Perl: [ ] - Character Class
[ ] - Character Class
A group of characters in square brackets will match any character in the brackets
A caret (^) negates the match
/[ab][cd]/ This will match a or b followed by c or d
/[aeiou]/ This will match all vowels
/[^aeiou]/ This will match anything but vowels
/[0123456789]/ All numerals
/[0-9] All numerals (Use the - to specify a range)