Executing A UNIX Shell Script

[dpittman36]

Hello,

I am a newbie to the forum.
I have a shell script in UNIX and I can run by piping:
echo 1| ctracer

In PHP I am trying to run script: (but it does not work)
$cmd = '1 | ctracer';
echo "<pre>".shell_exec('echo $cmd')."</pre>";

What am I doing wrong in php?

Thanks