http://www.indeed.com/jobtrends?q=perl%2C+python%2C+ruby&...
Python and Ruby aren't nearly as popular as Perl. CPAN, Perl's repository of libraries, is gigantic, having most everything you can think of already in it; which makes writing new programs much, much easier.
As much as Ruby and Python fanboys love to beat up on Perl, their favorite languages have their uglyness and their own faults (which you'll rarely hear them mention). However, their propaganda really has worked on a lot of people that really don't know any better. So my impression is that a lot of the newer stuff is being written for Ruby and Python. So it would probably pay to learn them for that, if nothing else. But I would definitely think twice before choosing them instead of Perl.