Find PHP legacy functions that are not in use in source code

removeable_functions.php

<?php
/**
 * Find unused functions in a legacy project that are safe to remove
 *
 * @author: Vijay Mahrra <[email protected]>
 */
$folder = 'legacy';
$cmd = "grep -aRi 'function ' $folder/*";
exec($cmd, $results);
$removeable = [];

foreach ($results as $k => $line) {
    if (preg_match('/^[\s]*(?<filename>[^:]+):[\s]*function[\s]*(?<function>[^\(]+)\(*/', $line, $matches)) {
        $cmd = "grep -laRi '" . $matches['function'] . "' $folder/* | grep -v " . $matches['filename'];
        $matching = [];
        $found = exec($cmd, $matching);
        if (empty($matching)) {
            $used = [];
            $cmd = "grep -i '" . $matches['function'] . "' " . $matches['filename'];
            $check = exec($cmd, $used);
            if (!empty($used) && count($used) == 1) {
                $removable[$matches['filename']][] = $matches['function'];
            }
        }
    }
}

print_r($removable);