| Git User's Manual (for version 1.5.3 or newer) |
| ______________________________________________ |
| |
| |
| Git is a fast distributed revision control system. |
| |
| This manual is designed to be readable by someone with basic UNIX |
| command-line skills, but no previous knowledge of Git. |
| |
| <<repositories-and-branches>> and <<exploring-git-history>> explain how |
| to fetch and study a project using git--read these chapters to learn how |
| to build and test a particular version of a software project, search for |
| regressions, and so on. |
| |
| People needing to do actual development will also want to read |
| <<Developing-With-git>> and <<sharing-development>>. |
| |
| Further chapters cover more specialized topics. |
| |
| Comprehensive reference documentation is available through the man |
| pages, or linkgit:git-help[1] command. For example, for the command |
| `git clone <repo>`, you can either use: |
| |
| ------------------------------------------------ |
| $ man git-clone |
| ------------------------------------------------ |
| |
| or: |
| |
| ------------------------------------------------ |
| $ git help clone |
| ------------------------------------------------ |
| |
| With the latter, you can use the manual viewer of your choice; see |
| linkgit:git-help[1] for more information. |
| |
| See also <<git-quick-start>> for a brief overview of Git commands, |
| without any explanation. |
| |
| Finally, see <<todo>> for ways that you can help make this manual more |
| complete. |
| |
| |
| [[repositories-and-branches]] |
| Repositories and Branches |
| ========================= |
| |
| [[how-to-get-a-git-repository]] |
| 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 linkgit:git-clone[1] command to |
| download a copy of an existing repository. If you don't already have a |
| project in mind, here are some interesting examples: |
| |
| ------------------------------------------------ |
| # Git itself (approx. 40MB download): |
| $ git clone git://git.kernel.org/pub/scm/git/git.git |
| # the Linux kernel (approx. 640MB download): |
| $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.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` in the examples above). After you cd into this |
| directory, you will see that it contains a copy of the project files, |
| called the <<def_working_tree,working tree>>, together with a special |
| top-level directory named `.git`, which contains all the information |
| about the history of the project. |
| |
| [[how-to-check-out]] |
| 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 of the project's contents. In Git each such |
| version is called a <<def_commit,commit>>. |
| |
| Those snapshots aren't necessarily all arranged in a single line from |
| oldest to newest; instead, work may simultaneously proceed along |
| parallel lines of development, called <<def_branch,branches>>, which may |
| merge and diverge. |
| |
| A single Git repository can track development on multiple branches. It |
| does this by keeping a list of <<def_head,heads>> which reference the |
| latest commit on each branch; the linkgit: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 |
| linkgit: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 linkgit: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 linkgit: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-commits]] |
| Understanding History: Commits |
| ------------------------------ |
| |
| Every change in the history of a project is represented by a commit. |
| The linkgit:git-show[1] command shows the most recent commit on the |
| current branch: |
| |
| ------------------------------------------------ |
| $ git show |
| commit 17cf781661e6d38f737f15f53ab552f1e95960d7 |
| Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)> |
| Date: Tue Apr 19 14:11:06 2005 -0700 |
| |
| Remove duplicate getenv(DB_ENVIRONMENT) call |
| |
| Noted by Tony Luck. |
| |
| diff --git a/init-db.c b/init-db.c |
| index 65898fa..b002dc6 100644 |
| --- a/init-db.c |
| +++ b/init-db.c |
| @@ -7,7 +7,7 @@ |
| |
| int main(int argc, char **argv) |
| { |
| - char *sha1_dir = getenv(DB_ENVIRONMENT), *path; |
| + char *sha1_dir, *path; |
| int len, i; |
| |
| if (mkdir(".git", 0755) < 0) { |
| ------------------------------------------------ |
| |
| 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 |
| "SHA-1 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-concepts>> 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-reachability]] |
| 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 linkgit: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 descendant of X, or that there is a chain of parents |
| leading from commit Y to commit X. |
| |
| [[history-diagrams]] |
| 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. |
| |
| [[what-is-a-branch]] |
| 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]] |
| 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 the current |
| 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 SHA-1 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 is an easy way to check out a particular version without having to |
| make up a name for the new branch. You can still create a new branch |
| (or tag) for this version later if you decide to. |
| |
| [[examining-remote-branches]] |
| 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, called |
| remote-tracking branches, which you |
| can view using the `-r` option to linkgit:git-branch[1]: |
| |
| ------------------------------------------------ |
| $ git branch -r |
| origin/HEAD |
| origin/html |
| origin/maint |
| origin/man |
| origin/master |
| origin/next |
| origin/pu |
| origin/todo |
| ------------------------------------------------ |
| |
| In this example, "origin" is called a remote repository, or "remote" |
| for short. The branches of this repository are called "remote |
