Something

system('ping -c1 -t1 192.168.0.11', $retval);
echo $retval; 
$findme = "56";
$pos = strstr($retval, $findme);
echo "<p>";
echo "pos=" .$pos;
echo "<p>";
if ($pos === false) { echo "false"; }
else { echo "true"; }

-------------------------------------------------------------------------

PING 192.168.0.11 (192.168.0.11): 56 data bytes
64 bytes from 192.168.0.11: icmp_seq=0 ttl=128 time=0.439 ms

--- 192.168.0.11 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.439/0.439/0.439/0.000 ms
0

pos=

false