index.js

/**
 * Module dependencies.
 */

const EventEmitter = require('events').EventEmitter;
const childProcess = require('child_process');
const path = require('path');
const fs = require('fs');

// @ts-check

// Although this is a class, methods are static in style to allow override using subclass or just functions.
class Help {
  constructor() {
    this.helpWidth = undefined;
    this.sortSubcommands = false;
    this.sortOptions = false;
  }

  /**
   * Get an array of the visible subcommands. Includes a placeholder for the implicit help command, if there is one.
   *
   * @param {Command} cmd
   * @returns {Command[]}
   */

  visibleCommands(cmd) {
    const visibleCommands = cmd.commands.filter(cmd => !cmd._hidden);
    if (cmd._hasImplicitHelpCommand()) {
      // Create a command matching the implicit help command.
      const args = cmd._helpCommandnameAndArgs.split(/ +/);
      const helpCommand = cmd.createCommand(args.shift())
        .helpOption(false);
      helpCommand.description(cmd._helpCommandDescription);
      helpCommand._parseExpectedArgs(args);
      visibleCommands.push(helpCommand);
    }
    if (this.sortSubcommands) {
      visibleCommands.sort((a, b) => {
        return a.name().localeCompare(b.name());
      });
    }
    return visibleCommands;
  }

  /**
   * Get an array of the visible options. Includes a placeholder for the implicit help option, if there is one.
   *
   * @param {Command} cmd
   * @returns {Option[]}
   */

  visibleOptions(cmd) {
    const visibleOptions = cmd.options.filter((option) => !option.hidden);
    // Implicit help
    const showShortHelpFlag = cmd._hasHelpOption && cmd._helpShortFlag && !cmd._findOption(cmd._helpShortFlag);
    const showLongHelpFlag = cmd._hasHelpOption && !cmd._findOption(cmd._helpLongFlag);
    if (showShortHelpFlag || showLongHelpFlag) {
      let helpOption;
      if (!showShortHelpFlag) {
        helpOption = cmd.createOption(cmd._helpLongFlag, cmd._helpDescription);
      } else if (!showLongHelpFlag) {
        helpOption = cmd.createOption(cmd._helpShortFlag, cmd._helpDescription);
      } else {
        helpOption = cmd.createOption(cmd._helpFlags, cmd._helpDescription);
      }
      visibleOptions.push(helpOption);
    }
    if (this.sortOptions) {
      const getSortKey = (option) => {
        // WYSIWYG for order displayed in help with short before long, no special handling for negated.
        return option.short ? option.short.replace(/^-/, '') : option.long.replace(/^--/, '');
      };
      visibleOptions.sort((a, b) => {
        return getSortKey(a).localeCompare(getSortKey(b));
      });
    }
    return visibleOptions;
  }

  /**
   * Get an array of the arguments which have descriptions.
   *
   * @param {Command} cmd
   * @returns {{ term: string, description:string }[]}
   */

  visibleArguments(cmd) {
    if (cmd._argsDescription && cmd._args.length) {
      return cmd._args.map((argument) => {
        return { term: argument.name, description: cmd._argsDescription[argument.name] || '' };
      }, 0);
    }
    return [];
  }

  /**
   * Get the command term to show in the list of subcommands.
   *
   * @param {Command} cmd
   * @returns {string}
   */

  subcommandTerm(cmd) {
    // Legacy. Ignores custom usage string, and nested commands.
    const args = cmd._args.map(arg => humanReadableArgName(arg)).join(' ');
    return cmd._name +
      (cmd._aliases[0] ? '|' + cmd._aliases[0] : '') +
      (cmd.options.length ? ' [options]' : '') + // simplistic check for non-help option
      (args ? ' ' + args : '');
  }

  /**
   * Get the option term to show in the list of options.
   *
   * @param {Option} option
   * @returns {string}
   */

  optionTerm(option) {
    return option.flags;
  }

  /**
   * Get the longest command term length.
   *
   * @param {Command} cmd
   * @param {Help} helper
   * @returns {number}
   */

  longestSubcommandTermLength(cmd, helper) {
    return helper.visibleCommands(cmd).reduce((max, command) => {
      return Math.max(max, helper.subcommandTerm(command).length);
    }, 0);
  };

  /**
   * Get the longest option term length.
   *
   * @param {Command} cmd
   * @param {Help} helper
   * @returns {number}
   */

  longestOptionTermLength(cmd, helper) {
    return helper.visibleOptions(cmd).reduce((max, option) => {
      return Math.max(max, helper.optionTerm(option).length);
    }, 0);
  };

  /**
   * Get the longest argument term length.
   *
   * @param {Command} cmd
   * @param {Help} helper
   * @returns {number}
   */

  longestArgumentTermLength(cmd, helper) {
    return helper.visibleArguments(cmd).reduce((max, argument) => {
      return Math.max(max, argument.term.length);
    }, 0);
  };

  /**
   * Get the command usage to be displayed at the top of the built-in help.
   *
   * @param {Command} cmd
   * @returns {string}
   */

  commandUsage(cmd) {
    // Usage
    let cmdName = cmd._name;
    if (cmd._aliases[0]) {
      cmdName = cmdName + '|' + cmd._aliases[0];
    }
    let parentCmdNames = '';
    for (let parentCmd = cmd.parent; parentCmd; parentCmd = parentCmd.parent) {
      parentCmdNames = parentCmd.name() + ' ' + parentCmdNames;
    }
    return parentCmdNames + cmdName + ' ' + cmd.usage();
  }

  /**
   * Get the description for the command.
   *
   * @param {Command} cmd
   * @returns {string}
   */

  commandDescription(cmd) {
    // @ts-ignore: overloaded return type
    return cmd.description();
  }

  /**
   * Get the command description to show in the list of subcommands.
   *
   * @param {Command} cmd
   * @returns {string}
   */

  subcommandDescription(cmd) {
    // @ts-ignore: overloaded return type
    return cmd.description();
  }

  /**
   * Get the option description to show in the list of options.
   *
   * @param {Option} option
   * @return {string}
   */

  optionDescription(option) {
    if (option.negate) {
      return option.description;
    }
    const extraInfo = [];
    if (option.argChoices) {
      extraInfo.push(
        // use stringify to match the display of the default value
        `choices: ${option.argChoices.map((choice) => JSON.stringify(choice)).join(', ')}`);
    }
    if (option.defaultValue !== undefined) {
      extraInfo.push(`default: ${option.defaultValueDescription || JSON.stringify(option.defaultValue)}`);
    }
    if (extraInfo.length > 0) {
      return `${option.description} (${extraInfo.join(', ')})`;
    }
    return option.description;
  };

  /**
   * Generate the built-in help text.
   *
   * @param {Command} cmd
   * @param {Help} helper
   * @returns {string}
   */

  formatHelp(cmd, helper) {
    const termWidth = helper.padWidth(cmd, helper);
    const helpWidth = helper.helpWidth || 80;
    const itemIndentWidth = 2;
    const itemSeparatorWidth = 2; // between term and description
    function formatItem(term, description) {
      if (description) {
        const fullText = `${term.padEnd(termWidth + itemSeparatorWidth)}${description}`;
        return helper.wrap(fullText, helpWidth - itemIndentWidth, termWidth + itemSeparatorWidth);
      }
      return term;
    };
    function formatList(textArray) {
      return textArray.join('\n').replace(/^/gm, ' '.repeat(itemIndentWidth));
    }

    // Usage
    let output = [`Usage: ${helper.commandUsage(cmd)}`, ''];

