A regular expression, or regex, is a sequence of characters that specifies a match pattern in text. Often times regex is used for form validations and string-searching algorithms. Here are a few regex that are handy for developers:

Letters

• Domain: ^([a-z][a-z0-9-]+(\.|-*\.))+[a-z]{2,6}$
• Email: ^[_]*([a-z0-9]+(\.|_*)?)+@([a-z][a-z0-9-]+(\.|-*\.))+[a-z]{2,6}$
• Letters only: ^[a-zA-Z]+$

Numbers

• Numbers only: ^[0-9]*$
• Positive numbers: ^\d*\.?\d+$
• Negative numbers: ^-\d*\.?\d+$
• Numbers with spaces and parenthesis: /^(?:\+\d{1,3}|0\d{1,3}|00\d{1,2})?(?:\s?\(\d+\))?(?:[-\/\s.]|\d)+$/
• Phone number: ^\+?[\d\s]{3,}$
• Phone number with code: ^\+?[\d\s]+\(?[\d\s]{10,}$

Useful for Inputs

• Letter and numbers only: ^[A-Z0-9]+$
• Match blank input: ^\s\t*$
• Match no input: ^$
• Match new line: [\r\n]|$
• Match URL: ^http\:\/\/[a-zA-Z0-9.-]+\.[a-zA-Z]{2,3}$
• Match white space: ^\s+$
• Match multiple white space: ^.\s{2,}.$