yank-ssh-key.sh

#!/bin/sh

BACKUP_TS=`date +%Y%m%d%H%S`

if [ -z "$1" ]
then
  echo "What host/IP?"
  exit 1
fi

DNS=`host $1 | grep 'has address' | sed -e 's/has address //' -e 's/ /|/' | tr '\n' '|'`
DNS=`echo $DNS | sed -e 's/^|//' -e 's/|$//'`

if [ -z "$DNS" ]
then
  echo "Got bad/empty hostname or IP list! ($DNS)."
  exit 1
fi

echo "Backup in ~/.ssh/known_hosts.$BACKUP_TS"
cp ~/.ssh/known_hosts ~/.ssh/known_hosts.$BACKUP_TS

TMPFILE=`mktemp /tmp/known_hosts.XXXXXXXX` || (echo "Couldn't make temp file!" && exit 1)
cp ~/.ssh/known_hosts $TMPFILE

egrep -ve "($DNS)" $TMPFILE > ~/.ssh/known_hosts
rm -f $TMPFILE