    // Description
    const commandDescription = helper.commandDescription(cmd);
    if (commandDescription.length > 0) {
      output = output.concat([commandDescription, '']);
    }

    // Arguments
    const argumentList = helper.visibleArguments(cmd).map((argument) => {
      return formatItem(argument.term, argument.description);
    });
    if (argumentList.length > 0) {
      output = output.concat(['Arguments:', formatList(argumentList), '']);
    }

    // Options
    const optionList = helper.visibleOptions(cmd).map((option) => {
      return formatItem(helper.optionTerm(option), helper.optionDescription(option));
    });
    if (optionList.length > 0) {
      output = output.concat(['Options:', formatList(optionList), '']);
    }

    // Commands
    const commandList = helper.visibleCommands(cmd).map((cmd) => {
      return formatItem(helper.subcommandTerm(cmd), helper.subcommandDescription(cmd));
    });
    if (commandList.length > 0) {
      output = output.concat(['Commands:', formatList(commandList), '']);
    }

    return output.join('\n');
  }

  /**
   * Calculate the pad width from the maximum term length.
   *
   * @param {Command} cmd
   * @param {Help} helper
   * @returns {number}
   */

  padWidth(cmd, helper) {
    return Math.max(
      helper.longestOptionTermLength(cmd, helper),
      helper.longestSubcommandTermLength(cmd, helper),
      helper.longestArgumentTermLength(cmd, helper)
    );
  };

  /**
   * Wrap the given string to width characters per line, with lines after the first indented.
   * Do not wrap if insufficient room for wrapping (minColumnWidth), or string is manually formatted.
   *
   * @param {string} str
   * @param {number} width
   * @param {number} indent
   * @param {number} [minColumnWidth=40]
   * @return {string}
   *
   */

  wrap(str, width, indent, minColumnWidth = 40) {
    // Detect manually wrapped and indented strings by searching for line breaks
    // followed by multiple spaces/tabs.
    if (str.match(/[\n]\s+/)) return str;
    // Do not wrap if not enough room for a wrapped column of text (as could end up with a word per line).
    const columnWidth = width - indent;
    if (columnWidth < minColumnWidth) return str;

    const leadingStr = str.substr(0, indent);
    const columnText = str.substr(indent);

    const indentString = ' '.repeat(indent);
    const regex = new RegExp('.{1,' + (columnWidth - 1) + '}([\\s\u200B]|$)|[^\\s\u200B]+?([\\s\u200B]|$)', 'g');
    const lines = columnText.match(regex) || [];
    return leadingStr + lines.map((line, i) => {
      if (line.slice(-1) === '\n') {
        line = line.slice(0, line.length - 1);
      }
      return ((i > 0) ? indentString : '') + line.trimRight();
    }).join('\n');
  }
}

class Option {
  /**
   * Initialize a new `Option` with the given `flags` and `description`.
   *
   * @param {string} flags
   * @param {string} [description]
   */

  constructor(flags, description) {
    this.flags = flags;
    this.description = description || '';

    this.required = flags.includes('<'); // A value must be supplied when the option is specified.
    this.optional = flags.includes('['); // A value is optional when the option is specified.
    // variadic test ignores <value,...> et al which might be used to describe custom splitting of single argument
    this.variadic = /\w\.\.\.[>\]]$/.test(flags); // The option can take multiple values.
    this.mandatory = false; // The option must have a value after parsing, which usually means it must be specified on command line.
    const optionFlags = _parseOptionFlags(flags);
    this.short = optionFlags.shortFlag;
    this.long = optionFlags.longFlag;
    this.negate = false;
    if (this.long) {
      this.negate = this.long.startsWith('--no-');
    }
    this.defaultValue = undefined;
    this.defaultValueDescription = undefined;
    this.parseArg = undefined;
    this.hidden = false;
    this.argChoices = undefined;
  }

  /**
   * Set the default value, and optionally supply the description to be displayed in the help.
   *
   * @param {any} value
   * @param {string} [description]
   * @return {Option}
   */

  default(value, description) {
    this.defaultValue = value;
    this.defaultValueDescription = description;
    return this;
  };

  /**
   * Set the custom handler for processing CLI option arguments into option values.
   *
   * @param {Function} [fn]
   * @return {Option}
   */

  argParser(fn) {
    this.parseArg = fn;
    return this;
  };

  /**
   * Whether the option is mandatory and must have a value after parsing.
   *
   * @param {boolean} [mandatory=true]
   * @return {Option}
   */

  makeOptionMandatory(mandatory = true) {
    this.mandatory = !!mandatory;
    return this;
  };

  /**
   * Hide option in help.
   *
   * @param {boolean} [hide=true]
   * @return {Option}
   */

  hideHelp(hide = true) {
    this.hidden = !!hide;
    return this;
  };

  /**
   * @api private
   */

  _concatValue(value, previous) {
    if (previous === this.defaultValue || !Array.isArray(previous)) {
      return [value];
    }

    return previous.concat(value);
  }

  /**
   * Only allow option value to be one of choices.
   *
   * @param {string[]} values
   * @return {Option}
   */

  choices(values) {
    this.argChoices = values;
    this.parseArg = (arg, previous) => {
      if (!values.includes(arg)) {
        throw new InvalidOptionArgumentError(`Allowed choices are ${values.join(', ')}.`);
      }
      if (this.variadic) {
        return this._concatValue(arg, previous);
      }
      return arg;
    };
    return this;
  };

  /**
   * Return option name.
   *
   * @return {string}
   */

  name() {
    if (this.long) {
      return this.long.replace(/^--/, '');
    }
    return this.short.replace(/^-/, '');
  };

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

  attributeName() {
    return camelcase(this.name().replace(/^no-/, ''));
  };

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

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

/**
 * CommanderError class
 * @class
 */
class CommanderError extends Error {
  /**
   * Constructs the CommanderError class
   * @param {number} exitCode suggested exit code which could be used with process.exit
   * @param {string} code an id string representing the error
   * @param {string} message human-readable description of the error
   * @constructor
   */
  constructor(exitCode, code, message) {
    super(message);
    // properly capture stack trace in Node.js
    Error.captureStackTrace(this, this.constructor);
    this.name = this.constructor.name;
    this.code = code;
    this.exitCode = exitCode;
    this.nestedError = undefined;
  }
}

/**
 * InvalidOptionArgumentError class
 * @class
 */
class InvalidOptionArgumentError extends CommanderError {
  /**
   * Constructs the InvalidOptionArgumentError class
   * @param {string} [message] explanation of why argument is invalid
   * @constructor
   */
  constructor(message) {
    super(1, 'commander.invalidOptionArgument', message);
    // properly capture stack trace in Node.js
    Error.captureStackTrace(this, this.constructor);
    this.name = this.constructor.name;
  }
}

class Command extends EventEmitter {
  /**
   * Initialize a new `Command`.
   *
   * @param {string} [name]
   */

  constructor(name) {
    super();
    this.commands = [];
    this.options = [];
    this.parent = null;
    this._allowUnknownOption = false;
    this._allowExcessArguments = true;
    this._args = [];
    this.rawArgs = null;
    this._scriptPath = null;
    this._name = name || '';
    this._optionValues = {};
    this._storeOptionsAsProperties = false;
    this._actionResults = [];
    this._actionHandler = null;
    this._executableHandler = false;
    this._executableFile = null; // custom name for executable
    this._defaultCommandName = null;
    this._exitCallback = null;
    this._aliases = [];
    this._combineFlagAndOptionalValue = true;
    this._description = '';
    this._argsDescription = undefined;
    this._enablePositionalOptions = false;
    this._passThroughOptions = false;

