get the verbose http header with curl command

A new workmate asked me how to get the verbose http header with the curl command in debian3.1. I used the curl command several times but I never used it to get the verbose information about http header. I tried the curl command with the verbose option, but I couldn't see the verbose infomation. Then I redirected the standard error stream into the standard output stream and redirected the output stream into a file. Finally, It worked. The following example is my resolution.
$output = array();
exec("curl -v  > /tmp/output.curl 2>&1", $output, $ret);
$output2 = array();
exec("cat /tmp/output.curl",$output2,$ret2);
print_r($output2);
?>