A small utility to automate replacement of ssh key on servers

replace-ssh-key.sh

#!/usr/bin/env bash
###################
# A small utility to automate replacement of ssh key on servers.
#
# USE WITH GREAT CARE !!!
# Author: [email protected]


set -e
set +x

copy_new() {
  echo ssh-copy-id -i "$new_key" "${user:+"$user@"}$host" "${port:+"-p $port"}"
  echo ssh -T -i "$new_key" "${user:+"$user@"}$host" "${port:+"-p $port"}" -o PasswordAuthentication=no
}

remove_old() {
  ssh_cmd="ssh -o PasswordAuthentication=no -i $new_key ${port:+"-p $port"} ${user:+"$user@"}$host"
  old_key_pub=$(cat "$old_key.pub")
  new_key_pub=$(cat "$new_key.pub")
  echo "$ssh_cmd" "\"sed -i 's#$old_key_pub##' ~/.ssh/authorized_keys\""
  echo "$ssh_cmd" "\"grep -l \"$old_key_pub\" /home/**/.ssh/authorized_keys | xargs -L 1 sed -i 's#$old_key_pub#$new_key_pub#'\""
}

usage() {
  echo "$0 [-h | --host] [-u | --user] [-p | --port] [-i | --new_key] [-k | --old_key]"
}

##### Main

host=
port=
user=
old_key="$HOME/.ssh/id_rsa"
new_key="$HOME/.ssh/id_rsa_new"

while [ "$1" != "" ]; do
  case $1 in
  -h | --host)
    shift
    host=$1
    ;;
  -u | --user)
    shift
    user=$1
    ;;
  -p | --port)
    shift
    port=$1
    ;;
  -i | --new_key)
    shift
    new_key=$1
    ;;
  -k | --old_key)
    shift
    old_key=$1
    ;;
  --help)
    usage
    exit
    ;;
  *)
    usage
    exit 1
    ;;
  esac
  shift
done

if [ -z "$host" ]; then
  echo "No host was given"
  usage
  exit 1
fi

echo "$old_key => $new_key on ${user:+"$user@"}$host${port:+":$port"}"

echo "Copying new file"
copy_new

echo "Removing old file"
remove_old

a little helper to list known hosts

$> cat ~/.ssh/known_hosts | cut -d ' ' -f 1 | cut -d ',' -f 1 | awk -F: '{gsub("\\[|\\]","",$1); if ($2){print "-h " $1 " -p " $2}else{print "-h " $1}}' | sort > ssh_hosts.txt