| Git User's Manual |
| _________________ |
| |
| This manual is designed to be readable by someone with basic unix |
| command-line skills, but no previous knowledge of git. |
| |
| Chapter 1 gives a brief overview of git commands, without any |
| explanation; you may prefer to skip to chapter 2 on a first reading. |
| |
| Chapters 2 and 3 explain how to fetch and study a project using |
| git--the tools you'd need to build and test a particular version of a |
| software project, to search for regressions, and so on. |
| |
| Chapter 4 explains how to do development with git, and chapter 5 how |
| to share that development with others. |
| |
| Further chapters cover more specialized topics. |
| |
| Comprehensive reference documentation is available through the man |
| pages. For a command such as "git clone", just use |
| |
| ------------------------------------------------ |
| $ man git-clone |
| ------------------------------------------------ |
| |
| Git Quick Start |
| =============== |
| |
| This is a quick summary of the major commands; the following chapters |
| will explain how these work in more detail. |
| |
| Creating a new repository |
| ------------------------- |
| |
| From a tarball: |
| |
| ----------------------------------------------- |
| $ tar xzf project.tar.gz |
| $ cd project |
| $ git init |
| Initialized empty Git repository in .git/ |
| $ git add . |
| $ git commit |
| ----------------------------------------------- |
| |
| From a remote repository: |
| |
| ----------------------------------------------- |
| $ git clone git://example.com/pub/project.git |
| $ cd project |
| ----------------------------------------------- |
| |
| Managing branches |
| ----------------- |
| |
| ----------------------------------------------- |
| $ git branch # list all branches in this repo |
| $ git checkout test # switch working directory to branch "test" |
| $ git branch new # create branch "new" starting at current HEAD |
| $ git branch -d new # delete branch "new" |
| ----------------------------------------------- |
| |
| Instead of basing new branch on current HEAD (the default), use: |
| |
| ----------------------------------------------- |
| $ git branch new test # branch named "test" |
| $ git branch new v2.6.15 # tag named v2.6.15 |
| $ git branch new HEAD^ # commit before the most recent |
| $ git branch new HEAD^^ # commit before that |
| $ git branch new test~10 # ten commits before tip of branch "test" |
| ----------------------------------------------- |
| |
| Create and switch to a new branch at the same time: |
| |
| ----------------------------------------------- |
| $ git checkout -b new v2.6.15 |
| ----------------------------------------------- |
| |
| Update and examine branches from the repository you cloned from: |
| |
| ----------------------------------------------- |
| $ git fetch # update |
| $ git branch -r # list |
| origin/master |
| origin/next |
| ... |
| $ git checkout -b masterwork origin/master |
| ----------------------------------------------- |
| |
| Fetch a branch from a different repository, and give it a new |
| name in your repository: |
| |
| ----------------------------------------------- |
| $ git fetch git://example.com/project.git theirbranch:mybranch |
| $ git fetch git://example.com/project.git v2.6.15:mybranch |
| ----------------------------------------------- |
| |
| Keep a list of repositories you work with regularly: |
| |
| ----------------------------------------------- |
| $ git remote add example git://example.com/project.git |
| $ git remote # list remote repositories |
| example |
| origin |
| $ git remote show example # get details |
| * remote example |
| URL: git://example.com/project.git |
| Tracked remote branches |
| master next ... |
| $ git fetch example # update branches from example |
| $ git branch -r # list all remote branches |
| ----------------------------------------------- |
| |
| |
| Exploring history |
| ----------------- |
| |
| ----------------------------------------------- |
| $ gitk # visualize and browse history |
| $ git log # list all commits |
| $ git log src/ # ...modifying src/ |
| $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15 |
| $ git log master..test # ...in branch test, not in branch master |
| $ git log test..master # ...in branch master, but not in test |
| $ git log test...master # ...in one branch, not in both |
| $ git log -S'foo()' # ...where difference contain "foo()" |
| $ git log --since="2 weeks ago" |
| $ git log -p # show patches as well |
| $ git show # most recent commit |
| $ git diff v2.6.15..v2.6.16 # diff between two tagged versions |
| $ git diff v2.6.15..HEAD # diff with current head |
| $ git grep "foo()" # search working directory for "foo()" |
| $ git grep v2.6.15 "foo()" # search old tree for "foo()" |
| $ git show v2.6.15:a.txt # look at old version of a.txt |
| ----------------------------------------------- |
| |
| Search for regressions: |
| |
| ----------------------------------------------- |
| $ git bisect start |
| $ git bisect bad # current version is bad |
| $ git bisect good v2.6.13-rc2 # last known good revision |
| Bisecting: 675 revisions left to test after this |
| # test here, then: |
| $ git bisect good # if this revision is good, or |
| $ git bisect bad # if this revision is bad. |
| # repeat until done. |
| ----------------------------------------------- |
| |
| Making changes |
| -------------- |
| |
| Make sure git knows who to blame: |
| |
| ------------------------------------------------ |
| $ cat >~/.gitconfig <<\EOF |
| [user] |
| name = Your Name Comes Here |
| email = you@yourdomain.example.com |
| EOF |
| ------------------------------------------------ |
| |
| Select file contents to include in the next commit, then make the |
| commit: |
| |
| ----------------------------------------------- |
| $ git add a.txt # updated file |
| $ git add b.txt # new file |
| $ git rm c.txt # old file |
| $ git commit |
| ----------------------------------------------- |
| |
| Or, prepare and create the commit in one step: |
| |
| ----------------------------------------------- |
| $ git commit d.txt # use latest content only of d.txt |
| $ git commit -a # use latest content of all tracked files |
| ----------------------------------------------- |
| |
| Merging |
| ------- |
| |
| ----------------------------------------------- |
| $ git merge test # merge branch "test" into the current branch |
| $ git pull git://example.com/project.git master |
| # fetch and merge in remote branch |
| $ git pull . test # equivalent to git merge test |
| ----------------------------------------------- |
| |
| Sharing your changes |
| -------------------- |
| |
| Importing or exporting patches: |
| |
| ----------------------------------------------- |
| $ git format-patch origin..HEAD # format a patch for each commit |
| # in HEAD but not in origin |
| $ git am mbox # import patches from the mailbox "mbox" |
| ----------------------------------------------- |
| |
| Fetch a branch in a different git repository, then merge into the |
| current branch: |
| |
| ----------------------------------------------- |
| $ git pull git://example.com/project.git theirbranch |
| ----------------------------------------------- |
| |
| Store the fetched branch into a local branch before merging into the |
| current branch: |
| |
| ----------------------------------------------- |
| $ git pull git://example.com/project.git theirbranch:mybranch |
| ----------------------------------------------- |
| |
| After creating commits on a local branch, update the remote |
| branch with your commits: |
| |
| ----------------------------------------------- |
| $ git push ssh://example.com/project.git mybranch:theirbranch |
| ----------------------------------------------- |
| |
| When remote and local branch are both named "test": |
| |
| ----------------------------------------------- |
| $ git push ssh://example.com/project.git test |
| ----------------------------------------------- |
| |
| Shortcut version for a frequently used remote repository: |
| |
| ----------------------------------------------- |
| $ git remote add example ssh://example.com/project.git |
| $ git push example test |
| ----------------------------------------------- |
| |
| Repository maintenance |
| ---------------------- |
| |
| Check for corruption: |
| |
| ----------------------------------------------- |
| $ git fsck |
| ----------------------------------------------- |
| |
| Recompress, remove unused cruft: |
| |
| ----------------------------------------------- |
| $ git gc |
| ----------------------------------------------- |
| |
| Repositories and Branches |
| ========================= |
| |
| How to get a git repository |
| --------------------------- |
| |
| It will be useful to have a git repository to experiment with as you |
| read this manual. |
| |
| The best way to get one is by using the gitlink:git-clone[1] command |
| to download a copy of an existing repository for a project that you |
| are interested in. If you don't already have a project in mind, here |
| are some interesting examples: |
| |
| ------------------------------------------------ |
| # git itself (approx. 10MB download): |
| $ git clone git://git.kernel.org/pub/scm/git/git.git |
| # the linux kernel (approx. 150MB download): |
| $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git |
| ------------------------------------------------ |
| |
| The initial clone may be time-consuming for a large project, but you |
| will only need to clone once. |
| |
| The clone command creates a new directory named after the project |
| ("git" or "linux-2.6" in the examples above). After you cd into this |
| directory, you will see that it contains a copy of the project files, |
| together with a special top-level directory named ".git", which |
| contains all the information about the history of the project. |
| |
| In most of the following, examples will be taken from one of the two |
| repositories above. |
| |
| How to check out a different version of a project |
| ------------------------------------------------- |
| |
| Git is best thought of as a tool for storing the history of a |
| collection of files. It stores the history as a compressed |
| collection of interrelated snapshots (versions) of the project's |
| contents. |
| |
| A single git repository may contain multiple branches. It keeps track |
| of them by keeping a list of <<def_head,heads>> which reference the |
| latest version on each branch; the gitlink:git-branch[1] command shows |
| you the list of branch heads: |
| |
| ------------------------------------------------ |
| $ git branch |
| * master |
| ------------------------------------------------ |
| |
| A freshly cloned repository contains a single branch head, by default |
| named "master", with the working directory initialized to the state of |
| the project referred to by that branch head. |
| |
| Most projects also use <<def_tag,tags>>. Tags, like heads, are |
| references into the project's history, and can be listed using the |
| gitlink:git-tag[1] command: |
| |
| ------------------------------------------------ |
| $ git tag -l |
| v2.6.11 |
| v2.6.11-tree |
| v2.6.12 |
| v2.6.12-rc2 |
| v2.6.12-rc3 |
| v2.6.12-rc4 |
| v2.6.12-rc5 |
| v2.6.12-rc6 |
| v2.6.13 |
| ... |
| ------------------------------------------------ |
| |
| Tags are expected to always point at the same version of a project, |
| while heads are expected to advance as development progresses. |
| |
| Create a new branch head pointing to one of these versions and check it |
| out using gitlink:git-checkout[1]: |
| |
| ------------------------------------------------ |
| $ git checkout -b new v2.6.13 |
| ------------------------------------------------ |
| |
| The working directory then reflects the contents that the project had |
| when it was tagged v2.6.13, and gitlink:git-branch[1] shows two |
| branches, with an asterisk marking the currently checked-out branch: |
| |
| ------------------------------------------------ |
| $ git branch |
| master |
| * new |
| ------------------------------------------------ |
| |
| If you decide that you'd rather see version 2.6.17, you can modify |
| the current branch to point at v2.6.17 instead, with |
| |
| ------------------------------------------------ |
| $ git reset --hard v2.6.17 |
| ------------------------------------------------ |
| |
| Note that if the current branch head was your only reference to a |
| particular point in history, then resetting that branch may leave you |
| with no way to find the history it used to point to; so use this command |
| carefully. |
| |
| Understanding History: Commits |
| ------------------------------ |
| |
| Every change in the history of a project is represented by a commit. |
| The gitlink:git-show[1] command shows the most recent commit on the |
| current branch: |
| |
| ------------------------------------------------ |
| $ git show |
| commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2 |
| Author: Jamal Hadi Salim <hadi@cyberus.ca> |
| Date: Sat Dec 2 22:22:25 2006 -0800 |
| |
| [XFRM]: Fix aevent structuring to be more complete. |
| |
| aevents can not uniquely identify an SA. We break the ABI with this |
| patch, but consensus is that since it is not yet utilized by any |
| (known) application then it is fine (better do it now than later). |
| |
| Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| |
| diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt |
| index 8be626f..d7aac9d 100644 |
| --- a/Documentation/networking/xfrm_sync.txt |
| +++ b/Documentation/networking/xfrm_sync.txt |
| @@ -47,10 +47,13 @@ aevent_id structure looks like: |
| |
| struct xfrm_aevent_id { |
| struct xfrm_usersa_id sa_id; |
| + xfrm_address_t saddr; |
| __u32 flags; |
| + __u32 reqid; |
| }; |
| ... |
| ------------------------------------------------ |
| |
| As you can see, a commit shows who made the latest change, what they |
| did, and why. |
| |
| Every commit has a 40-hexdigit id, sometimes called the "object name" or the |
| "SHA1 id", shown on the first line of the "git show" output. You can usually |
| refer to a commit by a shorter name, such as a tag or a branch name, but this |
| longer name can also be useful. Most importantly, it is a globally unique |
| name for this commit: so if you tell somebody else the object name (for |
| example in email), then you are guaranteed that name will refer to the same |
| commit in their repository that it does in yours (assuming their repository |
| has that commit at all). Since the object name is computed as a hash over the |
| contents of the commit, you are guaranteed that the commit can never change |
| without its name also changing. |
| |
| In fact, in <<git-internals>> we shall see that everything stored in git |
| history, including file data and directory contents, is stored in an object |
| with a name that is a hash of its contents. |
| |
| Understanding history: commits, parents, and reachability |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Every commit (except the very first commit in a project) also has a |
| parent commit which shows what happened before this commit. |
| Following the chain of parents will eventually take you back to the |
| beginning of the project. |
| |
| However, the commits do not form a simple list; git allows lines of |
| development to diverge and then reconverge, and the point where two |
| lines of development reconverge is called a "merge". The commit |
| representing a merge can therefore have more than one parent, with |
