Regex Basics Cheat Sheet

Learn fundamental regular expression patterns and metacharacters.

What this cheat sheet is for

This regex basics 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.

Literal Characters

Match exact characters.

abc     # Matches "abc"
123     # Matches "123"
hello   # Matches "hello"

Metacharacters

Special characters with meaning.

.       # Any character except newline
\d      # Any digit [0-9]
\D      # Any non-digit
\w      # Word character [a-zA-Z0-9_]
\W      # Non-word character
\s      # Whitespace character
\S      # Non-whitespace character

Escaping Special Characters

Use backslash to match literals.

\.      # Matches literal period
\*      # Matches literal asterisk
\?      # Matches literal question mark
\\      # Matches literal backslash
\[      # Matches literal bracket

Alternation

Match one pattern or another.

cat|dog           # Matches "cat" or "dog"
(red|blue|green)  # Matches any color
yes|no            # Matches "yes" or "no"

Dot Metacharacter

Match any character.

a.c     # Matches "abc", "a1c", "a@c"
...     # Matches any 3 characters
h.t     # Matches "hat", "hot", "h9t"

Case Sensitivity

Regex is case-sensitive by default.

cat     # Matches "cat" but not "Cat"
# Use flag for case-insensitive: /cat/i

Literal Strings

Match exact sequences.

hello world   # Matches "hello world"
test123       # Matches "test123"

Common Examples

Practical regex patterns.

\d\d\d-\d\d\d\d    # Phone: 123-4567
\w+@\w+\.com       # Simple email
https?://.*        # URL starting with http/https

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