The 3 week path to learning bash scripting

Hey guys, I just got my first job as a developer and I'm told that I will mostly be writing Python and Bash scripts. I know python but I feel like I'm going to be exposed for Bash scripting. I use Linux and Mac but I've never written bash scripts. I use the regular commands like ls, cd, mkdir, git, etc and I understand the file system. I'm very scared that they'll fire me since I can't write scripts. My question is this: My job starts in 3 weeks, what is the best resource for learning as much as possible about bash scripting so that they don't think I was a mistake to hire. I've been freaking out for the last day instead of being excited about my first programming job. Thank you guys.