With Perl, you can't just say "Perl", you have to be specific to which version of Perl.
What is the distribution of these different versions of Perl across various OSes and OS versions?
Hint: Lots of backward-incompatible changes tend to get made around different major versions. Having Perl 4 is not like having Perl 5 which is not like Perl 6.
Are there any contemporary distros that have the "perl" exectuable that is not Perl 5?
Perl 5 was released in 1994. It is incredibly portable. If you have a system that legitimately has Perl 4, I would love to hear about it, but …