Recruitment Grow your team. Employer Branding Reach the talent.

LIVE COHORT PROGRAM Technology Schools Explore industry-focused tech schools. INTERACTIVE LEARNING PLATFORM Coderspace Pro: Software & Data Specialize in Python and data with hands-on courses.

Events

FOR TALENT

Blog Explore the trends. Codebrew Stay up to date. Interview Questions Get prepared. Coder Glossary Learn the concepts. Portfolio Showcase your projects. University Preferences Make the right choice. Roadmap Move forward step by step. Cheat Sheets Look up the shortcuts. Free Software Tools Get a hand. Podcast Listen on the go. Salaries Learn what the market pays. AI Tools Explore AI.

FOR COMPANIES

Blog HR trends. Codebrew Stay in the loop. HR Webinars Hear from the experts. Case Studies Get inspired. E-book Download the guides. HR Calculation Tools Calculate with ease.

Recruitment Grow your team. Employer Branding Reach the talent.

Regex Cheat Sheets

This Regex cheat sheet includes symbols, ranges, grouping, assertions, and sample patterns

Getting Started

// Basic Regex Example

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

A simple regex pattern

// Regex in Code

re.match(r"pattern", string)

Python

// Regex in Code

Python

re.match(r"pattern", string)

JavaScript

string.match(/pattern/)

Java

Pattern.compile("pattern")

Grep

grep -E "pattern" file.txt

Ruby

string =~ /pattern/

PHP

preg_match("/pattern/", $string)

Perl

if ($string =~ /pattern/) { ... }

// Regex Resources

Regex101 regex101.com Regular-Expressions.info regular-expressions.info MDN Regex developer.mozilla.org Regexr regexr.com Pythex pythex.org

Metacharacters

// Common Metacharacters

Any character except newline

Start of string

End of string

Escape special character

Alternation (or)

// Metacharacter Example

^abc$

Using metacharacters

// Alternation

a|b

Matches a or b

cat|dog

Matches cat or dog

Character Classes

// Character Classes

[abc]

a, b, or c

[^abc]

Not a, b, or c

[a-z]

a to z

[A-Z]

A to Z

[0-9]

0 to 9

[a-zA-Z0-9_]

Alphanumeric or underscore

// Predefined Classes

Digit (0-9)

Non-digit

Word character (a-z, A-Z, 0-9, _)

Non-word character

Whitespace

Non-whitespace

// Character Class Example

[A-Za-z0-9_]+

Using character classes

Quantifiers

// Quantifiers

0 or more

1 or more

0 or 1

{n}

Exactly n

{n,}

n or more

{n,m}

Between n and m

// Greedy vs Lazy

Greedy (as much as possible)

Lazy (as little as possible)

Greedy

Lazy

// Quantifier Example

a{2,4}

Using quantifiers

Groups & Capturing

// Grouping & Capturing

(...)

Capture group

(?:...)

Non-capturing group

(?P<name>...)

Named group (Python)

\1, \2, ...

Backreference

// Backreference Examples

(\w+)

Matches repeated word (e.g. "word word")

(\d{2})-(\d{2})-\2

Matches 12-34-34

// Grouping Example

(\d{3})-(\d{2})-(\d{4})

Using groups and backreferences

Assertions

// Assertions

Start of string

End of string

Word boundary

(?=...)

Positive lookahead

(?!...)

Negative lookahead

(?<=...)

Positive lookbehind

(?<!...)

Negative lookbehind

// Lookaround Examples

(?<=@)\w+

Word after @

\d+(?=px)

Number before px

(?<!-)foo

foo not preceded by -

// Assertion Example

\bword\b

Using lookahead and lookbehind

Unicode & Multiline

// Unicode Classes

\uXXXX

Unicode code point

\p{L}

Any kind of letter (Unicode)

\p{N}

Any kind of numeric character

// Multiline Mode

Start of line (with m flag)

End of line (with m flag)

// Unicode Example

\p{L}+

Matching Unicode letters

Substitution & Replace

// Substitution Example

re.sub(r"\\d", "X", "abc123")  # abcXXX

Replace digits with X

// Replacement Patterns

First group

\g<name>

Named group

First group (JS/Java)

// Replace Example

re.sub(r"(\w+) (\w+)", r"\\2 \\1", "hello world")  # world hello

Swap words order

Flags & Modifiers

// Common Flags

Ignore case

Global search

Multiline

Dot matches newline

Verbose (Python)

Unicode (JS)

// Flag Usage

/pattern/gi

JS: global, ignore case

re.I

Python: ignore case

Pattern.CASE_INSENSITIVE

Java: ignore case

// Flag Example

/pattern/gi

Using flags in regex

Escaping & Literals

// Escaping Special Characters

\.

Escape with \

// Escapable Characters

Dot

Asterisk

Plus

Question mark

Left parenthesis

Right parenthesis

Left bracket

Right bracket

Left brace

Right brace

Caret

Dollar

Pipe

Slash

// Literal Example

\$\^\*\+

Match literal characters

Practical Examples

// Email Validation

[\w.-]+@[\w.-]+\\.[a-zA-Z]{2,6}

Regex for email addresses

// URL Validation

https?://[\w./-]+

Regex for URLs

// Phone Number

\(\d{3}\) \d{3}-\d{4}

US phone number

// Date (YYYY-MM-DD)

\d{4}-\d{2}-\d{2}

ISO date format

Common Mistakes & Debugging

// Common Mistakes

Unescaped metacharacters

Always escape . * + ? ( ) [ ] { } ^ $ | \

Greedy matching

Use lazy quantifiers if needed

Anchors

Remember ^ and $ match start/end of string, not line unless multiline

// Debugging Tools

Regex101 Debugger regex101.com Regexr Debugger regexr.com

// Performance Tips

Avoid catastrophic backtracking

Prefer atomic groups or possessive quantifiers

Test on large data

Performance can degrade quickly

Platform Differences & Security

// Platform Differences

Python

Supports named groups, verbose mode

JavaScript

No lookbehind before ES2018

Java

Possessive quantifiers, named groups

PCRE

Very rich feature set

// Security Tips

User input

Never trust user regex input

Denial of Service

Watch for catastrophic backtracking

// Platform Docs

Python re docs.python.org JavaScript RegExp developer.mozilla.org Java Pattern docs.oracle.com

Best Practices & Tips

// Best Practices

Test patterns

Use online tools to test regex

Use comments

Use verbose mode for complex patterns

Escape properly

Always escape special characters

Keep it simple

Prefer readable patterns

Document

Add comments for complex regex

// Further Reading

Regex101 regex101.com Regular-Expressions.info regular-expressions.info MDN Regex developer.mozilla.org Regexr regexr.com

Land the career of your dreams!

Get inspired, learn, join competitions and grow in your job!