Update a DNS zone file with AWK

dns_update.sh

#!/bin/bash

usage(){
cat <<EOF

Usage: $(basename $0) zone_file record_type hostname ip_address

EOF
}

if [[ $# -lt 4 ]]; then
    usage
    exit 255
fi

zone_file="$1"
record_type="$2"
hostname="$3"
ip_address="$4"
args="${AWK_ARGS:-}"

if ! [[ -f $zone_file ]]; then
    usage
    echo "ERROR: zone_file '$zone_file' does not exist"
    exit 1
fi

if [[ $hostname == ${hostname%.*.} ]]; then
    usage
    echo "ERROR: hostname '$hostname' does not match pattern 'host.tld.'"
    exit 2
fi

temp=$(mktemp)

awk $args -v FS='\t' -v OFS='\t' -v record_type=$record_type -v hostname=$hostname -v ip_address=$ip_address '
$1==hostname && $3==record_type {$4=ip_address}
{print}
' $zone_file > $temp

diff $zone_file $temp

if [[ $? == 0 ]]; then
    echo "No changes"
else
    [[ "$(read -e -p 'Apply this change? [y/N]> '; echo $REPLY)" == [Yy]* ]] && cat $temp > $zone_file
    # This next line is pretty specific to my env. You can remove it.
    [[ $? == 0 ]] && echo -e "Now consider doing:\n    sudo docker exec -it dns rndc reload ies"
fi

rm $temp