What are good regular expressions?

puts "Matched!" unless /d{3}-d{4}/.match("555-1234").nil?puts "Didn't match!" if /d{3}-d{4}/.match("Not phone number").nil?

match = /([^@]*)@(.*)/.match("[email protected]")name = match[1]domain = match[2]

/(bb|[^b]{2})/i

/^1?$|^(11+?)1+$/

def is_prime(n)
  str = "1" * n
  return str !~ /^1?$|^(11+?)1+$/
end

^(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])[a-zA-Z0-9]{5,10}$