I know what you mean with bash scripting for repetitive tasks. And also know the basic guidelines for that.
The standard arguments like: if/then/else, for/do, while/do but i can't find a handy handbook.
It seems that in the end it comes down to personal creativity.
If you want a good handbook for BASH, try this:
https://www.amazon.com/Bash-Pocket-...89275345&sr=8-4&keywords=bash+shell+scripting
The book
Classic Shell Scripting is good as well, but much larger. Get familiar with things like
sed,
awk,
grep, and the like. Python has a lot of handy modules available to help interface with a GNU/Linux-based system. I'm a Python programmer (mostly), and like Java, it's super popular but abused to hell and back. Document your code using Docstrings, use sensible variable and function names, and test the crap out of your functions/modules. Pass them weird inputs. Try to break them. Unfortunately Python will barf on corner cases in production code if you're not careful. A good thing to do is to check out some project from GitHub/GitLab/whatever and read the code. Does it make sense? What would you have done differently?
Keep in mind there are different standards for Python, namely 2.7 and 3. A lot of folks still use Python 2.7, and I wish they had called Python 3 something else, because you'll find a number of books on 2 or 3 just called "Python". C is similar, there are a few standards, but at least go for C99. Assembly is fun, but can be frustrating.
It sounds like you're on a good path. I don't really know anything about CCNA, but being comfortable with Python and BASH scripting is a huge plus and will make your job a lot easier, I'd imagine. They look good on a resume too.