title: Why would I not leave extglob enabled in bash?
body: <p>I just found out about the bash extglob shell option here:-
  <a href="https://stackoverflow.com/questions/216995/how-can-i-use-inverse-or-negative-wildcards-when-pattern-matching-in-a-unix-linu">How can I use inverse or negative wildcards when pattern matching in a unix/linux shell?</a></p>
  
  <p>All the answers that used <code>shopt -s extglob</code> also mentioned <code>shopt -u extglob</code> to turn it off.
  Why would I want to turn something so useful off? Indeed why isn't it on by default?
  Presumably it has the potential for giving some nasty surprises. 
  What are they?</p>