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Regular Expressions (Regex) Examples Cheatsheet

A comprehensive cheat sheet providing practical examples of regular expressions for various use cases. Master regex with these examples!

Basic Matching

Literal Matching

Pattern:

hello

Matches:

The literal string “hello”.

Example:

 
/hello/ =~ "hello world"
# => 0

Pattern:

world

Matches:

The literal string “world”.

Example:

 
/world/ =~ "hello world"
# => 6

Character Classes

Pattern:

[aeiou]

Matches:

Any single vowel (a, e, i, o, or u).

Example:

 
/[aeiou]/ =~ "hello"
# => 1

Pattern:

[0-9]

Matches:

Any single digit (0 to 9).

Example:

 
/[0-9]/ =~ "abc123def"
# => 3

Anchors

Pattern:

^hello

Matches:

“hello” only at the beginning of the string.

Example:

 
/^hello/ =~ "hello world"
# => 0
/^hello/ =~ "world hello"
# => nil

Pattern:

world$

Matches:

“world” only at the end of the string.

Example:

 
/world$/ =~ "hello world"
# => 6
/world$/ =~ "world hello"
# => nil

Quantifiers

Asterisk (*)

Pattern:

a*

Matches:

Zero or more occurrences of “a”.

Example:

 
/a*/ =~ "bbbbb"
# => 0 (matches empty string at the beginning)
/a*/ =~ "aaaaab"
# => 0

Plus (+)

Pattern:

a+

Matches:

One or more occurrences of “a”.

Example:

 
/a+/ =~ "bbbbb"
# => nil (no match)
/a+/ =~ "aaaaab"
# => 0

Question Mark (?)

Pattern:

a?

Matches:

Zero or one occurrence of “a”.

Example:

 
/a?/ =~ "bbbbb"
# => 0 (matches empty string at the beginning)
/a?/ =~ "aaaaab"
# => 0

Curly Braces ({})

Pattern:

a{3}

Matches:

Exactly three occurrences of “a”.

Example:

 
/a{3}/ =~ "aaab"
# => 0
/a{3}/ =~ "aab"
# => nil

Pattern:

a{2,4}

Matches:

Between two and four occurrences of “a”.

Example:

 
/a{2,4}/ =~ "aaab"
# => 0
/a{2,4}/ =~ "aaaaab"
# => 0
/a{2,4}/ =~ "aab"
# => 0

Special Characters and Escaping

Dot (.)

Pattern:

a.b

Matches:

“a”, followed by any character (except newline), followed by “b”.

Example:

 
/a.b/ =~ "acb"
# => 0
/a.b/ =~ "a\nb"
# => nil

Escaping Special Characters

Pattern:

\.

Matches:

A literal dot character.

Example:

 
/\./ =~ "abc.def"
# => 3

Pattern:

\*

Matches:

A literal asterisk character.

Example:

 
/\*/ =~ "abc*def"
# => 3

Character Classes Shorthand

Pattern:

\d

Matches:

Any digit (0-9).

Example:

 
/\d/ =~ "abc123def"
# => 3

Pattern:

\w

Matches:

Any word character (a-z, A-Z, 0-9, and _).

Example:

 
/\w/ =~ "abc_123"
# => 0

Grouping and Capturing

Basic Grouping

Pattern:

(abc)+

Matches:

One or more occurrences of the group “abc”.

Example:

 
/(abc)+/ =~ "abcabcabc"
# => 0

Capturing Groups

Pattern:

(\d+)-(\d+)-(\d+)

Matches:

A date format like “YYYY-MM-DD”. Captures the year, month, and day in separate groups.

Example:

 
/(\d+)-(\d+)-(\d+)/ =~ "2023-10-26"
# => 0
puts $1 # Output: 2023
puts $2 # Output: 10
puts $3 # Output: 26

Non-Capturing Groups

Pattern:

(?:abc)+

Matches:

One or more occurrences of the group “abc”, but without capturing the group.

Example:

 
/(?:abc)+/ =~ "abcabcabc"
# => 0
puts $1 # Output: nil
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