perl: not found
when you try to invoke Perl from the shell, your system administrator hasn't caught the fever yet. But even if it's not on your system, you can get it for free (or nearly so).
Perl is distributed under the GNU Public License, which says something like, "you can distribute binaries of Perl only if you make the source code available at no cost, and if you modify Perl, you have to distribute the source to your modifications as well." And that's essentially free. You can get the source to Perl for the cost of a blank tape or a few megabytes over a wire. And no one can lock Perl up and sell you just binaries for their particular idea of "supported hardware configurations."
 Or the slightly more liberal Artistic License, found in the distribution sources.
In fact, it's not only free, but it runs rather nicely on nearly everything that calls itself UNIX or UNIX-like and has a C compiler. This is because the package comes with an arcane configuration script called Configure that pokes and prods the system directories looking for things it requires, and adjusts the include files and defined symbols accordingly, turning to you for verification of its findings.
Besides UNIX or UNIX-like systems, people have also been addicted enough to Perl to port it to the Amiga, the Atari ST, the Macintosh family, VMS, OS/2, even MS/DOS and Windows NT and Windows 95 - and probably even more by the time you read this. The sources for Perl (and many precompiled binaries for non-UNIX architectures) are available from the Comprehensive Perl Archive Network (the CPAN). If you are web-savvy, visit http://www.perl.com/CPAN for one of the many mirrors. If you're absolutely stumped, write email@example.com and say "Where can I get Perl?!?!"