my @OpenCalls;

BEGIN {
    # See: http://www.perlmonks.org/?node_id=909403
    *CORE::GLOBAL::open = sub(*;$@) {
        push @OpenCalls, [ @_[1..$#_] ];
        use Symbol ();
        my $handle = Symbol::qualify_to_ref($_[0], scalar caller);
        $_[0] = $handle unless defined $_[0];  # pass up to caller

        if (@_ == 1) {
            CORE::open $handle;
        } elsif (@_ == 2) {
            CORE::open $handle, $_[1];
        } elsif (@_ == 3) {
            if (defined $_[2]) {
                CORE::open $handle, $_[1], $_[2];
            } else {
                CORE::open $handle, $_[1], undef;  # special case
            }
        } else {
            CORE::open $handle, $_[1], $_[2], @_[3..$#_];
        }
    };
}