longoption

Long option refers to a command-line option that starts with two hyphens and uses a descriptive name, such as --help or --output. Long options are commonly used in GNU and other Unix-like ecosystems to improve readability, as opposed to short options that use a single dash and a single letter (for example -h).

Parsing long options is typically done with libraries such as getopt_long, a GNU extension to the standard getopt. In such interfaces, each long option has a name, an argument requirement (no_argument, required_argument, or optional_argument), and an associated value used by the program to identify the option. Long options can often be supplied as --name=value or as --name value, depending on the implementation.

Examples of long options include --help, --version, --output=log.txt, and, in version control tools, --oneline or --decorate. Many applications support a mix of long and short options, allowing combinations like -h or --help to trigger the same behavior.

History and standards: Long options originated with GNU utilities and the getopt_long interface, which extends the POSIX option parsing model. They are not required by the POSIX standard, but are widely supported on modern Linux and BSD systems. Behavior, naming conventions, and argument handling can vary between libraries.

See also: getopt, getopt_long, command-line interface, options parsing.