    // see .configureOutput() for docs
    this._outputConfiguration = {
      writeOut: (str) => process.stdout.write(str),
      writeErr: (str) => process.stderr.write(str),
      getOutHelpWidth: () => process.stdout.isTTY ? process.stdout.columns : undefined,
      getErrHelpWidth: () => process.stderr.isTTY ? process.stderr.columns : undefined,
      outputError: (str, write) => write(str)
    };

    this._hidden = false;
    this._hasHelpOption = true;
    this._helpFlags = '-h, --help';
    this._helpDescription = 'display help for command';
    this._helpShortFlag = '-h';
    this._helpLongFlag = '--help';
    this._addImplicitHelpCommand = undefined; // Deliberately undefined, not decided whether true or false
    this._helpCommandName = 'help';
    this._helpCommandnameAndArgs = 'help [command]';
    this._helpCommandDescription = 'display help for command';
    this._helpConfiguration = {};
  }

  /**
   * Define a command.
   *
   * There are two styles of command: pay attention to where to put the description.
   *
   * Examples:
   *
   *      // Command implemented using action handler (description is supplied separately to `.command`)
   *      program
   *        .command('clone <source> [destination]')
   *        .description('clone a repository into a newly created directory')
   *        .action((source, destination) => {
   *          console.log('clone command called');
   *        });
   *
   *      // Command implemented using separate executable file (description is second parameter to `.command`)
   *      program
   *        .command('start <service>', 'start named service')
   *        .command('stop [service]', 'stop named service, or all if no name supplied');
   *
   * @param {string} nameAndArgs - command name and arguments, args are `<required>` or `[optional]` and last may also be `variadic...`
   * @param {Object|string} [actionOptsOrExecDesc] - configuration options (for action), or description (for executable)
   * @param {Object} [execOpts] - configuration options (for executable)
   * @return {Command} returns new command for action handler, or `this` for executable command
   */

  command(nameAndArgs, actionOptsOrExecDesc, execOpts) {
    let desc = actionOptsOrExecDesc;
    let opts = execOpts;
    if (typeof desc === 'object' && desc !== null) {
      opts = desc;
      desc = null;
    }
    opts = opts || {};
    const args = nameAndArgs.split(/ +/);
    const cmd = this.createCommand(args.shift());

    if (desc) {
      cmd.description(desc);
      cmd._executableHandler = true;
    }
    if (opts.isDefault) this._defaultCommandName = cmd._name;

    cmd._outputConfiguration = this._outputConfiguration;

    cmd._hidden = !!(opts.noHelp || opts.hidden); // noHelp is deprecated old name for hidden
    cmd._hasHelpOption = this._hasHelpOption;
    cmd._helpFlags = this._helpFlags;
    cmd._helpDescription = this._helpDescription;
    cmd._helpShortFlag = this._helpShortFlag;
    cmd._helpLongFlag = this._helpLongFlag;
    cmd._helpCommandName = this._helpCommandName;
    cmd._helpCommandnameAndArgs = this._helpCommandnameAndArgs;
    cmd._helpCommandDescription = this._helpCommandDescription;
    cmd._helpConfiguration = this._helpConfiguration;
    cmd._exitCallback = this._exitCallback;
    cmd._storeOptionsAsProperties = this._storeOptionsAsProperties;
    cmd._combineFlagAndOptionalValue = this._combineFlagAndOptionalValue;
    cmd._allowExcessArguments = this._allowExcessArguments;
    cmd._enablePositionalOptions = this._enablePositionalOptions;

    cmd._executableFile = opts.executableFile || null; // Custom name for executable file, set missing to null to match constructor
    this.commands.push(cmd);
    cmd._parseExpectedArgs(args);
    cmd.parent = this;

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

  /**
   * Factory routine to create a new unattached command.
   *
   * See .command() for creating an attached subcommand, which uses this routine to
   * create the command. You can override createCommand to customise subcommands.
   *
   * @param {string} [name]
   * @return {Command} new command
   */

  createCommand(name) {
    return new Command(name);
  };

  /**
   * You can customise the help with a subclass of Help by overriding createHelp,
   * or by overriding Help properties using configureHelp().
   *
   * @return {Help}
   */

  createHelp() {
    return Object.assign(new Help(), this.configureHelp());
  };

  /**
   * You can customise the help by overriding Help properties using configureHelp(),
   * or with a subclass of Help by overriding createHelp().
   *
   * @param {Object} [configuration] - configuration options
   * @return {Command|Object} `this` command for chaining, or stored configuration
   */

  configureHelp(configuration) {
    if (configuration === undefined) return this._helpConfiguration;

    this._helpConfiguration = configuration;
    return this;
  }

  /**
   * The default output goes to stdout and stderr. You can customise this for special
   * applications. You can also customise the display of errors by overriding outputError.
   *
   * The configuration properties are all functions:
   *
   *    // functions to change where being written, stdout and stderr
   *    writeOut(str)
   *    writeErr(str)
   *    // matching functions to specify width for wrapping help
   *    getOutHelpWidth()
   *    getErrHelpWidth()
   *    // functions based on what is being written out
   *    outputError(str, write) // used for displaying errors, and not used for displaying help
   *
   * @param {Object} [configuration] - configuration options
   * @return {Command|Object} `this` command for chaining, or stored configuration
   */

  configureOutput(configuration) {
    if (configuration === undefined) return this._outputConfiguration;

    Object.assign(this._outputConfiguration, configuration);
    return this;
  }

  /**
   * Add a prepared subcommand.
   *
   * See .command() for creating an attached subcommand which inherits settings from its parent.
   *
   * @param {Command} cmd - new subcommand
   * @param {Object} [opts] - configuration options
   * @return {Command} `this` command for chaining
   */

  addCommand(cmd, opts) {
    if (!cmd._name) throw new Error('Command passed to .addCommand() must have a name');

    // To keep things simple, block automatic name generation for deeply nested executables.
    // Fail fast and detect when adding rather than later when parsing.
    function checkExplicitNames(commandArray) {
      commandArray.forEach((cmd) => {
        if (cmd._executableHandler && !cmd._executableFile) {
          throw new Error(`Must specify executableFile for deeply nested executable: ${cmd.name()}`);
        }
        checkExplicitNames(cmd.commands);
      });
    }
    checkExplicitNames(cmd.commands);

    opts = opts || {};
    if (opts.isDefault) this._defaultCommandName = cmd._name;
    if (opts.noHelp || opts.hidden) cmd._hidden = true; // modifying passed command due to existing implementation

    this.commands.push(cmd);
    cmd.parent = this;
    return this;
  };

  /**
   * Define argument syntax for the command.
   */

  arguments(desc) {
    return this._parseExpectedArgs(desc.split(/ +/));
  };

  /**
   * Override default decision whether to add implicit help command.
   *
   *    addHelpCommand() // force on
   *    addHelpCommand(false); // force off
   *    addHelpCommand('help [cmd]', 'display help for [cmd]'); // force on with custom details
   *
   * @return {Command} `this` command for chaining
   */

  addHelpCommand(enableOrNameAndArgs, description) {
    if (enableOrNameAndArgs === false) {
      this._addImplicitHelpCommand = false;
    } else {
      this._addImplicitHelpCommand = true;
      if (typeof enableOrNameAndArgs === 'string') {
        this._helpCommandName = enableOrNameAndArgs.split(' ')[0];
        this._helpCommandnameAndArgs = enableOrNameAndArgs;
      }
      this._helpCommandDescription = description || this._helpCommandDescription;
    }
    return this;
  };

