erscores.
default
The default value for the option. For an option with argument it can be anything; for an option with no argument: it must be yes or no.
brief... without argument, else returns with code one.
An option must be of the form --option, only characters in the ranges A-Z, a-z, 0-9 and ... on with argument, else returns with code one.
An option must be of the form --option=value, only characters in the ranges A-Z, a-z, 0-... ut argument, else returns with code one.
A brief option must be of the form -aV (a is the option, V is the value), only characters in the ranges A
