With very few exceptions, code written to run on any Perl released since 2000 (38 stable releases of Perl in that time period, eight of them major releases) runs without modification
That’s from a great little article by Chromatic about modern Perl in the latest issue of PragPub. The article goes in to discuss a number of other strengths of Perl, such as its strong community dedication to testing across numerous architectures, services for understanding package dependencies (that sound like they go beyond anything presently available for Ruby), and legendary standards of documentation.
It’s good to be reminded of things that other, more mature programming communities do well. I’m fond of pointing out that Perl had the best, most informative error message of any language ever. And Perl has been at the forefront in a lot of areas. Notably, as far as I’m aware it was the first language to take unicode integration seriously, and I would not be surprised if still has better support than any other programming system.