Script to update DKIM entry in BIND zone file

This script takes two arguments:

1. a BIND DNS zone file
2. a DNS record generated by 'opendkim-genkey'

opendkim-genkey is part of the opendkim-tools Debian package

This script use regex to

1. extract the DKIM selector and the value of the TXT record from the DKIM TXT record generated by opendkim-genkey
2. replace the DKIM selector and TXT value in the zone file with the new values

Example

• generate a new DKIM key for mail.example.org
• remember to increase the increment if generating a new key on the same date

INCREMENT=1; /usr/sbin/opendkim-genkey -b 2048 -d mail -s $(/bin/date +%Y%m%d)-$INCREMENT

# generate a DNS DKIM TXT record such as '20210811-1.txt'
/usr/sbin/opendkim-genkey -b 2048 -d example.org -s $(/bin/date +%Y%m%d)-1

Then run this update-dkim.py, passing the zone file you want to update and the above .txt file:

update-dkim.py <zone file> 20210811-1.txt