Recently while conducting a vulnerability assessment for a rather large customer I was given a list of hostnames from around 20 domains culminating in a list of over 5000 targets that needed to go through the motions. Due to scale of the testing I needed to run the scans from several cloud nodes simultaneously to speed up the scanning. The other thing I needed to do was to extract all the IP addresses from the hostnames so as not to scan boxes multiple times when performing Port Scans for instance.
I had been playing with Perl for literally a couple of hours and decided to give writing my first Perl script a go in order to grab all the IP addresses from the list of hosts which I could then Unique and Sort to get the final list of target IP’s. I initially played with the idea of running ping commands or nslookups and then regex’ing the IP’s from there but I discovered a fantastic method called “gethostbyname” in Perl.