A straight-forward guide to using git
on the command line by git-evangelist Scott Chacon. It starts by covering the basics like installation, making commits and branching. Later chapters cover more arcane matters like how to set up your own git server, hooks and plumbing commands. There was also a brief overview of different workflows.
Even though the book was over a decade old when I read it1 nearly everything was still relevant and informative.
The writing was clear and it did a good job of mentioning the most important of the command line switches (see image below) of Git's many options. The final chapter which was on Git's internals, while not often applicable, was very interesting and gave me an appreciation for how things work.
The writing style wasn't the most exciting, so the book wasn't exactly gripping. There was a chapter on how to set up a Git server which is probably great if you need to do that but wasn't exactly what I needed right now.
To just upgrade your knowledge of git
commands I would recommend reading the chapters Git Basics, Git Branching and Git Tools. Read Git Internals if you're curious and Git on the Server if applicable.
1. A new print edition came out in 2014, but they didn't have it at the library. (Yes, I still favour printed books.) The book is open sourced and the online version is updated constantly. I did skim through the new version and it looks mostly the same with some new appendices added.