Use perl -v command.

This is perl, v5.8.7 built for i486-linux-gnu-thread-multi
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2005, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using `man perl' or `perldoc perl'. If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.

Or