I always wanted to have live formatting as I type Perl code.

The usual advice to pipe a text selection through perltidy is just too slow, and furthermore you might want to have only a visible snippet formatted to keep control, and tidy can fail here (emacs is mostly very tolerant)

The following code called with M-x my-indent-block is re-indenting the surrounding block you are in. The devadvice binds it to the cperls electric-semi feature which automatically does a return and and indentation of the following line (see M-x customize-group RET cperl-autoinsert-details for details)

before

for my$scalar(1..10){print"$scalar"."txt";}
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for my $scalar (1..10) {
   print"$scalar"."txt";
}
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(defun my-indent-block ()
  "reindent surroundig expression"
  (interactive)
  (save-excursion
    (backward-up-list)
    (cperl-indent-exp)
    )
  )



(defadvice cperl-electric-semi
  (after my-electric-indent-context)
  "indent whole context surrounding block/context"
  (my-indent-block)
  )

(add-hook
 'cperl-mode-hook
 (lambda ()
   (local-set-key (kbd "M-C-q") 'my-indent-block )
   )
 )
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Problems:

• Defadvice is a kind of wrapping, I tried to bind it to cperl-indent-line to always indent the whole block whenever and indentation is triggered (there are many ways to do so in cperl-mode) but this is causing an infinite recursion , since cperl-indent-exp calls cperl-indent-line. (this is for sure solvable with some kind of flag, but I'm tired now :)
• Toplevel In filescope this doesn't work cause there is no up-list! Thats good, because I didn't want to reindent distant code, without visual control. But it's still pretty easy in elisp to catch the error and to react otherwise, one option is to just reindent one paragraph or the whole file if that option is set.

Natural keybindings

cperl-indent-exp is normally bound to M-C-q , but is only useful after you've put the cursor in front of the block to highlight (here the for ), that's why I remapped it to work from inside the block.

M-q should be the far better choice ( I hate 3+ finger combinations). In cperl-mode it's bound to cperl-fill-paragraph which wraps text to 80 colums ONLY in POD, here-docs or comments, but isn't useful in code! ( well as long as you are not trying to obfuscate )

But now I'm not sure how to combine the old cperl-heuristic to distinguish between code and text with this new features, without patching cperl.

Nice to have for my-indent-block

my $a           =  {
         a      => 1,
         b      => {
              c => 3,
             }
        };
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