In Bash 4, to lowercase:
<pre class="language-bash"><code class="language-bash">var = 'Hello, World'
echo ${var,,}
</code></pre>
<pre><code>hello, world
</code></pre>
and to uppercase:
<pre class="language-bash"><code class="language-bash">var = 'Hello, World'
echo ${var^^}
</code></pre>
<pre><code>HELLO, WORLD
</code></pre>

Use `${var,,}` for lowercasing and `${var^^}` for uppercasing for Bash 4+


Bash: Uppercase, Lowercase