  /**
   * @return {boolean}
   * @api private
   */

  _hasImplicitHelpCommand() {
    if (this._addImplicitHelpCommand === undefined) {
      return this.commands.length && !this._actionHandler && !this._findCommand('help');
    }
    return this._addImplicitHelpCommand;
  };

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

  _parseExpectedArgs(args) {
    if (!args.length) return;
    args.forEach((arg) => {
      const 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) {
        this._args.push(argDetails);
      }
    });
    this._args.forEach((arg, i) => {
      if (arg.variadic && i < this._args.length - 1) {
        throw new Error(`only the last argument can be variadic '${arg.name}'`);
      }
    });
    return this;
  };

  /**
   * Register callback to use as replacement for calling process.exit.
   *
   * @param {Function} [fn] optional callback which will be passed a CommanderError, defaults to throwing
   * @return {Command} `this` command for chaining
   */

  exitOverride(fn) {
    if (fn) {
      this._exitCallback = fn;
    } else {
      this._exitCallback = (err) => {
        if (err.code !== 'commander.executeSubCommandAsync') {
          throw err;
        } else {
          // Async callback from spawn events, not useful to throw.
        }
      };
    }
    return this;
  };

  /**
   * Call process.exit, and _exitCallback if defined.
   *
   * @param {number} exitCode exit code for using with process.exit
   * @param {string} code an id string representing the error
   * @param {string} message human-readable description of the error
   * @return never
   * @api private
   */

  _exit(exitCode, code, message) {
    if (this._exitCallback) {
      this._exitCallback(new CommanderError(exitCode, code, message));
      // Expecting this line is not reached.
    }
    process.exit(exitCode);
  };

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

  action(fn) {
    const listener = (args) => {
      // The .action callback takes an extra parameter which is the command or options.
      const expectedArgsCount = this._args.length;
      const actionArgs = args.slice(0, expectedArgsCount);
      if (this._storeOptionsAsProperties) {
        actionArgs[expectedArgsCount] = this; // backwards compatible "options"
      } else {
        actionArgs[expectedArgsCount] = this.opts();
      }
      actionArgs.push(this);

      const actionResult = fn.apply(this, actionArgs);
      // Remember result in case it is async. Assume parseAsync getting called on root.
      let rootCommand = this;
      while (rootCommand.parent) {
        rootCommand = rootCommand.parent;
      }
      rootCommand._actionResults.push(actionResult);
    };
    this._actionHandler = listener;
    return this;
  };

  /**
   * Factory routine to create a new unattached option.
   *
   * See .option() for creating an attached option, which uses this routine to
   * create the option. You can override createOption to return a custom option.
   *
   * @param {string} flags
   * @param {string} [description]
   * @return {Option} new option
   */

  createOption(flags, description) {
    return new Option(flags, description);
  };

  /**
   * Add an option.
   *
   * @param {Option} option
   * @return {Command} `this` command for chaining
   */
  addOption(option) {
    const oname = option.name();
    const name = option.attributeName();

    let defaultValue = option.defaultValue;

    // preassign default value for --no-*, [optional], <required>, or plain flag if boolean value
    if (option.negate || option.optional || option.required || typeof defaultValue === 'boolean') {
      // when --no-foo we make sure default is true, unless a --foo option is already defined
      if (option.negate) {
        const positiveLongFlag = option.long.replace(/^--no-/, '--');
        defaultValue = this._findOption(positiveLongFlag) ? this._getOptionValue(name) : true;
      }
      // preassign only if we have a default
      if (defaultValue !== undefined) {
        this._setOptionValue(name, defaultValue);
      }
    }

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

    // when it's passed assign the value
    // and conditionally invoke the callback
    this.on('option:' + oname, (val) => {
      const oldValue = this._getOptionValue(name);

      // custom processing
      if (val !== null && option.parseArg) {
        try {
          val = option.parseArg(val, oldValue === undefined ? defaultValue : oldValue);
        } catch (err) {
          if (err.code === 'commander.invalidOptionArgument') {
            const message = `error: option '${option.flags}' argument '${val}' is invalid. ${err.message}`;
            this._displayError(err.exitCode, err.code, message);
          }
          throw err;
        }
      } else if (val !== null && option.variadic) {
        val = option._concatValue(val, oldValue);
      }

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

    return this;
  }

  /**
   * Internal implementation shared by .option() and .requiredOption()
   *
   * @api private
   */
  _optionEx(config, flags, description, fn, defaultValue) {
    const option = this.createOption(flags, description);
    option.makeOptionMandatory(!!config.mandatory);
    if (typeof fn === 'function') {
      option.default(defaultValue).argParser(fn);
    } else if (fn instanceof RegExp) {
      // deprecated
      const regex = fn;
      fn = (val, def) => {
        const m = regex.exec(val);
        return m ? m[0] : def;
      };
      option.default(defaultValue).argParser(fn);
    } else {
      option.default(fn);
    }

    return this.addOption(option);
  }

  /**
   * Define option with `flags`, `description` and optional
   * coercion `fn`.
   *
   * The `flags` string contains the short and/or 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 undefined
   *     program.option('-p, --pepper', 'add pepper');
   *
   *     program.pepper
   *     // => undefined
   *
   *     --pepper
   *     program.pepper
   *     // => true
   *
   *     // simple boolean defaulting to true (unless non-negated option is also defined)
   *     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] - custom option processing function or default value
   * @param {*} [defaultValue]
   * @return {Command} `this` command for chaining
   */

  option(flags, description, fn, defaultValue) {
    return this._optionEx({}, flags, description, fn, defaultValue);
  };

  /**
  * Add a required option which must have a value after parsing. This usually means
  * the option must be specified on the command line. (Otherwise the same as .option().)
  *
  * The `flags` string contains the short and/or long flags, separated by comma, a pipe or space.
  *
  * @param {string} flags
  * @param {string} [description]
  * @param {Function|*} [fn] - custom option processing function or default value
  * @param {*} [defaultValue]
  * @return {Command} `this` command for chaining
  */

  requiredOption(flags, description, fn, defaultValue) {
    return this._optionEx({ mandatory: true }, flags, description, fn, defaultValue);
  };

  /**
   * Alter parsing of short flags with optional values.
   *
   * Examples:
   *
   *    // for `.option('-f,--flag [value]'):
   *    .combineFlagAndOptionalValue(true)  // `-f80` is treated like `--flag=80`, this is the default behaviour
   *    .combineFlagAndOptionalValue(false) // `-fb` is treated like `-f -b`
   *
   * @param {Boolean} [combine=true] - if `true` or omitted, an optional value can be specified directly after the flag.
   */
  combineFlagAndOptionalValue(combine = true) {
    this._combineFlagAndOptionalValue = !!combine;
    return this;
  };

  /**
   * Allow unknown options on the command line.
   *
   * @param {Boolean} [allowUnknown=true] - if `true` or omitted, no error will be thrown
   * for unknown options.
   */
  allowUnknownOption(allowUnknown = true) {
    this._allowUnknownOption = !!allowUnknown;
    return this;
  };

  /**
   * Allow excess command-arguments on the command line. Pass false to make excess arguments an error.
   *
   * @param {Boolean} [allowExcess=true] - if `true` or omitted, no error will be thrown
   * for excess arguments.
   */
  allowExcessArguments(allowExcess = true) {
    this._allowExcessArguments = !!allowExcess;
    return this;
  };

