Changing grep /$host/, (@ip) to grep /^\w,$host$/, (@ip) should work (by requiring the pattern (the IP) to compose the entire line). Also be aware that . is a regex metacharacter (match anything but \n), and so the line above really should be grep /\w,\Q$host\E$/, (@ip) to escape any metachars in $host.

Update Didn't see the a, ... b, ... c, ... in ip.txt at first.