| opens a pipe (see perldoc perlopentut). ( ... ) delimits a subshell, and can be tested at the command line:

davido@somehost:~$ (
> date
> who
> )
Tue Jun 10 11:20:34 MDT 2014
davido   :0           2014-06-09 19:35 (:0)
davido   pts/0        2014-06-09 19:38 (:0)
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