如何将文件恢复到以前的版本

Question

Let's say I'm working on branch A and I merged some changes from branch B. Branch B has a file named setup.sh and I work on branch A and modify the setup.sh file and commit it and later perform let's say 3 different commits on other files of branch A.

Now I realise that I should not be making the changes in setup.sh file. I want to revert back to the branch B version of setup.sh. Obvious solution is git checkout and git commit, but it shows file modified by me in git blame. I do not want that. Any idea how to proceed?

Answer 1

To revert to a particular version of the file, you must make a new commit that contains that version of that file (along with its version of every other file, just like any other commit).

Obvious solution is git checkout and git commit, but it shows file modified by me in git blame.

That will always be the case, because git blame assigns the ownership of each line in a file based on the difference between each snapshot. That is, we are given the fact that we have a series of commits:

... <-F <-G <-H   <--branch

where the branch name branch tells Git that the last commit is commit H , and commit H tells Git that the previous commit is commit G , with commit G telling Git that the previous commit is commit F , and so on. What git blame does is extract the file from commit H , then extract the same file from commit G . Where the lines match, the ownership moves from H to G , but we're not done yet. Where the lines don't match, the ownership is at H .

Now, if we're at G , git blame extracts the file from commit G and again from commit F . Where the lines match, the ownership moves back to F , and where they don't, the ownership stays at G .

Once we're at F , Git extracts the file from the parent of F , and repeats this whole process.

Eventually, each line has an assigned commit, and that's what you see to the left of the line.

This means that no matter how you restore the file to the old commit , it's you that restored the file, and git blame will stop there. To keep going, you must run a second git blame that says starting from before my commit, look backwards the way you always do and now git blame will assign the lines to earlier commits. Git starts at an end and works backwards and if you want it to start at an end that comes before your commit, you simply start it there, instead of at the current commit (or the current working tree copy, which is where we really have git blame start, most of the time).