| each parent representing the most recent commit on one of the lines |
| of development leading to that point. |
| |
| The best way to see how this works is using the gitlink:gitk[1] |
| command; running gitk now on a git repository and looking for merge |
| commits will help understand how the git organizes history. |
| |
| In the following, we say that commit X is "reachable" from commit Y |
| if commit X is an ancestor of commit Y. Equivalently, you could say |
| that Y is a descendent of X, or that there is a chain of parents |
| leading from commit Y to commit X. |
| |
| Understanding history: History diagrams |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| We will sometimes represent git history using diagrams like the one |
| below. Commits are shown as "o", and the links between them with |
| lines drawn with - / and \. Time goes left to right: |
| |
| |
| ................................................ |
| o--o--o <-- Branch A |
| / |
| o--o--o <-- master |
| \ |
| o--o--o <-- Branch B |
| ................................................ |
| |
| If we need to talk about a particular commit, the character "o" may |
| be replaced with another letter or number. |
| |
| Understanding history: What is a branch? |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| When we need to be precise, we will use the word "branch" to mean a line |
| of development, and "branch head" (or just "head") to mean a reference |
| to the most recent commit on a branch. In the example above, the branch |
| head named "A" is a pointer to one particular commit, but we refer to |
| the line of three commits leading up to that point as all being part of |
| "branch A". |
| |
| However, when no confusion will result, we often just use the term |
| "branch" both for branches and for branch heads. |
| |
| Manipulating branches |
| --------------------- |
| |
| Creating, deleting, and modifying branches is quick and easy; here's |
| a summary of the commands: |
| |
| git branch:: |
| list all branches |
| git branch <branch>:: |
| create a new branch named <branch>, referencing the same |
| point in history as the current branch |
| git branch <branch> <start-point>:: |
| create a new branch named <branch>, referencing |
| <start-point>, which may be specified any way you like, |
| including using a branch name or a tag name |
| git branch -d <branch>:: |
| delete the branch <branch>; if the branch you are deleting |
| points to a commit which is not reachable from this branch, |
| this command will fail with a warning. |
| git branch -D <branch>:: |
| even if the branch points to a commit not reachable |
| from the current branch, you may know that that commit |
| is still reachable from some other branch or tag. In that |
| case it is safe to use this command to force git to delete |
| the branch. |
| git checkout <branch>:: |
| make the current branch <branch>, updating the working |
| directory to reflect the version referenced by <branch> |
| git checkout -b <new> <start-point>:: |
| create a new branch <new> referencing <start-point>, and |
| check it out. |
| |
| The special symbol "HEAD" can always be used to refer to the current |
| branch. In fact, git uses a file named "HEAD" in the .git directory to |
| remember which branch is current: |
| |
| ------------------------------------------------ |
| $ cat .git/HEAD |
| ref: refs/heads/master |
| ------------------------------------------------ |
| |
| [[detached-head]] |
| Examining an old version without creating a new branch |
| ------------------------------------------------------ |
| |
| The git-checkout command normally expects a branch head, but will also |
| accept an arbitrary commit; for example, you can check out the commit |
| referenced by a tag: |
| |
| ------------------------------------------------ |
| $ git checkout v2.6.17 |
| Note: moving to "v2.6.17" 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 427abfa... Linux v2.6.17 |
| ------------------------------------------------ |
| |
| The HEAD then refers to the SHA1 of the commit instead of to a branch, |
| and git branch shows that you are no longer on a branch: |
| |
| ------------------------------------------------ |
| $ cat .git/HEAD |
| 427abfa28afedffadfca9dd8b067eb6d36bac53f |
| git branch |
| * (no branch) |
| master |
| ------------------------------------------------ |
| |
| In this case we say that the HEAD is "detached". |
| |
| This can be an easy way to check out a particular version without having |
| to make up a name for a new branch. However, keep in mind that when you |
| switch away from the (for example, by checking out something else), you |
| can lose track of what the HEAD used to point to. |
| |
| Examining branches from a remote repository |
| ------------------------------------------- |
| |
| The "master" branch that was created at the time you cloned is a copy |
| of the HEAD in the repository that you cloned from. That repository |
| may also have had other branches, though, and your local repository |
| keeps branches which track each of those remote branches, which you |
| can view using the "-r" option to gitlink:git-branch[1]: |
| |
| ------------------------------------------------ |
| $ git branch -r |
| origin/HEAD |
| origin/html |
| origin/maint |
| origin/man |
| origin/master |
| origin/next |
| origin/pu |
| origin/todo |
| ------------------------------------------------ |
| |
| You cannot check out these remote-tracking branches, but you can |
| examine them on a branch of your own, just as you would a tag: |
| |
| ------------------------------------------------ |
| $ git checkout -b my-todo-copy origin/todo |
| ------------------------------------------------ |
| |
| Note that the name "origin" is just the name that git uses by default |
| to refer to the repository that you cloned from. |
| |
| [[how-git-stores-references]] |
| Naming branches, tags, and other references |
| ------------------------------------------- |
| |
| Branches, remote-tracking branches, and tags are all references to |
| commits. All references are named with a slash-separated path name |
| starting with "refs"; the names we've been using so far are actually |
| shorthand: |
| |
| - The branch "test" is short for "refs/heads/test". |
| - The tag "v2.6.18" is short for "refs/tags/v2.6.18". |
| - "origin/master" is short for "refs/remotes/origin/master". |
| |
| The full name is occasionally useful if, for example, there ever |
| exists a tag and a branch with the same name. |
| |
| As another useful shortcut, if the repository "origin" posesses only |
| a single branch, you can refer to that branch as just "origin". |
| |
| More generally, if you have defined a remote repository named |
| "example", you can refer to the branch in that repository as |
| "example". And for a repository with multiple branches, this will |
| refer to the branch designated as the "HEAD" branch. |
| |
| For the complete list of paths which git checks for references, and |
| the order it uses to decide which to choose when there are multiple |
| references with the same shorthand name, see the "SPECIFYING |
| REVISIONS" section of gitlink:git-rev-parse[1]. |
| |
| [[Updating-a-repository-with-git-fetch]] |
| Updating a repository with git fetch |
| ------------------------------------ |
| |
| Eventually the developer cloned from will do additional work in her |
| repository, creating new commits and advancing the branches to point |
| at the new commits. |
| |
| The command "git fetch", with no arguments, will update all of the |
| remote-tracking branches to the latest version found in her |
| repository. It will not touch any of your own branches--not even the |
| "master" branch that was created for you on clone. |
| |
| Fetching branches from other repositories |
| ----------------------------------------- |
| |
| You can also track branches from repositories other than the one you |
| cloned from, using gitlink:git-remote[1]: |
| |
| ------------------------------------------------- |
| $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git |
| $ git fetch linux-nfs |
| * refs/remotes/linux-nfs/master: storing branch 'master' ... |
| commit: bf81b46 |
| ------------------------------------------------- |
| |
| New remote-tracking branches will be stored under the shorthand name |
| that you gave "git remote add", in this case linux-nfs: |
| |
| ------------------------------------------------- |
| $ git branch -r |
| linux-nfs/master |
| origin/master |
| ------------------------------------------------- |
| |
| If you run "git fetch <remote>" later, the tracking branches for the |
| named <remote> will be updated. |
| |
| If you examine the file .git/config, you will see that git has added |
| a new stanza: |
| |
| ------------------------------------------------- |
| $ cat .git/config |
| ... |
| [remote "linux-nfs"] |
| url = git://linux-nfs.org/pub/nfs-2.6.git |
| fetch = +refs/heads/*:refs/remotes/linux-nfs/* |
| ... |
| ------------------------------------------------- |
| |
| This is what causes git to track the remote's branches; you may modify |
| or delete these configuration options by editing .git/config with a |
| text editor. (See the "CONFIGURATION FILE" section of |
| gitlink:git-config[1] for details.) |
| |
| Exploring git history |
| ===================== |
| |
| Git is best thought of as a tool for storing the history of a |
| collection of files. It does this by storing compressed snapshots of |
| the contents of a file heirarchy, together with "commits" which show |
| the relationships between these snapshots. |
| |
| Git provides extremely flexible and fast tools for exploring the |
| history of a project. |
| |
| We start with one specialized tool that is useful for finding the |
| commit that introduced a bug into a project. |
| |
| How to use bisect to find a regression |
| -------------------------------------- |
| |
| Suppose version 2.6.18 of your project worked, but the version at |
| "master" crashes. Sometimes the best way to find the cause of such a |
| regression is to perform a brute-force search through the project's |
| history to find the particular commit that caused the problem. The |
| gitlink:git-bisect[1] command can help you do this: |
| |
| ------------------------------------------------- |
| $ git bisect start |
| $ git bisect good v2.6.18 |
| $ git bisect bad master |
| Bisecting: 3537 revisions left to test after this |
| [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] |
| ------------------------------------------------- |
| |
| If you run "git branch" at this point, you'll see that git has |
| temporarily moved you to a new branch named "bisect". This branch |
| points to a commit (with commit id 65934...) that is reachable from |
| v2.6.19 but not from v2.6.18. Compile and test it, and see whether |
| it crashes. Assume it does crash. Then: |
| |
| ------------------------------------------------- |
| $ git bisect bad |
| Bisecting: 1769 revisions left to test after this |
| [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings |
| ------------------------------------------------- |
| |
| checks out an older version. Continue like this, telling git at each |
| stage whether the version it gives you is good or bad, and notice |
| that the number of revisions left to test is cut approximately in |
| half each time. |
| |
| After about 13 tests (in this case), it will output the commit id of |
| the guilty commit. You can then examine the commit with |
| gitlink:git-show[1], find out who wrote it, and mail them your bug |
| report with the commit id. Finally, run |
| |
| ------------------------------------------------- |
| $ git bisect reset |
| ------------------------------------------------- |
| |
| to return you to the branch you were on before and delete the |
| temporary "bisect" branch. |
| |
| Note that the version which git-bisect checks out for you at each |
| point is just a suggestion, and you're free to try a different |
| version if you think it would be a good idea. For example, |
| occasionally you may land on a commit that broke something unrelated; |
| run |
| |
| ------------------------------------------------- |
| $ git bisect visualize |
| ------------------------------------------------- |
| |
| which will run gitk and label the commit it chose with a marker that |
| says "bisect". Chose a safe-looking commit nearby, note its commit |
| id, and check it out with: |
| |
| ------------------------------------------------- |
| $ git reset --hard fb47ddb2db... |
| ------------------------------------------------- |
| |
| then test, run "bisect good" or "bisect bad" as appropriate, and |
| continue. |
| |
| Naming commits |
| -------------- |
| |
| We have seen several ways of naming commits already: |
| |
| - 40-hexdigit object name |
| - branch name: refers to the commit at the head of the given |
| branch |
| - tag name: refers to the commit pointed to by the given tag |
| (we've seen branches and tags are special cases of |
| <<how-git-stores-references,references>>). |
| - HEAD: refers to the head of the current branch |
| |
| There are many more; see the "SPECIFYING REVISIONS" section of the |
| gitlink:git-rev-parse[1] man page for the complete list of ways to |
| name revisions. Some examples: |
| |
| ------------------------------------------------- |
| $ git show fb47ddb2 # the first few characters of the object name |
| # are usually enough to specify it uniquely |
| $ git show HEAD^ # the parent of the HEAD commit |
| $ git show HEAD^^ # the grandparent |
| $ git show HEAD~4 # the great-great-grandparent |
| ------------------------------------------------- |
| |
| Recall that merge commits may have more than one parent; by default, |
| ^ and ~ follow the first parent listed in the commit, but you can |
| also choose: |
| |
| ------------------------------------------------- |
| $ git show HEAD^1 # show the first parent of HEAD |
| $ git show HEAD^2 # show the second parent of HEAD |
| ------------------------------------------------- |
| |
| In addition to HEAD, there are several other special names for |
| commits: |
| |
| Merges (to be discussed later), as well as operations such as |
| git-reset, which change the currently checked-out commit, generally |
| set ORIG_HEAD to the value HEAD had before the current operation. |
| |
| The git-fetch operation always stores the head of the last fetched |
| branch in FETCH_HEAD. For example, if you run git fetch without |
| specifying a local branch as the target of the operation |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git theirbranch |
| ------------------------------------------------- |
| |
| the fetched commits will still be available from FETCH_HEAD. |
| |
| When we discuss merges we'll also see the special name MERGE_HEAD, |
| which refers to the other branch that we're merging in to the current |
| branch. |
| |
| The gitlink:git-rev-parse[1] command is a low-level command that is |
| occasionally useful for translating some name for a commit to the object |
| name for that commit: |
| |
| ------------------------------------------------- |
| $ git rev-parse origin |
| e05db0fd4f31dde7005f075a84f96b360d05984b |
| ------------------------------------------------- |
| |
| Creating tags |
| ------------- |
| |
| We can also create a tag to refer to a particular commit; after |
| running |
| |
| ------------------------------------------------- |
| $ git tag stable-1 1b2e1d63ff |
| ------------------------------------------------- |
| |
| You can use stable-1 to refer to the commit 1b2e1d63ff. |
| |
