php-regexHow to use PHP regex lookbehind?

PHP regex lookbehind is a feature of regular expressions that allows you to match a pattern only if it is preceded by another pattern. It is written as (?<=pattern) and is used to match a pattern only if it is preceded by another pattern.

Example code

$string = 'This is a string';
$pattern = '/(?<=This\s)is/';

if (preg_match($pattern, $string)) {
    echo 'Match found';
}

Output example

Match found

Code explanation

• $string = 'This is a string';: This is the string that we are searching in.
• $pattern = '/(?<=This\s)is/';: This is the regular expression pattern. The (?<=This\s) part is the lookbehind assertion, which means that the pattern will only match if it is preceded by the string This.
• if (preg_match($pattern, $string)) {: This is the condition that checks if the pattern matches the string.
• echo 'Match found';: This is the output that will be printed if the pattern matches the string.

Helpful links

• PHP Regex Lookbehind Tutorial
• PHP preg_match() Function

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