#!/bin/bash

SSH_DIR="${HOME}/.ssh"
KNOWN_HOSTS="${SSH_DIR}/known_hosts"
NEW_KNOWN_HOSTS="${KNOWN_HOSTS}..SWAP$$"
BACKUP_KNOWN_HOSTS="${KNOWN_HOSTS}.old"

if [ "$1" = "" ]; then
    echo "Usage: $0 <ip / hostname> [private key file for testing]" >&2
    exit 1
fi
REMOTE_HOST=$1
TEST_KEY=$2

# Here flock is used, because we might be adding multiple hosts at the
# same time, resulting in race conditions on writing the known_hosts file.
echo "Add the target host $REMOTE_HOST to $KNOWN_HOSTS"
(
    flock -e 200
    touch $KNOWN_HOSTS
    (cat $KNOWN_HOSTS; ssh-keyscan $REMOTE_HOST 2>/dev/null) | sort | uniq > $NEW_KNOWN_HOSTS
    cp $KNOWN_HOSTS ${KNOWN_HOSTS}.bak
    cp $KNOWN_HOSTS $BACKUP_KNOWN_HOSTS
    mv $NEW_KNOWN_HOSTS $KNOWN_HOSTS
) 200>${KNOWN_HOSTS}..LCK

exit 0