This tutorial is intended for PHP programmers and web developers interested in
using their webserver to transfer files or communicate with other servers. You
will need some general knowledge of client-server protocol on the Internet, and
a basic knowledge of PHP syntax.
cURL and libcurl are libaries that allow a webserver to transfer files with a
remote computer using a variety of Internet protocols. The libaries are highly
configurable, allowing practically any type of client-server request to be peformed.
By using these tools, a webserver can act as a client, creating and responding
to requests using any technology built on HTTP, like XML-RPC, SOAP, or WebDAV.
In this tutorial you will learn:
- What cURL and libcurl
- How to use cURL on the command
- How to use libcurl within
cURL stands for “Client URLs”, and was developed by Daniel Stenberg in 1998 as
a command line tool. libcurl is a portable library that provides an easy interface
to the cURL functionality. It is thread safe, IPv6 compatible, and supports persistent
connections. The libcurl PHP binding was added by Sterling Hughes.
Both cURL and libcurl can transfer files using a wide variety
of protocols, including HTTP, HTTPS, FTP, FTPS, GOPHER, LDAP, DICT, TELNET and
FILE. The libraries run on practically any *NIX operating system, as well as
Windows, OS/2, BeOS, and many more.
The cURL libraries are truly open source, with an MIT/X
derivative license. This license is very liberal, allowing the use of cURL for
whatever you want, commercial or not. You can use libcurl for free, and even
include and distribute it with your own application, whether commercial or
cURL should not to be confused with the Curl Corporation, which is the commercial
producer of the client side programming language, Curl.
From PHP version 4.2.3 on, you need a cURL version of at least 7.9.0. From PHP
version 4.3.0 on, you need a cURL version of at least 7.9.8.
As with any PHP extension in Windows, you will need the PHP
distribution that includes external extensions. Once PHP is installed, you will
need to copy the files php4ts.dll, ssleay32.dll, php_curl.dll, msvcrt.dll from
the ‘DLLs’ folder to your Windows PATH, i.e.:
c:\windows\system for Windows 9x/Me
c:\windows\system32 for Windows XP
cURL can then be enabled by uncommenting the line
‘extension=php_curl.dll’ in the php.ini file. Alternatively you can load the
module dynamically in your script using:
Your local mirror for downloading cURL can be found at
http://curl.haxx.se. Precompiled binaries are
also available for a wide range of operating systems.
Because cURL relies on the
openssl library for SSL
openssl must be
installed first. If
not installed, SSL support will be omitted from the cURL build. After
installing cURL (./configure, make, make install), PHP must be recompiled to
include cURL support
If cURL support is enabled, the
phpinfo() function will display
it in its output.
Using cURL from the command line is extremely easy. The following example retrieves
a web page and prints the page to
$ curl -L zend.com
(The ‘-L’ tells cURL to follow
Of course, we can execute cURL on the command line using PHP.
The following example does just that, and gets 3 pages at once:
$var = echo shell_exec("/usr/bin/curl -L http://www.zend.com http://zend.com/developers.php http://zend.com/zend/tut/");
While using cURL from within PHP is an option, using the libcurl PHP binding is
much easier, especially for things like an HTTP POST operation.
The process of using libcurl from within PHP is a matter of
following these basic steps:
- Initialize the cURL
- Set the cURL options (The order of the
options is not important)
- Execute the options in
the cURL session
- Close the curl
Following this process, here are a few examples demonstrating
HTTP POST, HTTP Authentication, and FTP:
// FIND BOOKS ON PHP AND MYSQL ON AMAZON
$url = "http://www.amazon.com/exec/obidos/search-handle-form/002-5640957-2809605";
$ch = curl_init(); // initialize curl handle
curl_setopt($ch, CURLOPT_URL,$url); // set url to post to
Tip: If you are having trouble getting libcurl to do
what you want, add the following code before closing the cURL handle:
echo "\n\ncURL error:" . curl_error($ch);
// ...close cURL handle ($ch) below
This will force libcurl to report back on what
happened on the last transfer, making it easier to
The decision as to whether to use cURL or libcurl depends on the situation. For
instance, if I have a cron job running that e-mails me when a file changes on
a remote server, or if my ISP doesn’t have libcurl support in their PHP
install, using cURL makes more sense. However, if I have libcurl support in PHP
and I am building a PHP application requiring cURL functionality, libcurl is the
The cURL libraries provide a nice interface for file transfers to and from a webserver.
They have support for a wide variety of protocols (like HTTPS) giving them an
edge over built-in PHP functions like
fsockopen(). The libraries
are thread-safe, IPv6 compatible, and will work with any technology that is built
on top of HTTP. Whether you are building simple script to fetch a web page, or
a secure payment gateway, leveraging the functions built into cURL can save a
lot of time.
Whatever spare time Jim has left after working full-time as a web developer, he
spends developing websites like http://www.fatpigeon.com.
Feel free to send any questions or comments to firstname.lastname@example.org