REGEX CHEAT SHEET — ADVANCED PATTERNS & EXAMPLES
Complete regex reference with cheat sheet, lookaheads, lookbehinds, named groups, and 20+ real-world patterns you can copy and use.
📖 15 min read · Dev · Free guide by 67fresh.com
In this guide
Cheat SheetLookaheads & LookbehindsNamed Groups20+ Real-World PatternsFlags & ModesPerformance Tips
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Regex Cheat Sheet

Character Classes

. any character (except newline) · \d digit [0-9] · \D non-digit · \w word char [a-zA-Z0-9_] · \W non-word · \s whitespace · \S non-whitespace · \b word boundary · \B non-boundary

Quantifiers

* 0 or more · + 1 or more · ? 0 or 1 · {3} exactly 3 · {2,5} 2 to 5 · {3,} 3 or more · Add ? after any quantifier for lazy (non-greedy) matching: .*? matches as few characters as possible.

Anchors

^ start of string · $ end of string · \b word boundary · \A absolute start · \Z absolute end

Groups & References

(abc) capture group · (?:abc) non-capturing group · (?P<name>abc) named group · \1 backreference to group 1 · (a|b) alternation

Lookaheads & Lookbehinds

Lookarounds assert that something exists before or after your match without including it in the match result. They are zero-width — they check but don't consume characters.

(?=abc) — positive lookahead: matches if "abc" follows. Example: \d+(?= dollars) matches "100" in "100 dollars" but not the word "dollars".

(?!abc) — negative lookahead: matches if "abc" does NOT follow. Example: \d+(?! dollars) matches numbers NOT followed by "dollars".

(?<=abc) — positive lookbehind: matches if "abc" precedes. Example: (?<=\$)\d+ matches "100" in "$100" but not in "100 items".

(? — negative lookbehind: matches if "abc" does NOT precede.

Password validation example using lookaheads:
^(?=.*[A-Z])(?=.*[a-z])(?=.*\d)(?=.*[!@#$%]).{8,}$
This checks that a string has at least one uppercase, one lowercase, one digit, one special character, and is 8+ characters — all without consuming any characters.

Named Groups

Named groups make complex patterns readable and maintainable:

(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})

This matches dates like "2026-04-28" and captures year, month, and day as named variables you can reference in code.

20+ Real-World Patterns

Email Validation

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}

URL Matching

https?:\/\/[\w.-]+\.[a-z]{2,}[\/\w.?&=-]*

US Phone Numbers

\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}

Matches: (555) 123-4567, 555-123-4567, 5551234567, 555.123.4567

IP Address (IPv4)

\b(?:\d{1,3}\.){3}\d{1,3}\b

Date (MM/DD/YYYY)

(?:0[1-9]|1[0-2])\/(?:0[1-9]|[12]\d|3[01])\/\d{4}

ISO Date (YYYY-MM-DD)

\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])

Time (12-hour)

(?:1[0-2]|0?[1-9]):[0-5]\d\s?(?:AM|PM|am|pm)

Hex Color Code

#(?:[0-9a-fA-F]{3}){1,2}\b

HTML Tag

<([a-z][a-z0-9]*)\b[^>]*>(.*?)<\/\1>

Credit Card Number (basic)

\b\d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4}\b

US ZIP Code

\b\d{5}(?:-\d{4})?\b

SSN Format

\b\d{3}-\d{2}-\d{4}\b

Strong Password Check

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[!@#$%^&*]).{12,}$

Remove HTML Tags

<[^>]*>

Extract Domain from URL

https?:\/\/(?:www\.)?([^\/?#]+)

Trim Whitespace

^\s+|\s+$

Duplicate Words

\b(\w+)\s+\1\b

CSV Value (handling quoted fields)

"([^"]*(?:""[^"]*)*)"|([^,]+)

Markdown Bold

\*\*([^*]+)\*\*

YouTube Video ID

(?:youtube\.com\/watch\?v=|youtu\.be\/)([a-zA-Z0-9_-]{11})

Flags & Modes

g — global (find all matches, not just first) · i — case-insensitive · m — multiline (^ and $ match line boundaries) · s — dotall (. matches newlines too) · u — unicode support · x — extended (allows whitespace and comments in pattern)

Performance Tips