self._args.length) {
      args[self._args.length] = self;
    } else {
      args.push(self);
    }

    fn.apply(self, args);
  };
  var parent = this.parent || this;
  var name = parent === this ? '*' : this._name;
  parent.on('command:' + name, listener);
  if (this._alias) parent.on('command:' + this._alias, listener);
  return this;
};

/**
 * Define option with `flags`, `description` and optional
 * coercion `fn`.
 *
 * The `flags` string should contain both the short and long flags,
 * separated by comma, a pipe or space. The following are all valid
 * all will output this way when `--help` is used.
 *
 *    "-p, --pepper"
 *    "-p|--pepper"
 *    "-p --pepper"
 *
 * Examples:
 *
 *     // simple boolean defaulting to false
 *     program.option('-p, --pepper', 'add pepper');
 *
 *     --pepper
 *     program.pepper
 *     // => Boolean
 *
 *     // simple boolean defaulting to true
 *     program.option('-C, --no-cheese', 'remove cheese');
 *
 *     program.cheese
 *     // => true
 *
 *     --no-cheese
 *     program.cheese
 *     // => false
 *
 *     // required argument
 *     program.option('-C, --chdir <path>', 'change the working directory');
 *
 *     --chdir /tmp
 *     program.chdir
 *     // => "/tmp"
 *
 *     // optional argument
 *     program.option('-c, --cheese [type]', 'add cheese [marble]');
 *
 * @param {String} flags
 * @param {String} description
 * @param {Function|*} [fn] or default
 * @param {*} [defaultValue]
 * @return {Command} for chaining
 * @api public
 */

Command.prototype.option = function(flags, description, fn, defaultValue) {
  var self = this,
    option = new Option(flags, description),
    oname = option.name(),
    name = option.attributeName();

  // default as 3rd arg
  if (typeof fn !== 'function') {
    if (fn instanceof RegExp) {
      var regex = fn;
      fn = function(val, def) {
        var m = regex.exec(val);
        return m ? m[0] : def;
      };
    } else {
      defaultValue = fn;
      fn = null;
    }
  }

  // preassign default value only for --no-*, [optional], or <required>
  if (!option.bool || option.optional || option.required) {
    // when --no-* we make sure default is true
    if (!option.bool) defaultValue = true;
    // preassign only if we have a default
    if (defaultValue !== undefined) {
      self[name] = defaultValue;
      option.defaultValue = defaultValue;
    }
  }

  // register the option
  this.options.push(option);

  // when it's passed assign the value
  // and conditionally invoke the callback
  this.on('option:' + oname, function(val) {
    // coercion
    if (val !== null && fn) {
      val = fn(val, self[name] === undefined ? defaultValue : self[name]);
    }

    // unassigned or bool
    if (typeof self[name] === 'boolean' || typeof self[name] === 'undefined') {
      // if no value, bool true, and we have a default, then use it!
      if (val == null) {
        self[name] = option.bool
          ? defaultValue || true
          : false;
      } else {
        self[name] = val;
      }
    } else if (val !== null) {
      // reassign
      self[name] = val;
    }
  });

  return this;
};

/**
 * Allow unknown options on the command line.
 *
 * @param {Boolean} arg if `true` or omitted, no error will be thrown
 * for unknown options.
 * @api public
 */
Command.prototype.allowUnknownOption = function(arg) {
  this._allowUnknownOption = arguments.length === 0 || arg;
  return this;
};

/**
 * Parse `argv`, settings options and invoking commands when defined.
 *
 * @param {Array} argv
 * @return {Command} for chaining
 * @api public
 */

Command.prototype.parse = function(argv) {
  // implicit help
  if (this.executables) this.addImplicitHelpCommand();

  // store raw args
  this.rawArgs = argv;

  // guess name
  this._name = this._name || basename(argv[1], '.js');

  // github-style sub-commands with no sub-command
  if (this.executables && argv.length < 3 && !this.defaultExecutable) {
    // this user needs help
    argv.push('--help');
  }

  // process argv
  var parsed = this.parseOptions(this.normalize(argv.slice(2)));
  var args = this.args = parsed.args;

  var result = this.parseArgs(this.args, parsed.unknown);

