Lots of useful examples.
nixCraft Linux Bash Shell Scripting Tutorial
GNU reference is always the go to for the final words.
This is a very good guide that I used to learn Bash. Not too long and enough to get started to get a good foundation in Bash. I really thanks the author for a gentle introduction to Bash.
Bash Guide for Beginners [PDF]
Finally, I got this xargs. It solves my problem when I need to pipe
in arguments to commands.
Pipes vs Xargs: Which One To Use When Writing Bash Scripts In Linux