Regular Expression

A Regular Expression (RegEx, regex, regexp, RE, etc.) is a way to search through strings. It helps in doing validation, getting/matching certain pieces of a string, finding and replacing strings and more.

RegEx Format

• Every RE starts and ends with a /. Eg: /selena/
• RegEx should not be put within "" or ''.
• There can be flags after the last / and it can be
  • g: global
    • Match anywhere in the string
    • Without global, only the first result is found
  • i: case insensitive
  • m: multi line
  • s: single line (dotall)
  • u: unicode
  • y: sticky

Built-In JavaScript Functions

• "str".match(RegEx) to find all matching patterns (RT: array)
• "str".search(RegEx) to test for a single match (RT: index posn of first match)
• "str".replace(RegEx, "text") to replace all matching patterns
• "str".test(RegEx) to test whether pattern(s) were found or not (RT: boolean)

Resources

• Learn Regular Expressions In 20 Minutes
• Regular Expressions (RegEx) in 100 Seconds
• The Missing Semester of Your CS Education: Regular expressions
• Short interactive RegEx tutorial
• Online RegEx debugger
• RegEx cheat sheet
• regular-expressions.info
• Source code for this web site: github.com/HarshKapadia2/regex

Examples