unable to change php version on cli

Question

I have install php versions 5.6,7.0 and 7.1 . But php -v returns

PHP 5.5.9-1ubuntu4.21 (cli) (built:feb 9 2017) <br>
copyright (c) 1997-2014 The PHP Group

I also tried these commands

 a2enmod php7.1 
 a2dismod php5.6 
 service apache2 restart

but they don't work ..

so how can i run multiple versions of php on terminal?