I have to admit, I was entirely perplexed as well by this until I realized that my in Perl acts like an actual executed statement, not merely a declaration (like it would be, for example, in C). As a result, you get a new instance of $list_ref every time the function is called -- which is why it doesn't stay shared.

When I want to create a shared variable with long-term state like that (i.e., a C-style "static"), I put the applicable function definitions in a scope block with the my statement at the outer level -- e.g.: 

#!/usr/bin/perl -w

use strict;

my @firstlist = qw(1 2 3 4 5);
my @secondlist = qw(A B C D E);

process_list(\@firstlist);
process_list(\@secondlist);

{
   my $list_ref;

   sub process_list {
       ($list_ref) = @_;

       sub get_list { return @$list_ref; }

       print_list();
   }
}

sub print_list {
    foreach my $item (get_list()) {
        print "LIST ITEM: $item\n";
    }
}

[download]

which produces: 

LIST ITEM: 1
LIST ITEM: 2
LIST ITEM: 3
LIST ITEM: 4
LIST ITEM: 5
LIST ITEM: A
LIST ITEM: B
LIST ITEM: C
LIST ITEM: D
LIST ITEM: E

[download]

as expected. Naturally, you could (per ikegami, should) also move the get_list() subroutine outside the scope of process_list() for clarity, since it doesn't really add value there -- but I left it as-is to minimize changes from your original program.

Update: Strengthened some wording in response to comments from ikegami on Perl internals

In reply to Re^2: sub scope question by papidave
in thread sub scope question by perl45036

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