Hi,
I think you have the whole stuff mixed up. Please re-read all that has been posted on this thread already.
Then I think you also need to read up the documentation on $.
Simply, do perldoc -v $. from your CLI and you should have it.

Here is an example, if you may:

use warnings;
use strict;

my $look_for;

while(<DATA>){
    if (/^\./) {
        $look_for = $.;
        next;
    }
   print $., $_;
}

print "The dot came up on line ", $look_for, $/;

__DATA__
Mary has a little lamb
little lamb, little lamb
.
Mary has ....
[download]

1Mary has a little lamb
2little lamb, little lamb
4Mary has ....
The dot came up on line 3
[download]