What is cURL in PHP?

cURL is a library that lets you make HTTP requests in PHP. Everything you need to know about it (and most other extensions) can be found in the PHP manual.

In order to use PHP's cURL functions you need to install the » libcurl package. PHP requires that you use libcurl 7.0.2-beta or higher. In PHP 4.2.3, you will need libcurl version 7.9.0 or higher. From PHP 4.3.0, you will need a libcurl version that's 7.9.8 or higher. PHP 5.0.0 requires a libcurl version 7.10.5 or greater.

You can make HTTP requests without cURL, too, though it requires allow_url_fopen to be enabled in your php.ini file.

// Make a HTTP GET request and print it (requires allow_url_fopen to be enabled)
print file_get_contents('http://www.example.com/');

CURL in PHP:

Summary:

The curl_exec command in PHP is a bridge to use curl from console. curl_exec makes it easy to quickly and easily do GET/POST requests, receive responses from other servers like JSON and download files.

Warning, Danger:

curl is evil and dangerous if used improperly because it is all about getting data from out there in the internet. Someone can get between your curl and the other server and inject a rm -rf / into your response, and then why am I dropped to a console and ls -l doesn't even work anymore? Because you mis underestimated the dangerous power of curl. Don't trust anything that comes back from curl to be safe, even if you are talking to your own servers. You could be pulling back malware to relieve fools of their wealth.

Examples:

These were done on Ubuntu 12.10

1. Basic curl from the commandline:

   el@apollo:/home/el$ curl http://i.imgur.com/4rBHtSm.gif > mycat.gif
     % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                    Dload  Upload   Total   Spent    Left  Speed
   100  492k  100  492k    0     0  1077k      0 --:--:-- --:--:-- --:--:-- 1240k
   

   Then you can open up your gif in firefox:

   firefox mycat.gif
   

   Glorious cats evolving Toxoplasma gondii to cause women to keep cats around and men likewise to keep the women around.

2. cURL example get request to hit google.com, echo to the commandline:

   This is done through the phpsh terminal:

   php> $ch = curl_init();
   
   php> curl_setopt($ch, CURLOPT_URL, 'http://www.google.com');
   
   php> curl_exec($ch);
   

   Which prints and dumps a mess of condensed html and javascript (from google) to the console.

3. cURL example put the response text into a variable:

   This is done through the phpsh terminal:

   php> $ch = curl_init();
   
   php> curl_setopt($ch, CURLOPT_URL, 'http://i.imgur.com/wtQ6yZR.gif');
   
   php> curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
   
   php> $contents = curl_exec($ch);
   
   php> echo $contents;
   

   The variable now contains the binary which is an animated gif of a cat, possibilities are infinite.

4. Do a curl from within a PHP file:

   Put this code in a file called myphp.php:

   <?php
     $curl_handle=curl_init();
     curl_setopt($curl_handle,CURLOPT_URL,'http://www.google.com');
     curl_setopt($curl_handle,CURLOPT_CONNECTTIMEOUT,2);
     curl_setopt($curl_handle,CURLOPT_RETURNTRANSFER,1);
     $buffer = curl_exec($curl_handle);
     curl_close($curl_handle);
     if (empty($buffer)){
         print "Nothing returned from url.<p>";
     }
     else{
         print $buffer;
     }
   ?>
   

   Then run it via commandline:

   php < myphp.php
   

   You ran myphp.php and executed those commands through the php interpreter and dumped a ton of messy html and javascript to screen.

   You can do GET and POST requests with curl, all you do is specify the parameters as defined here: Using curl to automate HTTP jobs

Reminder of danger:

Be careful dumping curl output around, if any of it gets interpreted and executed, your box is owned and your credit card info will be sold to third parties and you'll get a mysterious $900 charge from an Alabama one-man flooring company that's a front for overseas credit card fraud crime ring.

cURL is a way you can hit a URL from your code to get a html response from it. cURL means client URL which allows you to connect with other URLs and use their responses in your code.