root@OpenWrt:~# cat test.sh
for tmp in 1 2 3 4 5 6 7 8 9 10; do
        [ -z foo ]
done
root@OpenWrt:~# time sh test.sh
real    0m 0.26s
user    0m 0.13s
sys     0m 0.12s
root@OpenWrt:~# wc -l < /usr/lib/webif/validate.awk 
    116
root@OpenWrt:~# time echo 'ip|foo|bar||192.168.1.1' | awk -f /usr/lib/webif/validate.awk 
real    0m 0.04s
user    0m 0.00s
sys     0m 0.02s
foo="192.168.1.1";
ERROR="";