Character classes and quantifiers in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a character class in regular expressions?

A character class lets you match any one character from a set of characters. It is written inside square brackets, like <code>[abc]</code>, which matches 'a', 'b', or 'c'.

beginner

What does the quantifier + mean in a regex?

The + quantifier means "one or more" of the preceding element. For example, a+ matches 'a', 'aa', 'aaa', and so on.

intermediate

Explain the difference between * and ? quantifiers.

* means "zero or more" of the preceding element, so it can match nothing or many. ? means "zero or one", so it matches either nothing or exactly one occurrence.

beginner

What does the character class \d match?

\d matches any digit character, which means any number from 0 to 9.

beginner

How do you specify a range of characters in a character class?

You use a hyphen - inside square brackets. For example, [a-z] matches any lowercase letter from 'a' to 'z'.

What does the regex [A-Z]+ match?

A One or more uppercase letters

B One or more lowercase letters

C Any single uppercase letter

D Any single digit

The character class [A-Z] matches any uppercase letter, and + means one or more times.

Which quantifier matches zero or one occurrence of the previous character?

A *

B +

C ?

D {2,}

The ? quantifier matches zero or one occurrence.

What does \w match in PHP regex?

A Any whitespace character

B Any word character (letters, digits, underscore)

C Any digit

D Any special character

\w matches letters, digits, and underscore characters.

How would you match exactly 3 digits in a row?

A \d{3}

B \d+

C \d*

D \d?

The quantifier {3} means exactly 3 occurrences.

What does the regex [a-zA-Z0-9] match?

A Any letter or digit

B Only lowercase letters

C Only uppercase letters

D Only digits

The character class includes lowercase letters, uppercase letters, and digits.

Describe how character classes and quantifiers work together in regular expressions.

Think about how you pick letters and how many times they repeat.

Explain the difference between the quantifiers *, +, and ? with examples.

Focus on how many times the character can appear.