# assume line is:
# ip;ip;ip;..     datum
#
my %ip_hash;
while ( my $line = <FILE> ) {
    my ( $ip, $datum ) = split /\s*/, $line;
    my @ip = split /\;/, $ip;
    foreach my $ipa ( @ip ) {
        $ip_hash{ $ipa } = $datum;
    }
}

# Later..

if ( exists $ip_hash{ $query_ip } ) {
   do_something_with_datum( $ip_hash{ $query_ip } );
} else {
   do_not_found_action( $query_ip );
}