A visual Git reference
marklodato.github.com
marklodato.github.com
This guide will only make your understanding of Git worse.
It uses incorrect terminology to mislead what Git is actually doing in a number of situations, starting with the first sentence of the first section: The four commands above copy files between the working directory, the stage (also called the index), and the history (in the form of commits).
Git doesn't care about files, but changesets so this should raise a red flag with anyone with even a passing knowledge of how Git works. This is either a fundamental flaw in the understanding of how Git works by the OP or intentionally misleading wording.
In the Commit section, the OP writes: It then points the current branch to this new commit. I don't like this wording because it makes it seem like a branch is something other than a reference to a particular commit (which is available in .git/refs/heads). Really, any reference to "current branch" should be replaced by HEAD, because the current branch is nothing other than HEAD, and HEAD of course is just a commit.
In the Checkout section, the OP writes: The checkout command is used to copy files from the history (or stage) to the working directory, and to optionally switch branches. This is blatantly false. `git checkout` doesn't "copy files"; it may move HEAD or it may get rid of any changes in the working directory, and in doing so may change the state of the files within the local repo.
In the Committing with a Detached HEAD section, the OP writes: Once you check out something else, say master, the commit is (presumably) no longer referenced by anything else, and gets lost. This is only partly true. The commit still remains in the reflog and can be retrieved up to the point that garbage collection is run. It's incorrect to tell someone their commits are lost as soon as they `git checkout` another treeish.
This guide should be binned in favor of EdgeCase's Git Immersion (http://gitimmersion.com/) and Scott Chacon's Pro Git (http://www.git-scm.com/book).
I think that it would be interesting to reread this after it's been worked over by someone to better represent the way that Git actually works.
> Git doesn't care about files, but changesets so this should raise a red flag with anyone with even a passing knowledge of how Git works. This is either a fundamental flaw in the understanding of how Git works by the OP or intentionally misleading wording.
Git absolutely cares about files. It cares about commits too, but a commit is mostly just a set of files with a pointer to its parent. The commands being discussed operate on individual files except for commit, which operates on the entire index (which is, conceptually, a snapshot of file).
> In the Commit section, the OP writes: It then points the current branch to this new commit. I don't like this wording because it makes it seem like a branch is something other than a reference to a particular commit (which is available in .git/refs/heads). Really, any reference to "current branch" should be replaced by HEAD, because the current branch is nothing other than HEAD, and HEAD of course is just a commit.
I don't understand your objection to this phrasing. A branch is a pointer to a commit; the statement talks about changing which commit the branch points to. I don't see where it implies anything else about what a branch is. As for "current branch"/"HEAD", using HEAD is more precise in terms of the actual implementation, but "current branch" is just as accurate and more (new-)user friendly. The author does discuss the relationship between the two prior to that point: "The current branch is identified by the special reference HEAD, which is "attached" to that branch."
> In the Checkout section, the OP writes: The checkout command is used to copy files from the history (or stage) to the working directory, and to optionally switch branches. This is blatantly false. `git checkout` doesn't "copy files"; it may move HEAD or it may get rid of any changes in the working directory, and in doing so may change the state of the files within the local repo.
When used as "git checkout <ref>", this is correct, but that is not what the author is talking about. "git checkout <ref> <file>" or "git checkout -- <file>" does exactly what the author describes, copying files from the given commit or index to the working directory.
> In the Committing with a Detached HEAD section, the OP writes: Once you check out something else, say master, the commit is (presumably) no longer referenced by anything else, and gets lost. This is only partly true. The commit still remains in the reflog and can be retrieved up to the point that garbage collection is run. It's incorrect to tell someone their commits are lost as soon as they `git checkout` another treeish.
Only partly true, but true enough. The commit isn't irretrievably lost, but the reflog falls more under "advanced usage"; certainly a git beginner shouldn't be making detached commits and relying on the reflog to get back to them.
In a sense. A commit is not a set of files, it is one or more blobs and one or more trees (which may in turn point to one or more blobs or trees.) A blob does refer to a file, both in content and location, but it's the blob that matters. The OP speaks of the files on disk, which Git doesn't copy around. Git does, however, change the state of the working directory to that which matches the trees referenced in the commit. What I don't like about this is that it tries to make it seem like the files on disk matter in a way that they don't from Git's perspective.
> I don't understand your objection to this phrasing.
I had a chat with a coworker and he agreed that my distaste with the "current branch" terminology is perhaps misplaced.
> When used as "git checkout <ref>", this is correct, but that is not what the author is talking about. "git checkout <ref> <file>" or "git checkout -- <file>" does exactly what the author describes, copying files from the given commit or index to the working directory.
Of course, the files that are being copied are not the files that the OP is talking about. The files being copied are the trees and blobs, not the files in the working directory. The effective result is the same, but thinking in files on disk will not improve one's knowledge of Git.
> Only partly true, but true enough. The commit isn't irretrievably lost, but the reflog falls more under "advanced usage"; certainly a git beginner shouldn't be making detached commits and relying on the reflog to get back to them.
Shunning the reflog doesn't do anyone any good. The OP not even mentioning the reflog is in poor taste, and makes the statement in the guide untrue.
I did a bit of research into the reflog after some questions arose and should update my prior comment about it to say: Any commit that Git determines to be unreachable (a list of which that you can see with `git fsck --unreachable`) will only be removed from the reflog after both the reflog's unreachable expiration time has passed (by default, 30 days for unreachable) and `git gc` has ran. At the very least, without mentioning the reflog, the OP should state that unreachable commits will remain for 30 days.
Git's first class objects are files, trees and commits. Changesets are never stored, only derived. Git stores snapshots, not changesets. So your statement seems to be a complete contradiction to what Git actually does.
> This guide will only make your understanding of Git worse.
I am so shocked by your assertion about git and changesets that I don't know how to begin to respond to this.
The statement I quoted when I mentioned changesets was talking about copying files between the working directory and the index, which is certainly not the case. What gets added to the index is the collection of trees and blobs that will make up the next commit when it is created. I mean changeset to be the collection of trees and blobs that will make up the commit. There is no "copying" of files here.
I wish someone would make a reference like this for remote branches and repos, I always keep forgetting commands for setting upstream branches, checking out remote branches and having them tracked, etc.
But every time I see something this I have to ask myself again why I'm just not using CVS (or SVN, i.e. a simpler tool).
Unless you are working across multiple groups with developers in different time zones and a choppy set of releases you'll see almost no benefit from git.
However, if you are in that situation the benefits are large and immediate.
Plus, you don't have to migrate your codebase to another SCM tool if the project unexpectedly grows into a larger one.
The biggest benefit I get is that I can work on a set of changes as a set rather than a linear sequence that only ever goes forwards in time. I use microcommits. As I make progress on a feature, I discover necessary refactoring that I would ideally have been done before I started to add the feature. Interactive rebase allows me to make this so, and the result is that when I am done I can review my own work and check it for correctness with much more confidence than otherwise.
When working in open source, you're expected to provide a patch series for easy review. Git lets me produce such a thing with the same workflow.
Developers who don't wish to work this way, or are unaware of the benefits that this can bring, use git linearly and will see no benefit over Subversion.
A commit knows about its history via its parent(s), thus the arrow pointing to the parent. As far as I know no commit can (or for that matter should) know about its descendants.
Does that help?