$href->{port_list}   # correct

##</code><code>##

  $href{port_list}     # incorrect - assumes a hash %href

##</code><code>##

#!/usr/bin/perl -l

use strict;   # !!!
use warnings;

my $module = bless { port_list => [qw(a b c)] }, "Foo";

print "size=", scalar @{$module->{port_list}};   # ok
print "size=", scalar @{$module{port_list}};     # not ok!

##</code><code>##

$ ./835728.pl
Name "main::module" used only once: possible typo at ./835728.pl line 9.
size=3
Use of uninitialized value $module{"port_list"} in array dereference at ./835728.pl line 9.
Use of uninitialized value $module{"port_list"} in concatenation (.) or string at ./835728.pl line 9.
size=

##</code><code>##

$ ./835728.pl
Global symbol "%module" requires explicit package name at ./835728.pl line 9.
Execution of ./835728.pl aborted due to compilation errors.