Hi,

Which version of perl do you have?

See CORE and ex::override

#!/usr/bin/perl --
use strict;
use warnings;
use diagnostics;

BEGIN {
    my $sleepcounter = 0;
    *CORE::GLOBAL::hex = sub {
        print qq{hex(@_)\n};
#        goto &CORE::hex; ## FAIL
        CORE::hex(@_);
    };
    *CORE::GLOBAL::sleep =  sub(;@) {
        print qq{sleep(@_)\n};
        $sleepcounter += $_[0];
        CORE::sleep(@_);
    };
    END { print "total sleep( $sleepcounter )\n"; }
}
print "\$]=$]       \$^V=$^V\n";
sleep 1; print hex("0x50"),"\n";
sleep 2; print hex("0x50"),"\n";
__END__
$ perl core-global-sleep-override.pl
$]=5.016001       $^V=v5.16.1
hex(0x50)
1
hex(0x50)
1
total sleep( 0 )


$ perl core-global-sleep-override.pl
$]=5.020003       $^V=v5.20.3
sleep(1)
hex(0x50)
1
sleep(2)
hex(0x50)
1
total sleep( 3 )
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