使用PHP运行bash脚本

I am working on little project. Task is get ip or address from input field and then run ping command for that ip and finally print result in the webpage.

I have written code:

<FORM ACTION="pingIp.php">
    Enter Host: <INPUT name="host">
    <INPUT TYPE=SUBMIT VALUE="Submit">
</FORM>

<div class="results"></div>

I don't know how to run ping command and retrieve results on webpage. Can you please give little php code as an example?