Preg_match for pattern matching in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the preg_match function do in PHP?

preg_match checks if a string matches a specific pattern defined by a regular expression. It returns 1 if a match is found, 0 if not, and false on error.

beginner

How do you write a basic preg_match call to check if the string "hello123" contains digits?

preg_match('/\d+/', 'hello123');

This checks if there is one or more digits anywhere in the string.

beginner

What is the purpose of the delimiters (like /) in a preg_match pattern?

Delimiters mark the start and end of the regular expression pattern. They tell PHP where the pattern begins and ends.

intermediate

How can you capture the matched part of a string using preg_match?

Use a third argument as an array to store matches. For example:

preg_match('/(\d+)/', 'abc123', $matches);
echo $matches[1]; // outputs '123'

beginner

What does preg_match return if the pattern is not found in the string?

It returns 0, which means no match was found.

What does preg_match('/abc/', 'abcdef') return?

A false

B 0

C 1

D null

It returns 1 because the pattern 'abc' is found at the start of the string.

Which symbol is commonly used as a delimiter in preg_match patterns?

A All of the above

B #

C /

D ~

All these symbols can be used as delimiters in PHP regular expressions.

How do you store the matched substring from preg_match?

A By passing a second argument as an array

B You cannot store matches

C By passing a fourth argument as a string

D By passing a third argument as an array

The second argument is the string to search, the third argument is an array to store matches.

What does the pattern /\d+/ match?

A Any special character

B One or more digits

C Any whitespace

D One or more letters

\d matches digits, + means one or more times.

If preg_match returns false, what does it mean?

A An error occurred

B No match found

C Match found

D Pattern is empty

False means an error happened, like invalid pattern syntax.

Explain how to use preg_match to check if a string contains a specific word and how to get the matched word.

Think about capturing groups and the third argument.

Describe the return values of preg_match and what each means.

There are three possible return values.