You've probably noticed how the following displays the number of lines read in from last read file handle is displayed along the program line number in a die. 

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

__DATA__
a
b
c
.
d
e

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Error! at script.pl line 2, <DATA> line 4.

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Further study shows this is not a property of the while. 

<DATA>;
die "Error!";

__DATA__
a
b

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Error! at script.pl line 2, <DATA> line 1.

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The data line number appears as long as the file handle is still open. 

<DATA>;
close(DATA);
die "Error!";

__DATA__
a
b

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Error! at script.pl line 3.

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You can even play with the number! 

<DATA>;
$. = 100;
die "Error!";

__DATA__
a
b

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Error! at script.pl line 3, <DATA> line 100.

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Setting $. to 0 hides the message. 

<DATA>;
$. = 0;
die "Error!";

__DATA__
a
b

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Error! at script.pl line 3.

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Is it also possible to play with the filehandle name? For example, could perl be tricked (suing XS, surely) into displaying 

Error! at script.pl line 3, filename.dat line 100.

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In reply to Playing with "<FH> line 123" die messages by ikegami

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