A string or array of strings argument names to always treat as strings.

A boolean, string or array of strings to always treat as booleans. If true will treat all double hyphenated arguments without equals signs as boolean (e.g. affects --foo, not -f or --foo=bar).

An object mapping string names to strings or arrays of string argument names to use as aliases.

An object mapping string argument names to default values.

When true, populate argv._ with everything after the first non-option.

A function which is invoked with a command line parameter not defined in the opts configuration object. If the function returns false, the unknown option is not added to argv.

When true, populate argv._ with everything before the -- and argv['--'] with everything after the --. Note that with -- set, parsing for arguments still stops after the --.