$_ = "\@abcde99\@";
if (/^([^ ]+)([a-z0-9]+)([^ ]+)$/) {
  # prints: *@abcde9*9*@*
  print "*$1*$2*$3*\n";
}

##</code><code>##

$_ = "\@abcde99\@";
if (/^([^ ]+?)([a-z0-9]{5,12})([^ a-z0-9]+)$/) {
  print "*$1*$2*$3*\n";
}