  /**
   * Enable positional options. Positional means global options are specified before subcommands which lets
   * subcommands reuse the same option names, and also enables subcommands to turn on passThroughOptions.
   * The default behaviour is non-positional and global options may appear anywhere on the command line.
   *
   * @param {Boolean} [positional=true]
   */
  enablePositionalOptions(positional = true) {
    this._enablePositionalOptions = !!positional;
    return this;
  };

  /**
   * Pass through options that come after command-arguments rather than treat them as command-options,
   * so actual command-options come before command-arguments. Turning this on for a subcommand requires
   * positional options to have been enabled on the program (parent commands).
   * The default behaviour is non-positional and options may appear before or after command-arguments.
   *
   * @param {Boolean} [passThrough=true]
   * for unknown options.
   */
  passThroughOptions(passThrough = true) {
    this._passThroughOptions = !!passThrough;
    if (!!this.parent && passThrough && !this.parent._enablePositionalOptions) {
      throw new Error('passThroughOptions can not be used without turning on enablePositionalOptions for parent command(s)');
    }
    return this;
  };

  /**
    * Whether to store option values as properties on command object,
    * or store separately (specify false). In both cases the option values can be accessed using .opts().
    *
    * @param {boolean} [storeAsProperties=true]
    * @return {Command} `this` command for chaining
    */

  storeOptionsAsProperties(storeAsProperties = true) {
    this._storeOptionsAsProperties = !!storeAsProperties;
    if (this.options.length) {
      throw new Error('call .storeOptionsAsProperties() before adding options');
    }
    return this;
  };

  /**
   * Store option value
   *
   * @param {string} key
   * @param {Object} value
   * @api private
   */

  _setOptionValue(key, value) {
    if (this._storeOptionsAsProperties) {
      this[key] = value;
    } else {
      this._optionValues[key] = value;
    }
  };

  /**
   * Retrieve option value
   *
   * @param {string} key
   * @return {Object} value
   * @api private
   */

  _getOptionValue(key) {
    if (this._storeOptionsAsProperties) {
      return this[key];
    }
    return this._optionValues[key];
  };

  /**
   * Parse `argv`, setting options and invoking commands when defined.
   *
   * The default expectation is that the arguments are from node and have the application as argv[0]
   * and the script being run in argv[1], with user parameters after that.
   *
   * Examples:
   *
   *      program.parse(process.argv);
   *      program.parse(); // implicitly use process.argv and auto-detect node vs electron conventions
   *      program.parse(my-args, { from: 'user' }); // just user supplied arguments, nothing special about argv[0]
   *
   * @param {string[]} [argv] - optional, defaults to process.argv
   * @param {Object} [parseOptions] - optionally specify style of options with from: node/user/electron
   * @param {string} [parseOptions.from] - where the args are from: 'node', 'user', 'electron'
   * @return {Command} `this` command for chaining
   */

  parse(argv, parseOptions) {
    if (argv !== undefined && !Array.isArray(argv)) {
      throw new Error('first parameter to parse must be array or undefined');
    }
    parseOptions = parseOptions || {};

    // Default to using process.argv
    if (argv === undefined) {
      argv = process.argv;
      // @ts-ignore: unknown property
      if (process.versions && process.versions.electron) {
        parseOptions.from = 'electron';
      }
    }
    this.rawArgs = argv.slice();

    // make it a little easier for callers by supporting various argv conventions
    let userArgs;
    switch (parseOptions.from) {
      case undefined:
      case 'node':
        this._scriptPath = argv[1];
        userArgs = argv.slice(2);
        break;
      case 'electron':
        // @ts-ignore: unknown property
        if (process.defaultApp) {
          this._scriptPath = argv[1];
          userArgs = argv.slice(2);
        } else {
          userArgs = argv.slice(1);
        }
        break;
      case 'user':
        userArgs = argv.slice(0);
        break;
      default:
        throw new Error(`unexpected parse option { from: '${parseOptions.from}' }`);
    }
    if (!this._scriptPath && require.main) {
      this._scriptPath = require.main.filename;
    }

    // Guess name, used in usage in help.
    this._name = this._name || (this._scriptPath && path.basename(this._scriptPath, path.extname(this._scriptPath)));

    // Let's go!
    this._parseCommand([], userArgs);

    return this;
  };

  /**
   * Parse `argv`, setting options and invoking commands when defined.
   *
   * Use parseAsync instead of parse if any of your action handlers are async. Returns a Promise.
   *
   * The default expectation is that the arguments are from node and have the application as argv[0]
   * and the script being run in argv[1], with user parameters after that.
   *
   * Examples:
   *
   *      program.parseAsync(process.argv);
   *      program.parseAsync(); // implicitly use process.argv and auto-detect node vs electron conventions
   *      program.parseAsync(my-args, { from: 'user' }); // just user supplied arguments, nothing special about argv[0]
   *
   * @param {string[]} [argv]
   * @param {Object} [parseOptions]
   * @param {string} parseOptions.from - where the args are from: 'node', 'user', 'electron'
   * @return {Promise}
   */

  parseAsync(argv, parseOptions) {
    this.parse(argv, parseOptions);
    return Promise.all(this._actionResults).then(() => this);
  };

  /**
   * Execute a sub-command executable.
   *
   * @api private
   */

  _executeSubCommand(subcommand, args) {
    args = args.slice();
    let launchWithNode = false; // Use node for source targets so do not need to get permissions correct, and on Windows.
    const sourceExt = ['.js', '.ts', '.tsx', '.mjs', '.cjs'];

    // Not checking for help first. Unlikely to have mandatory and executable, and can't robustly test for help flags in external command.
    this._checkForMissingMandatoryOptions();

    // Want the entry script as the reference for command name and directory for searching for other files.
    let scriptPath = this._scriptPath;
    // Fallback in case not set, due to how Command created or called.
    if (!scriptPath && require.main) {
      scriptPath = require.main.filename;
    }

    let baseDir;
    try {
      const resolvedLink = fs.realpathSync(scriptPath);
      baseDir = path.dirname(resolvedLink);
    } catch (e) {
      baseDir = '.'; // dummy, probably not going to find executable!
    }

    // name of the subcommand, like `pm-install`
    let bin = path.basename(scriptPath, path.extname(scriptPath)) + '-' + subcommand._name;
    if (subcommand._executableFile) {
      bin = subcommand._executableFile;
    }

    const localBin = path.join(baseDir, bin);
    if (fs.existsSync(localBin)) {
      // prefer local `./<bin>` to bin in the $PATH
      bin = localBin;
    } else {
      // Look for source files.
      sourceExt.forEach((ext) => {
        if (fs.existsSync(`${localBin}${ext}`)) {
          bin = `${localBin}${ext}`;
        }
      });
    }
    launchWithNode = sourceExt.includes(path.extname(bin));

    let proc;
    if (process.platform !== 'win32') {
      if (launchWithNode) {
        args.unshift(bin);
        // add executable arguments to spawn
        args = incrementNodeInspectorPort(process.execArgv).concat(args);

        proc = childProcess.spawn(process.argv[0], args, { stdio: 'inherit' });
      } else {
        proc = childProcess.spawn(bin, args, { stdio: 'inherit' });
      }
    } else {
      args.unshift(bin);
      // add executable arguments to spawn
      args = incrementNodeInspectorPort(process.execArgv).concat(args);
      proc = childProcess.spawn(process.execPath, args, { stdio: 'inherit' });
    }

    const signals = ['SIGUSR1', 'SIGUSR2', 'SIGTERM', 'SIGINT', 'SIGHUP'];
    signals.forEach((signal) => {
      // @ts-ignore
      process.on(signal, () => {
        if (proc.killed === false && proc.exitCode === null) {
          proc.kill(signal);
        }
      });
    });

