On that note, awk shows up a lot in the shortest solutions because of the ease with which it parses input files.
I haven't used perl myself, so can anyone comment on the merits of perl vs awk here? They often compete for this use case.
Oversimplifying a bit, I'm going to tell you that Perl was initially conceived as a mix between C, sed and awk. So, there are quite a few awk idioms that are directly translatable in Perl. As a matter of fact, there even is a section dedicated to awk in perltrap[1], enumerating the differences between the two languages.
http://rosalind.info/
The neat things is that you can use any language you want.