use strict;
use feature qw(say);
use Socket;
use File::Tail;

my $file = File::Tail->new("/some/log/file");
my $line;

while (defined($line = $file->read)) {
    if ($line =~ /^DATE (IP) (WHATEVER)/) {
       my $remote_ip   = $1;
       my $whatever    = $2;
       my $remote_host = gethostbyaddr(inet_aton($remote_ip),AF_INET);
       say join "\t", qw/$remote_ip $remote_host $whatever/;
    }
}