The source code to CPAN::Nox is:

package CPAN::Nox;
use strict;
use vars qw($VERSION @EXPORT);

BEGIN{
  $CPAN::Suppress_readline=1 unless defined $CPAN::term;
}

use base 'Exporter';
use CPAN;

$VERSION = "5.50";
$CPAN::META->has_inst('Digest::MD5','no');
$CPAN::META->has_inst('LWP','no');
$CPAN::META->has_inst('Compress::Zlib','no');
@EXPORT = @CPAN::EXPORT;

*AUTOLOAD = \&CPAN::AUTOLOAD;

1;
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So you probably only need:

#!/usr/bin/perl
use CPAN;
$CPAN::META->has_inst('LWP','no');
shell();
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