| This creates a "lightweight" tag. If the tag is a tag you wish to |
| share with others, and possibly sign cryptographically, then you |
| should create a tag object instead; see the gitlink:git-tag[1] man |
| page for details. |
| |
| Browsing revisions |
| ------------------ |
| |
| The gitlink:git-log[1] command can show lists of commits. On its |
| own, it shows all commits reachable from the parent commit; but you |
| can also make more specific requests: |
| |
| ------------------------------------------------- |
| $ git log v2.5.. # commits since (not reachable from) v2.5 |
| $ git log test..master # commits reachable from master but not test |
| $ git log master..test # ...reachable from test but not master |
| $ git log master...test # ...reachable from either test or master, |
| # but not both |
| $ git log --since="2 weeks ago" # commits from the last 2 weeks |
| $ git log Makefile # commits which modify Makefile |
| $ git log fs/ # ... which modify any file under fs/ |
| $ git log -S'foo()' # commits which add or remove any file data |
| # matching the string 'foo()' |
| ------------------------------------------------- |
| |
| And of course you can combine all of these; the following finds |
| commits since v2.5 which touch the Makefile or any file under fs: |
| |
| ------------------------------------------------- |
| $ git log v2.5.. Makefile fs/ |
| ------------------------------------------------- |
| |
| You can also ask git log to show patches: |
| |
| ------------------------------------------------- |
| $ git log -p |
| ------------------------------------------------- |
| |
| See the "--pretty" option in the gitlink:git-log[1] man page for more |
| display options. |
| |
| Note that git log starts with the most recent commit and works |
| backwards through the parents; however, since git history can contain |
| multiple independent lines of development, the particular order that |
| commits are listed in may be somewhat arbitrary. |
| |
| Generating diffs |
| ---------------- |
| |
| You can generate diffs between any two versions using |
| gitlink:git-diff[1]: |
| |
| ------------------------------------------------- |
| $ git diff master..test |
| ------------------------------------------------- |
| |
| Sometimes what you want instead is a set of patches: |
| |
| ------------------------------------------------- |
| $ git format-patch master..test |
| ------------------------------------------------- |
| |
| will generate a file with a patch for each commit reachable from test |
| but not from master. Note that if master also has commits which are |
| not reachable from test, then the combined result of these patches |
| will not be the same as the diff produced by the git-diff example. |
| |
| Viewing old file versions |
| ------------------------- |
| |
| You can always view an old version of a file by just checking out the |
| correct revision first. But sometimes it is more convenient to be |
| able to view an old version of a single file without checking |
| anything out; this command does that: |
| |
| ------------------------------------------------- |
| $ git show v2.5:fs/locks.c |
| ------------------------------------------------- |
| |
| Before the colon may be anything that names a commit, and after it |
| may be any path to a file tracked by git. |
| |
| Examples |
| -------- |
| |
| Check whether two branches point at the same history |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Suppose you want to check whether two branches point at the same point |
| in history. |
| |
| ------------------------------------------------- |
| $ git diff origin..master |
| ------------------------------------------------- |
| |
| will tell you whether the contents of the project are the same at the |
| two branches; in theory, however, it's possible that the same project |
| contents could have been arrived at by two different historical |
| routes. You could compare the object names: |
| |
| ------------------------------------------------- |
| $ git rev-list origin |
| e05db0fd4f31dde7005f075a84f96b360d05984b |
| $ git rev-list master |
| e05db0fd4f31dde7005f075a84f96b360d05984b |
| ------------------------------------------------- |
| |
| Or you could recall that the ... operator selects all commits |
| contained reachable from either one reference or the other but not |
| both: so |
| |
| ------------------------------------------------- |
| $ git log origin...master |
| ------------------------------------------------- |
| |
| will return no commits when the two branches are equal. |
| |
| Find first tagged version including a given fix |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Suppose you know that the commit e05db0fd fixed a certain problem. |
| You'd like to find the earliest tagged release that contains that |
| fix. |
| |
| Of course, there may be more than one answer--if the history branched |
| after commit e05db0fd, then there could be multiple "earliest" tagged |
| releases. |
| |
| You could just visually inspect the commits since e05db0fd: |
| |
| ------------------------------------------------- |
| $ gitk e05db0fd.. |
| ------------------------------------------------- |
| |
| Or you can use gitlink:git-name-rev[1], which will give the commit a |
| name based on any tag it finds pointing to one of the commit's |
| descendants: |
| |
| ------------------------------------------------- |
| $ git name-rev --tags e05db0fd |
| e05db0fd tags/v1.5.0-rc1^0~23 |
| ------------------------------------------------- |
| |
| The gitlink:git-describe[1] command does the opposite, naming the |
| revision using a tag on which the given commit is based: |
| |
| ------------------------------------------------- |
| $ git describe e05db0fd |
| v1.5.0-rc0-260-ge05db0f |
| ------------------------------------------------- |
| |
| but that may sometimes help you guess which tags might come after the |
| given commit. |
| |
| If you just want to verify whether a given tagged version contains a |
| given commit, you could use gitlink:git-merge-base[1]: |
| |
| ------------------------------------------------- |
| $ git merge-base e05db0fd v1.5.0-rc1 |
| e05db0fd4f31dde7005f075a84f96b360d05984b |
| ------------------------------------------------- |
| |
| The merge-base command finds a common ancestor of the given commits, |
| and always returns one or the other in the case where one is a |
| descendant of the other; so the above output shows that e05db0fd |
| actually is an ancestor of v1.5.0-rc1. |
| |
| Alternatively, note that |
| |
| ------------------------------------------------- |
| $ git log v1.5.0-rc1..e05db0fd |
| ------------------------------------------------- |
| |
| will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
| because it outputs only commits that are not reachable from v1.5.0-rc1. |
| |
| As yet another alternative, the gitlink:git-show-branch[1] command lists |
| the commits reachable from its arguments with a display on the left-hand |
| side that indicates which arguments that commit is reachable from. So, |
| you can run something like |
| |
| ------------------------------------------------- |
| $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 |
| ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if |
| available |
| ! [v1.5.0-rc0] GIT v1.5.0 preview |
| ! [v1.5.0-rc1] GIT v1.5.0-rc1 |
| ! [v1.5.0-rc2] GIT v1.5.0-rc2 |
| ... |
| ------------------------------------------------- |
| |
| then search for a line that looks like |
| |
| ------------------------------------------------- |
| + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if |
| available |
| ------------------------------------------------- |
| |
| Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and |
| from v1.5.0-rc2, but not from v1.5.0-rc0. |
| |
| |
| Developing with git |
| =================== |
| |
| Telling git your name |
| --------------------- |
| |
| Before creating any commits, you should introduce yourself to git. The |
| easiest way to do so is: |
| |
| ------------------------------------------------ |
| $ cat >~/.gitconfig <<\EOF |
| [user] |
| name = Your Name Comes Here |
| email = you@yourdomain.example.com |
| EOF |
| ------------------------------------------------ |
| |
| (See the "CONFIGURATION FILE" section of gitlink:git-config[1] for |
| details on the configuration file.) |
| |
| |
| Creating a new repository |
| ------------------------- |
| |
| Creating a new repository from scratch is very easy: |
| |
| ------------------------------------------------- |
| $ mkdir project |
| $ cd project |
| $ git init |
| ------------------------------------------------- |
| |
| If you have some initial content (say, a tarball): |
| |
| ------------------------------------------------- |
| $ tar -xzvf project.tar.gz |
| $ cd project |
| $ git init |
| $ git add . # include everything below ./ in the first commit: |
| $ git commit |
| ------------------------------------------------- |
| |
| [[how-to-make-a-commit]] |
| How to make a commit |
| -------------------- |
| |
| Creating a new commit takes three steps: |
| |
| 1. Making some changes to the working directory using your |
| favorite editor. |
| 2. Telling git about your changes. |
| 3. Creating the commit using the content you told git about |
| in step 2. |
| |
| In practice, you can interleave and repeat steps 1 and 2 as many |
| times as you want: in order to keep track of what you want committed |
| at step 3, git maintains a snapshot of the tree's contents in a |
| special staging area called "the index." |
| |
| At the beginning, the content of the index will be identical to |
| that of the HEAD. The command "git diff --cached", which shows |
| the difference between the HEAD and the index, should therefore |
| produce no output at that point. |
| |
| Modifying the index is easy: |
| |
| To update the index with the new contents of a modified file, use |
| |
| ------------------------------------------------- |
| $ git add path/to/file |
| ------------------------------------------------- |
| |
| To add the contents of a new file to the index, use |
| |
| ------------------------------------------------- |
| $ git add path/to/file |
| ------------------------------------------------- |
| |
| To remove a file from the index and from the working tree, |
| |
| ------------------------------------------------- |
| $ git rm path/to/file |
| ------------------------------------------------- |
| |
| After each step you can verify that |
| |
| ------------------------------------------------- |
| $ git diff --cached |
| ------------------------------------------------- |
| |
| always shows the difference between the HEAD and the index file--this |
| is what you'd commit if you created the commit now--and that |
| |
| ------------------------------------------------- |
| $ git diff |
| ------------------------------------------------- |
| |
| shows the difference between the working tree and the index file. |
| |
| Note that "git add" always adds just the current contents of a file |
| to the index; further changes to the same file will be ignored unless |
| you run git-add on the file again. |
| |
| When you're ready, just run |
| |
| ------------------------------------------------- |
| $ git commit |
| ------------------------------------------------- |
| |
| and git will prompt you for a commit message and then create the new |
| commit. Check to make sure it looks like what you expected with |
| |
| ------------------------------------------------- |
| $ git show |
| ------------------------------------------------- |
| |
| As a special shortcut, |
| |
| ------------------------------------------------- |
| $ git commit -a |
| ------------------------------------------------- |
| |
| will update the index with any files that you've modified or removed |
| and create a commit, all in one step. |
| |
| A number of commands are useful for keeping track of what you're |
| about to commit: |
| |
| ------------------------------------------------- |
| $ git diff --cached # difference between HEAD and the index; what |
| # would be commited if you ran "commit" now. |
| $ git diff # difference between the index file and your |
| # working directory; changes that would not |
| # be included if you ran "commit" now. |
| $ git status # a brief per-file summary of the above. |
| ------------------------------------------------- |
| |
| Creating good commit messages |
| ----------------------------- |
| |
| Though not required, it's a good idea to begin the commit message |
| with a single short (less than 50 character) line summarizing the |
| change, followed by a blank line and then a more thorough |
| description. Tools that turn commits into email, for example, use |
| the first line on the Subject line and the rest of the commit in the |
| body. |
| |
| How to merge |
| ------------ |
| |
| You can rejoin two diverging branches of development using |
| gitlink:git-merge[1]: |
| |
| ------------------------------------------------- |
| $ git merge branchname |
| ------------------------------------------------- |
| |
| merges the development in the branch "branchname" into the current |
| branch. If there are conflicts--for example, if the same file is |
| modified in two different ways in the remote branch and the local |
| branch--then you are warned; the output may look something like this: |
| |
| ------------------------------------------------- |
| $ git merge next |
| 100% (4/4) done |
| Auto-merged file.txt |
| CONFLICT (content): Merge conflict in file.txt |
| Automatic merge failed; fix conflicts and then commit the result. |
| ------------------------------------------------- |
| |
| Conflict markers are left in the problematic files, and after |
| you resolve the conflicts manually, you can update the index |
| with the contents and run git commit, as you normally would when |
| creating a new file. |
| |
| If you examine the resulting commit using gitk, you will see that it |
| has two parents, one pointing to the top of the current branch, and |
| one to the top of the other branch. |
| |
| In more detail: |
| |
| [[resolving-a-merge]] |
| Resolving a merge |
| ----------------- |
| |
| When a merge isn't resolved automatically, git leaves the index and |
| the working tree in a special state that gives you all the |
| information you need to help resolve the merge. |
| |
| Files with conflicts are marked specially in the index, so until you |
| resolve the problem and update the index, gitlink:git-commit[1] will |
| fail: |
| |
| ------------------------------------------------- |
| $ git commit |
| file.txt: needs merge |
| ------------------------------------------------- |
| |
| Also, gitlink:git-status[1] will list those files as "unmerged", and the |
| files with conflicts will have conflict markers added, like this: |
| |
| ------------------------------------------------- |
| <<<<<<< HEAD:file.txt |
| Hello world |
| ======= |
| Goodbye |
| >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt |
| ------------------------------------------------- |
| |
| All you need to do is edit the files to resolve the conflicts, and then |
| |
| ------------------------------------------------- |
| $ git add file.txt |
| $ git commit |
| ------------------------------------------------- |
| |
| Note that the commit message will already be filled in for you with |
| some information about the merge. Normally you can just use this |
| default message unchanged, but you may add additional commentary of |
| your own if desired. |
| |
