This module makes it possible to make calls to the UNIX shell.
The shell used is /bin/sh, so the environment might be
different to the one you commonly use. C shell expansions cannot
be used. The module is extremely easy to use and there is only one function.
Note that most UNIX commands produce a trailing new line.
Makes the call String to sh and returns the answer in a list of characters.
Example: (bizarre version of ls)
1> unix:cmd("for i in *; do echo $i; done").