execute awk linux command with php -

i want execute awk linux command php , command

 mpstat | awk '$12 ~ /[0-9.]+/ { print 100 - $12 }'

i eexcute wiht linux works , gave me cpu usage in presentage, try in php:

$cmd= system("mpstat | awk '$12 ~ /[0-9.]+/ { print 100 - $12 }'",$retval); echo $retval;

and

$cmd= passthru(" mpstat | awk '$12 ~ /[0-9.]+/ { print 100 - $12 }'",$retval);  echo $retval;

its not working , searches put awk command in variable execute :

$var='$12 ~ /[0-9.]+/ { print 100 - $12 }'; $cmd=  exec('mpstat | awk"$var"',$retval); echo $retval;

and output array

i wrote short program illustrate difference:

<?php $cmd = system("ls", $retval); echo "cmd: " . $cmd . "\n"; echo "retval: " . $retval . "\n"; ?>

output:

prog.php cmd: prog.php retval: 0

Three