What's the difference between git reset file and git checkout file?

Question

Why is it that git allows me to reset a file? I thought I understood reset, in the sense that it was moving the HEAD ... clearly I was wrong.

So, git reset sha file seems to do the same as git checkout sha file, with the exception that I see file in the index and in the working directory.

It doesn't make sense to me. Can someone please explain the difference?

Answer 1

tl;dr git reset COMMIT FILE changes only index, git checkout COMMIT FILE will change both index and working tree.

git reset has very important flags of --soft, --hard and --mixed ( and --keep and --merge )

http://git-scm.com/docs/git-reset

--mixed is the default and when you do git reset sha file you are doing mixed reset whereby:

--mixed

Resets the index but not the working tree (i.e., the changed files are preserved but not marked for commit) and reports what has not been updated. This is the default action.

Like it says above, the reset in this case would not touch your working tree at all and only the version in the index is reset to the one in the sha.

git checkout on the other hand:

When or --patch are given, git checkout does not switch branches. It updates the named paths in the working tree from the index file or from a named (most often a commit).

So when you do git checkout you will lose the changes in the file and it will be replaced with whatever was there in the version of file in sha, whereas when you do the mixed reset, only your index will be reset and your working directory will still have the changes which you can later stage again as needed.