| The above is all you need to know to resolve a simple merge. But git |
| also provides more information to help resolve conflicts: |
| |
| Getting conflict-resolution help during a merge |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| All of the changes that git was able to merge automatically are |
| already added to the index file, so gitlink:git-diff[1] shows only |
| the conflicts. It uses an unusual syntax: |
| |
| ------------------------------------------------- |
| $ git diff |
| diff --cc file.txt |
| index 802992c,2b60207..0000000 |
| --- a/file.txt |
| +++ b/file.txt |
| @@@ -1,1 -1,1 +1,5 @@@ |
| ++<<<<<<< HEAD:file.txt |
| +Hello world |
| ++======= |
| + Goodbye |
| ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt |
| ------------------------------------------------- |
| |
| Recall that the commit which will be commited after we resolve this |
| conflict will have two parents instead of the usual one: one parent |
| will be HEAD, the tip of the current branch; the other will be the |
| tip of the other branch, which is stored temporarily in MERGE_HEAD. |
| |
| During the merge, the index holds three versions of each file. Each of |
| these three "file stages" represents a different version of the file: |
| |
| ------------------------------------------------- |
| $ git show :1:file.txt # the file in a common ancestor of both branches |
| $ git show :2:file.txt # the version from HEAD, but including any |
| # nonconflicting changes from MERGE_HEAD |
| $ git show :3:file.txt # the version from MERGE_HEAD, but including any |
| # nonconflicting changes from HEAD. |
| ------------------------------------------------- |
| |
| Since the stage 2 and stage 3 versions have already been updated with |
| nonconflicting changes, the only remaining differences between them are |
| the important ones; thus gitlink:git-diff[1] can use the information in |
| the index to show only those conflicts. |
| |
| The diff above shows the differences between the working-tree version of |
| file.txt and the stage 2 and stage 3 versions. So instead of preceding |
| each line by a single "+" or "-", it now uses two columns: the first |
| column is used for differences between the first parent and the working |
| directory copy, and the second for differences between the second parent |
| and the working directory copy. (See the "COMBINED DIFF FORMAT" section |
| of gitlink:git-diff-files[1] for a details of the format.) |
| |
| After resolving the conflict in the obvious way (but before updating the |
| index), the diff will look like: |
| |
| ------------------------------------------------- |
| $ git diff |
| diff --cc file.txt |
| index 802992c,2b60207..0000000 |
| --- a/file.txt |
| +++ b/file.txt |
| @@@ -1,1 -1,1 +1,1 @@@ |
| - Hello world |
| -Goodbye |
| ++Goodbye world |
| ------------------------------------------------- |
| |
| This shows that our resolved version deleted "Hello world" from the |
| first parent, deleted "Goodbye" from the second parent, and added |
| "Goodbye world", which was previously absent from both. |
| |
| Some special diff options allow diffing the working directory against |
| any of these stages: |
| |
| ------------------------------------------------- |
| $ git diff -1 file.txt # diff against stage 1 |
| $ git diff --base file.txt # same as the above |
| $ git diff -2 file.txt # diff against stage 2 |
| $ git diff --ours file.txt # same as the above |
| $ git diff -3 file.txt # diff against stage 3 |
| $ git diff --theirs file.txt # same as the above. |
| ------------------------------------------------- |
| |
| The gitlink:git-log[1] and gitk[1] commands also provide special help |
| for merges: |
| |
| ------------------------------------------------- |
| $ git log --merge |
| $ gitk --merge |
| ------------------------------------------------- |
| |
| These will display all commits which exist only on HEAD or on |
| MERGE_HEAD, and which touch an unmerged file. |
| |
| Each time you resolve the conflicts in a file and update the index: |
| |
| ------------------------------------------------- |
| $ git add file.txt |
| ------------------------------------------------- |
| |
| the different stages of that file will be "collapsed", after which |
| git-diff will (by default) no longer show diffs for that file. |
| |
| [[undoing-a-merge]] |
| Undoing a merge |
| --------------- |
| |
| If you get stuck and decide to just give up and throw the whole mess |
| away, you can always return to the pre-merge state with |
| |
| ------------------------------------------------- |
| $ git reset --hard HEAD |
| ------------------------------------------------- |
| |
| Or, if you've already commited the merge that you want to throw away, |
| |
| ------------------------------------------------- |
| $ git reset --hard ORIG_HEAD |
| ------------------------------------------------- |
| |
| However, this last command can be dangerous in some cases--never |
| throw away a commit you have already committed if that commit may |
| itself have been merged into another branch, as doing so may confuse |
| further merges. |
| |
| Fast-forward merges |
| ------------------- |
| |
| There is one special case not mentioned above, which is treated |
| differently. Normally, a merge results in a merge commit, with two |
| parents, one pointing at each of the two lines of development that |
| were merged. |
| |
| However, if one of the two lines of development is completely |
| contained within the other--so every commit present in the one is |
| already contained in the other--then git just performs a |
| <<fast-forwards,fast forward>>; the head of the current branch is |
| moved forward to point at the head of the merged-in branch, without |
| any new commits being created. |
| |
| Fixing mistakes |
| --------------- |
| |
| If you've messed up the working tree, but haven't yet committed your |
| mistake, you can return the entire working tree to the last committed |
| state with |
| |
| ------------------------------------------------- |
| $ git reset --hard HEAD |
| ------------------------------------------------- |
| |
| If you make a commit that you later wish you hadn't, there are two |
| fundamentally different ways to fix the problem: |
| |
| 1. You can create a new commit that undoes whatever was done |
| by the previous commit. This is the correct thing if your |
| mistake has already been made public. |
| |
| 2. You can go back and modify the old commit. You should |
| never do this if you have already made the history public; |
| git does not normally expect the "history" of a project to |
| change, and cannot correctly perform repeated merges from |
| a branch that has had its history changed. |
| |
| Fixing a mistake with a new commit |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Creating a new commit that reverts an earlier change is very easy; |
| just pass the gitlink:git-revert[1] command a reference to the bad |
| commit; for example, to revert the most recent commit: |
| |
| ------------------------------------------------- |
| $ git revert HEAD |
| ------------------------------------------------- |
| |
| This will create a new commit which undoes the change in HEAD. You |
| will be given a chance to edit the commit message for the new commit. |
| |
| You can also revert an earlier change, for example, the next-to-last: |
| |
| ------------------------------------------------- |
| $ git revert HEAD^ |
| ------------------------------------------------- |
| |
| In this case git will attempt to undo the old change while leaving |
| intact any changes made since then. If more recent changes overlap |
| with the changes to be reverted, then you will be asked to fix |
| conflicts manually, just as in the case of <<resolving-a-merge, |
| resolving a merge>>. |
| |
| [[fixing-a-mistake-by-editing-history]] |
| Fixing a mistake by editing history |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| If the problematic commit is the most recent commit, and you have not |
| yet made that commit public, then you may just |
| <<undoing-a-merge,destroy it using git-reset>>. |
| |
| Alternatively, you |
| can edit the working directory and update the index to fix your |
| mistake, just as if you were going to <<how-to-make-a-commit,create a |
| new commit>>, then run |
| |
| ------------------------------------------------- |
| $ git commit --amend |
| ------------------------------------------------- |
| |
| which will replace the old commit by a new commit incorporating your |
| changes, giving you a chance to edit the old commit message first. |
| |
| Again, you should never do this to a commit that may already have |
| been merged into another branch; use gitlink:git-revert[1] instead in |
| that case. |
| |
| It is also possible to edit commits further back in the history, but |
| this is an advanced topic to be left for |
| <<cleaning-up-history,another chapter>>. |
| |
| Checking out an old version of a file |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| In the process of undoing a previous bad change, you may find it |
| useful to check out an older version of a particular file using |
| gitlink:git-checkout[1]. We've used git checkout before to switch |
| branches, but it has quite different behavior if it is given a path |
| name: the command |
| |
| ------------------------------------------------- |
| $ git checkout HEAD^ path/to/file |
| ------------------------------------------------- |
| |
| replaces path/to/file by the contents it had in the commit HEAD^, and |
| also updates the index to match. It does not change branches. |
| |
| If you just want to look at an old version of the file, without |
| modifying the working directory, you can do that with |
| gitlink:git-show[1]: |
| |
| ------------------------------------------------- |
| $ git show HEAD^:path/to/file |
| ------------------------------------------------- |
| |
| which will display the given version of the file. |
| |
| Ensuring good performance |
| ------------------------- |
| |
| On large repositories, git depends on compression to keep the history |
| information from taking up to much space on disk or in memory. |
| |
| This compression is not performed automatically. Therefore you |
| should occasionally run gitlink:git-gc[1]: |
| |
| ------------------------------------------------- |
| $ git gc |
| ------------------------------------------------- |
| |
| to recompress the archive. This can be very time-consuming, so |
| you may prefer to run git-gc when you are not doing other work. |
| |
| Ensuring reliability |
| -------------------- |
| |
| Checking the repository for corruption |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| The gitlink:git-fsck[1] command runs a number of self-consistency checks |
| on the repository, and reports on any problems. This may take some |
| time. The most common warning by far is about "dangling" objects: |
| |
| ------------------------------------------------- |
| $ git fsck |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
| dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb |
| dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f |
| dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e |
| dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 |
| dangling tree b24c2473f1fd3d91352a624795be026d64c8841f |
| ... |
| ------------------------------------------------- |
| |
| Dangling objects are objects that are harmless, but also unnecessary; |
| you can remove them at any time with gitlink:git-prune[1] or the --prune |
| option to gitlink:git-gc[1]: |
| |
| ------------------------------------------------- |
| $ git gc --prune |
| ------------------------------------------------- |
| |
| This may be time-consuming. Unlike most other git operations (including |
| git-gc when run without any options), it is not safe to prune while |
| other git operations are in progress in the same repository. |
| |
| For more about dangling objects, see <<dangling-objects>>. |
| |
| |
| Recovering lost changes |
| ~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Reflogs |
| ^^^^^^^ |
| |
| Say you modify a branch with gitlink:git-reset[1] --hard, and then |
| realize that the branch was the only reference you had to that point in |
| history. |
| |
| Fortunately, git also keeps a log, called a "reflog", of all the |
| previous values of each branch. So in this case you can still find the |
| old history using, for example, |
| |
| ------------------------------------------------- |
| $ git log master@{1} |
| ------------------------------------------------- |
| |
| This lists the commits reachable from the previous version of the head. |
| This syntax can be used to with any git command that accepts a commit, |
| not just with git log. Some other examples: |
| |
| ------------------------------------------------- |
| $ git show master@{2} # See where the branch pointed 2, |
| $ git show master@{3} # 3, ... changes ago. |
| $ gitk master@{yesterday} # See where it pointed yesterday, |
| $ gitk master@{"1 week ago"} # ... or last week |
| ------------------------------------------------- |
| |
| The reflogs are kept by default for 30 days, after which they may be |
| pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn |
| how to control this pruning, and see the "SPECIFYING REVISIONS" |
| section of gitlink:git-rev-parse[1] for details. |
| |
| Note that the reflog history is very different from normal git history. |
| While normal history is shared by every repository that works on the |
| same project, the reflog history is not shared: it tells you only about |
| how the branches in your local repository have changed over time. |
| |
| Examining dangling objects |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| In some situations the reflog may not be able to save you. For |
| example, suppose you delete a branch, then realize you need the history |
| it contained. The reflog is also deleted; however, if you have not |
| yet pruned the repository, then you may still be able to find |
| the lost commits; run git-fsck and watch for output that mentions |
| "dangling commits": |
| |
| ------------------------------------------------- |
| $ git fsck |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
| ... |
| ------------------------------------------------- |
| |
| You can examine |
| one of those dangling commits with, for example, |
| |
| ------------------------------------------------ |
| $ gitk 7281251ddd --not --all |
| ------------------------------------------------ |
| |
| which does what it sounds like: it says that you want to see the commit |
| history that is described by the dangling commit(s), but not the |
| history that is described by all your existing branches and tags. Thus |
| you get exactly the history reachable from that commit that is lost. |
| (And notice that it might not be just one commit: we only report the |
| "tip of the line" as being dangling, but there might be a whole deep |
| and complex commit history that was dropped.) |
| |
| If you decide you want the history back, you can always create a new |
| reference pointing to it, for example, a new branch: |
| |
| ------------------------------------------------ |
| $ git branch recovered-branch 7281251ddd |
| ------------------------------------------------ |
| |
| |
| Sharing development with others |
| =============================== |
| |
| [[getting-updates-with-git-pull]] |
| Getting updates with git pull |
| ----------------------------- |
| |
| After you clone a repository and make a few changes of your own, you |
