SYSTEM

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

    Execute a command from the operating system, or create a subshell.

    If no argument is given, start a  subshell  based  on  the  SIC  logical
    GAG\PROCESS.  If it is not defined, the user $SHELL environment variable
    is used. If it is also not defined, the last fallback  is  /bin/sh.  The
    subshell can be terminated by typing 'exit' or 'bye' or case.

    If an argument is given, execute the command in a /bin/sh subshell (note
    that /bin/sh is system-dependent and might behave differently  from  one
    system  to  another). It must be a single argument: use double-quotes to
    enclose multiple arguments separated by blanks. Note that  an  error  is
    raised if the shell command returns a non-zero status. This behavior can
    be modified in 2 manners:
    - use dedicated command options, if any, to ensure it does not return  a
      non-zero status (for example -q option for grep),
    - catch the error in the shell way, e.g. terminate the command line with
      " || true" which executes the "true" command if an error occurs. Obvi-
      ously ignoring errors is at your own risk.

    Note  that  Unix  environment variables cannot be defined in such a way,
    since it is a subshell (i.e. the environment modifications are lost when
    the  subshell  ends). 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.