Commonly used regular expressions - Cheatsheet

CopyHOST = /\A[a-z0-9]+[a-z0-9\-\.]*[a-z0-9]+\z/i
BANK_CODE = /\A\d{8}\z/                                          # Germany
BANK_ACCOUNT_NUMBER = /\A\d{1,10}\z/                             # Germany
ZIP_CODE = /\A\d{5}\z/                                           # Germany
HEX_COLOR = /\A([a-fA-F0-9]{3}){1,2}\z/
IP_ADDRESS = /\A(?:25[0-5]|(?:2[0-4]|1\d|[1-9])?\d)(?:\.(?:25[0-5]|(?:2[0-4]|1\d|[1-9])?\d)){3}\z/