| may wish to check the original repository for updates and merge them |
| into your own work. |
| |
| We have already seen <<Updating-a-repository-with-git-fetch,how to |
| keep remote tracking branches up to date>> with gitlink:git-fetch[1], |
| and how to merge two branches. So you can merge in changes from the |
| original repository's master branch with: |
| |
| ------------------------------------------------- |
| $ git fetch |
| $ git merge origin/master |
| ------------------------------------------------- |
| |
| However, the gitlink:git-pull[1] command provides a way to do this in |
| one step: |
| |
| ------------------------------------------------- |
| $ git pull origin master |
| ------------------------------------------------- |
| |
| In fact, "origin" is normally the default repository to pull from, |
| and the default branch is normally the HEAD of the remote repository, |
| so often you can accomplish the above with just |
| |
| ------------------------------------------------- |
| $ git pull |
| ------------------------------------------------- |
| |
| See the descriptions of the branch.<name>.remote and |
| branch.<name>.merge options in gitlink:git-config[1] to learn |
| how to control these defaults depending on the current branch. |
| |
| In addition to saving you keystrokes, "git pull" also helps you by |
| producing a default commit message documenting the branch and |
| repository that you pulled from. |
| |
| (But note that no such commit will be created in the case of a |
| <<fast-forwards,fast forward>>; instead, your branch will just be |
| updated to point to the latest commit from the upstream branch.) |
| |
| The git-pull command can also be given "." as the "remote" repository, |
| in which case it just merges in a branch from the current repository; so |
| the commands |
| |
| ------------------------------------------------- |
| $ git pull . branch |
| $ git merge branch |
| ------------------------------------------------- |
| |
| are roughly equivalent. The former is actually very commonly used. |
| |
| Submitting patches to a project |
| ------------------------------- |
| |
| If you just have a few changes, the simplest way to submit them may |
| just be to send them as patches in email: |
| |
| First, use gitlink:git-format-patch[1]; for example: |
| |
| ------------------------------------------------- |
| $ git format-patch origin |
| ------------------------------------------------- |
| |
| will produce a numbered series of files in the current directory, one |
| for each patch in the current branch but not in origin/HEAD. |
| |
| You can then import these into your mail client and send them by |
| hand. However, if you have a lot to send at once, you may prefer to |
| use the gitlink:git-send-email[1] script to automate the process. |
| Consult the mailing list for your project first to determine how they |
| prefer such patches be handled. |
| |
| Importing patches to a project |
| ------------------------------ |
| |
| Git also provides a tool called gitlink:git-am[1] (am stands for |
| "apply mailbox"), for importing such an emailed series of patches. |
| Just save all of the patch-containing messages, in order, into a |
| single mailbox file, say "patches.mbox", then run |
| |
| ------------------------------------------------- |
| $ git am -3 patches.mbox |
| ------------------------------------------------- |
| |
| Git will apply each patch in order; if any conflicts are found, it |
| will stop, and you can fix the conflicts as described in |
| "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells |
| git to perform a merge; if you would prefer it just to abort and |
| leave your tree and index untouched, you may omit that option.) |
| |
| Once the index is updated with the results of the conflict |
| resolution, instead of creating a new commit, just run |
| |
| ------------------------------------------------- |
| $ git am --resolved |
| ------------------------------------------------- |
| |
| and git will create the commit for you and continue applying the |
| remaining patches from the mailbox. |
| |
| The final result will be a series of commits, one for each patch in |
| the original mailbox, with authorship and commit log message each |
| taken from the message containing each patch. |
| |
| [[setting-up-a-public-repository]] |
| Setting up a public repository |
| ------------------------------ |
| |
| Another way to submit changes to a project is to simply tell the |
| maintainer of that project to pull from your repository, exactly as |
| you did in the section "<<getting-updates-with-git-pull, Getting |
| updates with git pull>>". |
| |
| If you and maintainer both have accounts on the same machine, then |
| then you can just pull changes from each other's repositories |
| directly; note that all of the commands (gitlink:git-clone[1], |
| git-fetch[1], git-pull[1], etc.) that accept a URL as an argument |
| will also accept a local directory name; so, for example, you can |
| use |
| |
| ------------------------------------------------- |
| $ git clone /path/to/repository |
| $ git pull /path/to/other/repository |
| ------------------------------------------------- |
| |
| If this sort of setup is inconvenient or impossible, another (more |
| common) option is to set up a public repository on a public server. |
| This also allows you to cleanly separate private work in progress |
| from publicly visible work. |
| |
| You will continue to do your day-to-day work in your personal |
| repository, but periodically "push" changes from your personal |
| repository into your public repository, allowing other developers to |
| pull from that repository. So the flow of changes, in a situation |
| where there is one other developer with a public repository, looks |
| like this: |
| |
| you push |
| your personal repo ------------------> your public repo |
| ^ | |
| | | |
| | you pull | they pull |
| | | |
| | | |
| | they push V |
| their public repo <------------------- their repo |
| |
| Now, assume your personal repository is in the directory ~/proj. We |
| first create a new clone of the repository: |
| |
| ------------------------------------------------- |
| $ git clone --bare proj-clone.git |
| ------------------------------------------------- |
| |
| The resulting directory proj-clone.git will contains a "bare" git |
| repository--it is just the contents of the ".git" directory, without |
| a checked-out copy of a working directory. |
| |
| Next, copy proj-clone.git to the server where you plan to host the |
| public repository. You can use scp, rsync, or whatever is most |
| convenient. |
| |
| If somebody else maintains the public server, they may already have |
| set up a git service for you, and you may skip to the section |
| "<<pushing-changes-to-a-public-repository,Pushing changes to a public |
| repository>>", below. |
| |
| Otherwise, the following sections explain how to export your newly |
| created public repository: |
| |
| [[exporting-via-http]] |
| Exporting a git repository via http |
| ----------------------------------- |
| |
| The git protocol gives better performance and reliability, but on a |
| host with a web server set up, http exports may be simpler to set up. |
| |
| All you need to do is place the newly created bare git repository in |
| a directory that is exported by the web server, and make some |
| adjustments to give web clients some extra information they need: |
| |
| ------------------------------------------------- |
| $ mv proj.git /home/you/public_html/proj.git |
| $ cd proj.git |
| $ git update-server-info |
| $ chmod a+x hooks/post-update |
| ------------------------------------------------- |
| |
| (For an explanation of the last two lines, see |
| gitlink:git-update-server-info[1], and the documentation |
| link:hooks.txt[Hooks used by git].) |
| |
| Advertise the url of proj.git. Anybody else should then be able to |
| clone or pull from that url, for example with a commandline like: |
| |
| ------------------------------------------------- |
| $ git clone http://yourserver.com/~you/proj.git |
| ------------------------------------------------- |
| |
| (See also |
| link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] |
| for a slightly more sophisticated setup using WebDAV which also |
| allows pushing over http.) |
| |
| [[exporting-via-git]] |
| Exporting a git repository via the git protocol |
| ----------------------------------------------- |
| |
| This is the preferred method. |
| |
| For now, we refer you to the gitlink:git-daemon[1] man page for |
| instructions. (See especially the examples section.) |
| |
| [[pushing-changes-to-a-public-repository]] |
| Pushing changes to a public repository |
| -------------------------------------- |
| |
| Note that the two techniques outline above (exporting via |
| <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other |
| maintainers to fetch your latest changes, but they do not allow write |
| access, which you will need to update the public repository with the |
| latest changes created in your private repository. |
| |
| The simplest way to do this is using gitlink:git-push[1] and ssh; to |
| update the remote branch named "master" with the latest state of your |
| branch named "master", run |
| |
| ------------------------------------------------- |
| $ git push ssh://yourserver.com/~you/proj.git master:master |
| ------------------------------------------------- |
| |
| or just |
| |
| ------------------------------------------------- |
| $ git push ssh://yourserver.com/~you/proj.git master |
| ------------------------------------------------- |
| |
| As with git-fetch, git-push will complain if this does not result in |
| a <<fast-forwards,fast forward>>. Normally this is a sign of |
| something wrong. However, if you are sure you know what you're |
| doing, you may force git-push to perform the update anyway by |
| proceeding the branch name by a plus sign: |
| |
| ------------------------------------------------- |
| $ git push ssh://yourserver.com/~you/proj.git +master |
| ------------------------------------------------- |
| |
| As with git-fetch, you may also set up configuration options to |
| save typing; so, for example, after |
| |
| ------------------------------------------------- |
| $ cat >.git/config <<EOF |
| [remote "public-repo"] |
| url = ssh://yourserver.com/~you/proj.git |
| EOF |
| ------------------------------------------------- |
| |
| you should be able to perform the above push with just |
| |
| ------------------------------------------------- |
| $ git push public-repo master |
| ------------------------------------------------- |
| |
| See the explanations of the remote.<name>.url, branch.<name>.remote, |
| and remote.<name>.push options in gitlink:git-config[1] for |
| details. |
| |
| Setting up a shared repository |
| ------------------------------ |
| |
| Another way to collaborate is by using a model similar to that |
| commonly used in CVS, where several developers with special rights |
| all push to and pull from a single shared repository. See |
| link:cvs-migration.txt[git for CVS users] for instructions on how to |
| set this up. |
| |
| Allow web browsing of a repository |
| ---------------------------------- |
| |
| The gitweb cgi script provides users an easy way to browse your |
| project's files and history without having to install git; see the file |
| gitweb/INSTALL in the git source tree for instructions on setting it up. |
| |
| Examples |
| -------- |
| |
| TODO: topic branches, typical roles as in everyday.txt, ? |
| |
| |
| [[cleaning-up-history]] |
| Rewriting history and maintaining patch series |
| ============================================== |
| |
| Normally commits are only added to a project, never taken away or |
| replaced. Git is designed with this assumption, and violating it will |
| cause git's merge machinery (for example) to do the wrong thing. |
| |
| However, there is a situation in which it can be useful to violate this |
| assumption. |
| |
| Creating the perfect patch series |
| --------------------------------- |
| |
| Suppose you are a contributor to a large project, and you want to add a |
| complicated feature, and to present it to the other developers in a way |
| that makes it easy for them to read your changes, verify that they are |
| correct, and understand why you made each change. |
| |
| If you present all of your changes as a single patch (or commit), they |
| may find that it is too much to digest all at once. |
| |
| If you present them with the entire history of your work, complete with |
| mistakes, corrections, and dead ends, they may be overwhelmed. |
| |
| So the ideal is usually to produce a series of patches such that: |
| |
| 1. Each patch can be applied in order. |
| |
| 2. Each patch includes a single logical change, together with a |
| message explaining the change. |
| |
| 3. No patch introduces a regression: after applying any initial |
| part of the series, the resulting project still compiles and |
| works, and has no bugs that it didn't have before. |
| |
| 4. The complete series produces the same end result as your own |
| (probably much messier!) development process did. |
| |
| We will introduce some tools that can help you do this, explain how to |
| use them, and then explain some of the problems that can arise because |
| you are rewriting history. |
| |
| Keeping a patch series up to date using git-rebase |
| -------------------------------------------------- |
| |
| Suppose that you create a branch "mywork" on a remote-tracking branch |
| "origin", and create some commits on top of it: |
| |
| ------------------------------------------------- |
| $ git checkout -b mywork origin |
| $ vi file.txt |
| $ git commit |
| $ vi otherfile.txt |
| $ git commit |
| ... |
| ------------------------------------------------- |
| |
| You have performed no merges into mywork, so it is just a simple linear |
| sequence of patches on top of "origin": |
| |
| ................................................ |
| o--o--o <-- origin |
| \ |
| o--o--o <-- mywork |
| ................................................ |
| |
| Some more interesting work has been done in the upstream project, and |
| "origin" has advanced: |
| |
| ................................................ |
| o--o--O--o--o--o <-- origin |
| \ |
| a--b--c <-- mywork |
| ................................................ |
| |
| At this point, you could use "pull" to merge your changes back in; |
| the result would create a new merge commit, like this: |
| |
| ................................................ |
| o--o--O--o--o--o <-- origin |
| \ \ |
| a--b--c--m <-- mywork |
| ................................................ |
| |
| However, if you prefer to keep the history in mywork a simple series of |
| commits without any merges, you may instead choose to use |
| gitlink:git-rebase[1]: |
| |
| ------------------------------------------------- |
| $ git checkout mywork |
| $ git rebase origin |
| ------------------------------------------------- |
| |
| This will remove each of your commits from mywork, temporarily saving |
| them as patches (in a directory named ".dotest"), update mywork to |
| point at the latest version of origin, then apply each of the saved |
| patches to the new mywork. The result will look like: |
| |
| |
| ................................................ |
| o--o--O--o--o--o <-- origin |
| \ |
| a'--b'--c' <-- mywork |
| ................................................ |
| |
| In the process, it may discover conflicts. In that case it will stop |
