X-Git-Url: https://git.cworth.org/git?a=blobdiff_plain;f=tour.mdwn;h=e9e02776d86cddd7b8a19c9bd8815303584cfc4c;hb=5bbd7299aa73ba64a701912203c84c733697efcb;hp=7ff65f635f2d5f665232672d5354f581ffa72f93;hpb=44d0c1f81ac57725e18f56431bf37609a68778b2;p=hgbook-git diff --git a/tour.mdwn b/tour.mdwn index 7ff65f6..e9e0277 100644 --- a/tour.mdwn +++ b/tour.mdwn @@ -1,11 +1,11 @@ -## Chapter 2 +## Chapter 2 A tour of git: the basics ### 2.0 Copyright -This document is a modified version originally known as "Distributed -revision control with Mercurial" and originally authored by Bryan -O’Sullivan. The original document was obtained from +This document is a modified version of a document originally titled +"Distributed revision control with Mercurial" and originally authored +by Bryan O’Sullivan. The original document was obtained from . Copyright © 2006, 2007 Bryan O’Sullivan. @@ -29,6 +29,16 @@ Changes made by Carl include the following: * Eliminate line numbers from examples * Modified to describe git instead of mercurial +The source of this modified version can be obtained via git: + + git clone git://cworth.org/git/hgbook-git + +or + + git clone http://cworth.org/git/hgbook-git + +and can be [browsed online](http://git.cworth.org/git/hgbook-git) + ### 2.1 Installing git on your system Prebuilt binary packages of git are available for many popular @@ -50,25 +60,25 @@ install git with a single click. The package name to look for is often git, but is sometimes git-core, (due to an unfortunate name with git, meaning GNU Interactive Tools). - * Debian + * Debian apt-get install git-core - * Fedora Core + * Fedora Core yum install git - * Gentoo + * Gentoo emerge git - * OpenSUSE + * OpenSUSE yum install git - * Ubuntu + * Ubuntu - apt-get install git + apt-get install git-core #### 2.1.2 Mac OS X @@ -90,7 +100,7 @@ installers. These include GitMe, a package to install the entire development environment necessary to work on improving the msysgit port of git, and WinGit, a package for installing just git itself without the development environment, (still in Alpha as of September -2008). +2007). ### 2.2 Getting started @@ -100,7 +110,7 @@ more friendly to new users than versions 1.4 and older. If you aren't yet running version 1.5 or newer, it's highly recommended that you upgrade. - $ git version + $ git version git version 1.5.3.2 #### 2.2.1 Built-in help @@ -257,7 +267,7 @@ By default, this command prints a brief paragraph of output for each change to the project that was recorded. In git terminology, we call each of these recorded events a commit. -The fields in a record of output from “git log” are as follows. +The fields in a record of output from “git log” are as follows. * commit This field consists of a string of 40 hexadecimal characters. This is a unique identifier for referring to particular commits. @@ -279,20 +289,6 @@ The fields in a record of output from “git log” are as follows. The default output printed by “git log” is purely a summary; it is missing a lot of detail. -Figure [2.1][8] provides a graphical representation of the history of -the hello repository, to make it a little easier to see which -direction history is “flowing” in. We’ll be returning to this figure -several times in this chapter and the chapter that follows. - -* * * - -![PIC][9] - -Figure 2.1: -Graphical history of the hello repository - -* * * - #### 2.4.1 Commits, revisions, and talking to other people As English is a notoriously sloppy language, and computer science has @@ -343,7 +339,7 @@ in the current branch, "HEAD~", refers to the previous commit, and Another useful syntax is .. which can be used to specify a range of commits. So "origin..master" specifies everything that has been -committed to master since it derived from origin. +committed to master since it diverged from origin. #### 2.4.3 Viewing specific revisions @@ -399,7 +395,7 @@ created: Another useful option is -n or --max-count which, unsurprisingly, limits the maximum number of commits to be displayed. -#### 2.4.3 More detailed information +#### 2.4.5 More detailed information While the default information printed by “git log” is useful if you already know what you’re looking for, you may need to see more details @@ -529,7 +525,7 @@ disk space in most cases, too. $ 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), @@ -564,7 +560,7 @@ scripted example this way. Since you’re not under the same constraint, you probably won’t want to use sed; simply use your preferred text editor to do the same thing.) - $ sed -i '/printf/a\\tprintf("hello again!\\n");' hello.c + $ sed -i '/printf/a\\tprintf("hello again!\\n");' hello.c The “git status” command will tell us what git knows about the files in the repository. @@ -683,7 +679,7 @@ the files directly. Use your favorite editor to create a file called then it will be there already). The initial contents of your .gitconfig should look like this. - # This is a git configuration file. + # This is a git configuration file. [user] name = Your Name email = you@example.com @@ -911,8 +907,8 @@ Bryan's original chapter. -Carl] ### 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. @@ -922,224 +918,206 @@ To get started, let’s clone our original hello repository, which does 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 - -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. - - $ cd hello-pull - $ hg incoming ../my-hello - comparing with ../my-hello - searching for changes - changeset: 5:fa1321bf0c80 - tag: tip - user: Bryan O'Sullivan - 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. + $ cd .. + $ git clone hello hello-pull + Initialized empty Git repository in /tmp/hello-pull/.git/ + 0 blocks - $ hg tip - changeset: 4:b57f9a090b62 - tag: tip - user: Bryan O'Sullivan - 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 - date: Sun Jun 17 18:05:50 2007 +0000 - summary: Added an extra line of output - +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: -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 - date: Sun Jun 17 18:05:50 2007 +0000 - summary: Added an extra line of output + $ cd hello-pull + $ 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 + 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 - 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. + +[XXX: The structure of the preceding section follows that of the +original hgbook. But an alternate structure that arranged to pull from +the originally cloned repository (as would be common) would allow for +more straightforward use of git's features. For example, instead of +the silly FETCH_HEAD stuff it would allow for "git fetch" and "git log +master..origin" to be a very nice replacement for "hg +incoming". Similarly, below, "git log origin..master" would make a +nice replacement for "hg outgoing" which is something I didn't offer +at all. One could also use git's remotes with the myriad repositories +as used here, but it would require doing things like "git remote add + ../hello-pull" and that seems like a bit much to introduce +for a turorial of this level. If nothing else, if the above section +seems a little intimidating, understand that it's because things are +not presented in the most natural "git way", (and I'm a little too +tired to fix it tonight).] + +#### 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 + 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 - 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 - date: Sun Jun 17 18:05:50 2007 +0000 - summary: Added an extra line of output - +same fashion over a network connection; simply pass in a URL or an ssh +host:/path/name specification instead of a local path. -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 - -## Appendix D +## Appendix D Open Publication License Version 1.0, 8 June 1999