  // executable sub-commands
  var name = result.args[0];

  var aliasCommand = null;
  // check alias of sub commands
  if (name) {
    aliasCommand = this.commands.filter(function(command) {
      return command.alias() === name;
    })[0];
  }

  if (this._execs[name] && typeof this._execs[name] !== 'function') {
    return this.executeSubCommand(argv, args, parsed.unknown);
  } else if (aliasCommand) {
    // is alias of a subCommand
    args[0] = aliasCommand._name;
    return this.executeSubCommand(argv, args, parsed.unknown);
  } else if (this.defaultExecutable) {
    // use the default subcommand
    args.unshift(this.defaultExecutable);
    return this.executeSubCommand(argv, args, parsed.unknown);
  }

  return result;
};

/**
 * Execute a sub-command executable.
 *
 * @param {Array} argv
 * @param {Array} args
 * @param {Array} unknown
 * @api private
 */

Command.prototype.executeSubCommand = function(argv, args, unknown) {
  args = args.concat(unknown);

  if (!args.length) this.help();
  if (args[0] === 'help' && args.length === 1) this.help();

  // <cmd> --help
  if (args[0] === 'help') {
    args[0] = args[1];
    args[1] = '--help';
  }

  // executable
  var f = argv[1];
  // name of the subcommand, link `pm-install`
  var bin = basename(f, '.js') + '-' + args[0];

  // In case of globally installed, get the base dir where executable
  //  subcommand file should be located at
  var baseDir,
    link = fs.lstatSync(f).isSymbolicLink() ? fs.readlinkSync(f) : f;

  // when symbolink is relative path
  if (link !== f && link.charAt(0) !== '/') {
    link = path.join(dirname(f), link);
  }
  baseDir = dirname(link);

  // prefer local `./<bin>` to bin in the $PATH
  var localBin = path.join(baseDir, bin);

  // whether bin file is a js script with explicit `.js` extension
  var isExplicitJS = false;
  if (exists(localBin + '.js')) {
    bin = localBin + '.js';
    isExplicitJS = true;
  } else if (exists(localBin)) {
    bin = localBin;
  }

  args = args.slice(1);

  var proc;
  if (process.platform !== 'win32') {
    if (isExplicitJS) {
      args.unshift(bin);
      // add executable arguments to spawn
      args = (process.execArgv || []).concat(args);

      proc = spawn(process.argv[0], args, { stdio: 'inherit', customFds: [0, 1, 2] });
    } else {
      proc = spawn(bin, args, { stdio: 'inherit', customFds: [0, 1, 2] });
    }
  } else {
    args.unshift(bin);
    proc = spawn(process.execPath, args, { stdio: 'inherit' });
  }

  var signals = ['SIGUSR1', 'SIGUSR2', 'SIGTERM', 'SIGINT', 'SIGHUP'];
  signals.forEach(function(signal) {
    process.on(signal, function() {
      if (proc.killed === false && proc.exitCode === null) {
        proc.kill(signal);
      }
    });
  });
  proc.on('close', process.exit.bind(process));
  proc.on('error', function(err) {
    if (err.code === 'ENOENT') {
      console.error('\n  %s(1) does not exist, try --help\n', bin);
    } else if (err.code === 'EACCES') {
      console.error('\n  %s(1) not executable. try chmod or run with root\n', bin);
    }
    process.exit(1);
  });

  // Store the reference to the child process
  this.runningCommand = proc;
};

/**
 * Normalize `args`, splitting joined short flags. For example
 * the arg "-abc" is equivalent to "-a -b -c".
 * This also normalizes equal sign and splits "--abc=def" into "--abc def".
 *
 * @param {Array} args
 * @return {Array}
 * @api private
 */

Command.prototype.normalize = function(args) {
  var ret = [],
    arg,
    lastOpt,
    index;

  for (var i = 0, len = args.length; i < len; ++i) {
    arg = args[i];
    if (i > 0) {
      lastOpt = this.optionFor(args[i - 1]);
    }

    if (arg === '--') {
      // Honor option terminator
      ret = ret.concat(args.slice(i));
      break;
    } else if (lastOpt && lastOpt.required) {
      ret.push(arg);
    } else if (arg.length > 1 && arg[0] === '-' && arg[1] !== '-') {
      arg.slice(1).split('').forEach(function(c) {
        ret.push('-' + c);
      });
    } else if (/^--/.test(arg) && ~(index = arg.indexOf('='))) {
      ret.push(arg.slice(0, index), arg.slice(index + 1));
    } else {
      ret.push(arg);
    }
  }

  return ret;
};

