Hi Bill,

That's most likely a compile time effect.

What happens if you override sleep before using Existing_Module ?

Just move the use after the BEGIN block.

update

To demonstrate my point:

The first sleep is compiled before hitting the BEGIN block, only the second after is compiled to bind to the override.

Keep in mind that use is executed at compile time.

use strict;
use warnings;

warn "Version $]";
warn "Prototype", prototype "CORE::sleep";



my $sleepcounter;

sleep 2;

BEGIN {
    my $old = \&CORE::sleep;

    *CORE::GLOBAL::sleep =  sub {
        warn  "start wrapper $_[0]";
        $sleepcounter += $_[0];
        $old->(@_);

    };
}


sleep 3;

warn "total sleep( $sleepcounter )";
[download]

Version 5.016003 at d:/Users/lanx/pm/core_sleep.pl line 4.
Prototype;$ at d:/Users/lanx/pm/core_sleep.pl line 5.
start wrapper 3 at d:/Users/lanx/pm/core_sleep.pl line 16.
total sleep( 3 ) at d:/Users/lanx/pm/core_sleep.pl line 26.
[download]