As stated in the official PHP documentation:
PHP supports libcurl, a library created by Daniel Stenberg, that allows you to connect and communicate to many different types of servers with many different types of protocols. libcurl currently supports the http, https, ftp, gopher, telnet, dict, file, and ldap protocols. libcurl also supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading (this can also be done with PHP’s ftp extension), HTTP form based upload, proxies, cookies, and user+password authentication.
Sometimes when you work in your own server or virtual machine, you can run into some issues when you call functions that use the curl library, such as:
Call to undefined function curl_init ()
This happens because CURL is not installed in your system
To fix this, you can execute (as superuser)
sudo apt-get install php5-curl
sudo service apache2 restart(often not necessary)
In this way the problem should be solved without further editing of files like php.ini
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