How to ssh to remote server using a private key?

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http://unix.stackexchange.com – I have two servers. Both servers are in CentOS 5.6. I want to SSH from Server 1 to Server 2 using a private key I have (OpenSSH SSH-2 Private Key). I don't know how to do it over unix. But what I did on windows using Putty was to feed my OpenSSH private key to putty-gen and generate a private key in PPK format. However, I would be creating a bash script from server 1 that will execute some commands on server 2 via SSH. How do I SSH to Server 2 using my private key file from Server 1? (HowTos)