This requires enabling the [derive
feature flag][crate::_features].
Help:
$ echo --help
Usage: echo --text <TEXT>
Options:
-h, --help Print help
Echo:
-t, --text <TEXT> The text to be echoed [aliases: text]
$ ping --help
Usage: ping
Options:
-h, --help Print help
$ exit --help
Usage: exit
Options:
-h, --help Print help
Echo:
$ echo -t 'Hello, world!'
Hello, world!
Ping:
$ ping
pong
Exit:
$ exit
Exiting ...