It starts at zero...

Quoth perlvar (emphases added): Each filehandle in Perl counts the number of lines that have been read from it. ... When a line is read from a filehandle (via "readline()" or "<>") ... $. becomes an alias to the line counter for that filehandle.

So I would say davido's assertion is not without justification:  $. starts out undefined (which is very like zero) and happily becomes 1 by aliasing when the first line is read. I assume the internal filehandle line counter is 0 or undefined prior to any read on the handle. So there.

>perl -wMstrict -le
"my $filename = 'text';
 open my $fh, '<', $filename or die qq{opening '$filename': $!};
 ;;
 print qq{\$. initially: }, defined $. ? qq{'$.'} : 'undefined';
 ;;
 while (<$fh>) {
   chomp;
   print qq{$.: '$_'};
   }
 ;;
 close $fh or die qq{closing '$filename': $!};
"
$. initially: undefined
1: 'now is the time'
2: 'foo bar baz'
3: 'how now brown cow'
4: 'four score and seven'
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