if ($str =~ /some_re/){
  do something ...
}

##</code><code>##

foreach (qw/one one.five two two.one two.ten 
            two.ten.12 three three.nine four five/){
   print "$_\n";
   if($_ =~ /\./){ # if the word has a dot ".".
      # Keep everything after the last "." in the string   
      my ($label) = /\.([^\.]*)$/;	# a dot, followed by zero 
                                   # or more letters that are
                                   # not dots, attached to the 
                                   # end of the string.
                                   # return those letters
                                   # since they're between 
                                   # brackets.    
      $tree->add($_, -text  => $label , # add the label to $tree
                     -image => $mw->Getimage(folder));
   }
}