Re: new to git
[jc: I think this is really worth saving somewhere. Could some kind soul make this into a patch to have under Documentation/ somewhere?]
Kyle Rose <krose@krose.org> writes:
> (1) Let's say I:
>
> git clone something
Origin repository's history is copied and you get their master
in remotes/origin/master (aka remotes/origin/HEAD aka
remotes/origin), and you can call that 'origin' for brevity.
At the same time, you get your own 'master' branch that points
at the same commit as the 'origin'. Your current branch
pointed at by your HEAD is 'master'.
['origin' repository]
---A---B---C
^master ==>
[your cloned repository]
---A---B---C
^master = HEAD
^remotes/origin> git branch foo
You create a new branch of your own 'foo' in your repository,
initially pointing at the same commit as your current commit
(i.e. C as you are on 'master' after the clone).
==>
[your cloned repository]
---A---B---C
^master = HEAD
^remotes/origin
^foo> git checkout foo
You switch from your current branch (i.e. 'master') to the
named branch (i.e. 'foo'), making the latter the current
branch. Your work tree will largely match the commit at the
tip of the branch you are switching to, except that if you had
any local changes (i.e. uncommitted) in your work tree, you
take it along (but in this example you do not have any).
==>
[your cloned repository]
---A---B---C
^master
^remotes/origin
^foo = HEAD> <make some changes>
> git commit -a
You build a commit whose parent is the commit your HEAD used
to point at; the tip of your current branch advances.
==>
[your cloned repository]
---A---B---C---D
^foo = HEAD
^master
^remotes/origin> git checkout master
You switch from your current branch (i.e. 'foo') to the
named branch (i.e. 'master'), making the latter the current
branch. Your work tree will largely match the commit at the
tip of the branch you are switching to, except that if you had
any local changes (i.e. uncommitted) in your work tree, you
take it along (but in this example you do not have any).
==>
[your cloned repository]
---A---B---C---D
^foo
^master = HEAD
^remotes/origin> git pull . foo
This "git pull" command instructs git to "from the repository
'.', grab the commit the repository calls 'foo', and update my
current branch by merging that commit". Because '.' is "the
current directory", which in turn means "my repository", you
do not have to really "grab the commit" --- you already have
it locally.
"git merge foo" is more natural way to write this since 1.5.0
days. The latter command instructs git "update my current
branch by merging commit I call 'foo'".
Now, looking at the above history graph, your current
branch'es tip is at C (you are on 'master', remember?), and
'foo' is at D, which is an descendant of C. By definition, a
merge between such commit pair is the descendant D, so your
current branch is updated to D (this is called "fast
forward").
==>
[your cloned repository]
---A---B---C---D
^foo
^master = HEAD
^remotes/origin> git push
This is kind of "lazy" and "very not-git-like" command I
literally *hate*. What "git push" does, whey you do not say
anything about "where to" nor "what", is to "push all
corresponding branches and tags to the repository you call
'origin'".
If you recall the very initial picture, the 'origin'
repository has 'master' branch but not 'foo'. The only
matching branch is 'master', and that is pointing at C over
there, which is replaced by your 'master' which now points at
'D'.
['origin' repository]
---A---B---C
^master ==>
['origin' repository]
---A---B---C---D
^master Note that this update *MUST* be fast-forward by default. IOW,
if somebody worked elsewhere and updated the 'master' branch
at the 'origin' repository before your push, your 'push' will
be prevented with an error message that tells you that remote
'master' is not a strict subset of what you are pushing.
> git pull
Instruct git to "grab the history from the 'origin' repository
and update remotes/origin/* with its branch, and then update my
current branch by merging its tip".
The first step of updating the remotes/origin again *MUST* be
fast-forward by default.
==>
[your cloned repository]
---A---B---C---D
^foo
^master = HEAD
^remotes/origin If you recall, you are on 'master' branch whose tip is at D.
Now you are telling git to update it by merging what you
fetched, which also is D. So nothing happens.
> (2) Any way to disable this warning:
>
> Warning: No merge candidate found because value of config option
> "branch.local.merge" does not match any remote branch fetched.
Do as the warning says; I do not think the message can be any clearer (see Documentation/config.txt, or even better "The User's Manual"). Set branch.local.merge configuration variable if you want to always merge specific branch you obtain from the remote.
E.g.
[branch "local"]
remote = origin
merge = refs/heads/masterif you want "git pull", without saying what to pull from where, to fetch from 'origin' and merge its 'master' branch, when you are on your 'local' branch.
> (3) I notice I can't reset --hard a single file. So, if I want to
> revert a single file to some revision, blowing away my changes, what is
> the accepted way of doing this? Is there a way to do the equivalent of
> a p4 print foo@some_revision?
I have no idea what p4 does, but:
git checkout -- path
updates the work tree file with the last version of paths you did "git add path",
git checkout HEAD -- path
updates the work tree file with the version of paths in the HEAD commit, and
git checkout some_version -- path
updates the work tree file with the version of paths in the named commit. For various ways to name commits, see git-rev-parse(1).
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> (4) I'm still not clear on when a dst should and should not be used in a
> refspec. It appears that one can only do non-fast forward updates to
> the branch that is checked out (which makes sense, since you may need to
> resolve), but other than that, what is the difference between
>
> git checkout foo
> git pull . master
>
> and
>
> git checkout master
> git push . master:foo
The obvious difference is which branch you end up with.
> (5) Are there any tools for managing some of the metadata (e.g., the
> origin URL) or is it expected that one edit it directly?
Kyle Rose
