apt-get install apt-transport-https lsb-release ca-certificates
wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list
apt-get update

apt-get install php7.1
apt-get install php7.1-cli php7.1-common php7.1-curl php7.1-gd php7.1-json php7.1-mbstring php7.1-mysql php7.1-opcache php7.1-readline php7.1-xml