$ cat /tmp/io.pl
#!/usr/bin/perl

use strict;
use warnings;
use IO::Handle;

my $filename = shift || $0;
my $fh = IO::Handle->new;
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
$ perl /tmp/io.pl
Can't call method "input_line_number" on unblessed reference at /tmp/io.pl line 10, <GEN0> line 1.