To diagnose this issue check an ouput of the php -v command:
The right case («cli»)
A wrong case («cgi-fcgi» instead of «cli»)
In a wrong case you should install or reconfigure the PHP Command Line Interface
An example of solution for PHP 7: http://magento.stackexchange.com/a/101262
Another solution (for some hostings) is to try to use php-cli instead of php