This appendix highlights the options and features of PHP/CURL that will be of greatest interest to webbot developers. In addition to the features described here, you should know that PHP/CURL is an extremely powerful interface with a dizzying array of options. A full specification of PHP/CURL is available at the PHP website.[93]
In some regards, a PHP/CURL session is similar to a PHP file I/O session. Both create a session (or file handle) to reference an external file. And in both cases, when the file transfer is complete, the session is closed. However, PHP/CURL differs from standard file I/O because it requires a series of options that define the nature of the file transfer set before the exchange takes place. These options are set individually, in any order. When many options are required, the list of settings can be long and confusing. For simplicity, Listing A-1 shows the minimal options required to create a PHP/CURL session that will put a downloaded file into a variable.
<? # Open a PHP/CURL session $s = curl_init(); # Configure the cURL command curl_setopt($s, CURLOPT_URL, "http://www.schrenk.com"); // Define target site curl_setopt($s, CURLOPT_RETURNTRANSFER, TRUE); // Return in string # Execute the cURL command (send contents of target web page to string) $downloaded_page = curl_exec($s); # Close PHP/CURL session curl_close($s); ?>
Listing A-1: A minimal PHP/CURL session
The rest of this section details how to initiate sessions, set options, execute commands, and close sessions in PHP/CURL. We'll also look at how PHP/CURL provides transfer status and error messages.