| and allow you to fix the conflicts; after fixing conflicts, use "git |
| add" to update the index with those contents, and then, instead of |
| running git-commit, just run |
| |
| ------------------------------------------------- |
| $ git rebase --continue |
| ------------------------------------------------- |
| |
| and git will continue applying the rest of the patches. |
| |
| At any point you may use the --abort option to abort this process and |
| return mywork to the state it had before you started the rebase: |
| |
| ------------------------------------------------- |
| $ git rebase --abort |
| ------------------------------------------------- |
| |
| Modifying a single commit |
| ------------------------- |
| |
| We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the |
| most recent commit using |
| |
| ------------------------------------------------- |
| $ git commit --amend |
| ------------------------------------------------- |
| |
| which will replace the old commit by a new commit incorporating your |
| changes, giving you a chance to edit the old commit message first. |
| |
| You can also use a combination of this and gitlink:git-rebase[1] to edit |
| commits further back in your history. First, tag the problematic commit with |
| |
| ------------------------------------------------- |
| $ git tag bad mywork~5 |
| ------------------------------------------------- |
| |
| (Either gitk or git-log may be useful for finding the commit.) |
| |
| Then check out that commit, edit it, and rebase the rest of the series |
| on top of it (note that we could check out the commit on a temporary |
| branch, but instead we're using a <<detached-head,detached head>>): |
| |
| ------------------------------------------------- |
| $ git checkout bad |
| $ # make changes here and update the index |
| $ git commit --amend |
| $ git rebase --onto HEAD bad mywork |
| ------------------------------------------------- |
| |
| When you're done, you'll be left with mywork checked out, with the top |
| patches on mywork reapplied on top of your modified commit. You can |
| then clean up with |
| |
| ------------------------------------------------- |
| $ git tag -d bad |
| ------------------------------------------------- |
| |
| Note that the immutable nature of git history means that you haven't really |
| "modified" existing commits; instead, you have replaced the old commits with |
| new commits having new object names. |
| |
| Reordering or selecting from a patch series |
| ------------------------------------------- |
| |
| Given one existing commit, the gitlink:git-cherry-pick[1] command |
| allows you to apply the change introduced by that commit and create a |
| new commit that records it. So, for example, if "mywork" points to a |
| series of patches on top of "origin", you might do something like: |
| |
| ------------------------------------------------- |
| $ git checkout -b mywork-new origin |
| $ gitk origin..mywork & |
| ------------------------------------------------- |
| |
| And browse through the list of patches in the mywork branch using gitk, |
| applying them (possibly in a different order) to mywork-new using |
| cherry-pick, and possibly modifying them as you go using commit |
| --amend. |
| |
| Another technique is to use git-format-patch to create a series of |
| patches, then reset the state to before the patches: |
| |
| ------------------------------------------------- |
| $ git format-patch origin |
| $ git reset --hard origin |
| ------------------------------------------------- |
| |
| Then modify, reorder, or eliminate patches as preferred before applying |
| them again with gitlink:git-am[1]. |
| |
| Other tools |
| ----------- |
| |
| There are numerous other tools, such as stgit, which exist for the |
| purpose of maintaining a patch series. These are outside of the scope of |
| this manual. |
| |
| Problems with rewriting history |
| ------------------------------- |
| |
| The primary problem with rewriting the history of a branch has to do |
| with merging. Suppose somebody fetches your branch and merges it into |
| their branch, with a result something like this: |
| |
| ................................................ |
| o--o--O--o--o--o <-- origin |
| \ \ |
| t--t--t--m <-- their branch: |
| ................................................ |
| |
| Then suppose you modify the last three commits: |
| |
| ................................................ |
| o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin |
| ................................................ |
| |
| If we examined all this history together in one repository, it will |
| look like: |
| |
| ................................................ |
| o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin |
| \ \ |
| t--t--t--m <-- their branch: |
| ................................................ |
| |
| Git has no way of knowing that the new head is an updated version of |
| the old head; it treats this situation exactly the same as it would if |
| two developers had independently done the work on the old and new heads |
| in parallel. At this point, if someone attempts to merge the new head |
| in to their branch, git will attempt to merge together the two (old and |
| new) lines of development, instead of trying to replace the old by the |
| new. The results are likely to be unexpected. |
| |
| You may still choose to publish branches whose history is rewritten, |
| and it may be useful for others to be able to fetch those branches in |
| order to examine or test them, but they should not attempt to pull such |
| branches into their own work. |
| |
| For true distributed development that supports proper merging, |
| published branches should never be rewritten. |
| |
| Advanced branch management |
| ========================== |
| |
| Fetching individual branches |
| ---------------------------- |
| |
| Instead of using gitlink:git-remote[1], you can also choose just |
| to update one branch at a time, and to store it locally under an |
| arbitrary name: |
| |
| ------------------------------------------------- |
| $ git fetch origin todo:my-todo-work |
| ------------------------------------------------- |
| |
| The first argument, "origin", just tells git to fetch from the |
| repository you originally cloned from. The second argument tells git |
| to fetch the branch named "todo" from the remote repository, and to |
| store it locally under the name refs/heads/my-todo-work. |
| |
| You can also fetch branches from other repositories; so |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git master:example-master |
| ------------------------------------------------- |
| |
| will create a new branch named "example-master" and store in it the |
| branch named "master" from the repository at the given URL. If you |
| already have a branch named example-master, it will attempt to |
| "fast-forward" to the commit given by example.com's master branch. So |
| next we explain what a fast-forward is: |
| |
| [[fast-forwards]] |
| Understanding git history: fast-forwards |
| ---------------------------------------- |
| |
| In the previous example, when updating an existing branch, "git |
| fetch" checks to make sure that the most recent commit on the remote |
| branch is a descendant of the most recent commit on your copy of the |
| branch before updating your copy of the branch to point at the new |
| commit. Git calls this process a "fast forward". |
| |
| A fast forward looks something like this: |
| |
| ................................................ |
| o--o--o--o <-- old head of the branch |
| \ |
| o--o--o <-- new head of the branch |
| ................................................ |
| |
| |
| In some cases it is possible that the new head will *not* actually be |
| a descendant of the old head. For example, the developer may have |
| realized she made a serious mistake, and decided to backtrack, |
| resulting in a situation like: |
| |
| ................................................ |
| o--o--o--o--a--b <-- old head of the branch |
| \ |
| o--o--o <-- new head of the branch |
| ................................................ |
| |
| In this case, "git fetch" will fail, and print out a warning. |
| |
| In that case, you can still force git to update to the new head, as |
| described in the following section. However, note that in the |
| situation above this may mean losing the commits labeled "a" and "b", |
| unless you've already created a reference of your own pointing to |
| them. |
| |
| Forcing git fetch to do non-fast-forward updates |
| ------------------------------------------------ |
| |
| If git fetch fails because the new head of a branch is not a |
| descendant of the old head, you may force the update with: |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git +master:refs/remotes/example/master |
| ------------------------------------------------- |
| |
| Note the addition of the "+" sign. Be aware that commits that the |
| old version of example/master pointed at may be lost, as we saw in |
| the previous section. |
| |
| Configuring remote branches |
| --------------------------- |
| |
| We saw above that "origin" is just a shortcut to refer to the |
| repository that you originally cloned from. This information is |
| stored in git configuration variables, which you can see using |
| gitlink:git-config[1]: |
| |
| ------------------------------------------------- |
| $ git config -l |
| core.repositoryformatversion=0 |
| core.filemode=true |
| core.logallrefupdates=true |
| remote.origin.url=git://git.kernel.org/pub/scm/git/git.git |
| remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* |
| branch.master.remote=origin |
| branch.master.merge=refs/heads/master |
| ------------------------------------------------- |
| |
| If there are other repositories that you also use frequently, you can |
| create similar configuration options to save typing; for example, |
| after |
| |
| ------------------------------------------------- |
| $ git config remote.example.url git://example.com/proj.git |
| ------------------------------------------------- |
| |
| then the following two commands will do the same thing: |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git master:refs/remotes/example/master |
| $ git fetch example master:refs/remotes/example/master |
| ------------------------------------------------- |
| |
| Even better, if you add one more option: |
| |
| ------------------------------------------------- |
| $ git config remote.example.fetch master:refs/remotes/example/master |
| ------------------------------------------------- |
| |
| then the following commands will all do the same thing: |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git master:ref/remotes/example/master |
| $ git fetch example master:ref/remotes/example/master |
| $ git fetch example example/master |
| $ git fetch example |
| ------------------------------------------------- |
| |
| You can also add a "+" to force the update each time: |
| |
| ------------------------------------------------- |
| $ git config remote.example.fetch +master:ref/remotes/example/master |
| ------------------------------------------------- |
| |
| Don't do this unless you're sure you won't mind "git fetch" possibly |
| throwing away commits on mybranch. |
| |
| Also note that all of the above configuration can be performed by |
| directly editing the file .git/config instead of using |
| gitlink:git-config[1]. |
| |
| See gitlink:git-config[1] for more details on the configuration |
| options mentioned above. |
| |
| |
| [[git-internals]] |
| Git internals |
| ============= |
| |
| Git depends on two fundamental abstractions: the "object database", and |
| the "current directory cache" aka "index". |
| |
| The Object Database |
| ------------------- |
| |
| The object database is literally just a content-addressable collection |
| of objects. All objects are named by their content, which is |
| approximated by the SHA1 hash of the object itself. Objects may refer |
| to other objects (by referencing their SHA1 hash), and so you can |
| build up a hierarchy of objects. |
| |
| All objects have a statically determined "type" aka "tag", which is |
| determined at object creation time, and which identifies the format of |
| the object (i.e. how it is used, and how it can refer to other |
| objects). There are currently four different object types: "blob", |
| "tree", "commit", and "tag". |
| |
| A <<def_blob_object,"blob" object>> cannot refer to any other object, |
| and is, as the name implies, a pure storage object containing some |
| user data. It is used to actually store the file data, i.e. a blob |
| object is associated with some particular version of some file. |
| |
| A <<def_tree_object,"tree" object>> is an object that ties one or more |
| "blob" objects into a directory structure. In addition, a tree object |
| can refer to other tree objects, thus creating a directory hierarchy. |
| |
| A <<def_commit_object,"commit" object>> ties such directory hierarchies |
| together into a <<def_DAG,directed acyclic graph>> of revisions - each |
| "commit" is associated with exactly one tree (the directory hierarchy at |
| the time of the commit). In addition, a "commit" refers to one or more |
| "parent" commit objects that describe the history of how we arrived at |
| that directory hierarchy. |
| |
| As a special case, a commit object with no parents is called the "root" |
| object, and is the point of an initial project commit. Each project |
| must have at least one root, and while you can tie several different |
| root objects together into one project by creating a commit object which |
| has two or more separate roots as its ultimate parents, that's probably |
| just going to confuse people. So aim for the notion of "one root object |
| per project", even if git itself does not enforce that. |
| |
| A <<def_tag_object,"tag" object>> symbolically identifies and can be |
| used to sign other objects. It contains the identifier and type of |
| another object, a symbolic name (of course!) and, optionally, a |
| signature. |
| |
| Regardless of object type, all objects share the following |
| characteristics: they are all deflated with zlib, and have a header |
| that not only specifies their type, but also provides size information |
| about the data in the object. It's worth noting that the SHA1 hash |
| that is used to name the object is the hash of the original data |
| plus this header, so `sha1sum` 'file' does not match the object name |
| for 'file'. |
| (Historical note: in the dawn of the age of git the hash |
| was the sha1 of the 'compressed' object.) |
| |
| As a result, the general consistency of an object can always be tested |
| independently of the contents or the type of the object: all objects can |
| be validated by verifying that (a) their hashes match the content of the |
| file and (b) the object successfully inflates to a stream of bytes that |
| forms a sequence of <ascii type without space> + <space> + <ascii decimal |
| size> + <byte\0> + <binary object data>. |
| |
| The structured objects can further have their structure and |
| connectivity to other objects verified. This is generally done with |
| the `git-fsck` program, which generates a full dependency graph |
| of all objects, and verifies their internal consistency (in addition |
| to just verifying their superficial consistency through the hash). |
| |
| The object types in some more detail: |
| |
| Blob Object |
| ----------- |
| |
