#!/usr/bin/env perl
use strict;
use warnings;
my $total_sleep_time = 0;
BEGIN {
    *CORE::GLOBAL::rand = sub {
        my $parent = (caller(1))[3] // "";
        if( $parent =~ /abc/ ){ return CORE::rand() } 
        return 123;
   };
}
print "fake rand: ".rand()."\n";
abc();
sub abc { print "real rand(): ".rand()."\n" }