If you're just spitting out the results of a quick shell command, like ls -l or wget on a not-too-slow page, then backticks are a quick-and-dirty solution (you can also do open(CMD,"some/shell/cmd |")). If your intention is to watch a longer process, like 'top', then check out Merlyn's Watching long processes through CGI.

As an aside, I'd use LWP::Simple or LWP::UserAgent rather than wget.