| A "blob" object is nothing but a binary blob of data, and doesn't |
| refer to anything else. There is no signature or any other |
| verification of the data, so while the object is consistent (it 'is' |
| indexed by its sha1 hash, so the data itself is certainly correct), it |
| has absolutely no other attributes. No name associations, no |
| permissions. It is purely a blob of data (i.e. normally "file |
| contents"). |
| |
| In particular, since the blob is entirely defined by its data, if two |
| files in a directory tree (or in multiple different versions of the |
| repository) have the same contents, they will share the same blob |
| object. The object is totally independent of its location in the |
| directory tree, and renaming a file does not change the object that |
| file is associated with in any way. |
| |
| A blob is typically created when gitlink:git-update-index[1] |
| is run, and its data can be accessed by gitlink:git-cat-file[1]. |
| |
| Tree Object |
| ----------- |
| |
| The next hierarchical object type is the "tree" object. A tree object |
| is a list of mode/name/blob data, sorted by name. Alternatively, the |
| mode data may specify a directory mode, in which case instead of |
| naming a blob, that name is associated with another TREE object. |
| |
| Like the "blob" object, a tree object is uniquely determined by the |
| set contents, and so two separate but identical trees will always |
| share the exact same object. This is true at all levels, i.e. it's |
| true for a "leaf" tree (which does not refer to any other trees, only |
| blobs) as well as for a whole subdirectory. |
| |
| For that reason a "tree" object is just a pure data abstraction: it |
| has no history, no signatures, no verification of validity, except |
| that since the contents are again protected by the hash itself, we can |
| trust that the tree is immutable and its contents never change. |
| |
| So you can trust the contents of a tree to be valid, the same way you |
| can trust the contents of a blob, but you don't know where those |
| contents 'came' from. |
| |
| Side note on trees: since a "tree" object is a sorted list of |
| "filename+content", you can create a diff between two trees without |
| actually having to unpack two trees. Just ignore all common parts, |
| and your diff will look right. In other words, you can effectively |
| (and efficiently) tell the difference between any two random trees by |
| O(n) where "n" is the size of the difference, rather than the size of |
| the tree. |
| |
| Side note 2 on trees: since the name of a "blob" depends entirely and |
| exclusively on its contents (i.e. there are no names or permissions |
| involved), you can see trivial renames or permission changes by |
| noticing that the blob stayed the same. However, renames with data |
| changes need a smarter "diff" implementation. |
| |
| A tree is created with gitlink:git-write-tree[1] and |
| its data can be accessed by gitlink:git-ls-tree[1]. |
| Two trees can be compared with gitlink:git-diff-tree[1]. |
| |
| Commit Object |
| ------------- |
| |
| The "commit" object is an object that introduces the notion of |
| history into the picture. In contrast to the other objects, it |
| doesn't just describe the physical state of a tree, it describes how |
| we got there, and why. |
| |
| A "commit" is defined by the tree-object that it results in, the |
| parent commits (zero, one or more) that led up to that point, and a |
| comment on what happened. Again, a commit is not trusted per se: |
| the contents are well-defined and "safe" due to the cryptographically |
| strong signatures at all levels, but there is no reason to believe |
| that the tree is "good" or that the merge information makes sense. |
| The parents do not have to actually have any relationship with the |
| result, for example. |
| |
| Note on commits: unlike real SCM's, commits do not contain |
| rename information or file mode change information. All of that is |
| implicit in the trees involved (the result tree, and the result trees |
| of the parents), and describing that makes no sense in this idiotic |
| file manager. |
| |
| A commit is created with gitlink:git-commit-tree[1] and |
| its data can be accessed by gitlink:git-cat-file[1]. |
| |
| Trust |
| ----- |
| |
| An aside on the notion of "trust". Trust is really outside the scope |
| of "git", but it's worth noting a few things. First off, since |
| everything is hashed with SHA1, you 'can' trust that an object is |
| intact and has not been messed with by external sources. So the name |
| of an object uniquely identifies a known state - just not a state that |
| you may want to trust. |
| |
| Furthermore, since the SHA1 signature of a commit refers to the |
| SHA1 signatures of the tree it is associated with and the signatures |
| of the parent, a single named commit specifies uniquely a whole set |
| of history, with full contents. You can't later fake any step of the |
| way once you have the name of a commit. |
| |
| So to introduce some real trust in the system, the only thing you need |
| to do is to digitally sign just 'one' special note, which includes the |
| name of a top-level commit. Your digital signature shows others |
| that you trust that commit, and the immutability of the history of |
| commits tells others that they can trust the whole history. |
| |
| In other words, you can easily validate a whole archive by just |
| sending out a single email that tells the people the name (SHA1 hash) |
| of the top commit, and digitally sign that email using something |
| like GPG/PGP. |
| |
| To assist in this, git also provides the tag object... |
| |
| Tag Object |
| ---------- |
| |
| Git provides the "tag" object to simplify creating, managing and |
| exchanging symbolic and signed tokens. The "tag" object at its |
| simplest simply symbolically identifies another object by containing |
| the sha1, type and symbolic name. |
| |
| However it can optionally contain additional signature information |
| (which git doesn't care about as long as there's less than 8k of |
| it). This can then be verified externally to git. |
| |
| Note that despite the tag features, "git" itself only handles content |
| integrity; the trust framework (and signature provision and |
| verification) has to come from outside. |
| |
| A tag is created with gitlink:git-mktag[1], |
| its data can be accessed by gitlink:git-cat-file[1], |
| and the signature can be verified by |
| gitlink:git-verify-tag[1]. |
| |
| |
| The "index" aka "Current Directory Cache" |
| ----------------------------------------- |
| |
| The index is a simple binary file, which contains an efficient |
| representation of a virtual directory content at some random time. It |
| does so by a simple array that associates a set of names, dates, |
| permissions and content (aka "blob") objects together. The cache is |
| always kept ordered by name, and names are unique (with a few very |
| specific rules) at any point in time, but the cache has no long-term |
| meaning, and can be partially updated at any time. |
| |
| In particular, the index certainly does not need to be consistent with |
| the current directory contents (in fact, most operations will depend on |
| different ways to make the index 'not' be consistent with the directory |
| hierarchy), but it has three very important attributes: |
| |
| '(a) it can re-generate the full state it caches (not just the |
| directory structure: it contains pointers to the "blob" objects so |
| that it can regenerate the data too)' |
| |
| As a special case, there is a clear and unambiguous one-way mapping |
| from a current directory cache to a "tree object", which can be |
| efficiently created from just the current directory cache without |
| actually looking at any other data. So a directory cache at any one |
| time uniquely specifies one and only one "tree" object (but has |
| additional data to make it easy to match up that tree object with what |
| has happened in the directory) |
| |
| '(b) it has efficient methods for finding inconsistencies between that |
| cached state ("tree object waiting to be instantiated") and the |
| current state.' |
| |
| '(c) it can additionally efficiently represent information about merge |
| conflicts between different tree objects, allowing each pathname to be |
| associated with sufficient information about the trees involved that |
| you can create a three-way merge between them.' |
| |
| Those are the ONLY three things that the directory cache does. It's a |
| cache, and the normal operation is to re-generate it completely from a |
| known tree object, or update/compare it with a live tree that is being |
| developed. If you blow the directory cache away entirely, you generally |
| haven't lost any information as long as you have the name of the tree |
| that it described. |
| |
| At the same time, the index is at the same time also the |
| staging area for creating new trees, and creating a new tree always |
| involves a controlled modification of the index file. In particular, |
| the index file can have the representation of an intermediate tree that |
| has not yet been instantiated. So the index can be thought of as a |
| write-back cache, which can contain dirty information that has not yet |
| been written back to the backing store. |
| |
| |
| |
| The Workflow |
| ------------ |
| |
| Generally, all "git" operations work on the index file. Some operations |
| work *purely* on the index file (showing the current state of the |
| index), but most operations move data to and from the index file. Either |
| from the database or from the working directory. Thus there are four |
| main combinations: |
| |
| working directory -> index |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| You update the index with information from the working directory with |
| the gitlink:git-update-index[1] command. You |
| generally update the index information by just specifying the filename |
| you want to update, like so: |
| |
| ------------------------------------------------- |
| $ git-update-index filename |
| ------------------------------------------------- |
| |
| but to avoid common mistakes with filename globbing etc, the command |
| will not normally add totally new entries or remove old entries, |
| i.e. it will normally just update existing cache entries. |
| |
| To tell git that yes, you really do realize that certain files no |
| longer exist, or that new files should be added, you |
| should use the `--remove` and `--add` flags respectively. |
| |
| NOTE! A `--remove` flag does 'not' mean that subsequent filenames will |
| necessarily be removed: if the files still exist in your directory |
| structure, the index will be updated with their new status, not |
| removed. The only thing `--remove` means is that update-cache will be |
| considering a removed file to be a valid thing, and if the file really |
| does not exist any more, it will update the index accordingly. |
| |
| As a special case, you can also do `git-update-index --refresh`, which |
| will refresh the "stat" information of each index to match the current |
| stat information. It will 'not' update the object status itself, and |
| it will only update the fields that are used to quickly test whether |
| an object still matches its old backing store object. |
| |
| index -> object database |
| ~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| You write your current index file to a "tree" object with the program |
| |
| ------------------------------------------------- |
| $ git-write-tree |
| ------------------------------------------------- |
| |
| that doesn't come with any options - it will just write out the |
| current index into the set of tree objects that describe that state, |
| and it will return the name of the resulting top-level tree. You can |
| use that tree to re-generate the index at any time by going in the |
| other direction: |
| |
| object database -> index |
| ~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| You read a "tree" file from the object database, and use that to |
| populate (and overwrite - don't do this if your index contains any |
| unsaved state that you might want to restore later!) your current |
| index. Normal operation is just |
| |
| ------------------------------------------------- |
| $ git-read-tree <sha1 of tree> |
| ------------------------------------------------- |
| |
| and your index file will now be equivalent to the tree that you saved |
| earlier. However, that is only your 'index' file: your working |
| directory contents have not been modified. |
| |
| index -> working directory |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| You update your working directory from the index by "checking out" |
| files. This is not a very common operation, since normally you'd just |
| keep your files updated, and rather than write to your working |
| directory, you'd tell the index files about the changes in your |
| working directory (i.e. `git-update-index`). |
| |
| However, if you decide to jump to a new version, or check out somebody |
| else's version, or just restore a previous tree, you'd populate your |
| index file with read-tree, and then you need to check out the result |
| with |
| |
| ------------------------------------------------- |
| $ git-checkout-index filename |
| ------------------------------------------------- |
| |
| or, if you want to check out all of the index, use `-a`. |
| |
| NOTE! git-checkout-index normally refuses to overwrite old files, so |
| if you have an old version of the tree already checked out, you will |
| need to use the "-f" flag ('before' the "-a" flag or the filename) to |
| 'force' the checkout. |
| |
| |
| Finally, there are a few odds and ends which are not purely moving |
| from one representation to the other: |
| |
| Tying it all together |
| ~~~~~~~~~~~~~~~~~~~~~ |
| |
| To commit a tree you have instantiated with "git-write-tree", you'd |
| create a "commit" object that refers to that tree and the history |
| behind it - most notably the "parent" commits that preceded it in |
| history. |
| |
| Normally a "commit" has one parent: the previous state of the tree |
| before a certain change was made. However, sometimes it can have two |
| or more parent commits, in which case we call it a "merge", due to the |
| fact that such a commit brings together ("merges") two or more |
| previous states represented by other commits. |
| |
| In other words, while a "tree" represents a particular directory state |
| of a working directory, a "commit" represents that state in "time", |
| and explains how we got there. |
| |
| You create a commit object by giving it the tree that describes the |
| state at the time of the commit, and a list of parents: |
| |
| ------------------------------------------------- |
| $ git-commit-tree <tree> -p <parent> [-p <parent2> ..] |
| ------------------------------------------------- |
| |
| and then giving the reason for the commit on stdin (either through |
| redirection from a pipe or file, or by just typing it at the tty). |
| |
| git-commit-tree will return the name of the object that represents |
| that commit, and you should save it away for later use. Normally, |
| you'd commit a new `HEAD` state, and while git doesn't care where you |
| save the note about that state, in practice we tend to just write the |
| result to the file pointed at by `.git/HEAD`, so that we can always see |
| what the last committed state was. |
| |
| Here is an ASCII art by Jon Loeliger that illustrates how |
| various pieces fit together. |
| |
