use subs 'die';

my $filename = 'filename.dat';

while (<DATA>) {
   $. = 100;
   die "Error!" if $_ eq ".\n";
}


sub die {
    my @caller = caller();
    print $_[0], " at $0 line $caller[2], $filename line ${.}.";
    exit;
}

__DATA__
a
b
c
.
d
e
[download]

Cheers,
Rob