Perl is also installed on virtually every server. Seems most people are using Ubuntu nowadays and it's definitely there by default (much of the Debian infrastructure is written in Perl). I believe the same goes for Red Hat.
As to your actual question, I'm not sure I'd say that Perl is better than Php/Ruby/Python. I really consider them all mostly the same. There are bits and pieces of each that is better than the others, but nothing overarching. If you know one of them really well, I don't see a huge reason to learn another one of them to the same level (unless some sort of outside influence compels you).
Perl's strength has traditionally been CPAN, but Ruby and Python both have their own copies and communities big enough that most of the stuff you look for is already there.
The Perl community's documentation is also superior to almost anything else out there. Once I've CPAN installed a package (say Template::Toolkit), I just "man Template::Toolkit" and there's a ton of documentation sitting there, including examples. The convention in the community is to put the example at the very beginning, which is heavenly, and cannot be appreciated enough.
In contrast, the Ruby community's documentation is largely a joke. It seems most of the time the documentation for a gem is in the README on github. And even then, to really learn it requires diving into the code. But then it isn't clear what is or isn't supposed to be a stable API. Perl seems to do that way better than Ruby.
Python always seems to have docs you can get to with pydoc but from what I've seen they tend to be auto-generated from the API with a lot of "FrotzBlubb() - This function Frotzes your Blubb" style non-documentation. So it has the sheen of documentation but it's not actually really helpful.
That being said, I learned Perl in 1994 or so and recently did a Ruby project. I quite enjoyed it and have been forcing myself to do new things in Ruby to keep up my language skills. I do miss the good documentation in Perl though (the Ruby community really needs to take note). Also Perl just seems faster than Ruby (I have no evidence, it just feels that way).
As to your actual question, I'm not sure I'd say that Perl is better than Php/Ruby/Python. I really consider them all mostly the same. There are bits and pieces of each that is better than the others, but nothing overarching. If you know one of them really well, I don't see a huge reason to learn another one of them to the same level (unless some sort of outside influence compels you).
Perl's strength has traditionally been CPAN, but Ruby and Python both have their own copies and communities big enough that most of the stuff you look for is already there.
The Perl community's documentation is also superior to almost anything else out there. Once I've CPAN installed a package (say Template::Toolkit), I just "man Template::Toolkit" and there's a ton of documentation sitting there, including examples. The convention in the community is to put the example at the very beginning, which is heavenly, and cannot be appreciated enough.
In contrast, the Ruby community's documentation is largely a joke. It seems most of the time the documentation for a gem is in the README on github. And even then, to really learn it requires diving into the code. But then it isn't clear what is or isn't supposed to be a stable API. Perl seems to do that way better than Ruby.
Python always seems to have docs you can get to with pydoc but from what I've seen they tend to be auto-generated from the API with a lot of "FrotzBlubb() - This function Frotzes your Blubb" style non-documentation. So it has the sheen of documentation but it's not actually really helpful.
That being said, I learned Perl in 1994 or so and recently did a Ruby project. I quite enjoyed it and have been forcing myself to do new things in Ruby to keep up my language skills. I do miss the good documentation in Perl though (the Ruby community really needs to take note). Also Perl just seems faster than Ruby (I have no evidence, it just feels that way).