Just to highlight this, one telling example...
A friend of mine started to learn Ruby for a new job and found this "totally cool feature" for parsing text:
A flip-flop operator based on the range ".." syntax. °
So he asked himself why Perl doesn't have it and was surprised to find out that Ruby stole it from Perl.
Then he started to read the perldocs more closely and some years later he shocked the world by revealing a DOS attack problem based on the hash key order in many web languages ...
... except Perl, which fixed it already 10 years ago, and documented it in the perldocs. *
°) please note how it's first explained with Perl syntax and almost literally translated to Ruby, before repeating it in more "idiomatic" Ruby
*) "Perl was updated to fix this problem in version 5.8.1, which was released in September of 2003. For some reason most of the other languages did not take the cue from Perl and are still vulnerable to these attacks"