Some mistakes i noticed in this thread:
jordanjay29 referring to installation directory starting with a / will try to install it in the root of the system. You won't have access to that folder and you shouldn't install your Flarum there anyway 😉 Use a relative path: installation_directory, full command
php composer.phar create-project flarum/flarum installation_directory --stability=beta
santiagobiali creating a directory beforehand is not necessary and will prevent the "not empty" issue. Simply run the above command for "installation_directory" to be created by composer. If the directory exists, you can remove it using:
rm -rf installation_directory
One other tip:
If you want to skip unnecessary development resources (and so disk space) append --no-dev to the command:
php composer.phar create-project flarum/flarum installation_directory --stability=beta --no-dev
