That's easy.

1. The label is there to show that the block is emulating as a SWITCH statement.
2. The label is also there to show what the last statements refer to.
3. the for with just one variable is simply there to assign $value to $_ without explicitly doing it
4. it's also there to keep the original content of $_ outside the SWITCH ("loop"). Try this

   my $v="V";
   $_="_";
   for ( $v ) {
       print "inside: $_\n";
   }
   print "outside: $_\n";
   [download]

5. It looks good ;-) (to me). I read this as "switch for value ..."

It looks good ;-) (to me). I read this as "switch for value ..."

Ah, style. Still, I deem it a misuse of for. It sets up the context of a loop whilst none needed.

This one looks better (for me, that is :-)

# SWITCH
{
  local $_ = $MyValue;
  /$reg2/ && do {
      sub_for_key_a();
      last;
    };
  /$reg1/ && do {
      whatever();
      sub_for_key_b();
      last;
    };
  #default
    sub_for_default();
} # END SWITCH
[download]

since a bare block does the job and is less clutter. And I also read it as "switch for $MyValue" ;-)

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

It wasn't my idea. I took it from "Programming Perl" by Wall, Christiansen & Schwartz. Chapter 2: You might think it odd to write a loop over a single value, but a common idiom for a switch statement is to use foreach's aliasing capability to make a temporary assignment to $_ for convenient matching.

---

s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e