Awk script to convert from a list of IPv4s and hostnames to a zonefile format rdns entry.

rdnslistconv.sh

awk '{print gensub(/([0-9]*)\.([0-9]*)\.([0-9]*)\.([0-9]*) - (.*)/,"\\4.\\3.\\2.\\1.in-addr.arpa. IN PTR \\5.", $0)}' << "EOF"
192.168.1.101 - test.localdomain
192.168.1.105 - test2.example.com
EOF

Probably lower resource usage in sed, but awk is more familiar.