I have lots of files with lots of text. In those files, I'm looking for a string, let's say "av" that is not surrounded by any letter (a-zA-Z), like in hAVing. No case sensitive. My tool supports perl compatible syntax.

Some examples:
Match: av
Match: av-link
Match: let's AV something
Match: av/dc
Match: ab,ac,av,az
NO Match: having 
NO Match: average
NO Match: textav