all-in-one/regex

REGEX Quick Guide

• Regex 101 : Have sample code generator

• Atom and Notepad++ support Regex Find / Replace. Can use to test regex expression

• Javascript : Enclosed within /.../

• Control characters

  • . : Any Character Except New Line
  • \d : Digit (0-9)
  • \D : Not a Digit
  • \w : Word Character (a-z, A-Z, 0-9, _)
  • \W : Not Word Character
  • \s : Whitespace (space, tab, newline)
  • \S : Not Whitespace
  • \b : Word Boundary
  • \B : Not Word Boundary
  • ^ : Beginning of a String
  • $ : End of a String

• Other

  • [] : Matches Characters in brackets
  • [^ ] : Matches Characters NOT in brackets
  • | : Either Or
  • ( ) : Group

• Quantifiers

  • * : 0 or more
  • + : 1 or more
  • ? : 0 or One
  • {3} : Exact Number
  • {3,4} : Range of Numbers (Minimum, Maximun)

• MetaCharacters (Need to be escaped)

  • .[{()\^$|?*+ : Need to be escaped with \.
  • Eg String = \*
    • To form the character list, escape it as shown \\\*

• Useful regex

  regex	Description	Sample javascript
  /\d(?=\d{4})/g	mask digits and keep remaining 4 digits	'12345678'.replace(/\d(?=\d{4})/g, "*")
  /(\d+)(\d{4})/	mask digit. Group into group1 (length - 4 digits) and group2 (4-digit)	'12345678'.replace(/(\d+)(\d{4})/, (match, g1, g2) => { return g1.replace(/\d+/, '*'.repeat(g1.length) + g2) });