Returns a logical value stating whether S-PLUS is being used interactively
or in batch mode.
USAGE:
interactive()
VALUE:
a logical value: TRUE if the input to S-PLUS is an interactive
terminal, FALSE if it is not.
DETAILS:
Use interactive to prevent inappropriate
execution.
For example, the menu and browser functions
only work when executed interactively.
interactive is TRUE if and only if both the standard input
and standard error file descriptors are terminals
(as determined by the isatty system routine).
This is not foolproof.