HOST. HOST COMMAND=['command'...].
HOST suspends the current pspp session and temporarily returns control
to the operating system.
This command cannot be used if the SAFER (see SET) setting is active.
COMMAND subcommand is specified, as a sequence of shell
commands as quoted strings within square brackets, then pspp executes
them together in a single subshell.
If no subcommands are specified, then pspp invokes an interactive subshell.