Installing WP-CLI with a Single Command

One command:

curl -sS -o /usr/local/bin/wp https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar && chmod +x /usr/local/bin/wp

MySQL Client if needed for WP-CLI database related commands:

apk update && apk add -f mysql-client

apt-get update && apt-get install -y mariadb-client