Make cURL output STDERR to file (or string)

You are making couple mistakes in your example:

1) you have to call curl_exec() prior to reading from the "verbose log", because curl_setopt() doesn't perform any action, so nothing can be logged prior to the curl_exec().

2) you are opening $curl_log = fopen("curl.txt", 'w'); only for write, so nothing could be read, even after you write to the file and rewind the internal file pointer.

So the correct shortened code should look like:

<?php
$curl = curl_init();
$curl_log = fopen("curl.txt", 'rw'); // open file for READ and write
$url = "http://www.google.com";

curl_setopt_array($curl, array(
    CURLOPT_URL             => $url,
    CURLOPT_VERBOSE         => 1,
    CURLOPT_STDERR          => $curl_log,
    CURLOPT_RETURNTRANSFER  => 1
));

$response = curl_exec($curl);

rewind($curl_log);
$output= fread($curl_log, 2048);
echo "<pre>". print_r($output, 1). "</pre>";
fclose($curl_log);

// ...

?>

NOTE: verbose log could be longer than 2048 bytes, so you could "fclose" the $curl_log after curl_exec() and then read the whole file with for example file_get_contents(). In that case, the point 2) should not be considered as mistake :-)

A bit late to the party, but this page still pops up high in Google, so let's go.

It seems that CURLOPT_VERBOSE doesn't log anything if CURLINFO_HEADER_OUT is also set to TRUE.

This is a know bug in PHP (#65348), and due to reasons they decided not to fix it.