Quickly generate an SSH key

generate_ssh_key.sh

#!/usr/bin/env sh

SCRIPT_NAME="${0##*/}"
SSH_USER="${USER}"
KEY_DIR="${HOME}/.ssh"
KEY_TYPE="ed25519"
HOSTNAME="$(hostname)"

_log() {
  [ "${QUIET}" != "quiet" ] && echo "[$(date +'%Y-%m-%d %H:%M:%S')] ${1}"
}

_error() {
  echo "[$(date +'%Y-%m-%d %H:%M:%S')] ${1}"
}

_print_usage() {
cat <<EOF
Usage: ${SCRIPT_NAME} [option] [switch] --server <server name>
Switches:
 --from   (-f)      Server name the user will connect from (default is "$(hostname)")
 --output (-o)      Output directory to save the key (default is "${HOME}/.ssh")
 --server (-s)      Server name to generate the key for (required)
 --user   (-u)      User who will be using the key (default is "${USER}")

Options:
 --quiet  (-q)      Display only errors
 --legacy (-l),
 --rsa    (-r)      Use legacy RSA mode (for older servers)

Commands:
--help (-h)         Display this help message
EOF
}

while :
do
  case "${1}" in
    -s|--server )
      SERVER="${2}"
      shift 2
      ;;
    -u|--user )
      SSH_USER="${2}"
      shift 2
      ;;
    -o|--output )
      KEY_DIR="${2}"
      shift 2
      ;;
    -q|--quiet )
      QUIET="quiet"
      shift 1
      ;;
    -l|--legacy|-r|--rsa )
      KEY_TYPE="rsa"
      shift 1
      ;;
    -f|--from )
      HOSTNAME="${2}"
      shift 2
      ;;
    -h|--help )
      _print_usage
      exit 0
      ;;
    * )
      break
      ;;
  esac
done

if [ -z "${SERVER}" ]; then
  echo $SERVER
  echo "No server set."
  echo
  _print_usage
  exit 1
fi

if [ "${HOSTNAME}" != "$(hostname)" ]; then
  echo "yes"
  FILENAME="${SSH_USER}@${HOSTNAME}@${SERVER}"
else
  echo "no $(hostname)"
  FILENAME="${SERVER}"
fi

_log "Generating SSH key for ${SSH_USER}@${SERVER} ..."

FULLPATH="$(readlink -m "${KEY_DIR}/${FILENAME}")"

ssh-keygen -t ed25519 -b 4096 -C "${SSH_USER}@${HOSTNAME}" -f "${FULLPATH}" -N ""