Many people think that because Perl is distributed under the GNU General Public License, any program written in Perl must also be distributed under this license. This is not the case.
Perl is distributed with two licences, the GPL and the less strict Artistic License. Neither of these specify that works created using Perl must be made free - only works whose source code is directly derived from the source code of the Perl interpreter itself.
This means that you can sell Perl scripts or applications for money, if you wish, and that the use of Perl within a business does not require that the business give away its proprietary tools and systems.