The following commands will safely reinstall WordPress after creating a backup of the existing installation.
replace latest.tar.gz with the correct tar.gz for the version of WordPress you are reinstalling. This can be determined by viewing the contents of yoursite/wp-includes/version.php. You can find older versions in wordpress archive at https://wordpress.org/download/release-archive/. Simply copy the URL of tar.gz (e.g. https://wordpress.org/wordpress-4.7.tar.gz) that you need and replace latest.tar.gz with that URL below.
IMPORTANT: Make sure you are in the WordPress directory when running these commands! You should see the usual structure; wp-admin, wp-content, wp-includes, etc.
wget https://wordpress.org/latest.tar.gz tar xfz latest.tar.gz mv ./wp-includes ./wp-includes.backup mv ./wp-admin ./wp-admin.backup cd wordpress/ yes | cp -R * ../ cd .. rm -rf ./wordpress/ latest.tar.gz
Make sure to fix permissions of all files which you have replaced.
