$ head -n 1 *.pm
==> AA.pm <==
package AA; use base qw/Exporter/; our @EXPORT=qw/$knob1/; our $knob1 = 'no'; 1
==> BB.pm <==
package BB; use base qw/AA/; our @EXPORT=qw/$knob1/; 1
==> CC.pm <==
package CC; use base qw/BB/; our @EXPORT=qw/$knob1/; 1
$ perl -MCC -MBB -lwe '$BB::knob1=42; print for $AA::knob1, $BB::knob1, $CC::knob1'
no
42
Use of uninitialized value in print at -e line 1.