Install Drupal Console Launcher using the phar

curl https://drupalconsole.com/installer -L -o drupal.phar
mv drupal.phar /usr/local/bin/drupal
chmod +x /usr/local/bin/drupal

NOTE: If you don't have curl you can try

php -r "readfile('https://drupalconsole.com/installer');" > drupal.phar

Update DrupalConsole Launcher

drupal self-update

Run Drupal Console using the Launcher

drupal

Installing the Launcher using Composer

Set Composer global minimum-stability and prefer-stable configurations.

composer config minimum-stability dev
composer config prefer-stable true
composer global require drupal/console-launcher:~1.0

You must execute the launcher within a drupal site directory or use --root=/path/to/drupal8.dev to specify your drupal site path.

NOTE: The name drupal is just an alias you can name it anything you like.