Shell正则表达式验证IP地址

ifconfig | awk '/inet/{print $2}' | awk -F: '{print $2}' 

CheckIPAddress()       
{
        echo $1 > /tmp/tmpserverip
        echo $1 |grep "^[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}$" > /dev/null
        if [ $? = 1 ];    then
                return 1
        else
                a=$(cut -d. -f1 /tmp/tmpserverip)
                b=$(cut -d. -f2 /tmp/tmpserverip)
                c=$(cut -d. -f3 /tmp/tmpserverip)
                d=$(cut -d. -f4 /tmp/tmpserverip)
   
                for loop in $a $b $c $d
                do
                        if [ $loop -ge 255 ] || [ $loop -le 0 ]; then
                                return 2
                        fi
                done
        fi
           
        return 0
}

grep "^([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.$"

echo -n 'Enter the Server-ip:'
        read BISSip
        echo $BISSip > /tmp/tmpserverip
        echo $BISSip|grep "^[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}$" > /dev/null
        num=$?
        if [ $num = 1 ]
        then
                echo error ip,please enter correct
      
        else
  {
        a=$(cut -d. -f1 /tmp/tmpserverip)
        b=$(cut -d. -f2 /tmp/tmpserverip)
        c=$(cut -d. -f3 /tmp/tmpserverip)
        d=$(cut -d. -f4 /tmp/tmpserverip)
  
        {
                if [ $a -ge 255 ]||[ $a -le 0 ]
                then
                        echo a:error ip
                else
                        echo 1 > /tmp/jack
                 fi
        }
  
        {
                if [ $b -ge 255 ]||[ $b -lt 0 ]
                then
                        echo b:error ip
        else
                        echo 1 >>/tmp/jack
        fi
  
        }
   
        { if [ $c -ge 255 ]||[ $c -lt 0 ]
                 then
                         echo c:error ip
                else
                        echo 1 >>/tmp/jack
                    fi
         }
  
         { if [ $d -ge 255 ]||[ $d -le 0 ]
                then
                        echo d:error ip
                else
                        echo 1 >> /tmp/jack
                fi
         }