Preg_match for pattern matching in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this preg_match code?

Consider the following PHP code snippet using preg_match. What will it output?

PHP

<?php
$pattern = '/^hello/';
$subject = 'hello world';
if (preg_match($pattern, $subject)) {
    echo 'Match found';
} else {
    echo 'No match';
}
?>

A Match foundhello

B No match

C Warning: preg_match(): Unknown modifier '^'

D Match found

💡 Hint

Check if the pattern matches the start of the string.

The pattern /^hello/ matches strings starting with 'hello'. The subject string starts with 'hello', so preg_match returns true and 'Match found' is printed.

❓ Predict Output

intermediate

What does this preg_match return?

What will be the output of this PHP code?

PHP

<?php
$pattern = '/\d+/';
$subject = 'abc123xyz';
if (preg_match($pattern, $subject, $matches)) {
    echo $matches[0];
} else {
    echo 'No digits';
}
?>

A Warning: preg_match(): Unknown modifier '\'

B 123

C No digits

D abc123xyz

💡 Hint

Look for digits in the string.

The pattern /\d+/ matches one or more digits. The subject contains '123', so preg_match finds it and stores it in $matches[0].

❓ Predict Output

advanced

What is the output of this preg_match with capturing groups?

Analyze this PHP code and determine its output.

PHP

<?php
$pattern = '/(foo)(bar)?/';
$subject = 'foobar';
if (preg_match($pattern, $subject, $matches)) {
    echo count($matches);
} else {
    echo 'No match';
}
?>

A 3

B 2

C 1

D No match

💡 Hint

Count how many capturing groups matched.

The pattern has two capturing groups: (foo) and (bar)?. The subject 'foobar' matches both groups, so $matches has 3 elements: full match, group 1, and group 2.

❓ Predict Output

advanced

What error does this preg_match code produce?

What error will this PHP code produce when run?

PHP

<?php
$pattern = '/[a-z/';
$subject = 'abc';
preg_match($pattern, $subject);
?>

A Warning: preg_match(): Compilation failed: missing terminating ] for character class

B No output, runs fine

C Fatal error: Uncaught Error: Call to undefined function preg_match()

D Parse error: syntax error, unexpected '/'

💡 Hint

Check the regex pattern syntax carefully.

The pattern /[a-z/ is missing the closing bracket for the character class, causing a compilation error in preg_match.

🧠 Conceptual

expert

How many matches does preg_match find here?

Given this PHP code, how many matches will preg_match find?

PHP

<?php
$pattern = '/cat/';
$subject = 'cat concatenate catapult';
$result = preg_match($pattern, $subject, $matches);
echo $result;
?>

A 0

B 2

C 1

D 3

💡 Hint

Remember that preg_match finds only the first match.

preg_match returns 1 if it finds at least one match, but it only finds the first match, so the result is 1.