Recently I did an automation task involving the automated generation of ppk files when ssh-keygen is run. I also wanted to generate ppk files for the existing keys on this machine.

The command I ended up using, to generate a ppk file for every /home/*/.ssh/id_rsa file was:

set -x;for user in $(find /home/*/.ssh -name id_rsa -type f);do puttygen ${user} --ppk-param version=2 -o ${user}.ppk;chown $(ls -l ${user} | awk '{print $3":"$4}') ${user}.ppk;chmod 600 ${user}.ppk;done;set +x