my ($data_in, $data_out);

$data_in = q|<container><a>smile!!! </a><b> smile again!! </b></container><?query?>|;

while ($data_in =~ /<container><a>(.+?)<\/a><b>(.+?)<\/b><\/container>(<\?query\?>)?/ig)  {
  $data_out = "$2, $1$3 ";  #errors here
  ; #further processing here 
  print $data_out;
}

##</code><code>##

Use of uninitialized value $3 in concatenation (.) or string at perlmonks_700143.pl line 8.