$ cd ..
$ git clone hello my-hello
- Initialized empty Git repository in /home/cworth/src/hgbook-git/my-hello/.git/
+ Initialized empty Git repository in /tmp/my-hello/.git/
0 blocks
[XXX We say "empty" here, (presumably from the git-init part),
### 2.8 Sharing changes
-We mentioned earlier that repositories in Mercurial are
-self-contained. This means that the changeset we just created exists
+We mentioned earlier that repositories in git are
+self-contained. This means that the commit we just created exists
only in our my-hello repository. Let’s look at a few ways that we can
propagate this change into other repositories.
not contain the change we just committed. We’ll call our temporary
repository hello-pull.
- $ cd ..
- $ hg clone hello hello-pull
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+ $ cd ..
+ $ git clone hello hello-pull
+ Initialized empty Git repository in /tmp/hello-pull/.git/
+ 0 blocks
-We’ll use the “hg pull” command to bring changes from my-hello into
-hello-pull. However, blindly pulling unknown changes into a repository
-is a somewhat scary prospect. Mercurial provides the “hg incoming”
-command to tell us what changes the “hg pull” command would pull into
-the repository, without actually pulling the changes in.
+We could use the “git pull” command to apply changes from my-hello to
+our master branch in hello-pull. However, blindly pulling unknown
+changes into a repository is a somewhat scary prospect. The "git pull"
+command is coneptually the combination of two commands, "git fetch"
+and "git merge"; we can run those separately to examine the changes
+before applying them locally. First we do the fetch:
$ cd hello-pull
- $ hg incoming ../my-hello
- comparing with ../my-hello
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
-
-(Of course, someone could cause more changesets to appear in the
-repository that we ran “hg incoming” in, before we get a chance to “hg
-pull” the changes, so that we could end up pulling changes that we
-didn’t expect.)
-
-Bringing changes into a repository is a simple matter of running the
-“hg pull” command, and telling it which repository to pull from.
-
- $ hg tip
- changeset: 4:b57f9a090b62
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 15:43:07 2005 -0700
- summary: Trim comments.
-
- $ hg pull ../my-hello
- pulling from ../my-hello
- searching for changes
- adding changesets
- adding manifests
- adding file changes
- added 1 changesets with 1 changes to 1 files
- (run 'hg update' to get a working copy)
- $ hg tip
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
-
-As you can see from the before-and-after output of “hg tip”, we have
-successfully pulled changes into our repository. There remains one
-step before we can see these changes in the working directory.
-
-#### 2.8.2 Updating the working directory
-
-We have so far glossed over the relationship between a repository and
-its working directory. The “hg pull” command that we ran in
-section [2.8.1][12] brought changes into the repository, but if we
-check, there’s no sign of those changes in the working directory. This
-is because “hg pull” does not (by default) touch the working
-directory. Instead, we use the “hg update” command to do this.
-
- $ grep printf hello.c
- printf("hello, world!∖");
- $ hg update tip
- 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
- $ grep printf hello.c
- printf("hello, world!∖");
- printf("hello again!∖n");
-
-It might seem a bit strange that “hg pull” doesn’t update the working
-directory automatically. There’s actually a good reason for this: you
-can use “hg update” to update the working directory to the state it
-was in at any revision in the history of the repository. If you had
-the working directory updated to an old revision—to hunt down the
-origin of a bug, say—and ran a “hg pull” which automatically updated
-the working directory to a new revision, you might not be terribly
-happy.
-
-However, since pull-then-update is such a common thing to do,
-Mercurial lets you combine the two by passing the -u option to “hg
-pull”.
-
- hg pull -u
-
-If you look back at the output of “hg pull” in section [2.8.1][12]
-when we ran it without -u, you can see that it printed a helpful
-reminder that we’d have to take an explicit step to update the working
-directory:
-
- (run 'hg update' to get a working copy)
-
-To find out what revision the working directory is at, use the “hg
-parents” command.
-
- $ hg parents
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
+ $ git fetch ../my-hello
+ remote: Generating pack...
+ Unpacking 3 objects...
+ 100% (3/3) done
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ 100% remote: (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+
+The fetched commits (or commit in this case) are available as the name
+FETCH_HEAD. [XXX: Shouldn't git-fetch print that name out to the user
+if the user didn't provide a specific branch name to fetch into.] And
+the difference between what we had before and what exists on
+FETCH_HEAD can easily be examined with the ..FETCH_HEAD range
+notation:
+
+ $ git log ..FETCH_HEAD
+ commit 839b58d021c618bd0e1d336d4d5878a0082672e6
+ Author: Carl Worth <cworth@cworth.org>
+ Date: Thu Sep 27 23:55:00 2007 -0700
+ Added an extra line of output and fixed the typo bug.
