shell script to replace authorized_keys in an EC2 instance

cycle-pem.sh

#!/bin/bash

# this script should be used in a dir with both the old
# private key and the new public key

oldpem=$1
user=$2
newpub=$3
newpem=$4

# fill in any hosts you want to use
# each host should require the same user, like 'ubuntu' or 'centos'
HOSTS="localhost"

[ $# -ne 4 ] && { echo "Usage: $0 <old_privkey.pem> <user> <new_pubkey> <new_privkey.pem>"; exit 1; }

for HOSTNAME in ${HOSTS} ; do
        scp -i $oldpem $newpub $user@$HOSTNAME:$newpub
        ssh -i $oldpem $user@$HOSTNAME "cat $newpub >> .ssh/authorized_keys"
        ssh -i $newpem $user@$HOSTNAME "cat $newpub > .ssh/authorized_keys"
        ssh -i $newpem $user@$HOSTNAME "if [ -x \"$(command -v restorecon)\" ]; then restorecon -Rv .ssh/authorized_keys; fi"
done

exit 0;