How can I check if an iptables rule already exists?

Question

I need to add a rule to iptables to block connections to a tcp port from the Internet.

Since my script may be called multiple times and there is not a script to delete the rule, I want to check if an iptables rule already exists before inserting it - otherwise there will be a lot of dup rules in the INPUT chain.

How can I check if an iptables rule already exists?

Answer 1

Just list and search for it?

iptables --list | grep $ip

... or however you have the rule specified. If you use grep -q it won't output anything, and you can just check the return value with $?