从php Raspberry Pi运行.sh文件

I am trying to run a .sh file from within a php file in Apache2 html folder. I have installed Apache2 and PHP on the Pi. I have given permission to www-data to execute the file. The .sh file excutes from the terminal.

<?php 

if (isset($_GET['led1'])) { 
    if($_GET['led1'] == 1) {
        echo "**RESPONSE**";
        echo "  ";
        exec('sh /home/pi/AlarmCode/StartAlarm.sh');
        echo "**POSITIVE**";
    } else {
        exec("gpio write 0 0");
    }
}

?>

I can call the web server and get a response from my pc. Any help would be greatly appreciated.

I have also tried echo shell_exe

Thanks in advance