use Data::Dumper;

my $h =
{
    1 =>
    {
        nick => 'rbush',
        phone => '5551212',
        bday => '3/12/1965',
    },

    3 =>
    {
        nick => 'ernest',
        phone => '5553300',
        bday => '3/12/1971',
    },

    5 =>
    {
        nick => 'fred',
        phone => '1112300',
        bday => '5/01/1972',
    },

};

sub hmap
{
    my ($h, $code) = @_;

    return undef unless defined $h;

    my $rv = {};
    while (my ($k, $v) = each %$h)
    {
        my $x = &$code($k, $v);
        $rv->{$k} = $x if (defined $x);
    }
    return $rv;
}
my $new =
    hmap $h, sub { $_[1]->{nick} =~ /rbush|fred/ ? $_[1] : undef };

my $new2 =
    hmap $h,
    sub
    {
        return hmap $_[1]->{nick} =~ /rbush|fred/ ? $_[1] : undef,
           sub { $_[0] =~ /nick|phone/ ? $_[1] : undef }
    };

print "new = " . Dumper ($new) . "\n";
print "new2 = " . Dumper ($new2) . "\n";