I've been helping someone with their Perl scripts, so after about 10 months of only working with Ruby, I'm doing some Perl hacking recently.

It's very interesting, switching languages like this, and Perl is definitely a different beast than Ruby. Ruby is like a mix of Lisp and Eiffel with some Perl-y goodness mixed into the cake batter. They're all excellent languages, and I'm not sure which one I like the best, but I sure do love that Ruby, it just feels so right.

File globbing in Perl
Reading files with Perl
Environments with Perl
Running system commands with Perl
More running external programs in Perl
Perl FAQ Part 5 - External Program Interaction
Subroutines in Perl
Modules in Perl
Functions in Perl