    // By default terminate process when spawned process terminates.
    // Suppressing the exit if exitCallback defined is a bit messy and of limited use, but does allow process to stay running!
    const exitCallback = this._exitCallback;
    if (!exitCallback) {
      proc.on('close', process.exit.bind(process));
    } else {
      proc.on('close', () => {
        exitCallback(new CommanderError(process.exitCode || 0, 'commander.executeSubCommandAsync', '(close)'));
      });
    }
    proc.on('error', (err) => {
      // @ts-ignore
      if (err.code === 'ENOENT') {
        const executableMissing = `'${bin}' does not exist
 - if '${subcommand._name}' is not meant to be an executable command, remove description parameter from '.command()' and use '.description()' instead
 - if the default executable name is not suitable, use the executableFile option to supply a custom name`;
        throw new Error(executableMissing);
      // @ts-ignore
      } else if (err.code === 'EACCES') {
        throw new Error(`'${bin}' not executable`);
      }
      if (!exitCallback) {
        process.exit(1);
      } else {
        const wrappedError = new CommanderError(1, 'commander.executeSubCommandAsync', '(error)');
        wrappedError.nestedError = err;
        exitCallback(wrappedError);
      }
    });

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

  /**
   * @api private
   */
  _dispatchSubcommand(commandName, operands, unknown) {
    const subCommand = this._findCommand(commandName);
    if (!subCommand) this.help({ error: true });

    if (subCommand._executableHandler) {
      this._executeSubCommand(subCommand, operands.concat(unknown));
    } else {
      subCommand._parseCommand(operands, unknown);
    }
  };

  /**
   * Process arguments in context of this command.
   *
   * @api private
   */

  _parseCommand(operands, unknown) {
    const parsed = this.parseOptions(unknown);
    operands = operands.concat(parsed.operands);
    unknown = parsed.unknown;
    this.args = operands.concat(unknown);

    if (operands && this._findCommand(operands[0])) {
      this._dispatchSubcommand(operands[0], operands.slice(1), unknown);
    } else if (this._hasImplicitHelpCommand() && operands[0] === this._helpCommandName) {
      if (operands.length === 1) {
        this.help();
      } else {
        this._dispatchSubcommand(operands[1], [], [this._helpLongFlag]);
      }
    } else if (this._defaultCommandName) {
      outputHelpIfRequested(this, unknown); // Run the help for default command from parent rather than passing to default command
      this._dispatchSubcommand(this._defaultCommandName, operands, unknown);
    } else {
      if (this.commands.length && this.args.length === 0 && !this._actionHandler && !this._defaultCommandName) {
        // probably missing subcommand and no handler, user needs help
        this.help({ error: true });
      }

      outputHelpIfRequested(this, parsed.unknown);
      this._checkForMissingMandatoryOptions();

      // We do not always call this check to avoid masking a "better" error, like unknown command.
      const checkForUnknownOptions = () => {
        if (parsed.unknown.length > 0) {
          this.unknownOption(parsed.unknown[0]);
        }
      };

      const commandEvent = `command:${this.name()}`;
      if (this._actionHandler) {
        checkForUnknownOptions();
        // Check expected arguments and collect variadic together.
        const args = this.args.slice();
        this._args.forEach((arg, i) => {
          if (arg.required && args[i] == null) {
            this.missingArgument(arg.name);
          } else if (arg.variadic) {
            args[i] = args.splice(i);
            args.length = Math.min(i + 1, args.length);
          }
        });
        if (args.length > this._args.length) {
          this._excessArguments(args);
        }

        this._actionHandler(args);
        if (this.parent) this.parent.emit(commandEvent, operands, unknown); // legacy
      } else if (this.parent && this.parent.listenerCount(commandEvent)) {
        checkForUnknownOptions();
        this.parent.emit(commandEvent, operands, unknown); // legacy
      } else if (operands.length) {
        if (this._findCommand('*')) { // legacy default command
          this._dispatchSubcommand('*', operands, unknown);
        } else if (this.listenerCount('command:*')) {
          // skip option check, emit event for possible misspelling suggestion
          this.emit('command:*', operands, unknown);
        } else if (this.commands.length) {
          this.unknownCommand();
        } else {
          checkForUnknownOptions();
        }
      } else if (this.commands.length) {
        // This command has subcommands and nothing hooked up at this level, so display help.
        this.help({ error: true });
      } else {
        checkForUnknownOptions();
        // fall through for caller to handle after calling .parse()
      }
    }
  };

  /**
   * Find matching command.
   *
   * @api private
   */
  _findCommand(name) {
    if (!name) return undefined;
    return this.commands.find(cmd => cmd._name === name || cmd._aliases.includes(name));
  };

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

  _findOption(arg) {
    return this.options.find(option => option.is(arg));
  };

  /**
   * Display an error message if a mandatory option does not have a value.
   * Lazy calling after checking for help flags from leaf subcommand.
   *
   * @api private
   */

  _checkForMissingMandatoryOptions() {
    // Walk up hierarchy so can call in subcommand after checking for displaying help.
    for (let cmd = this; cmd; cmd = cmd.parent) {
      cmd.options.forEach((anOption) => {
        if (anOption.mandatory && (cmd._getOptionValue(anOption.attributeName()) === undefined)) {
          cmd.missingMandatoryOptionValue(anOption);
        }
      });
    }
  };

  /**
   * Parse options from `argv` removing known options,
   * and return argv split into operands and unknown arguments.
   *
   * Examples:
   *
   *    argv => operands, unknown
   *    --known kkk op => [op], []
   *    op --known kkk => [op], []
   *    sub --unknown uuu op => [sub], [--unknown uuu op]
   *    sub -- --unknown uuu op => [sub --unknown uuu op], []
   *
   * @param {String[]} argv
   * @return {{operands: String[], unknown: String[]}}
   */

  parseOptions(argv) {
    const operands = []; // operands, not options or values
    const unknown = []; // first unknown option and remaining unknown args
    let dest = operands;
    const args = argv.slice();

    function maybeOption(arg) {
      return arg.length > 1 && arg[0] === '-';
    }

    // parse options
    let activeVariadicOption = null;
    while (args.length) {
      const arg = args.shift();

      // literal
      if (arg === '--') {
        if (dest === unknown) dest.push(arg);
        dest.push(...args);
        break;
      }

      if (activeVariadicOption && !maybeOption(arg)) {
        this.emit(`option:${activeVariadicOption.name()}`, arg);
        continue;
      }
      activeVariadicOption = null;

      if (maybeOption(arg)) {
        const option = this._findOption(arg);
        // recognised option, call listener to assign value with possible custom processing
        if (option) {
          if (option.required) {
            const value = args.shift();
            if (value === undefined) this.optionMissingArgument(option);
            this.emit(`option:${option.name()}`, value);
          } else if (option.optional) {
            let value = null;
            // historical behaviour is optional value is following arg unless an option
            if (args.length > 0 && !maybeOption(args[0])) {
              value = args.shift();
            }
            this.emit(`option:${option.name()}`, value);
          } else { // boolean flag
            this.emit(`option:${option.name()}`);
          }
          activeVariadicOption = option.variadic ? option : null;
          continue;
        }
      }

      // Look for combo options following single dash, eat first one if known.
      if (arg.length > 2 && arg[0] === '-' && arg[1] !== '-') {
        const option = this._findOption(`-${arg[1]}`);
        if (option) {
          if (option.required || (option.optional && this._combineFlagAndOptionalValue)) {
            // option with value following in same argument
            this.emit(`option:${option.name()}`, arg.slice(2));
          } else {
            // boolean option, emit and put back remainder of arg for further processing
            this.emit(`option:${option.name()}`);
            args.unshift(`-${arg.slice(2)}`);
          }
          continue;
        }
      }

      // Look for known long flag with value, like --foo=bar
      if (/^--[^=]+=/.test(arg)) {
        const index = arg.indexOf('=');
        const option = this._findOption(arg.slice(0, index));
        if (option && (option.required || option.optional)) {
          this.emit(`option:${option.name()}`, arg.slice(index + 1));
          continue;
        }
      }

      // Not a recognised option by this command.
      // Might be a command-argument, or subcommand option, or unknown option, or help command or option.

