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