#!/bin/bash

function helpexit() {
    echo "Remove hosts from ~/.ssh/known_hosts"
    echo "-f  no questions."
    exit
}

for (( i=1; i<=$#; i++ )); do
  [[ "${!i}" = "--help" ]] && helpexit                                            
  [[ "${!i}" = "-h" ]] && helpexit                                            
  [[ "${!i}" = "-f" ]] && { FORCE=1; continue; }
  HOST="${!i}"
done
[[ -z "$HOST" ]] && helpexit

REALHOST=$( ssh -G "$HOST" 2> /dev/null | awk '/^hostname / { print $2 }' )
[[ -z "$REALHOST" ]] && REALHOST="$HOST"
IP=$( getent hosts "$REALHOST" | awk '{ print $1 }' )

[[ "$FORCE" -ne 1 ]] && {
  echo "Sure to remove ${REALHOST} (IP: ${IP}) from known_hosts? [y/N]"
  read resp
} || {
  resp=y
}

[[ "$resp" = "y" ]] && {
  echo ssh-keygen -R "$REALHOST"
  ssh-keygen -R "$REALHOST"
  [[ -n "$IP" ]] && {
    echo ssh-keygen -R "$IP"
    ssh-keygen -R "$IP"
  }
}