delete-duplicate-iptables-rules.sh

#!/bin/bash

# Delete all duplicate rules
/sbin/service iptables save
/sbin/iptables-save | awk '/^COMMIT$/ { delete x; }; !x[$0]++' > /tmp/iptables.conf
/sbin/iptables -F
/sbin/iptables-restore < /tmp/iptables.conf
/sbin/service iptables save
/sbin/service iptables restart
if [ -f /tmp/iptables.conf ] ; then /bin/rm -f /tmp/iptables.conf ; fi

How about just iptables-save | awk '/^COMMIT$/ { delete x; }; !x[$0]++' | iptables-restore?

Yes, it would be enough. And it is nice to type in console but, as script, I prefer to flush before restore because we are doing a replacement of all rules.