$ perl -MIO::Handle -le 'open my $fh, "<", shift or die $!; print $fh->input_line_number while <$fh>' a_file_name
1
2
3
4
.
.
.

$ perl -MIO::Handle -le 'open my $fh, "<", shift or die $!; print (\$fh)->input_line_number while <$fh>' a_filename
REF(0x99d7cdc)
Can't call method "input_line_number" without a package or object reference at -e line 1, <$fh> line 1.

# $fh = do {local *FH};   #bad
$ perl -MIO::Handle -le 'my $fh = do {local *FH}; open $fh, "<", shift or die $!; print (\$fh)->input_line_number while <$fh>' a_file_name
GLOB(0x846ccdc)
Can't call method "input_line_number" without a package or object reference at -e line 1, <FH> line 1.