wget https://codeception.com/codecept.phardownload 

Execute it as php codecept.phar

wget https://codeception.com/php56/codecept.phardownload 

Execute it as php codecept.phar

sudo curl -LsS https://codeception.com/php80/codecept.phar -o /usr/local/bin/codecept

sudo chmod a+x /usr/local/bin/codecept

Execute it as codecept