Regex Cheat Sheet - A Regular Expressions Guide

This blog post is firstly published on my personal blogging site kanby.net

TL;DR

• Most common regex patterns
• Examples of regex patterns

Most Common Patterns

Important: a x b in this example a is preceeding by x and b is followed by x

• ^ means the start of each line in string
• $ means the end of each line in string
• () groups specific pattern
• (?:) means this pattern will match in string BUT will not return it. E.g., A phone number regex pattern must include country code but does not have to extract that part even though it must match on string.
• [] matches specified single character, e.g. [abc] will match a or b or c. Ranges are supported too [a-c] will match the same.
• [^] matches every character except specified ones
• . matches any single character
• * 0 or more of the preceding element
• + 1 or more of the preceding element
• ? 0 or 1 of the preceding element
• {n} Exactly n occurrences of the preceding element.
• {n,} n or more occurrences of the preceding element.
• {n,m} Between n and m occurrences of the preceding element
• \d any digit
• \D any non-digit
• \w any word character (alphanumeric + underscore)
• \W any non-word character
• \s Matches any whitespace character
• \S Matches any non-whitespace character
• \ escape character, e.g., İf you want to find . (which is a special character) in your string, you need to do this \.

By combining these, you can create highly complicated pattern match/extraction functions with Regex.

Examples

1. \^[a-z_]+\.com$\ will match .com domains

   • [a-z_] means characters from a to z and underscore

   • + means at least one of them

   • \. means period (.)

   • com is for just com

   • ^ and $ is for searching from the start of the string to the end of each line

2. ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$ will match emails

• ^ Asserts the start of the string.
• [a-zA-Z0-9._%+-]+ Matches one or more characters that can be:
  • Letters (a-z, A-Z)
  • Digits (0-9)
  • Underscores (_)
  • Dots (.)
  • Percent signs (%)
  • Plus signs (+)
  • Hyphens (-)
• @ Matches the "@" symbol which is mandatory in all email addresses.
• [a-zA-Z0-9.-]+ Matches one or more characters for the domain name, allowing:
  • Letters (a-z, A-Z)
  • Digits (0-9)
  • Hyphens (-)
  • Dots (.)
• \. Matches a literal dot (.) separating the domain name from the top-level domain (TLD).
• [a-zA-Z]{2,} Matches the top-level domain (TLD) consisting of at least two letters (e.g., .com, .org).
• $ Asserts the end of the string.

If you have any questions, here is my Instagram @emrekanbay.en