-If you look back at figure [2.1][8], you’ll see arrows connecting each
-changeset. The node that the arrow leads from in each case is a
-parent, and the node that the arrow leads to is its child. The working
-directory has a parent in just the same way; this is the changeset
-that the working directory currently contains.
-
-To update the working directory to a particular revision, give a
-revision number or changeset ID to the “hg update” command.
-
- $ hg update 2
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
- $ hg parents
- changeset: 2:057d3c2d823c
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Tue Sep 06 13:15:43 2005 -0700
- summary: Introduce a typo into hello.c.
-
- $ hg update
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+Since these commits actually exist in the local repository now, we
+don't need to fetch or pull them from the remote repository again---we
+can now use "git merge" to apply the previously fetched commits. (A
+mercurial user might notice here that git does not have the race
+condition between "hg incoming" and "hg pull" that mercurial has since
+the commits are fetched only once.)
+
+ $ git merge FETCH_HEAD
+ Updating a1a0e8b..839b58d
+ Fast forward
+ hello.c | 3 ++-
+ 1 files changed, 2 insertions(+), 1 deletions(-)
+
+Notice that "git merge" reports that our branch pointer has been
+updated from a1a0e8b to 839b58d. Also, this is a "fast forward"
+meaning that the new commits are a linear sequence on top of the
+commit we already hand. In other words, there wasn't any divergence
+between these two repositories so no actual "merge" commit was
+created.
+
+This separation of fetch and merge is useful when you need to
+carefully review some changes before applying them. But often you're
+in a situation where you know you trust the remote repository and you
+simply want to pull those changes as conveniently as possible, (no
+extra commands, no typing a magic name like FETCH_HEAD). This is the
+case when the tracking upstream development of a project with git. And
+in that case, the above steps are as simple as just executing "git
+pull". So let's repeat all that the simpler way:
-If you omit an explicit revision, “hg update” will update to the tip
-revision, as shown by the second call to “hg update” in the example
-above.
+ $ cd ..
+ $ git clone hello hello-tracking
+ Initialized empty Git repository in /tmp/hello-tracking/.git/
+ 0 blocks
+ $ cd hello-tracking
+ $ git pull ../my-hello
+ remote: Generating pack...
+ remote: Done counting 5 objects.
+ Result has 3 objects.
+ Deltifying 3 objects...
+ Unpacking 3 objects...
+ remote: 100% (3/3) done
+ Total 3 (delta 1), reused 0 (delta 0)
+ 100% (3/3) done
+ Updating a1a0e8b..839b58d
+ Fast forward
+ hello.c | 3 ++-
+ 1 files changed, 2 insertions(+), 1 deletions(-)
+
+It should be plain to see that the "git pull" command really did the
+combined sequence of "git fetch" and "git merge". Also, if you want to
+pull from the same repository you cloned from originally, (which is
+the common case for the upstream-tracking scenario), then "git pull"
+with no explicit repository is suffcient, and it will default to
+pulling from the same repository as the original clone.
+
+#### 2.8.2 Checking out previous revisions
+
+If any users of mercurial are reading this, they might wonder if
+there's a need for the equivalent of "hg update" after doing a "git
+pull". And the answer is no. Unlike mercurial, "git pull" and "git
+merge" will automatically update the workind-directory files as
+necessary.
+
+But there's another function provided by "hg update" which is to
+update the working-directory files to a particular revision. In git,
+this functionality is provided by the "git checkout" command. To
+checkout a particular branch, tag, or an arbitrary revions, simply
+give the appropriate name to the "git checkout" command. For example,
+to examine the files as they existed before the original typo
+introduction, we could do:
+
+ $ git checkout 0a633bf5
+ Note: moving to "0a633bf5" which isn't a local branch
+ If you want to create a new branch from this checkout, you may do so
+ (now or later) by using -b with the checkout command again. Example:
+ git checkout -b <new_branch_name>
+ HEAD is now at 0a633bf... Create a makefile
+
+The note that git gives us is to indicate that we are checking out a
+non-branch revision. This is perfectly fine if we are just exploring
+history, but if we actually wanted to use this revision as the basis
+for new commits, we would first have to create a new branch name as it
+describes.
+
+For now, let's return back to the tip of the master branch by just
+checking it out again:
+
+ $ git checkout master
+ Previous HEAD position was 0a633bf... Create a makefile
+ Switched to branch "master"
#### 2.8.3 Pushing changes to another repository
-Mercurial lets us push changes to another repository, from the
-repository we’re currently visiting. As with the example of “hg pull”
-above, we’ll create a temporary repository to push our changes into.
