As an iOS developer i find bash scripts as a integral part of my development workflow. These scripts have lot of uses which include uploading your builds, writing Xcode run scripts. Knowing how to write these scripts not only helps your daily iOS development efforts but can supercharge your productivity in other ways too. Therefore spending some time in learning basics of ShellScripting is an investment which has greater returns.
After learning basics of shell scripting it gave me a kind of freedom. I felt a sense of accomplishment when i was able to understand scripts being used in my app which were written by other awesome developers. Also i was able to write of couple of scripts for myself according to my needs.
Overall, this is a skill an iOS developer should invest over time. very useful.
Here are some References if you are interested in learning ShellScripting.