Install wp_cli

1curl -O https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
2php wp-cli.phar --info                ## check if it's working.
3chmod +x wp-cli.phar
4sudo mv wp-cli.phar /usr/local/bin/wp
5wp --info                             ## re-check if it's working as 'wp'