$SIG{__DIE__} = sub {
   return if $^S;

   ...

   print(STDERR $_[0]);
   exit($! || ($? >> 8) || 255);
};
[download]

I did something similar on one of my first tries to find out what was going on and to fix this. I looked at the call stack and if there wasn't a ".cgi" file in the list then assumed I was in the "compile" stage and just returned. Not as elegent as using $^S but it worked. If I had to do something like this, I like the $^S way better now that I know about it.

In the end, I'd really like to know why I had to do anything like this. If we have code like:

package X;

BEGIN { whatever; }

$main::SIG{__DIE__} = \&some_function; # when does this get run?

sub new { ... }
[download]

In what phase is that SIG handler assigned? I would have thought it was in an implied INIT, but the code acts like it's in an implied BEGIN. I ended up solving the entire issue by putting that line in an explicit INIT block, but why did I have to do that?

$main::SIG{__DIE__} = \&some_function; # when does this get run?
[download]

It gets run at the same time as any other code in the same place would. Give it a try:

#!/usr/bin/perl

use strict;
use warnings;
use feature qw/say/;

sub function {
    say "Howdy!";
}

#die "horribly";

$main::SIG{__DIE__} = \&function;

#die "horribly";

#BEGIN { die "horribly"; }
[download]

Try uncommenting each of the various dies; only the one that dies after the signal handler has been assigned will produce a "Howdy!". No implicit blocks of any kind are involved.

Alternatively, check with -MO=Deparse.