Do you want to limit by $var ( element of @attrs) or by $value (element of @$attr)?

Here is an example with 3 extra lines compare to yours that only prints givenname and department, assuming that those are of the latter form, limiting to values of $value

 # configuration:  Put the fields you want here.
 my @fields_i_want_to_see= qw(givenname department);

 my %show_field = map { $_ => 1 } @fields_i_want_to_see;
 use Net::LDAP;

 $ldap = Net::LDAP->new('ldap.acme.com') or die "$@";
 $mesg = $ldap->search(
                       base   => "o=acme.com",
                       scope  => 'sub',
                       filter => "sn=smith",
                      );
  #
  # At this point the user can get the returned data
  # as an array or as a stack.
  # In this example we will use an array

  # How many entries were returned from the search
  my $max = $mesg->count; 

  for( my $index = 0 ; $index < $max ; $index++) 
  {
    my $entry = $mesg->entry($index);
    my $dn = $entry->dn; # Obtain DN of this entry

    @attrs = $entry->attributes; # Obtain attributes for this entry.
    foreach my $var (@attrs)
    {
     #get a list of values for a given attribute
     $attr = $entry->get_value( $var, asref => 1 );
     if ( defined($attr) )         
     {          
         foreach my $value ( @$attr )          
         {           
          print "$var: $value\n" if $show_field{$var};# Print each val
+ue for the attribute.
         }         
     }                                                                
+       
    }
  }
[download]