Flip a string or a list

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• reverse LIST

  In list context, returns a list value consisting of the elementsof LIST in the opposite order. In scalar context, concatenates theelements of LIST and returns a string value with all charactersin the opposite order.

   print join(", ", reverse "world", "Hello"); # Hello, world
   
   
   print scalar reverse "dlrow ,", "olleH"; # Hello, world
   

  Used without arguments in scalar context, reverse() reverses $_.

   $_ = "dlrow ,olleH";
   
   print reverse;  # No output, list context
   
   print scalar reverse;   # Hello, world
   

  Note that reversing an array to itself (as in @a = reverse @a) willpreserve non-existent elements whenever possible, i.e., for non magicalarrays or tied arrays with EXISTS and DELETE methods.

  This operator is also handy for inverting a hash, although there are somecaveats. If a value is duplicated in the original hash, only one of thosecan be represented as a key in the inverted hash. Also, this has tounwind one hash and build a whole new one, which may take some timeon a large hash, such as from a DBM file.

   %by_name = reverse %by_address;  # Invert the hash