For the first chuck of code, I think it works better if you don't use comma in qw() and the DBG variables need to have a $ in front.

Here are the changes that I made to the first chunk code and the output.

bruce:1:~/tmp $ cat p.pl
#!/usr/bin/env perl

use strict;
use warnings;
use Readonly;

my @EXPORTs = qw(DBG_ONE DBG_TWO DBG_FOUR) ;

Readonly  my $DBG_ONE => 1;
Readonly  my $DBG_TWO => 2;
Readonly  my $DBG_FOUR => 4;

no strict 'refs';
foreach my $flag (@EXPORTs) {
  printf "flag = %s, value = 0x%04x\n", $flag, ${$flag};
}
bruce:1:~/tmp $ ./p.pl
Use of uninitialized value in printf at ./p.pl line 15.
flag = DBG_ONE, value = 0x0000
Use of uninitialized value in printf at ./p.pl line 15.
flag = DBG_TWO, value = 0x0000
Use of uninitialized value in printf at ./p.pl line 15.
flag = DBG_FOUR, value = 0x0000
[download]

In pondering why the uninitialized value warnings were being displayed I remembered that you can't use symbolic references on my variables. So change the my to our and retry ...

#!/usr/bin/env perl

use strict;
use warnings;
use Readonly;

my @EXPORTs = qw(DBG_ONE DBG_TWO DBG_FOUR) ;

Readonly  our $DBG_ONE => 1;
Readonly  our $DBG_TWO => 2;
Readonly  our $DBG_FOUR => 4;

no strict 'refs';
foreach my $flag (@EXPORTs) {
  printf "flag = %s, value = 0x%04x\n", $flag, ${$flag};
}
bruce:1:~/tmp $ ./p.pl
flag = DBG_ONE, value = 0x0001
flag = DBG_TWO, value = 0x0002
flag = DBG_FOUR, value = 0x0004
[download]

Much better.