$ perl - foo
use strict;
use warnings;
use IO::Handle;

my $filename = shift || $0;
my $fh = do {local *FH};
open $fh, $filename or die "failed on $filename: $!\n";
print((\$fh)->input_line_number, "\n") while <$fh>; #1
#print $fh->input_line_number, "\n" while <$fh>; #2
__END__
Name "main::FH" used only once: possible typo at - line 6.
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