linux安装composer
https://www.runoob.com/w3cnote/composer-install-and-usage.html
Linux 平台可以使用以下命令来安装：
1、下载配置文件并安装
前提条件，已经安装了php73he mysql8
php73 -r "copy('https://install.phpcomposer.com/installer', 'composer-setup.php');"
php73 composer-setup.php
All settings correct for using Composer
Downloading...
Composer (version 1.9.0) successfully installed to: /usr/share/nginx/composer.phar
Use it: php composer.phar
移动 composer.phar，这样 composer 就可以进行全局调用：
2、调整php73为 php，
cd usr/bin
cp php73 php
/*
这一步很重要，否则会报错
/usr/bin/env: php: 没有那个文件或目录
*/
mv composer.phar /usr/local/bin/composer
切换为国内镜像：
3、安装composer
composer config -g repo.packagist composer https://packagist.phpcomposer.com
更新 composer：
composer selfupdate