即使在所有权限之后，shell_exec也无法在php中工作

I have been trying to execute a shell script that executes a perl program and i am doing that using the shell_exec() in php.

I have given all the permissions to the folders as well as the executables. Also, shell_exec() is not disabled in the php.ini. I have even tried using the 2>&1 after the command. Kindly help.

Following is the code.

<?php
if(isset($_POST['EI']) && isset($_POST['OP']) && isset($_POST['GC']) && isset($_POST['PA']) && isset($_POST['HT']) && isset($_POST['AB'])) {
    $data = 'Option entered by user  :'.$_POST['OP'] . "
" . 'The Threshold for GC is :'.$_POST['GC'] . "
" . 'The Threshold for PA is :'.$_POST['PA'] . "
" . 'The Threshold for HT is :'.$_POST['HT'] . "
" . 'The Threshold for AB is :'.$_POST['AB'] . "
" . 'The email id of the user is :'.$_POST['EI'] . "
";
    $ret = file_put_contents('/..path../out.txt', $data);

    if($ret === false) {
        die('There was an error writing this file');
    } else {
        echo "$ret bytes written to file";
    }
} else {
    die('no post data to process');
}
$output=shell_exec("./testing.sh");
?>