| ------------ |
| |
| commit-tree |
| commit obj |
| +----+ |
| | | |
| | | |
| V V |
| +-----------+ |
| | Object DB | |
| | Backing | |
| | Store | |
| +-----------+ |
| ^ |
| write-tree | | |
| tree obj | | |
| | | read-tree |
| | | tree obj |
| V |
| +-----------+ |
| | Index | |
| | "cache" | |
| +-----------+ |
| update-index ^ |
| blob obj | | |
| | | |
| checkout-index -u | | checkout-index |
| stat | | blob obj |
| V |
| +-----------+ |
| | Working | |
| | Directory | |
| +-----------+ |
| |
| ------------ |
| |
| |
| Examining the data |
| ------------------ |
| |
| You can examine the data represented in the object database and the |
| index with various helper tools. For every object, you can use |
| gitlink:git-cat-file[1] to examine details about the |
| object: |
| |
| ------------------------------------------------- |
| $ git-cat-file -t <objectname> |
| ------------------------------------------------- |
| |
| shows the type of the object, and once you have the type (which is |
| usually implicit in where you find the object), you can use |
| |
| ------------------------------------------------- |
| $ git-cat-file blob|tree|commit|tag <objectname> |
| ------------------------------------------------- |
| |
| to show its contents. NOTE! Trees have binary content, and as a result |
| there is a special helper for showing that content, called |
| `git-ls-tree`, which turns the binary content into a more easily |
| readable form. |
| |
| It's especially instructive to look at "commit" objects, since those |
| tend to be small and fairly self-explanatory. In particular, if you |
| follow the convention of having the top commit name in `.git/HEAD`, |
| you can do |
| |
| ------------------------------------------------- |
| $ git-cat-file commit HEAD |
| ------------------------------------------------- |
| |
| to see what the top commit was. |
| |
| Merging multiple trees |
| ---------------------- |
| |
| Git helps you do a three-way merge, which you can expand to n-way by |
| repeating the merge procedure arbitrary times until you finally |
| "commit" the state. The normal situation is that you'd only do one |
| three-way merge (two parents), and commit it, but if you like to, you |
| can do multiple parents in one go. |
| |
| To do a three-way merge, you need the two sets of "commit" objects |
| that you want to merge, use those to find the closest common parent (a |
| third "commit" object), and then use those commit objects to find the |
| state of the directory ("tree" object) at these points. |
| |
| To get the "base" for the merge, you first look up the common parent |
| of two commits with |
| |
| ------------------------------------------------- |
| $ git-merge-base <commit1> <commit2> |
| ------------------------------------------------- |
| |
| which will return you the commit they are both based on. You should |
| now look up the "tree" objects of those commits, which you can easily |
| do with (for example) |
| |
| ------------------------------------------------- |
| $ git-cat-file commit <commitname> | head -1 |
| ------------------------------------------------- |
| |
| since the tree object information is always the first line in a commit |
| object. |
| |
| Once you know the three trees you are going to merge (the one "original" |
| tree, aka the common case, and the two "result" trees, aka the branches |
| you want to merge), you do a "merge" read into the index. This will |
| complain if it has to throw away your old index contents, so you should |
| make sure that you've committed those - in fact you would normally |
| always do a merge against your last commit (which should thus match what |
| you have in your current index anyway). |
| |
| To do the merge, do |
| |
| ------------------------------------------------- |
| $ git-read-tree -m -u <origtree> <yourtree> <targettree> |
| ------------------------------------------------- |
| |
| which will do all trivial merge operations for you directly in the |
| index file, and you can just write the result out with |
| `git-write-tree`. |
| |
| |
| Merging multiple trees, continued |
| --------------------------------- |
| |
| Sadly, many merges aren't trivial. If there are files that have |
| been added.moved or removed, or if both branches have modified the |
| same file, you will be left with an index tree that contains "merge |
| entries" in it. Such an index tree can 'NOT' be written out to a tree |
| object, and you will have to resolve any such merge clashes using |
| other tools before you can write out the result. |
| |
| You can examine such index state with `git-ls-files --unmerged` |
| command. An example: |
| |
| ------------------------------------------------ |
| $ git-read-tree -m $orig HEAD $target |
| $ git-ls-files --unmerged |
| 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c |
| 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c |
| 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c |
| ------------------------------------------------ |
| |
| Each line of the `git-ls-files --unmerged` output begins with |
| the blob mode bits, blob SHA1, 'stage number', and the |
| filename. The 'stage number' is git's way to say which tree it |
| came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD` |
| tree, and stage3 `$target` tree. |
| |
| Earlier we said that trivial merges are done inside |
| `git-read-tree -m`. For example, if the file did not change |
| from `$orig` to `HEAD` nor `$target`, or if the file changed |
| from `$orig` to `HEAD` and `$orig` to `$target` the same way, |
| obviously the final outcome is what is in `HEAD`. What the |
| above example shows is that file `hello.c` was changed from |
| `$orig` to `HEAD` and `$orig` to `$target` in a different way. |
| You could resolve this by running your favorite 3-way merge |
| program, e.g. `diff3` or `merge`, on the blob objects from |
| these three stages yourself, like this: |
| |
| ------------------------------------------------ |
| $ git-cat-file blob 263414f... >hello.c~1 |
| $ git-cat-file blob 06fa6a2... >hello.c~2 |
| $ git-cat-file blob cc44c73... >hello.c~3 |
| $ merge hello.c~2 hello.c~1 hello.c~3 |
| ------------------------------------------------ |
| |
| This would leave the merge result in `hello.c~2` file, along |
| with conflict markers if there are conflicts. After verifying |
| the merge result makes sense, you can tell git what the final |
| merge result for this file is by: |
| |
| ------------------------------------------------- |
| $ mv -f hello.c~2 hello.c |
| $ git-update-index hello.c |
| ------------------------------------------------- |
| |
| When a path is in unmerged state, running `git-update-index` for |
| that path tells git to mark the path resolved. |
| |
| The above is the description of a git merge at the lowest level, |
| to help you understand what conceptually happens under the hood. |
| In practice, nobody, not even git itself, uses three `git-cat-file` |
| for this. There is `git-merge-index` program that extracts the |
| stages to temporary files and calls a "merge" script on it: |
| |
| ------------------------------------------------- |
| $ git-merge-index git-merge-one-file hello.c |
| ------------------------------------------------- |
| |
| and that is what higher level `git merge -s resolve` is implemented with. |
| |
| How git stores objects efficiently: pack files |
| ---------------------------------------------- |
| |
| We've seen how git stores each object in a file named after the |
| object's SHA1 hash. |
| |
| Unfortunately this system becomes inefficient once a project has a |
| lot of objects. Try this on an old project: |
| |
| ------------------------------------------------ |
| $ git count-objects |
| 6930 objects, 47620 kilobytes |
| ------------------------------------------------ |
| |
| The first number is the number of objects which are kept in |
| individual files. The second is the amount of space taken up by |
| those "loose" objects. |
| |
| You can save space and make git faster by moving these loose objects in |
| to a "pack file", which stores a group of objects in an efficient |
| compressed format; the details of how pack files are formatted can be |
| found in link:technical/pack-format.txt[technical/pack-format.txt]. |
| |
| To put the loose objects into a pack, just run git repack: |
| |
| ------------------------------------------------ |
| $ git repack |
| Generating pack... |
| Done counting 6020 objects. |
| Deltifying 6020 objects. |
| 100% (6020/6020) done |
| Writing 6020 objects. |
| 100% (6020/6020) done |
| Total 6020, written 6020 (delta 4070), reused 0 (delta 0) |
| Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. |
| ------------------------------------------------ |
| |
| You can then run |
| |
| ------------------------------------------------ |
| $ git prune |
| ------------------------------------------------ |
| |
| to remove any of the "loose" objects that are now contained in the |
| pack. This will also remove any unreferenced objects (which may be |
| created when, for example, you use "git reset" to remove a commit). |
| You can verify that the loose objects are gone by looking at the |
| .git/objects directory or by running |
| |
| ------------------------------------------------ |
| $ git count-objects |
| 0 objects, 0 kilobytes |
| ------------------------------------------------ |
| |
| Although the object files are gone, any commands that refer to those |
| objects will work exactly as they did before. |
| |
| The gitlink:git-gc[1] command performs packing, pruning, and more for |
| you, so is normally the only high-level command you need. |
| |
| [[dangling-objects]] |
| Dangling objects |
| ---------------- |
| |
| The gitlink:git-fsck[1] command will sometimes complain about dangling |
| objects. They are not a problem. |
| |
| The most common cause of dangling objects is that you've rebased a |
| branch, or you have pulled from somebody else who rebased a branch--see |
| <<cleaning-up-history>>. In that case, the old head of the original |
| branch still exists, as does obviously everything it pointed to. The |
| branch pointer itself just doesn't, since you replaced it with another |
| one. |
| |
| There are also other situations too that cause dangling objects. For |
| example, a "dangling blob" may arise because you did a "git add" of a |
| file, but then, before you actually committed it and made it part of the |
| bigger picture, you changed something else in that file and committed |
| that *updated* thing - the old state that you added originally ends up |
| not being pointed to by any commit or tree, so it's now a dangling blob |
| object. |
| |
| Similarly, when the "recursive" merge strategy runs, and finds that |
| there are criss-cross merges and thus more than one merge base (which is |
| fairly unusual, but it does happen), it will generate one temporary |
| midway tree (or possibly even more, if you had lots of criss-crossing |
| merges and more than two merge bases) as a temporary internal merge |
| base, and again, those are real objects, but the end result will not end |
| up pointing to them, so they end up "dangling" in your repository. |
| |
| Generally, dangling objects aren't anything to worry about. They can |
| even be very useful: if you screw something up, the dangling objects can |
| be how you recover your old tree (say, you did a rebase, and realized |
| that you really didn't want to - you can look at what dangling objects |
| you have, and decide to reset your head to some old dangling state). |
| |
| For commits, the most useful thing to do with dangling objects tends to |
| be to do a simple |
| |
| ------------------------------------------------ |
| $ gitk <dangling-commit-sha-goes-here> --not --all |
| ------------------------------------------------ |
| |
| For blobs and trees, you can't do the same, but you can examine them. |
| You can just do |
| |
| ------------------------------------------------ |
| $ git show <dangling-blob/tree-sha-goes-here> |
| ------------------------------------------------ |
| |
| to show what the contents of the blob were (or, for a tree, basically |
| what the "ls" for that directory was), and that may give you some idea |
| of what the operation was that left that dangling object. |
| |
| Usually, dangling blobs and trees aren't very interesting. They're |
| almost always the result of either being a half-way mergebase (the blob |
| will often even have the conflict markers from a merge in it, if you |
| have had conflicting merges that you fixed up by hand), or simply |
| because you interrupted a "git fetch" with ^C or something like that, |
| leaving _some_ of the new objects in the object database, but just |
| dangling and useless. |
| |
| Anyway, once you are sure that you're not interested in any dangling |
| state, you can just prune all unreachable objects: |
| |
| ------------------------------------------------ |
| $ git prune |
| ------------------------------------------------ |
| |
| and they'll be gone. But you should only run "git prune" on a quiescent |
| repository - it's kind of like doing a filesystem fsck recovery: you |
| don't want to do that while the filesystem is mounted. |
| |
| (The same is true of "git-fsck" itself, btw - but since |
| git-fsck never actually *changes* the repository, it just reports |
| on what it found, git-fsck itself is never "dangerous" to run. |
| Running it while somebody is actually changing the repository can cause |
| confusing and scary messages, but it won't actually do anything bad. In |
| contrast, running "git prune" while somebody is actively changing the |
| repository is a *BAD* idea). |
| |
| include::glossary.txt[] |
| |
| Notes and todo list for this manual |
| =================================== |
| |
| This is a work in progress. |
| |
| The basic requirements: |
| - It must be readable in order, from beginning to end, by |
| someone intelligent with a basic grasp of the unix |
| commandline, but without any special knowledge of git. If |
| necessary, any other prerequisites should be specifically |
| mentioned as they arise. |
| - Whenever possible, section headings should clearly describe |
| the task they explain how to do, in language that requires |
| no more knowledge than necessary: for example, "importing |
| patches into a project" rather than "the git-am command" |
| |
| Think about how to create a clear chapter dependency graph that will |
| allow people to get to important topics without necessarily reading |
| everything in between. |
| |
| Say something about .gitignore. |
| |
| Scan Documentation/ for other stuff left out; in particular: |
| howto's |
| some of technical/? |
| hooks |
| list of commands in gitlink:git[1] |
| |
| Scan email archives for other stuff left out |
| |
| Scan man pages to see if any assume more background than this manual |
| provides. |
| |
| Simplify beginning by suggesting disconnected head instead of |
| temporary branch creation? |
| |
| Add more good examples. Entire sections of just cookbook examples |
| might be a good idea; maybe make an "advanced examples" section a |
| standard end-of-chapter section? |
| |
| Include cross-references to the glossary, where appropriate. |
| |
| Document shallow clones? See draft 1.5.0 release notes for some |
| documentation. |
| |
| Add a section on working with other version control systems, including |
| CVS, Subversion, and just imports of series of release tarballs. |
| |
| More details on gitweb? |
| |
| Write a chapter on using plumbing and writing scripts. |