/**
 * Parse command `args`.
 *
 * When listener(s) are available those
 * callbacks are invoked, otherwise the "*"
 * event is emitted and those actions are invoked.
 *
 * @param {Array} args
 * @return {Command} for chaining
 * @api private
 */

Command.prototype.parseArgs = function(args, unknown) {
  var name;

  if (args.length) {
    name = args[0];
    if (this.listeners('command:' + name).length) {
      this.emit('command:' + args.shift(), args, unknown);
    } else {
      this.emit('command:*', args);
    }
  } else {
    outputHelpIfNecessary(this, unknown);

    // If there were no args and we have unknown options,
    // then they are extraneous and we need to error.
    if (unknown.length > 0) {
      this.unknownOption(unknown[0]);
    }
    if (this.commands.length === 0 &&
        this._args.filter(function(a) { return a.required }).length === 0) {
      this.emit('command:*');
    }
  }

  return this;
};

/**
 * Return an option matching `arg` if any.
 *
 * @param {String} arg
 * @return {Option}
 * @api private
 */

Command.prototype.optionFor = function(arg) {
  for (var i = 0, len = this.options.length; i < len; ++i) {
    if (this.options[i].is(arg)) {
      return this.options[i];
    }
  }
};

/**
 * Parse options from `argv` returning `argv`
 * void of these options.
 *
 * @param {Array} argv
 * @return {Array}
 * @api public
 */

Command.prototype.parseOptions = function(argv) {
  var args = [],
    len = argv.length,
    literal,
    option,
    arg;

  var unknownOptions = [];

  // parse options
  for (var i = 0; i < len; ++i) {
    arg = argv[i];

    // literal args after --
    if (literal) {
      args.push(arg);
      continue;
    }

    if (arg === '--') {
      literal = true;
      continue;
    }

    // find matching Option
    option = this.optionFor(arg);

    // option is defined
    if (option) {
      // requires arg
      if (option.required) {
        arg = argv[++i];
        if (arg == null) return this.optionMissingArgument(option);
        this.emit('option:' + option.name(), arg);
      // optional arg
      } else if (option.optional) {
        arg = argv[i + 1];
        if (arg == null || (arg[0] === '-' && arg !== '-')) {
          arg = null;
        } else {
          ++i;
        }
        this.emit('option:' + option.name(), arg);
      // bool
      } else {
        this.emit('option:' + option.name());
      }
      continue;
    }

    // looks like an option
    if (arg.length > 1 && arg[0] === '-') {
      unknownOptions.push(arg);

      // If the next argument looks like it might be
      // an argument for this option, we pass it on.
      // If it isn't, then it'll simply be ignored
      if ((i + 1) < argv.length && argv[i + 1][0] !== '-') {
        unknownOptions.push(argv[++i]);
      }
      continue;
    }

    // arg
    args.push(arg);
  }

  return { args: args, unknown: unknownOptions };
};

/**
 * Return an object containing options as key-value pairs
 *
 * @return {Object}
 * @api public
 */
Command.prototype.opts = function() {
  var result = {},
    len = this.options.length;

  for (var i = 0; i < len; i++) {
    var key = this.options[i].attributeName();
    result[key] = key === this._versionOptionName ? this._version : this[key];
  }
  return result;
};

/**
 * Argument `name` is missing.
 *
 * @param {String} name
 * @api private
 */

Command.prototype.missingArgument = function(name) {
  console.error();
  console.error("  error: missing required argument `%s'", name);
  console.error();
  process.exit(1);
};

/**
 * `Option` is missing an argument, but received `flag` or nothing.
 *
 * @param {String} option
 * @param {String} flag
 * @api private
 */

Command.prototype.optionMissingArgument = function(option, flag) {
  console.error();
  if (flag) {
    console.error("  error: option `%s' argument missing, got `%s'", option.flags, flag);
  } else {
    console.error("  error: option `%s' argument missing", option.flags);
  }
  console.error();
  process.exit(1);
};

/**
 * Unknown option `flag`.
 *
 * @param {String} flag
 * @api private
 */

Command.prototype.unknownOption = function(flag) {
  if (this._allowUnknownOption) return;
  console.error();
  console.error("  error: unknown option `%s'", flag);
  console.error();
  process.exit(1);
};

