clap/examples/tutorial_builder/04_01_enum.md

$ 04_01_enum --help
A simple to use, efficient, and full-featured Command Line Argument Parser

Usage: 04_01_enum[EXE] <MODE>

Arguments:
  <MODE>
          What mode to run the program in

          Possible values:
          - fast: Run swiftly
          - slow: Crawl slowly but steadily

Options:
  -h, --help
          Print help information (use `-h` for a summary)

  -V, --version
          Print version information

$ 04_01_enum -h
A simple to use, efficient, and full-featured Command Line Argument Parser

Usage: 04_01_enum[EXE] <MODE>

Arguments:
  <MODE>  What mode to run the program in [possible values: fast, slow]

Options:
  -h, --help     Print help information (use `--help` for more detail)
  -V, --version  Print version information

$ 04_01_enum fast
Hare

$ 04_01_enum slow
Tortoise

$ 04_01_enum medium
? failed
error: 'medium' isn't a valid value for '<MODE>'
  [possible values: fast, slow]

For more information try '--help'