compared to system(), qx'', open "...|", open "|...":

    + redirects more than one file descriptor
    + returns TRUE on success, FALSE on failure
    + throws an error if problems occur in the parent process (or the pre-exec child)
    + allows a very perlish interface to Perl data structures and subroutines
    + allows 1 word invocations to avoid the shell easily:

         run3 ["foo"];  # does not invoke shell

    - does not return the exit code, leaves it in $?