ENVIRONMENT
The following two environment variables (if defined) are used by :

$PROMPT_USER
    If this variable exists and is non-empty, then the user will be interactively prompted for any missing required arguments.

$USAGE_LEVEL
    This variable controls the verboseness of usage messages that are printed. If This variable is empty or is undefined, then verbose messages are printed. If this variable exists and is non-empty, it may be set to one of the following values:

    0   No usage message is printed.

    1   A terse usage message is printed

    2   A verbose usage message is printed.