apt-get update && apt-get install -y language-pack-en-base && export LC_ALL=en_US.UTF-8 && export LANG=en_US.UTF-8 && apt-get install -y software-properties-common && add-apt-repository -y ppa:ondrej/php5-5.6 && add-apt-repository -y ppa:ondrej/mariadb-10.0 && apt-get update && apt-get -y upgrade apt install php5.6
Results
root@ubuntu:~# php -v
PHP 5.6.29-1+deb.sury.org~xenial+1 (cli)
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies