<?php

$string = file_get_contents("sample-file.txt");
$found = false;
$n = 0;
do {

    $found = (strpos($string, 'eval') !== false);

    if ($found) {
        ob_start();
        eval(str_replace("eval", "print", $string));
        $string = ob_get_clean();
    }

    $n++;
} while ($found);

//echo $n;
//print $string;
file_put_contents ("result.php", $string);