S-PLUS allows escape to the operating system at any time in the session. If a command, on a new line, begins with an exclamation mark then the rest of the line is interpreted as a UNIX command. So for example to look through a data file without leaving S-PLUS you could use
!more curious.dat
When you finish paging the file the S-PLUS session is resumed.
In fact the integration of S-PLUS into UNIX is very complete. For example, there is a command, unix(...), that executes any unix command, (specified as a character string argument), and passes on any output from the command as a character string to the program. Essentially the full power of the operating system remains easily available to the user of the S-PLUS program during any session.
There are non-UNIX implementations of S-PLUS, for example for DOS. Users should consult the appropriate user guides for more information.