Here's a step-by-step guide to install Moosh on a MoodleBox.

You should first log into the MoodleBox via SSH.

Download Composer

Follow instructions given on https://getcomposer.org/download/ to download Composer:

php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php -r "if (hash_file('sha384', 'composer-setup.php') === 'e0012edf3e80b6978849f5eff0d4b4e4c79ff1609dd1e613307e16318854d24ae64f26d17af3ef0bf7cfb710ca74755a') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"

Install Composer, then remove the installer

We install the Composer binary so that it's globally available, then remove the installer:

sudo php composer-setup.php --install-dir=/usr/local/bin --filename=composer
php -r "unlink('composer-setup.php');"

Install Moosh

We download Moosh to MoodleBox user dir, then link the Moosh binary so that it's globally available:

cd
git clone https://github.com/tmuras/moosh.git
cd moosh/
composer install
sudo ln -s $PWD/moosh.php /usr/local/bin/moosh

Test that Moosh is installed and works correctly

Type this command:

moosh -n --moodle-path=/var/www/moodle config-get core release

It should return installed Moodle version, e.g. 3.9 (Build: 20200615).