第一个case将被执行，否则（意味着任何其他参数）default将被执行。
The option string (optstring) is one character per option. Options that have arguments, such as the -l and -o options in the example, are followed by a : character. The optstring used by the example is Il...
The option string (optstring) is one character per option. Options that have arguments, such as the -l and -o options in the example, are followed by a : character. The optstring used by the example is Il...