/**
 * Variadic argument with `name` is not the last argument as required.
 *
 * @param {String} name
 * @api private
 */

Command.prototype.variadicArgNotLast = function(name) {
  console.error();
  console.error("  error: variadic arguments must be last `%s'", name);
  console.error();
  process.exit(1);
};

/**
 * Set the program version to `str`.
 *
 * This method auto-registers the "-V, --version" flag
 * which will print the version number when passed.
 *
 * @param {String} str
 * @param {String} [flags]
 * @return {Command} for chaining
 * @api public
 */

Command.prototype.version = function(str, flags) {
  if (arguments.length === 0) return this._version;
  this._version = str;
  flags = flags || '-V, --version';
  var versionOption = new Option(flags, 'output the version number');
  this._versionOptionName = versionOption.long.substr(2) || 'version';
  this.options.push(versionOption);
  this.on('option:' + this._versionOptionName, function() {
    process.stdout.write(str + '\n');
    process.exit(0);
  });
  return this;
};

/**
 * Set the description to `str`.
 *
 * @param {String} str
 * @param {Object} argsDescription
 * @return {String|Command}
 * @api public
 */

Command.prototype.description = function(str, argsDescription) {
  if (arguments.length === 0) return this._description;
  this._description = str;
  this._argsDescription = argsDescription;
  return this;
};

/**
 * Set an alias for the command
 *
 * @param {String} alias
 * @return {String|Command}
 * @api public
 */

Command.prototype.alias = function(alias) {
  var command = this;
  if (this.commands.length !== 0) {
    command = this.commands[this.commands.length - 1];
  }

  if (arguments.length === 0) return command._alias;

  if (alias === command._name) throw new Error('Command alias can\'t be the same as its name');

  command._alias = alias;
  return this;
};

/**
 * Set / get the command usage `str`.
 *
 * @param {String} str
 * @return {String|Command}
 * @api public
 */

Command.prototype.usage = function(str) {
  var args = this._args.map(function(arg) {
    return humanReadableArgName(arg);
  });

  var usage = '[options]' +
    (this.commands.length ? ' [command]' : '') +
    (this._args.length ? ' ' + args.join(' ') : '');

  if (arguments.length === 0) return this._usage || usage;
  this._usage = str;

  return this;
};

/**
 * Get or set the name of the command
 *
 * @param {String} str
 * @return {String|Command}
 * @api public
 */

Command.prototype.name = function(str) {
  if (arguments.length === 0) return this._name;
  this._name = str;
  return this;
};

/**
 * Return prepared commands.
 *
 * @return {Array}
 * @api private
 */

Command.prototype.prepareCommands = function() {
  return this.commands.filter(function(cmd) {
    return !cmd._noHelp;
  }).map(function(cmd) {
    var args = cmd._args.map(function(arg) {
      return humanReadableArgName(arg);
    }).join(' ');

    return [
      cmd._name +
        (cmd._alias ? '|' + cmd._alias : '') +
        (cmd.options.length ? ' [options]' : '') +
        (args ? ' ' + args : ''),
      cmd._description
    ];
  });
};

/**
 * Return the largest command length.
 *
 * @return {Number}
 * @api private
 */

Command.prototype.largestCommandLength = function() {
  var commands = this.prepareCommands();
  return commands.reduce(function(max, command) {
    return Math.max(max, command[0].length);
  }, 0);
};

/**
 * Return the largest option length.
 *
 * @return {Number}
 * @api private
 */

Command.prototype.largestOptionLength = function() {
  var options = [].slice.call(this.options);
  options.push({
    flags: '-h, --help'
  });
  return options.reduce(function(max, option) {
    return Math.max(max, option.flags.length);
  }, 0);
};

/**
 * Return the largest arg length.
 *
 * @return {Number}
 * @api private
 */

Command.prototype.largestArgLength = function() {
  return this._args.reduce(function(max, arg) {
    return Math.max(max, arg.name.length);
  }, 0);
};

/**
 * Return the pad width.
 *
 * @return {Number}
 * @api private
 */

Command.prototype.padWidth = function() {
  var width = this.largestOptionLength();
  if (this._argsDescription && this._args.length) {
    if (this.largestArgLength() > width) {
      width = this.largestArgLength();
    }
  }

  if (this.commands && this.commands.length) {
    if (this.largestCommandLength() > width) {
      width = this.largestCommandLength();
    }
  }

  return width;
};

