Regex really never. Unless you're munging data in Python it's usually a bad idea to use regex. Clean strings? Use a library. Parsing? Use a parser. Raw regex implies filtering stuff or banning certain characters in strings which breaks all kinds of multi language compatibility
Well, I am obviously the guy who write the tools and the libraries, so you don't have to know these things yourself but I do :D
Every time I see a regex cleaning strings I instantly know the app was written by an ametuer and probably horrible and full of security issues. Oh it globally replaces this bad token but not recursively? Great
I use regex for searching logs all the time but never in production apps. I can write some pretty mean regex but I can't remember the function call for string replace off the top of my head. For me regex is 99% in a text editor.
Really when do you split up strings without using a tokenizer or parser of some sort? Manual string manipulation is usually dumb and error prone. The only time I find myself doing it is when stuffing crap into bobs "extras" db field which is actually a bunch of 80 char strings delimited by the pipe character.
And don't assimilate fizzbuzz with half hour problems. There are for sure some difficult half hour interviews questions; they are not comparable to trivial exercises like printing the numbers from 1 to 10.
P.S. If you never use console, strings or regex. I really wonder what kind of applications you're writing.