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Reverting in "git"

I'm slowly learning "git". The learning curve is hard at first and gets better as time goes on. (I'm also teaching myself Mercurial, so let's not start a 'which is better' war in the comments).

Reverting a file can be a little confusing in git because git uses a different model than, say, SubVersion. You are in a catch-22 because to learn the model you need to know the terminology. To learn the terminology you need to know the model. I think the best explanations I've read so far have been in the book Pro Git, written by Scott Chacon and published by Apress. Scott put the entire book up online, and for that he deserves a medal. You can also buy a dead-tree version.

How far back do you want to revert a file? To like it was the last time you did a commit? The last time you did a pull? Or revert it back to as it is on the server right now (which might be neither of those)

Revert to like it was when I did my last "git commit":

git checkout HEAD -- file1 file2 file3

Revert to like it was when I did my last "pull":

git checkout FETCH_HEAD -- file1 file2 file3

Revert to like it is on the server right now:

git fetch
git checkout FETCH_HEAD -- file1 file2 file3

How do these work?

The first thing you need to understand is that HEAD is an alias for the last time you did "git commit".

FETCH_HEAD is an alias for the last time you did a "git fetch". "git fetch" pulls the lastest release from the server, but hides it away. It does not merge it into your workspace. "git merge" merges the recently fetched files into your current workspace. "git pull" is simply a fetch followed by a merge. I didn't know about "git fetch" for a long time; I happily used "git pull" all the time.

You can set up aliases in your ~/.gitconfig file. They act exactly like real git commands. Here are the aliases I have:

  br = branch
  st = status
  co = checkout
  revert-file = checkout HEAD --
  revert-file-server = checkout FETCH_HEAD --
  lg = log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit --date=relative

This means I can do git br instead of "git branch", saving me a lot of typing. git revert-file file1 file2 file3 is just like the first example above. git revert-file-server is a terrible name, but it basically diffs between the last fetch and my current workspace. git lg outputs a very pretty log of recent changes (I stole that from someone who probably stole it from someone else. Don't ask me how it works).

To add these aliases on your system, find or add a [alias] stanza to your ~/.gitconfig file and add them there.

Posted by Tom Limoncelli in Technical Tips

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2 Comments | Leave a comment

git was much easier for me to understand if i understood how it works. (this is totally not true at all with svn or p4 - i could be functional by spending 15-30 minutes reading up on syntax.) a useful guide for that: git-for-computer-scientists

If you haven't read Eric Sink's Version Control by Example, I highly recommend it as a good starting point. He's no longer giving away the free dead-tree version, but it's available on Amazon.

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