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Alex Spinov
Alex Spinov

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Regex Cheatsheet That Actually Makes Sense (With Real Examples)

#beginners #python #javascript #tutorial

I've been writing regex for 8 years. I still google basic patterns.

The problem isn't regex itself — it's that every cheatsheet shows you the theory without the practice. Here's the one I wish existed when I started.

The Essentials (90% of what you'll ever need)

Pattern Means Example Matches
. Any character h.t hat, hit, hot
\d Any digit \d{3} 123, 456
\w Letter, digit, _ \w+ hello, test_1
\s Whitespace \s+ spaces, tabs
^ Start of string ^Hello "Hello world"
$ End of string end$ "the end"
* 0 or more ab*c ac, abc, abbc
+ 1 or more ab+c abc, abbc
? 0 or 1 colou?r color, colour
{n} Exactly n \d{4} 2026
{n,m} Between n and m \d{2,4} 12, 123, 1234
[abc] a, b, or c [aeiou] vowels
[^abc] Not a, b, or c [^0-9] non-digits
(...) Capture group (\d+)px captures "12" from "12px"
`\ ` Or `cat\

Real-World Patterns (Copy-Paste Ready)

Email Validation

{% raw %}

import re

# Simple but effective
pattern = r'^[\w.+-]+@[\w-]+\.[\w.]+$'

re.match(pattern, 'user@example.com')   # ✓
re.match(pattern, 'user@.com')          # ✗
re.match(pattern, 'user+tag@gmail.com') # ✓
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URL Extraction 

pattern = r'https?://[\w.-]+(?:/[\w./-]*)?'

text = 'Visit https://example.com/path and http://test.org'
urls = re.findall(pattern, text)
# ['https://example.com/path', 'http://test.org']
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Phone Numbers (US) 

pattern = r'\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}'

# Matches: (555) 123-4567, 555-123-4567, 5551234567, 555.123.4567
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IP Address 

pattern = r'\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b'

text = 'Server 192.168.1.1 responded, backup at 10.0.0.1'
ips = re.findall(pattern, text)
# ['192.168.1.1', '10.0.0.1']
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HTML Tag Content 

pattern = r'<(\w+)[^>]*>(.*?)</\1>'

html = '<div class="main">Hello World</div>'
match = re.search(pattern, html)
# group(1) = 'div', group(2) = 'Hello World'
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Date (Multiple Formats) 

# YYYY-MM-DD or DD/MM/YYYY
pattern = r'\d{4}-\d{2}-\d{2}|\d{2}/\d{2}/\d{4}'

text = 'Created 2026-03-25, updated 25/03/2026'
dates = re.findall(pattern, text)
# ['2026-03-25', '25/03/2026']
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Password Strength 

# At least 8 chars, 1 upper, 1 lower, 1 digit, 1 special
pattern = r'^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$'
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CSV Line Parser 

# Handle quoted fields with commas inside
pattern = r'"([^"]*)"|([^,]+)'

line = 'John,"Smith, Jr.",42,"New York, NY"'
fields = [g1 or g2 for g1, g2 in re.findall(pattern, line)]
# ['John', 'Smith, Jr.', '42', 'New York, NY']
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Python vs JavaScript Differences

Feature Python JavaScript
Named groups (?P<name>...) (?<name>...)
Non-greedy .*? .*?
Flags re.IGNORECASE /pattern/i
Multiline re.MULTILINE /pattern/m
Find all re.findall() str.matchAll()
Replace re.sub() str.replace()

Pro Tips

  1. Always use raw strings in Python: r'\d+' not '\\d+'
  2. Be lazy, not greedy: .*? instead of .* when possible
  3. Use named groups for readability: (?P<year>\d{4})
  4. Test at regex101.com — it explains your pattern step by step
  5. Don't parse HTML with regex (use BeautifulSoup/lxml instead)

Resources

What's the most complex regex you've ever written? Or the one that took you the longest to debug? 👇

Tutorials at dev.to/0012303

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