This might help:

#!/usr/bin/perl

use strict;
use warnings;
use CGI;

my $q = new CGI;
print $q->header;
print $q->start_html('Stage1.cgi');
unless ($q->param) {
    print $q->startform;
    print $q->h3("Select Stage: ");
    print $q->scrolling_list(
        -values => [
             'Stage1',
             'Stage1left',
             'Stage1right' ],
        -size => 10,
        -multiple => 'true' );
    print $q->br;
    print $q->submit(-value => "Your Stage selection");
    print $q->endform;
}
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