or download this
'booga' =~ /[^.]*/ matches.
'booga.' =~ /[^.]*/ matches.
...
'4.6.8' =~ /((?=.*\.))\1(\d)/ returns 8 in $2. .* matched a "4.6"
'4.6.8' =~ /.*\.(\d)/ returns 8 in $1. Lookahead not needed.
'4.6.8' =~ /(?:(?!\.).)*(\d)/ returns 6 in $1. You want neg lookahead