One distinguishing trait of Perl (I think this is unique in programming languages) is that Perl has
context.
Upon my first encounter with Perl (coming from languages with "context-free" grammars) I thought this were a design flaw, but it is intentional - Perl is designed after natural languages - and some of the advantages are described by
chromatic in
his book.
The linked chapter also contains information on other points that make Perl stand out.