#!/usr/bin/env bash
#
# Update serial in a zone file
# Casper Gielen, 2016

usage() {
        echo "usage: update-serial <zonefile>"
        echo "Updates the serial of a zonefile to the current date + a counter"
        exit 1
}

zonefile="$1"
[ -z "$zonefile" ] && usage

# FIXME: improve the way we find the serial
old=$(awk '/;serial/{print $1}' $zonefile)
old_date=${old:0:8}
old_count=${old:(-2)}
new_date=$(date +%Y%m%d)
new_count="00"
if [ "$new_date" == "$old_date" ]; then
        new_count=$(printf "%02d" "$[ 10#$old_count + 1 ]")
fi
new="${new_date}${new_count}"
# FIXME: make sure we change the right line
sed -i "s/$old/$new/" $zonefile