if (
  /foo       # Match starting at foo
   (?:       # Complex expression:
     (?!baz) #   make sure we're not at the beginning of baz
     .       #   accept any character
   )*        # any number of times
   bar       # and ending at bar
  /x
  )
{
  # print stuff out.
}
else
{
  print "Failed to match against '$_'\n";
}