docker-entrypoint.sh

#!/bin/bash

array=(
    'WP_CACHE::false'
    'WPCACHEHOME::'
    'DB_NAME::dbname'
    'DB_USER::dbuser'
    'DB_PASSWORD::dbpass'
    'DB_HOST::localhost'
    'DB_CHARSET::utf8'
    'DB_COLLATE::'
    'AUTH_KEY::put your unique phrase here'
    'SECURE_AUTH_KEY::put your unique phrase here'
    'LOGGED_IN_KEY::put your unique phrase here'
    'NONCE_KEY::put your unique phrase here'
    'AUTH_SALT::put your unique phrase here'
    'SECURE_AUTH_SALT::put your unique phrase here'
    'LOGGED_IN_SALT::put your unique phrase here'
    'NONCE_SALT::put your unique phrase here'
    'table_prefix::wp_'
    'WP_DEBUG::false'
    'WP_AUTO_UPDATE_CORE::false'    
)

sed_escape() {
    echo "$@" | sed -e 's/[\/&]/\\&/g'
}

for index in "${array[@]}" ; do
    KEY="${index%%::*}"
    VALUE="${index##*::}"

    if [ -z "${!KEY}" ]
    then
        declare ${KEY}=$VALUE
    fi

    sed -i -e 's/{'"$KEY"'}/'"$(sed_escape ${!KEY})"'/g' wp-config.php

done

cd /var/www && curl -O https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
su - www-data -s /bin/bash -c 'php wp-cli.phar core update-db --path=/var/www/html/'
rm wp-cli.phar

exec "$@"