@input_lines =    
        sort {my ($a_name_last,$a_name_first,$a_city ) 
                                = split(/\s+/,$a);
              my ($b_name_last,$b_name_first,$b_city) 
                                = split(/\s+/,$b);
                   $a_name_last cmp $b_name_last
                                 or
                   $a_name_first cmp $b_name_first
                                 or
                         $a_city cmp $b_city            
                         
             }@input_lines;