您的两个选项是DirectoryIterator或glob：

$string = 'something';

$dir = new DirectoryIterator('some_dir');
foreach ($dir as $file) {
    $content = file_get_contents($file->getPathname());
    if (strpos($content, $string) !== false) {
        // Bingo
    }
}

$dir = 'some_dir';
foreach (glob("$dir/*") as $file) {
    $content = file_get_contents("$dir/$file");
    if (strpos($content, $string) !== false) {
        // Bingo
    }
}