SYSTEM

        [SIC\]SYSTEM ["Command"]
        $ Command

    Execute a command from the operating system, or create a subshell. If no
    argument is given, start a subshell by running the default  user  shell.
    The  subshell  can  be terminated by typing 'exit' or 'bye' or 'logout',
    depending on system version, and controls return to SIC in this case.

    If an argument is given, executes the command in a subshell.

    Note that Unix environment variables cannot be defined in  such  a  way,
    since  it  is  a  subshell.  In particular, use command SIC DIRECTORY to
    change your working directory.

        $ Command
    System commands can also be executed directly from the SIC  level  using
    the  $  token. "Command" must be a valid operating system command in the
    default shell of the user.