下载并安装 composer：

php -r "readfile('https://getcomposer.org/installer');" > composer-setup.php
php -r "if (hash_file('SHA384', 'composer-setup.php') === 'a52be7b8724e47499b039d53415953cc3d5b459b9d9c0308301f867921c19efc623b81dfef8fc2be194a5cf56945d223') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"

把 composer 放到 /usrlocal/bin:

mv composer.phar /usr/local/bin/composer

参考:

• Composer 主页
• Installation - Linux / Unix / OSX