$fh = do {local *FH};
open ($fh, $filename)

##</code><code>##

use strict;
use warnings;

use IO::Handle;
my $fh;
# $fh = do {local *FH};   #bad
open ($fh, './test') or die("open failed: $!");
print "line: " . $fh->input_line_number();

__END__

output with "#bad" commented out:
line: 0

output with "#bad" included:
Can't call method "input_line_number" without a package or object reference at test line 10.