#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $ref = { A => 1 }; print "pre: " . Dumper($ref) . "\n"; &add($ref,'B','2'); sub add { my ($struct,$key,$value) = @_; $struct->{$key} = $value; } print "post: " . Dumper($ref) . "\n";