Regex Practical Guide

Regex clicks once you stop memorizing patterns and start thinking in pieces.

Core syntax

Pattern	Meaning
`.`	any character except newline
`*`	0 or more
`+`	1 or more
`?`	0 or 1 (optional)
`^`	start of string
`$`	end of string
`[abc]`	character class
`[^abc]`	negated class
`\d`	digit `[0-9]`
`\w`	word char `[a-zA-Z0-9_]`
`\s`	whitespace

Useful patterns

# Email (basic)
[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}

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

# IPv4
\b\d{1,3}(\.\d{1,3}){3}\b

# Date YYYY-MM-DD
\d{4}-\d{2}-\d{2}

# Hex color
#[0-9a-fA-F]{6}

Python example

import re

text = "Contact: hello@example.com or support@test.org"
emails = re.findall(r'[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}', text)
print(emails)  # ['hello@example.com', 'support@test.org']

Tip

Use regex101.com to test interactively. Always test on real data before deploying.