探测某一网络ip地址段中哪些ip的主机可以ping通

#!/bin/sh

if [ a$1 = a"" ] ; then
    count0=1
    count1=1
    count2=1
    count3=1
    while [ $count0 -le 255 ]
    do
        date
        while [ $count1 -le 255 ]
        do
            while [ $count2 -le 255 ]
            do
                while [ $count3 -le 255 ]
                do
                    echo "==================================================================="
                    dev="$count0.$count1.$count2.$count3"
                    ping $dev
                    if [ -z "$?" ] ; then
                        echo "Pass: $dev is active!"
                    else
                        echo "Fail: $dev is not active!"
                    fi
                    count3=`expr $count3 + 1`
                done
                count2=`expr $count2 + 1`
            done
            count1=`expr $count1 + 1`
        done
        date
        count0=`expr $count0 + 1`
    done
else
    dev=$1
fi