      // An unknown option means further arguments also classified as unknown so can be reprocessed by subcommands.
      if (maybeOption(arg)) {
        dest = unknown;
      }

      // If using positionalOptions, stop processing our options at subcommand.
      if ((this._enablePositionalOptions || this._passThroughOptions) && operands.length === 0 && unknown.length === 0) {
        if (this._findCommand(arg)) {
          operands.push(arg);
          if (args.length > 0) unknown.push(...args);
          break;
        } else if (arg === this._helpCommandName && this._hasImplicitHelpCommand()) {
          operands.push(arg);
          if (args.length > 0) operands.push(...args);
          break;
        } else if (this._defaultCommandName) {
          unknown.push(arg);
          if (args.length > 0) unknown.push(...args);
          break;
        }
      }

      // If using passThroughOptions, stop processing options at first command-argument.
      if (this._passThroughOptions) {
        dest.push(arg);
        if (args.length > 0) dest.push(...args);
        break;
      }

      // add arg
      dest.push(arg);
    }

    return { operands, unknown };
  };

  /**
   * Return an object containing options as key-value pairs
   *
   * @return {Object}
   */
  opts() {
    if (this._storeOptionsAsProperties) {
      // Preserve original behaviour so backwards compatible when still using properties
      const result = {};
      const len = this.options.length;

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

    return this._optionValues;
  };

  /**
   * Internal bottleneck for handling of parsing errors.
   *
   * @api private
   */
  _displayError(exitCode, code, message) {
    this._outputConfiguration.outputError(`${message}\n`, this._outputConfiguration.writeErr);
    this._exit(exitCode, code, message);
  }

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

  missingArgument(name) {
    const message = `error: missing required argument '${name}'`;
    this._displayError(1, 'commander.missingArgument', message);
  };

  /**
   * `Option` is missing an argument.
   *
   * @param {Option} option
   * @api private
   */

  optionMissingArgument(option) {
    const message = `error: option '${option.flags}' argument missing`;
    this._displayError(1, 'commander.optionMissingArgument', message);
  };

  /**
   * `Option` does not have a value, and is a mandatory option.
   *
   * @param {Option} option
   * @api private
   */

  missingMandatoryOptionValue(option) {
    const message = `error: required option '${option.flags}' not specified`;
    this._displayError(1, 'commander.missingMandatoryOptionValue', message);
  };

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

  unknownOption(flag) {
    if (this._allowUnknownOption) return;
    const message = `error: unknown option '${flag}'`;
    this._displayError(1, 'commander.unknownOption', message);
  };

  /**
   * Excess arguments, more than expected.
   *
   * @param {string[]} receivedArgs
   * @api private
   */

  _excessArguments(receivedArgs) {
    if (this._allowExcessArguments) return;

    const expected = this._args.length;
    const s = (expected === 1) ? '' : 's';
    const forSubcommand = this.parent ? ` for '${this.name()}'` : '';
    const message = `error: too many arguments${forSubcommand}. Expected ${expected} argument${s} but got ${receivedArgs.length}.`;
    this._displayError(1, 'commander.excessArguments', message);
  };

  /**
   * Unknown command.
   *
   * @api private
   */

  unknownCommand() {
    const partCommands = [this.name()];
    for (let parentCmd = this.parent; parentCmd; parentCmd = parentCmd.parent) {
      partCommands.unshift(parentCmd.name());
    }
    const fullCommand = partCommands.join(' ');
    const message = `error: unknown command '${this.args[0]}'.` +
      (this._hasHelpOption ? ` See '${fullCommand} ${this._helpLongFlag}'.` : '');
    this._displayError(1, 'commander.unknownCommand', message);
  };

  /**
   * Set the program version to `str`.
   *
   * This method auto-registers the "-V, --version" flag
   * which will print the version number when passed.
   *
   * You can optionally supply the  flags and description to override the defaults.
   *
   * @param {string} str
   * @param {string} [flags]
   * @param {string} [description]
   * @return {this | string} `this` command for chaining, or version string if no arguments
   */

  version(str, flags, description) {
    if (str === undefined) return this._version;
    this._version = str;
    flags = flags || '-V, --version';
    description = description || 'output the version number';
    const versionOption = this.createOption(flags, description);
    this._versionOptionName = versionOption.attributeName();
    this.options.push(versionOption);
    this.on('option:' + versionOption.name(), () => {
      this._outputConfiguration.writeOut(`${str}\n`);
      this._exit(0, 'commander.version', str);
    });
    return this;
  };

  /**
   * Set the description to `str`.
   *
   * @param {string} [str]
   * @param {Object} [argsDescription]
   * @return {string|Command}
   */
  description(str, argsDescription) {
    if (str === undefined && argsDescription === undefined) return this._description;
    this._description = str;
    this._argsDescription = argsDescription;
    return this;
  };

  /**
   * Set an alias for the command.
   *
   * You may call more than once to add multiple aliases. Only the first alias is shown in the auto-generated help.
   *
   * @param {string} [alias]
   * @return {string|Command}
   */

  alias(alias) {
    if (alias === undefined) return this._aliases[0]; // just return first, for backwards compatibility

    let command = this;
    if (this.commands.length !== 0 && this.commands[this.commands.length - 1]._executableHandler) {
      // assume adding alias for last added executable subcommand, rather than this
      command = this.commands[this.commands.length - 1];
    }

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

    command._aliases.push(alias);
    return this;
  };

  /**
   * Set aliases for the command.
   *
   * Only the first alias is shown in the auto-generated help.
   *
   * @param {string[]} [aliases]
   * @return {string[]|Command}
   */

  aliases(aliases) {
    // Getter for the array of aliases is the main reason for having aliases() in addition to alias().
    if (aliases === undefined) return this._aliases;

    aliases.forEach((alias) => this.alias(alias));
    return this;
  };

  /**
   * Set / get the command usage `str`.
   *
   * @param {string} [str]
   * @return {String|Command}
   */

  usage(str) {
    if (str === undefined) {
      if (this._usage) return this._usage;

      const args = this._args.map((arg) => {
        return humanReadableArgName(arg);
      });
      return [].concat(
        (this.options.length || this._hasHelpOption ? '[options]' : []),
        (this.commands.length ? '[command]' : []),
        (this._args.length ? args : [])
      ).join(' ');
    }

    this._usage = str;
    return this;
  };

  /**
   * Get or set the name of the command
   *
   * @param {string} [str]
   * @return {string|Command}
   */

  name(str) {
    if (str === undefined) return this._name;
    this._name = str;
    return this;
  };

  /**
   * Return program help documentation.
   *
   * @param {{ error: boolean }} [contextOptions] - pass {error:true} to wrap for stderr instead of stdout
   * @return {string}
   */

  helpInformation(contextOptions) {
    const helper = this.createHelp();
    if (helper.helpWidth === undefined) {
      helper.helpWidth = (contextOptions && contextOptions.error) ? this._outputConfiguration.getErrHelpWidth() : this._outputConfiguration.getOutHelpWidth();
    }
    return helper.formatHelp(this, helper);
  };

