I am assuming that the parent CGI script is trying to call another CGI script on the same web server. In that case, you don't need to use LWP. The parent can execute the other CGI script directly. Although, if the parent detaches from child, then the child has no way to communicate back to the browser.

The reason system doesn't work is that it waits for the child process to return. The solution is to use fork and then exec. When running under a web server, you must close STDERR and STDOUT, or the browser won't know that the CGI script has finished.

if ($pid = fork()) {
   # parent

} else {
    die "Cannot fork:$!" unless defined $pid;
    close(STDOUT);
    close(STDERR);
    exec("otherscript.pl");
}
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