Parallel PHP Linter

<?php

$directories = ['application', 'library', 'database', ''];

define("CWD", dirname(__FILE__));

echo '<h1>Parallel PHP Linter</h1>';

$time_start = microtime(true);

foreach ($directories as $directory) {
    $path = escapeshellcmd(CWD . DIRECTORY_SEPARATOR . $directory);
    echo "<h2>Checking $path:</h2>";
    $out = [];
    $maxdepth = '';
    if (empty($directory)) {
        $maxdepth = '-maxdepth 1';
    }
    exec("find $path $maxdepth -type f -name '*.php' -print0 | xargs -0 -n1 -P8 sh -c 'php -l -n \"$0\" || exit 1' | (! grep -v 'No syntax errors detected' )", $out, $status);

    if ($status !== 0) {
        echo '<pre>';
        echo join("\n", $out);
        echo '</pre>';
        echo '<span style="color:red"><strong>Failed!</strong></span>' . "\n\n";
    } else {
        echo '<span style="color:green"><strong>OK!</strong></span>' . "\n\n";
    }
}


echo '<p>Total execution time in seconds: ' . (microtime(true) - $time_start) . '</p>';