PHP多语句执行背景

I have a PHP script that needs to run some background command line calls to create some files in the background. I do not want the user to have to wait until the command line stuff is done before the page loads. I have tried using the answers from other threads on SO and it is not working for me.

Here is what I have tried via exec() and shell_exec() to get it to run in the background:

'{ [multiple commands here] }  &> /dev/null &;

If it is helpful, this is the server info:

uname -or
2.6.39-400.17.1.el6uek.x86_64 GNU/Linux

lsb_release -irc
Distributor ID: OracleServer
Release:    6.4
Codename:   n/a

Maybe this example will help you out. Replace the commands with your commands.

<?php
shell_exec("{ sleep 10; touch /tmp/asdf; } > /dev/null 2>&1 &");