For those who want a GUI around this on Mac, https://rowanj.github.io/gitx/ is an incredible secret weapon. You can swipe over a bunch of lines or let the software identify a whole span of contiguous changed lines, click a button, and see just those changes move over from your unstaged to staged changes, then commit exactly what you want.

A lot of times people don't even understand how powerful the staging area is; they're just used to saying git add && git commit without realizing that it can be an incredible way to take a day of chaotic fixes and turn it into a set of commits you can be proud of!

It also provides an incredible tree view of commit parentage, perfect for when you need to instantly understand what happened with this weird merge/rebase that broke things, and to screenshare it to teach colleagues who might not have developed an internal understanding of the tree structure that Git is based on.

The software is now 9 years old and abandoned, but I've used this specific fork at least weekly - often daily - for every one of those years, across Intel and M1 Macs, and it's never let me down!