Welcome :)
I asume you're trying to highlight bash, right? If that's the case, I have run a couple of tests and I could get it working with 'prettify' and 'highlightjs'. According to coderay's site bash is not supported and pygments is not working for me due to some problems with the ruby gem when using it from Java with asciidoctorj.
If you're using directly the ruby command I think that you need to install and set the additional gems to do the highlighting. If you are not a Ruby person (like myself :P), I can recommend you to use gvm with Asciidoctorj to ease the use of shell renderings and gem managing (
http://gvmtool.net/).
Finally, here's an example of the block I used:
[source,bash]
----
#!/bin/bash
HELLO=Hello
function hello {
local HELLO=World
echo $HELLO
}
echo $HELLO
hello
echo $HELLO
----
Please, let us know if this helps.