test if hostname exists from command line without ping

we have a script that needs to take action on a finite list of hosts. but every time we add or remove a host to the /etc/hosts file, we end up having to update this script. basically, say my hosts file looks like: ``` 192.168.100.1 hostip_1 192.168.100.2 hostip_2 192.168.100.10 hostip_3 192.168.100.20 hostip_5 ``` and my script (bash) does something like: ``` callmyfunction hostip_1 callmyfunction hostip_2 callmyfunction hostip_3 callmyfunction hostip_5 ``` if i want to add hostip_4 to the list of hosts, i now have to go in and edit my script and add it to the list. while it's a small edit, it is still a step that can be forgotten in the process (especially if someone new to the system comes in). is there a way i can test to see if 'hostip_1' is a valid hostname within the system (without pinging the host or grepping the /etc/hosts file)? we may use multiple hosts files, and different configurations may have different filenames, so i can't rely on trying to grep a single file. i need the system to do that work for me. any clues?