$hashref->{"key1"} = "value1", {"key2"} = "value2";

##</code><code>##

use strict;
use warnings;

my %employees=  ( "key1"   => undef,
                  "key2"   => undef,
                  "key3"   => undef,
                 );

my $hashref = \%employees;
$hashref->{"key1"} = "value1";
$hashref->{"key2"} = "value2";
$hashref->{"key3"} = "value3";

print %$hashref,"\n";