<?php
// Create a curl handle
$ch = curl_init();

// Set CURLOPT_USERAGENT option
curl_setopt($ch, CURLOPT_USERAGENT, "My test user-agent");

// Reset all previously set options
curl_reset($ch);

// Send HTTP request
curl_setopt($ch, CURLOPT_URL, 'http://example.com/');
curl_exec($ch); // the previously set user-agent will be not sent, it has been reset by curl_reset
?>