ensure_host.sh

#!/bin/sh

IP="192.168.0.1"
HOST="myhost.mydomain"
ALIAS="myhost"

augtool -sAt "Hosts.lns incl /etc/hosts" << EOC
  # \$noentry will match /files/etc/hosts if the entry isn't there yet
  defvar noentry /files/etc/hosts[count(*[ipaddr="${IP}" or canonical="${HOST}"])=0]

  # Create the entry if it's missing
  set \$noentry/01/ipaddr "${IP}"
  set \$noentry/01/canonical "${HOST}"
  set \$noentry/01/alias "${ALIAS}"

  # Amend existing entry
  defvar entry /files/etc/hosts/*[ipaddr="${IP}" or canonical="${HOST}"]

  # This will fail if more than one entry was found
  set \$entry/ipaddr "${IP}"
  set \$entry/canonical "${HOST}"
  # Remove all aliases
  rm \$entry/alias
  set \$entry/alias "${ALIAS}"
EOC