What is the mechanism of a git checkout?
does a git checkout pull the contents of a branch? how does it physically separate files in your working directory from other branches?
The speed of which it works leads me to the logical conclusion that the files in the working directory are all there for all branches and git simply only shows you the files of the active branch.
Can anyone shed more light on the underlying mechanisms of git checkout maybe even branch and merge as well?
thanks
-diego
www.greyrobot.com
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Quoted 3 lines · mastermindxs
Can anyone shed more light on the underlying mechanisms of git checkout maybe even branch and merge as well?
This may help you understand Git: http://www.youtube.com/watch?v=8dhZ9BXQgc4
Also: http://eagain.net/articles/git-for-computer-scientists/
Peter Harris
Quoted 10 lines · mastermindxs
does a git checkout pull the contents of a branch? how does it physically separate files in your working directory from other branches?
The speed of which it works leads me to the logical conclusion that the files in the working directory are all there for all branches and git simply only shows you the files of the active branch.
Can anyone shed more light on the underlying mechanisms of git checkout maybe even branch and merge as well?
I explain it as below when I get asked this question. It's a simplified answer but largely correct, I believe. Corrections from git.gods welcome :-)
When you checkout a branch, you are moving from a "before" branch to an "after" branch. git does this:
- untracked files are never touched; the rest of this discussion does not apply to them
- files which do NOT show up in "git status" (ie unchanged with respect to the "before" branch) are changed as per their status in the "after" branch.
- if they exist in the "after" branch, and are the same as in the "before" branch, they are left alone
This is where all the speed you see comes from!
- if they exist in the "after" branch, and they are **different** than in the "before" branch, they are checked out from the "after" branch
This is the bulk of the disk activity; if there are few of these, it's fast enough for you think nothing is actually happening ;-)
- if they do not exist in the "after" branch, they are deleted
- files that do show up in "git status" in the "before" branch, are either modified or staged.
- if the "before" branch version is the same as the "after" branch version, that also is not touched. In the new branch, running "git status" will show you the same files.
- if the "before" branch version and the "after" branch version are *not* the same, git would lose your local (uncommitted) changes, so it refuses to do the checkout and stays where it is.
Quoted 16 lines · Sitaram Chamarty
Quoted 5 lines · mastermindxs
does a git checkout pull the contents of a branch? how does it physically separate files in your working directory from other branches?
Quoted 7 lines
The speed of which it works leads me to the logical conclusion that the files in the working directory are all there for all branches and git simply only shows you the files of the active branch.
Can anyone shed more light on the underlying mechanisms of git checkout maybe even branch and merge as well?
I explain it as below when I get asked this question. It's a simplified answer but largely correct, I believe.
[...]
Quoted 8 lines
- files that do show up in "git status" in the "before" branch, are either modified or staged.
- if the "before" branch version is the same as the "after" branch version, that also is not touched. In the new branch, running "git status" will show you the same files.
Quoted 4 lines
- if the "before" branch version and the "after" branch version are *not* the same, git would lose your local (uncommitted) changes, so it refuses to do the checkout and stays where it is.
In which case (there is file which is different in "before" and "after", and which is modified in working area) you can ask git to try to 'move' (merge) changes from "before" to "after" version of a file with '-m' / --merge option, see git-checkout(1):
git checkout -m after
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Jakub Narebski Poland ShadeHawk on #git