sub schlep($$$)
{
    my( $map_ref, $from_ref, $to_ref ) = ( shift, shift, shift );
    for( keys %{ $from_ref } )
    {
        $to_ref->{ $map_ref->{$_} } = $from_ref->{$_}
            if( exists $map_ref->{$_} && exists $to_ref->{ $map_ref->{$_} } )
    }
}

schlep(\%map_foo_to_bar, \%foo, \%bar);

use Data::Dumper;
print Dumper \%bar;