Perhaps someone can use this:
My "Hello World" in Perl:CheckNewMac.pl
# Description: This script loops through the nodes-table from nedi and
# compares the year/month/day/hour part of the -firstseen- attribute with
# the current time. If there is a match, that means a new mac address was
# found in the last hour, an email with the new found mac address will be
# sent via localhost.
# For correct function you should run it after the hourly nedi-run.
# Moreover the arp aging time in your switches should be one hour.