In addition to the other comments( of which I tend to agree that it is a permissions issue for sure!). Check Apache's logs for errors. Also, I don't know if you are use CGI::Carp or not, but that helps to spit errors out to the browser when things go wrong.
I would also try writing a simple test case:

use CGI qw(:standard);
my $cgi = CGI->new();
print $cgi->header;
print $cgi->start_html;
my $rv = `set `;  # see your environment

print $cgi->p( $rv );
print $cgi->end_html;
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JamesNC