  /**
   * @api private
   */

  _getHelpContext(contextOptions) {
    contextOptions = contextOptions || {};
    const context = { error: !!contextOptions.error };
    let write;
    if (context.error) {
      write = (arg) => this._outputConfiguration.writeErr(arg);
    } else {
      write = (arg) => this._outputConfiguration.writeOut(arg);
    }
    context.write = contextOptions.write || write;
    context.command = this;
    return context;
  }

  /**
   * Output help information for this command.
   *
   * Outputs built-in help, and custom text added using `.addHelpText()`.
   *
   * @param {{ error: boolean } | Function} [contextOptions] - pass {error:true} to write to stderr instead of stdout
   */

  outputHelp(contextOptions) {
    let deprecatedCallback;
    if (typeof contextOptions === 'function') {
      deprecatedCallback = contextOptions;
      contextOptions = undefined;
    }
    const context = this._getHelpContext(contextOptions);

    const groupListeners = [];
    let command = this;
    while (command) {
      groupListeners.push(command); // ordered from current command to root
      command = command.parent;
    }

    groupListeners.slice().reverse().forEach(command => command.emit('beforeAllHelp', context));
    this.emit('beforeHelp', context);

    let helpInformation = this.helpInformation(context);
    if (deprecatedCallback) {
      helpInformation = deprecatedCallback(helpInformation);
      if (typeof helpInformation !== 'string' && !Buffer.isBuffer(helpInformation)) {
        throw new Error('outputHelp callback must return a string or a Buffer');
      }
    }
    context.write(helpInformation);

    this.emit(this._helpLongFlag); // deprecated
    this.emit('afterHelp', context);
    groupListeners.forEach(command => command.emit('afterAllHelp', context));
  };

  /**
   * You can pass in flags and a description to override the help
   * flags and help description for your command. Pass in false to
   * disable the built-in help option.
   *
   * @param {string | boolean} [flags]
   * @param {string} [description]
   * @return {Command} `this` command for chaining
   */

  helpOption(flags, description) {
    if (typeof flags === 'boolean') {
      this._hasHelpOption = flags;
      return this;
    }
    this._helpFlags = flags || this._helpFlags;
    this._helpDescription = description || this._helpDescription;

    const helpFlags = _parseOptionFlags(this._helpFlags);
    this._helpShortFlag = helpFlags.shortFlag;
    this._helpLongFlag = helpFlags.longFlag;

    return this;
  };

  /**
   * Output help information and exit.
   *
   * Outputs built-in help, and custom text added using `.addHelpText()`.
   *
   * @param {{ error: boolean }} [contextOptions] - pass {error:true} to write to stderr instead of stdout
   */

  help(contextOptions) {
    this.outputHelp(contextOptions);
    let exitCode = process.exitCode || 0;
    if (exitCode === 0 && contextOptions && typeof contextOptions !== 'function' && contextOptions.error) {
      exitCode = 1;
    }
    // message: do not have all displayed text available so only passing placeholder.
    this._exit(exitCode, 'commander.help', '(outputHelp)');
  };

  /**
   * Add additional text to be displayed with the built-in help.
   *
   * Position is 'before' or 'after' to affect just this command,
   * and 'beforeAll' or 'afterAll' to affect this command and all its subcommands.
   *
   * @param {string} position - before or after built-in help
   * @param {string | Function} text - string to add, or a function returning a string
   * @return {Command} `this` command for chaining
   */
  addHelpText(position, text) {
    const allowedValues = ['beforeAll', 'before', 'after', 'afterAll'];
    if (!allowedValues.includes(position)) {
      throw new Error(`Unexpected value for position to addHelpText.
Expecting one of '${allowedValues.join("', '")}'`);
    }
    const helpEvent = `${position}Help`;
    this.on(helpEvent, (context) => {
      let helpStr;
      if (typeof text === 'function') {
        helpStr = text({ error: context.error, command: context.command });
      } else {
        helpStr = text;
      }
      // Ignore falsy value when nothing to output.
      if (helpStr) {
        context.write(`${helpStr}\n`);
      }
    });
    return this;
  }
};

/**
 * Expose the root command.
 */

exports = module.exports = new Command();
exports.program = exports; // More explicit access to global command.

/**
 * Expose classes
 */

exports.Command = Command;
exports.Option = Option;
exports.CommanderError = CommanderError;
exports.InvalidOptionArgumentError = InvalidOptionArgumentError;
exports.Help = Help;

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

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

/**
 * Output help information if help flags specified
 *
 * @param {Command} cmd - command to output help for
 * @param {Array} args - array of options to search for help flags
 * @api private
 */

function outputHelpIfRequested(cmd, args) {
  const helpOption = cmd._hasHelpOption && args.find(arg => arg === cmd._helpLongFlag || arg === cmd._helpShortFlag);
  if (helpOption) {
    cmd.outputHelp();
    // (Do not have all displayed text available so only passing placeholder.)
    cmd._exit(0, 'commander.helpDisplayed', '(outputHelp)');
  }
}

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

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

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

/**
 * Parse the short and long flag out of something like '-m,--mixed <value>'
 *
 * @api private
 */

function _parseOptionFlags(flags) {
  let shortFlag;
  let longFlag;
  // Use original very loose parsing to maintain backwards compatibility for now,
  // which allowed for example unintended `-sw, --short-word` [sic].
  const flagParts = flags.split(/[ |,]+/);
  if (flagParts.length > 1 && !/^[[<]/.test(flagParts[1])) shortFlag = flagParts.shift();
  longFlag = flagParts.shift();
  // Add support for lone short flag without significantly changing parsing!
  if (!shortFlag && /^-[^-]$/.test(longFlag)) {
    shortFlag = longFlag;
    longFlag = undefined;
  }
  return { shortFlag, longFlag };
}

/**
 * Scan arguments and increment port number for inspect calls (to avoid conflicts when spawning new command).
 *
 * @param {string[]} args - array of arguments from node.execArgv
 * @returns {string[]}
 * @api private
 */

function incrementNodeInspectorPort(args) {
  // Testing for these options:
  //  --inspect[=[host:]port]
  //  --inspect-brk[=[host:]port]
  //  --inspect-port=[host:]port
  return args.map((arg) => {
    if (!arg.startsWith('--inspect')) {
      return arg;
    }
    let debugOption;
    let debugHost = '127.0.0.1';
    let debugPort = '9229';
    let match;
    if ((match = arg.match(/^(--inspect(-brk)?)$/)) !== null) {
      // e.g. --inspect
      debugOption = match[1];
    } else if ((match = arg.match(/^(--inspect(-brk|-port)?)=([^:]+)$/)) !== null) {
      debugOption = match[1];
      if (/^\d+$/.test(match[3])) {
        // e.g. --inspect=1234
        debugPort = match[3];
      } else {
        // e.g. --inspect=localhost
        debugHost = match[3];
      }
    } else if ((match = arg.match(/^(--inspect(-brk|-port)?)=([^:]+):(\d+)$/)) !== null) {
      // e.g. --inspect=localhost:1234
      debugOption = match[1];
      debugHost = match[3];
      debugPort = match[4];
    }

    if (debugOption && debugPort !== '0') {
      return `${debugOption}=${debugHost}:${parseInt(debugPort) + 1}`;
    }
    return arg;
  });
}