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. It must be
    a single argument: use double-quotes to enclose multiple arguments sepa-
    rated by blanks.

    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:
    At the interactive prompt, system commands can also be executed directly
    from the SIC level using the $ token. "Command" must be a valid  operat-
    ing  system command in the default shell of the user. The $ token is in-
    valid in procedures.