Regex Cheat Sheet

Here's a quick regular expressions cheat sheet with examples to get started:

1. Basic Characters:

   • .: Matches any character except newline. Example: a.c matches abc, adc.
   • \w: Matches a word character (letters, digits, _). Example: \w+ matches hello123.
   • \d: Matches any digit (0-9). Example: \d+ matches 123.
   • \s: Matches whitespace (space, tab, newline). Example: \s+ matches spaces in hello world.

2. Anchors:

   • ^: Matches the start of a string. Example: ^hello matches hello world.
   • $: Matches the end of a string. Example: world$ matches hello world.

3. Quantifiers:

   • *: Matches 0 or more occurrences. Example: a* matches aaa, a, or nothing.
   • +: Matches 1 or more occurrences. Example: a+ matches aaa, a, but not empty.
   • {n}: Matches exactly n occurrences. Example: a{3} matches aaa.

4. Groups:

   • (abc): Captures abc as a group.
   • (?:abc): Matches abc without capturing.
   • (?<name>abc): Captures abc and names it name.

Regular expressions (regex) are powerful tools for text matching and manipulation. This regex cheat sheet is a quick start regex tutorial, helping you understand regex patterns, regex syntax, and some practical applications. Whether you need a Python regex, Java regex, or JavaScript regex, this guide is a definite beginner must. Use the flavor filter to check compatibility and help you save time before pulling your hair out wondering why \w does not work in your Bash Script or why \p{Devanagari} is not working in your JavaScript Regex. I have also provided compatibility in table form later on in the page.

Regex Features and Examples

Character Classes

"John.Doe@techearl.com, 123-456-7890, 2024-01-15"

Anchors and Boundaries

"SuperHero saves the day! Not so super villain"

Quantifiers

Groups and Capturing

Lookaheads and Lookbehinds

Flags and Modifiers

PCRE Control Verbs

Control verbs are advanced features specific to PCRE (Perl-Compatible Regular Expressions). They allow you to manipulate the regex engine's backtracking and matching behavior directly, providing a level of control unavailable in most other regex engines. These verbs can optimize performance, enforce logic, or debug complex patterns by altering how the engine handles matches and failures.

Below is a brief introduction to each control verb and its function.

These verbs provide a high degree of control over how the regex engine processes and evaluates patterns, making them powerful tools for optimizing regex performance and logic in PCRE.

Advanced Examples

Validate an Email Address

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

Matches: user@example.com, hello.world@domain.org.

Match a Phone Number

^\+?\d{1,3}?[-.\s]?\(?\d{1,4}?\)?[-.\s]?\d{1,4}[-.\s]?\d{1,9}$

Matches: +1-800-555-5555, (800) 555-5555.

Extract URLs

https?:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,}(\/\S*)?

Matches: https://example.com, http://domain.org/path.

Replace Multiple Spaces with One

\s{2,}

Replace with a single space to clean up text like "Hello world" into "Hello world".

Find Duplicate Words

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

Matches: the the, hello hello.

Zero Punctuation and Regex in Action

Regex excels at handling edge cases, such as matching patterns without punctuation. For example, this regex ensures no punctuation in a string:

^[\w\s]+$

Matches: Hello World but not Hello, World!.

Tools for Testing and Debugging Regex

• Regex101: Interactive online regex tester.
• RegExr: Explore and test regular expressions visually.
• Regex Cheat Sheets: Downloadable PDFs for quick reference.