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 $code = shift;
    my @i = @_;
    local @_;
    my @rv;
    push @rv, $code->(@_=(shift @i,shift @i)) while @i;
    @rv;
}
                                    
my %new =
hmap { $_[1]{nick} =~ /rbush|fred/ ? ($_[0], $_[1]) : () } %$h;
                       
my %new2 =
hmap { $_[1]{nick} =~ /rbush|fred/ ?
      ($_[0], hmap { $_[0], $_[1] } %{$_[1]}) : () } %$h;

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

##</code><code>##

owncloselady-lm:scratch rbush$ perl hmap_ex1.pl 
new = $VAR1 = {
          '1' => {
                   'nick' => 'rbush',
                   'bday' => '3/12/1965',
                   'phone' => '5551212'
                 },
          '5' => {
                   'nick' => 'fred',
                   'bday' => '5/01/1972',
                   'phone' => '1112300'
                 }
        };

new2 = $VAR1 = {
          'rbush' => 'bday',
          '1' => 'nick',
          '3/12/1965' => 'phone',
          'nick' => 'fred',
          'phone' => '1112300',
          'bday' => '5/01/1972',
          '5551212' => '5'
        };

##</code><code>##

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";

##</code><code>##

owncloselady-lm:scratch rbush$ perl hmap_ex2.pl
new = $VAR1 = {
          '1' => {
                   'nick' => 'rbush',
                   'bday' => '3/12/1965',
                   'phone' => '5551212'
                 },
          '5' => {
                   'nick' => 'fred',
                   'bday' => '5/01/1972',
                   'phone' => '1112300'
                 }
        };

new2 = $VAR1 = {
          '1' => {
                   'nick' => 'rbush',
                   'phone' => '5551212'
                 },
          '5' => {
                   'nick' => 'fred',
                   'phone' => '1112300'
                 }
        };