$ 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 $!; print (\$f
+h)->input_line_number while <$fh>' a_filename
REF(0x99d7cdc)
Can't call method "input_line_number" without a package or object refe
+rence 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 refe
+rence at -e line 1, <FH> line 1.
[download]

Always always always use warnings; teach your fingers to type -wle, not -le. You are doing (print(\$fh))->input_line_number there, not print((\$fh)->input_line_number).

OK, how about this?

$ 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/i
+o.pl line 10, <GEN0> line 1.
[download]

The #2 prints the line numbers correctly. Did I miss something? Please shed some light.

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