chewlim

sudo yum -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
sudo yum -y install https://rpms.remirepo.net/enterprise/remi-release-7.rpm
sudo yum -y install yum-utils
sudo yum-config-manager --disable 'remi-php*'
sudo yum-config-manager --enable remi-php81
sudo yum repolist
sudo yum -y install php php-{cli,fpm,mysqlnd,zip,devel,gd,mbstring,curl,xml,pear,bcmath,json,opcache,redis,memcache}

chewlim

$ cd ~
$ sudo curl -sS https://getcomposer.org/installer | sudo php
$ sudo mv composer.phar /usr/local/bin/composer
$ sudo ln -s /usr/local/bin/composer /usr/bin/composer

then you can run 
$ sudo composer install