Regex Character Classes Cheat Sheet

Match sets of characters using character classes and ranges.

What this cheat sheet is for

This regex character classes reference helps you complete common developer tasks quickly and avoid repeated trial-and-error when working under deadlines.

When you need a reliable command or pattern during debugging and incident response.
When you are implementing a feature and want a known-good syntax example immediately.
When onboarding teammates and documenting repeatable workflows for daily use.
When reviewing pull requests and verifying that command usage follows best practices.

Character Sets

Match any character in set.

[abc]       # Matches "a", "b", or "c"
[aeiou]     # Matches any vowel
[0-9]       # Matches any digit
[a-z]       # Matches lowercase letter
[A-Z]       # Matches uppercase letter
[a-zA-Z]    # Matches any letter

Ranges

Match character ranges.

[0-9]       # Digits 0 through 9
[a-f]       # Letters a through f
[A-F]       # Letters A through F
[a-z0-9]    # Lowercase letters and digits
[A-Za-z]    # All letters

Negated Classes

Match anything NOT in set.

[^abc]      # Anything except a, b, c
[^0-9]      # Any non-digit
[^a-z]      # Any non-lowercase letter
[^\s]       # Any non-whitespace

Shorthand Classes

Common character classes.

\d          # Digit [0-9]
\D          # Non-digit [^0-9]
\w          # Word char [a-zA-Z0-9_]
\W          # Non-word char
\s          # Whitespace [ \t\n\r\f\v]
\S          # Non-whitespace

Multiple Ranges

Combine multiple ranges.

[a-zA-Z0-9]     # Alphanumeric
[a-z0-9_-]      # Letters, digits, underscore, hyphen
[^a-zA-Z]       # Non-alphabetic

Special Characters in Sets

Most metacharacters are literal in [].

[.]         # Literal period
[*]         # Literal asterisk
[+]         # Literal plus
[?]         # Literal question mark
[\^]        # Literal caret (escaped)

Practical Examples

Real-world character class usage.

[0-9]{3}         # 3 digits
[a-z]+           # One or more lowercase letters
[A-Z][a-z]*      # Capitalized word
[^0-9]+          # Non-numeric characters

Common mistakes / Pitfalls

People often copy a command or pattern without adapting placeholders, which can break production workflows unexpectedly.
It is easy to forget environment-specific differences, so always verify behavior in your shell, runtime, or API gateway before shipping.
Many errors come from skipping small validation steps, so test with realistic sample input before relying on the result.

Last updated: February 2026