checking for file extension using split vs regex

is_valid?.rb

# The is_valid?(filename) checks if the filename has either a .txt.gz or a .txt extension
def is_valid?(filename)
  arr = filename.split(/\.|\/|\\/)
  return true if arr.last == "txt"
  if arr.last = "gz"
    return true if arr[-2, 1] == "txt"
  end
  return false
end

# becomes

def is_valid?(filename)
 filename =~ /[\.txt\.gz|\.txt]$/ ? true : false
end

# Regex rocks!