Well I needed to install composer in my Ubuntu even though the installation it’s very simple in the official composer page doesn’t tell you directly how to setting it to use it as “composer” in the terminal.
Install it with:
curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
Now you can just run composer on your terminal and it’s working.
I’m just making it easier for you 🙂