<?php
function dua_get_files($path)
{
    $data = array();
    $files = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($path), RecursiveIteratorIterator::SELF_FIRST);

    foreach ($files as $file)
    {
            $ext= strtolower(strrchr($file, "."));
            if($ext==".php") $data[] = strval($file);

    }

    return $data;
}

$searchthis = "eval(";
$matches = array();
$aa = dua_get_files('./');

foreach($aa as $file)
{
    $content = file_get_contents($file);
    if(strpos($content, $searchthis) !== FALSE)
            $matches[] = $file;
}

print_r($matches);