#! perl
use strict;
use warnings;
use Data::Dump;

my %h = (1 => 'Fred');
dd %h;
fn(%h);
dd %h;

sub fn
{
    print "BEGIN fn()\n";
    dd @_;
    $_[0]++;
    $_[1] = 'Barney';
    dd @_;
    print "-END- fn()\n";
}

##</code><code>##

12:02 >perl 541_SoPW.pl
(1, "Fred")
BEGIN fn()
(1, "Fred")
(2, "Barney")
-END- fn()
(1, "Barney")

12:02 >