This prevents the call to the standard open to autovivify a GLOB when none is available.

It shouldn't be prevented. If it autovivifies, I want to know about that. This Blorfldyick is meant to be transparent, while adding overhead and slowing things down... ;-)

It's not easy, open is a complex beast. I'm reaching into the pile of rhinos... open can be provided a lexical var, a package var (populated or not), a typeglob, a bareword, a Symbol (via gensym) and what not, as the first argument. Trying to wrap my head around all that... thanks for your input, Eily++

In order to avoid the wrong caller package issue, you can create a wrapping sub for open in the caller package and jump there using goto &$sub which overwrites the current stack frame. Something similar to the following code:

package MyOpen;
use Carp ();
use Data::Dumper;
use 5.010;

my %cache;

BEGIN {
    *CORE::GLOBAL::open = sub {
        my $pkg = caller;
        my $sub = $cache{$pkg} //= do {
            my $code = <<EOS;
package $pkg;
sub {
    my \$r = CORE::open \$_[0], \@_[1..\$#_];
    Carp::cluck(Data::Dumper::Dumper(\@_));
    return \$r;
}
EOS
            eval $code or die "Bad sub: $@";
        };
        goto &$sub;
    };
}


package main;

open $fh, '>&', 'STDOUT';
open FOO, ">", "/tmp/FOO";
[download]

Thank you. I was thinking about taking this road, using eval to switch package. I can't goto &$sub to erase the current stack frame, because I need to do the track housekeeping after the open, and record the (possible mutated) $_[0]. OTOH... thinking about it, I could switch package in that eval'ed sub again and do the housekeeping there. To that end, the %fh fieldhash must be a package var. Oh well.

Currently, I am inspecting $_[0] with Devel::Caller etc. to find out whether the filehandle variable is lexical, package global, typeglob, bareword etc and trying to do the right thing. Anyways the overridden open would show up in the stack trace of Carp::cluck, so another stack frame wouldn't matter I guess. But with Sub::Name I could make that sub into the calling package. Maybe that's the best way to do it. It is definitely the cheapest in effort :-) update: and maybe the most robust also...

Thanks again, salva!

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'