How to set custom request headers (e.g., User-Agent) in a cURL request in PHP?

To set custom request headers, including the User-Agent header, in a cURL request in PHP, you can use the curl_setopt() function. Here's an example:

// Initialize cURL
$ch = curl_init();

// Set the URL to send the request to
curl_setopt($ch, CURLOPT_URL, 'http://example.com');

// Set the User-Agent header
curl_setopt($ch, CURLOPT_USERAGENT, 'Custom User-Agent');

// Execute the request
$response = curl_exec($ch);

// Check for errors
if ($response === false) {
    $error = curl_error($ch);
    // Handle error
}

// Close cURL
curl_close($ch);

// Process the response
// ...

In the example above, curl_setopt() is used to set the CURLOPT_USERAGENT option to specify the custom User-Agent header ('Custom User-Agent') in the cURL request.

Note that you can set any other custom headers using curl_setopt() with the CURLOPT_HTTPHEADER option. The value for this option should be an array of header strings. For example:

// Set additional custom headers
$headers = array(
    'Header1: Value1',
    'Header2: Value2',
);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

This allows you to set multiple custom headers if needed.