Regex Cheat Sheet - Regular Expressions Tutorial

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 start of each line in string

• $ means end of each line in string

• () groups spesific pattern

• (?:) means this pattern will match in string BUT will not return it. Eg. 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, eg. [abc] will macth a or b or c. Ranges are supported too [a-c] will match 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, eg. İf you want to find . (which is a special character) in your string, you need to do this \.

With 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 start of strin to 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.

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