#!/bin/bash
# Copyright (C) 2016 Ian Kelling

# chost: get canonical hostname

set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR

host=$1
# ||: because if we are using 2+ resolvers, 1 may fail, causing error, but we still get
# a valid address and we just use that
addr=$(host $host | sed -rn 's/^\S+ has address //p;T;q' ||:)
h=$(host $addr)
case $h in
  *"no PTR record")
    echo "error: chost: $h" >&2
    exit 1
    ;;
esac
h=${h##* }
# trailing dot in a hostname will mess up rsync
h=${h%.}
echo $h