<?php
// INIT CURL
$ch = curl_init();

// SET URL FOR THE POST FORM LOGIN
curl_setopt($ch, CURLOPT_URL, ‘http://www.external-site.com/Members/Login.php’);

// ENABLE HTTP POST
curl_setopt ($ch, CURLOPT_POST, 1);

// SET POST PARAMETERS : FORM VALUES FOR EACH FIELD
curl_setopt ($ch, CURLOPT_POSTFIELDS, ‘fieldname1=fieldvalue1&fieldname2=fieldvalue2′);

// IMITATE CLASSIC BROWSER’S BEHAVIOUR : HANDLE COOKIES
curl_setopt ($ch, CURLOPT_COOKIEJAR, ‘cookie.txt’);

# Setting CURLOPT_RETURNTRANSFER variable to 1 will force cURL
# not to print out the results of its query.
# Instead, it will return the results as a string return value
# from curl_exec() instead of the usual true/false.
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);

// EXECUTE 1st REQUEST (FORM LOGIN)
$store = curl_exec ($ch);

// SET FILE TO DOWNLOAD
curl_setopt($ch, CURLOPT_URL, ‘http://www.external-site.com/Members/Downloads/AnnualReport.pdf’);

// EXECUTE 2nd REQUEST (FILE DOWNLOAD)
$content = curl_exec ($ch);

// CLOSE CURL
curl_close ($ch);

?>

libcurl (the library behind the PHP cURL extension) currently supports a wide range of protocols, including HTTP, HTTPS, FTP, TELNET, FILE, LDAP, DICT, GOPHER and HTTPS, as well as HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, and user:password authentication. There are alternatives for some of these, such as streams, sockets or the FTP extension, but cURL is the master of them all – they are less flexible, and don’t perform as well.

A first cURL script
Let’s dive right in with a simple script.

//examle.php

// initialise the cURL session, passing an optional URL
$ch = curl_init('http://www.ex.com/doc.php');

//Execute the session
curl_exec($ch);

//Close the cURL session
curl_close($ch);
?>

The recipient script is:

// recipient.php

print "Welcome, visitor from {$_SERVER['REMOTE_ADDR']}";
?>

The example.php script connects to the URL supplied (doc.php), handing over control to that script. Not particularly useful, but it introduces you to three of the main functions: curl_init(), which returns a cURL handle (hence the results are usually assigned to a variable called $ch), curl_exec(), which executes the session you’ve set up, and curl_close(), which frees all resources associated with the session. curl_exec() returns a boolean in the above context, but most often you will ask it to return the output from the call, which we look at later.

A simple cURL script to look up the meaning of a word
Let’s look at a more practical use. One of the protocols cURL supports is dict. In this example, we’ll create a simple tool to return the definition of a word from dict.org’s database, connecting to dict.org with the dict protocol. Using something similar you can create an online dictionary, or integrate a word search into other applications. This article is not about using forms to submit values to a PHP script – I assume you already know how to do that, and can build upon this skeleton, taking proper care to validate all variables.

// example1.php

//get the word submitted from the form
$word = addslashes($_POST['word']);

// validate the word
if ($word != '') {

// initialise the session, this time with no URL
$ch = curl_init();

// Set the URL, which includes $word, and is of the dict protocol
curl_setopt($ch, CURLOPT_URL, "dict://dict.org/d:($word)");

// Return the output from the cURL session rather than displaying in the browser.
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

//Execute the session, returning the results to $definition, and close.
$definition = curl_exec($ch);
curl_close($ch);

//display the results - I'll leave the formatting to you
print "Definition of $x: $definition";
}
?>

The new function introduced here is curl_setopt(). This takes a cURL handle, an option and a value for this option as arguments. $ch is of course the handle, while we introduce two of the options, CURLOPT_URL and CURLOPT_RETURNTRANSFER. CURLOPT_URL takes the URL for the script to fetch, and can also be set by passing the argument to curl_init(), as we did in the previous example. CURLOPT_RETURNTRANSFER is also one you’ll probably be using most of the time – setting it to true returns the results as a string for processing in your script, rather than just simply displaying it, as in the previous example.