iptables port block

#!/bin/bash

IPT=/sbin/iptables

# MD5 fname="`date | md5sum | cut -d ' ' -f 1`.tmp"

function ln_join {
    items="$1"
    delim="$2"
    joined=""
    for i in $items; do
        joined=`[ -z "$joined" ] && echo "$i" || echo "$joined$delim$i"`
    done
    echo $joined
}

function usage {
    echo "Usge: hadoop-mask [ -l | -u ]"
    exit 1
}
[ $# -ne 0 ] && [ "$1" != "-u" ] && [ "$1" != "-l" ] && usage && exit 1


raw_ports=`netstat -plten | grep java | awk '{print $4}' | cut -d : -f 2`
ports=`ln_join "$raw_ports" ","`
echo \"$ports\"
[ -z "$ports" ] && echo "No ports open! Exitting ..." && exit 1

if [ "$1" == '-l' ]; then                   # list if -l
    netstat -plten | grep java && echo $ports && exit 0
fi

cmd="INPUT -p tcp -m tcp ! -s localhost -m multiport --dports $ports -j DROP"
[ "$1" == "-u" ] && $IPT -D $cmd && exit 0  # unmask if -u
$IPT -A $cmd                                # mask if -m