Some errors:

• "Why use perl? Most powerful onliners one-liners".
• Two examples produce an error: print $var";
• "{m,n} Match atleast at least n m times but not more than m n times."
• "(?(?<!) Match if expr wouldn't match previously."
• "We have to define the handler in capital letters but its it's not manditory mandatory."
  (In addition to typos, "have to" and "not mandatory" are conflicting.)

Update: Small wording change.