-
- $ cd ..
- $ hg clone hello hello-push
- 2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-
-The “hg outgoing” command tells us what changes would be pushed into
-another repository.
-
- $ cd my-hello
- $ hg outgoing ../hello-push
- comparing with ../hello-push
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
-
-And the “hg push” command does the actual push.
-
- $ hg push ../hello-push
- pushing to ../hello-push
- searching for changes
- adding changesets
- adding manifests
- adding file changes
- added 1 changesets with 1 changes to 1 files
+Git lets us push changes to another repository, from the repository
+we’re currently visiting. As with previous examples, above, we’ll
+first create a temporary repository to push our changes into. But
+instead of using "git clone", this time we'll use "git init" to make a
+repository from an empty directory. We do this to create a "bare"
+repository which is simply a repository that has no working-directory
+files associated with it. In general, you should only push to bare
+repositories.
-As with “hg pull”, the “hg push” command does not update the working
-directory in the repository that it’s pushing changes into. (Unlike
-“hg pull”, “hg push” does not provide a -u option that updates the
-other repository’s working directory.)
+ $ cd ..
+ $ mkdir hello-push
+ $ cd hello-push
+ $ git --bare init
+ Initialized empty Git repository in /tmp/hello-push/
+
+And then we'll go back to our my-hello repository to perform the
+push. Since this is our very first push into this repository we need
+to tell git which branches to push. The easiest way to do this is to
+use --all to indicate all branches:
+
+ $ cd ../my-hello
+ $ git push ../hello-push --all
+ updating 'refs/heads/master'
+ from 0000000000000000000000000000000000000000
+ to 839b58d021c618bd0e1d336d4d5878a0082672e6
+ Generating pack...
+ Done counting 18 objects.
+ Deltifying 18 objects...
+ 100% (18/18) done
+ Writing 18 objects...
+ 100% (18/18) done
+ Total 18 (delta 3), reused 0 (delta 0)
+ Unpacking 18 objects...
+ 100% (18/18) done
+ refs/heads/master: 0000000000000000000000000000000000000000 -> 839b58d021c618bd0e1d336d4d5878a0082672e6
+
+For subsequent pushes we don't need to specify --all as "git push"
+will push all branches that exist in both the local and remote
+repositories.
What happens if we try to pull or push changes and the receiving
repository already has those changes? Nothing too exciting.
- $ hg push ../hello-push
- pushing to ../hello-push
- searching for changes
- no changes found
+ $ git push ../hello-push
+ Everything up-to-date
#### 2.8.4 Sharing changes over a network
The commands we have covered in the previous few sections are not
limited to working with local repositories. Each works in exactly the
-same fashion over a network connection; simply pass in a URL instead
-of a local path.
-
- $ hg outgoing http://hg.serpentine.com/tutorial/hello
- comparing with http://hg.serpentine.com/tutorial/hello
- searching for changes
- changeset: 5:fa1321bf0c80
- tag: tip
- user: Bryan O'Sullivan <bos@serpentine.com>
- date: Sun Jun 17 18:05:50 2007 +0000
- summary: Added an extra line of output
-
-
-In this example, we can see what changes we could push to the remote
-repository, but the repository is understandably not set up to let
-anonymous users push to it.
-
- $ hg push http://hg.serpentine.com/tutorial/hello
- pushing to http://hg.serpentine.com/tutorial/hello
- searching for changes
- ssl required
-
- [1]: http://hgbook.red-bean.com/hgbookch3.html
- [2]: http://hgbook.red-bean.com/hgbookch1.html
- [3]: http://hgbook.red-bean.com/hgbookch1.html#tailhgbookch1.html
- [4]: #tailhgbookch2.html
- [5]: http://hgbook.red-bean.com/hgbook.html#hgbookch2.html
- [6]: http://mercurial.berkwood.com/
- [7]: http://hgbook.red-bean.com/hgbookli4.html#Xweb:macpython
- [8]: #x6-340581
- [9]: hgbookch2_files/tour-history.png
- [10]: http://hgbook.red-bean.com/hgbookch12.html#x16-27100012.4
- [11]: #x6-420002.7.1
- [12]: #x6-490002.8.1
- [13]: http://hgbook.red-bean.com/hgbookch2.html
+same fashion over a network connection; simply pass in a URL or an ssh
+host:/path/name specification instead of a local path.
## Appendix D
Open Publication License
projects / hgbook-git / commitdiff