/**
 * Return help for options.
 *
 * @return {String}
 * @api private
 */

Command.prototype.optionHelp = function() {
  var width = this.padWidth();

  // Append the help information
  return this.options.map(function(option) {
    return pad(option.flags, width) + '  ' + option.description +
      ((option.bool && option.defaultValue !== undefined) ? ' (default: ' + option.defaultValue + ')' : '');
  }).concat([pad('-h, --help', width) + '  ' + 'output usage information'])
    .join('\n');
};

/**
 * Return command help documentation.
 *
 * @return {String}
 * @api private
 */

Command.prototype.commandHelp = function() {
  if (!this.commands.length) return '';

  var commands = this.prepareCommands();
  var width = this.padWidth();

  return [
    '  Commands:',
    '',
    commands.map(function(cmd) {
      var desc = cmd[1] ? '  ' + cmd[1] : '';
      return (desc ? pad(cmd[0], width) : cmd[0]) + desc;
    }).join('\n').replace(/^/gm, '    '),
    ''
  ].join('\n');
};

/**
 * Return program help documentation.
 *
 * @return {String}
 * @api private
 */

Command.prototype.helpInformation = function() {
  var desc = [];
  if (this._description) {
    desc = [
      '  ' + this._description,
      ''
    ];

    var argsDescription = this._argsDescription;
    if (argsDescription && this._args.length) {
      var width = this.padWidth();
      desc.push('  Arguments:');
      desc.push('');
      this._args.forEach(function(arg) {
        desc.push('    ' + pad(arg.name, width) + '  ' + argsDescription[arg.name]);
      });
      desc.push('');
    }
  }

  var cmdName = this._name;
  if (this._alias) {
    cmdName = cmdName + '|' + this._alias;
  }
  var usage = [
    '',
    '  Usage: ' + cmdName + ' ' + this.usage(),
    ''
  ];

  var cmds = [];
  var commandHelp = this.commandHelp();
  if (commandHelp) cmds = [commandHelp];

  var options = [
    '  Options:',
    '',
    '' + this.optionHelp().replace(/^/gm, '    '),
    ''
  ];

  return usage
    .concat(desc)
    .concat(options)
    .concat(cmds)
    .concat([''])
    .join('\n');
};

/**
 * Output help information for this command
 *
 * @api public
 */

Command.prototype.outputHelp = function(cb) {
  if (!cb) {
    cb = function(passthru) {
      return passthru;
    };
  }
  process.stdout.write(cb(this.helpInformation()));
  this.emit('--help');
};

/**
 * Output help information and exit.
 *
 * @api public
 */

Command.prototype.help = function(cb) {
  this.outputHelp(cb);
  process.exit();
};

/**
 * Camel-case the given `flag`
 *
 * @param {String} flag
 * @return {String}
 * @api private
 */

function camelcase(flag) {
  return flag.split('-').reduce(function(str, word) {
    return str + word[0].toUpperCase() + word.slice(1);
  });
}

/**
 * Pad `str` to `width`.
 *
 * @param {String} str
 * @param {Number} width
 * @return {String}
 * @api private
 */

function pad(str, width) {
  var len = Math.max(0, width - str.length);
  return str + Array(len + 1).join(' ');
}

/**
 * Output help information if necessary
 *
 * @param {Command} command to output help for
 * @param {Array} array of options to search for -h or --help
 * @api private
 */

function outputHelpIfNecessary(cmd, options) {
  options = options || [];
  for (var i = 0; i < options.length; i++) {
    if (options[i] === '--help' || options[i] === '-h') {
      cmd.outputHelp();
      process.exit(0);
    }
  }
}

/**
 * Takes an argument an returns its human readable equivalent for help usage.
 *
 * @param {Object} arg
 * @return {String}
 * @api private
 */

function humanReadableArgName(arg) {
  var nameOutput = arg.name + (arg.variadic === true ? '...' : '');

  return arg.required
    ? '<' + nameOutput + '>'
    : '[' + nameOutput + ']';
}

// for versions before node v0.8 when there weren't `fs.existsSync`
function exists(file) {
  try {
    if (fs.statSync(file).isFile()) {
      return true;
    }
  } catch (e) {
    return false;
  }
}