1、下载composer.phar文件

curl -sS https://getcomposer.org/installer | php

将composer.phar移动到环境变量中并且更名为composer

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

使用国内镜像
composer config -g repo.packagist composer https://packagist.phpcomposer.com

2、直接简单粗暴的

wget https://dl.laravel-china.org/composer.phar -O /usr/local/bin/composer
chmod a+x /usr/local/bin/composer