Couldn't find any package by regex 'php5.6'
<p>I am trying to upgrade from PHP 5.5.38 to PHP 5.6. I am following instructions <a href="https://stackoverflow.com/a/38737323/520957">available on SO</a>, but I am getting the following error messages:</p>

<pre><code>sudo apt-get -y install php5.6 php5.6-mcrypt php5.6-mbstring php5.6-curl php5.6-cli php5.6-mysql php5.6-gd php5.6-intl php5.6-xsl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package php5.6
E: Couldn't find any package by regex 'php5.6'
E: Unable to locate package php5.6-mcrypt
E: Couldn't find any package by regex 'php5.6-mcrypt'
E: Unable to locate package php5.6-mbstring
E: Couldn't find any package by regex 'php5.6-mbstring'
E: Unable to locate package php5.6-curl
E: Couldn't find any package by regex 'php5.6-curl'
E: Unable to locate package php5.6-cli
E: Couldn't find any package by regex 'php5.6-cli'
E: Unable to locate package php5.6-mysql
E: Couldn't find any package by regex 'php5.6-mysql'
E: Unable to locate package php5.6-gd
E: Couldn't find any package by regex 'php5.6-gd'
E: Unable to locate package php5.6-intl
E: Couldn't find any package by regex 'php5.6-intl'
E: Unable to locate package php5.6-xsl
E: Couldn't find any package by regex 'php5.6-xsl'
</code></pre>

<p>Does anyone know what is causing this issue?</p>

<p><strong>P.S.</strong>: I am on Debian GNU/Linux 7 (wheezy)</p>