Regex recompiled in loop (ARCH7073)

Key php.performance.regex-recompiled-in-loop · Severity info · Category performance

A constant pattern is recompiled by preg_match on every iteration. Define the pattern once outside the loop; PHP reuses it.

Incorrect

<?php
foreach ($lines as $line) {
    if (preg_match('/^\d{4}-\d{2}-\d{2}/', $line)) {
        $dates[] = $line;
    }
}

Correct

<?php
$pattern = '/^\d{4}-\d{2}-\d{2}/';
foreach ($lines as $line) {
    if (preg_match($pattern, $line)) {
        $dates[] = $line;
    }
}

Fix

Hoist constant regex patterns into a variable outside the loop and reuse it inside.