Automatically add several hosts to known_hosts

add-host-to-known_hosts.sh

#! /usr/bin/env bash
#
# In a situation in which you are ssh'ing into a set of servers, and you are
# confident about their trustability, but the current server doesn't "know"
# them yet. This script will add their signatures into your known_hosts file
# if it is not yet there.
##

declare KNOWN_HOSTS_FILE="$HOME/.ssh/known_hosts"
declare server_ip=
declare server_ssh_key=

for server in $(< ~/Temp/pod4101.hosts); do
  if ! grep -q "^${server}" "$KNOWN_HOSTS_FILE"; then
    echo "$server was not found in the user's known_hosts file, automatically adding it..."

    server_ip=$(dig +short "$server")
    if [[ -z "$server_ip" ]]; then
      echo "*** Encountered an unknown error with getting ip address for $server using dig command ***"
      exit 1
    fi

    server_ssh_key=$(ssh-keyscan -t rsa -H "$server" | awk '{print $2 " " $3}')
    if [[ -z "$server_ssh_key" ]]; then
      echo "*** Encountered an unknown error with getting ssh key for $server using ssh-keyscan command ***"
      exit 1
    fi

    echo "$server,$server_ip $server_ssh_key" >> $KNOWN_HOSTS_FILE
  fi
done