$ sudo add-apt-repository ppa:ondrej/php
$ sudo apt-get update
$ sudo apt-get install php7.3 php7.3-cli php7.3-curl php7.3-mysql php7.3-xml php7.3-zip php7.3-gd php7.3-mbstring php7.3-xmlrpc php7.3-soap php7.3-zip php7.3-bcmath php7.3-bz2 php7.3-intl
$ sudo apt-get install curl
$ curl -sS https://getcomposer.org/installer | sudo php -- --install-dir=/usr/local/bin --filename=composer