Fatal error: Call to undefined function curl_init()

<?php
$filename = "xx.gif";
$handle = fopen($filename, "r");
$data = fread($handle, filesize($filename));

// $data is file data
$pvars   = array('image' => base64_encode($data), 'key' => IMGUR_API_KEY);
$timeout = 30;
$curl    = curl_init();

curl_setopt($curl, CURLOPT_URL, 'http://api.imgur.com/2/upload.xml');
curl_setopt($curl, CURLOPT_TIMEOUT, $timeout);
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($curl, CURLOPT_POSTFIELDS, $pvars);

$xml = curl_exec($curl);

curl_close ($curl);

var_dump($xml);
?>

I'm playing with the Imgur API, but it doesn't seems to work. PHP.net says that curl_init() is in PHP5, but my host says it isn't. How can I make this work?

On old versions of Debian and Ubuntu, you solved this by installing the Curl extension for PHP, and restarting the webserver. Assuming the webserver is Apache 2:

sudo apt-get install php5-curl
sudo service apache2 restart

On newer versions, the package name as changed:

sudo apt install php-curl

It's possible you'll need to install more:

sudo apt-get install curl libcurl3 libcurl3-dev;

curl is an extension that needs to be installed, it's got nothing to do with the PHP version.

http://www.php.net/manual/en/curl.setup.php

Don't have enough reputation to comment yet. Using Ubuntu and a simple:

sudo apt-get install php5-curl
sudo /etc/init.d/apache2 restart

Did NOT work for me.

For some reason curl.so was installed in a location not picked up by default. I checked the extension_dir in my php.ini and copied over the curl.so to my extension_dir

cp /usr/lib/php5/20090626/curl.so  /usr/local/lib/php/extensions/no-debug-non-zts-20090626

Hope this helps someone, adjust your path locations accordingly.