I’m not a Linux admin, but I think there are certifications you can get and exams you can take to show you understand stuff about shell scripting and related topics, if that’s what you’re interested in.

I think they have questions like “Make it so a welcome message and the time display when someone logs into your Linux server”, among other, harder things.

I don’t know a huge amount about the job market, but just saying you have those kinds of skills on your CV along with a bit of experience in some other tech/coding/data stuff might even be enough.