"Idiomatic perl" is often more like "perl that a non-expert will never be able to read." Things like map/grep tricks (Schwartzian transform, for example), lots of use of $_, typeglob manipulation, hash-slices, chaining lots of things with and/or constructs, using lots of closures... In short, things that are fine in small doses but get hard to read very quickly. Writing things out in a less compact way is usually seen as more Java/C-like and less idiomatic.