update dns record in Ubuntu 16.04 LTS (ref:http://qiita.com/nanopico-san/items/70bb58595a6c7cf77a53)

register_dns.sh

#!/bin/bash
SED=/bin/sed
PHASE=`echo "$script" | $SED -r 's%^.*/[^/]*-(enter|exit)-.*/[^/]*$%\1%i'`
NSUPDATE=/usr/bin/nsupdate

AWK=/usr/bin/awk
convert_ip4_inaddr() {
  #=- $1  ... ip4 address
  #=- ret ... in-addr string
  ###
  [ -n "$1" ] && echo `echo $1 | $AWK -F . '{ printf( "%d.%d.%d.%d.in-addr.arpa.", $4, $3, $2, $1 ) }'`
}

case ${reason} in
  BOUND|RENEW|REBIND|REBOOT)
    if [ $PHASE = "exit" ]; then
      new_fqdn=`hostname -f`
      new_inaddr=`convert_ip4_inaddr ${new_ip_address}`
      if [ ! -z ${new_fqdn} ]; then
        echo "nsupdate update add ${new_fqdn} 3600 IN A ${new_ip_address}."
        echo "nsupdate update delete ${new_inaddr} 3600 IN PTR ${new_fqdn}."
        $NSUPDATE <<__END__
update add ${new_fqdn} 3600 IN A ${new_ip_address}
send
update add ${new_inaddr} 3600 IN PTR ${new_fqdn}
send
__END__
      fi
    fi
    ;;
  EXPIRE|FAIL|RELEASE|STOP)
    if [ $PHASE = "enter" ]; then
      old_fqdn=`hostname -f`
      old_inaddr=`convert_ip4_inaddr ${old_ip_address}`
      if [ ! -z ${old_fqdn} ]; then
        echo "nsupdate update delete ${old_fqdn} 3600 IN A ${old_ip_address}."
        echo "nsupdate update delete ${old_inaddr} 3600 IN PTR ${old_fqdn}."
        $NSUPDATE <<__END__
prereq yxrrset ${old_fqdn} IN A ${old_ip_address}
update delete ${old_fqdn} 3600 IN A ${old_ip_address}
send
prereq yxrrset ${old_inaddr} IN PTR ${old_fqdn}
update delete ${old_inaddr} 3600 IN PTR ${old_fqdn}
send
__END__
      fi
    fi
    ;;
esac