| branches" from our point of view. The remote-tracking branches listed |
| above were created based on the remote branches at clone time and will |
| be updated by `git fetch` (hence `git pull`) and `git push`. See |
| <<Updating-a-repository-With-git-fetch>> for details. |
| |
| You might want to build on one of these remote-tracking branches |
| on a branch of your own, just as you would for a tag: |
| |
| ------------------------------------------------ |
| $ git checkout -b my-todo-copy origin/todo |
| ------------------------------------------------ |
| |
| You can also check out `origin/todo` directly to examine it or |
| write a one-off patch. See <<detached-head,detached head>>. |
| |
| 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. |
| |
| (Newly created refs are actually stored in the `.git/refs` directory, |
| under the path given by their name. However, for efficiency reasons |
| they may also be packed together in a single file; see |
| linkgit:git-pack-refs[1]). |
| |
| As another useful shortcut, the "HEAD" of a repository can be referred |
| to just using the name of that repository. So, for example, "origin" |
| is usually a shortcut for the HEAD branch in the repository "origin". |
| |
| 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 linkgit:gitrevisions[7]. |
| |
| [[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]] |
| Fetching branches from other repositories |
| ----------------------------------------- |
| |
| You can also track branches from repositories other than the one you |
| cloned from, using linkgit:git-remote[1]: |
| |
| ------------------------------------------------- |
| $ git remote add staging git://git.kernel.org/.../gregkh/staging.git |
| $ git fetch staging |
| ... |
| From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging |
| * [new branch] master -> staging/master |
| * [new branch] staging-linus -> staging/staging-linus |
| * [new branch] staging-next -> staging/staging-next |
| ------------------------------------------------- |
| |
| New remote-tracking branches will be stored under the shorthand name |
| that you gave `git remote add`, in this case `staging`: |
| |
| ------------------------------------------------- |
| $ git branch -r |
| origin/HEAD -> origin/master |
| origin/master |
| staging/master |
| staging/staging-linus |
| staging/staging-next |
| ------------------------------------------------- |
| |
| If you run `git fetch <remote>` later, the remote-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 "staging"] |
| url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git |
| fetch = +refs/heads/*:refs/remotes/staging/* |
| ... |
| ------------------------------------------------- |
| |
| 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 |
| linkgit:git-config[1] for details.) |
| |
| [[exploring-git-history]] |
| 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 hierarchy, 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. |
| |
| [[using-bisect]] |
| 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 |
| linkgit: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 in "(no branch)". HEAD is now detached from any |
| branch and points directly to a commit (with commit id 65934...) that |
| is reachable from "master" 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 |
| linkgit: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. |
| |
| 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". Choose 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. |
| |
| Instead of `git bisect visualize` and then `git reset --hard |
| fb47ddb2db...`, you might just want to tell Git that you want to skip |
| the current commit: |
| |
| ------------------------------------------------- |
| $ git bisect skip |
| ------------------------------------------------- |
| |
| In this case, though, Git may not eventually be able to tell the first |
| bad one between some first skipped commits and a later bad commit. |
| |
| There are also ways to automate the bisecting process if you have a |
| test script that can tell a good from a bad commit. See |
| linkgit:git-bisect[1] for more information about this and other `git |
| bisect` features. |
| |
| [[naming-commits]] |
| 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 |
| linkgit:gitrevisions[7] 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 linkgit: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]] |
| 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 you would also like to include a |
| comment with the tag, and possibly sign it cryptographically, then you |
| should create a tag object instead; see the linkgit:git-tag[1] man page |
| for details. |
| |
| [[browsing-revisions]] |
| Browsing revisions |
| ------------------ |
| |
| The linkgit: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 linkgit: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]] |
| Generating diffs |
| ---------------- |
| |
| You can generate diffs between any two versions using |
| linkgit:git-diff[1]: |
| |
| ------------------------------------------------- |
| $ git diff master..test |
| ------------------------------------------------- |
| |
| That will produce the diff between the tips of the two branches. If |
| you'd prefer to find the diff from their common ancestor to test, you |
| can use three dots instead of two: |
| |
| ------------------------------------------------- |
| $ git diff master...test |
| ------------------------------------------------- |
| |
| Sometimes what you want instead is a set of patches; for this you can |
| use linkgit:git-format-patch[1]: |
| |
| ------------------------------------------------- |
| $ git format-patch master..test |
| ------------------------------------------------- |
| |
| will generate a file with a patch for each commit reachable from test |
| but not from master. |
| |
| [[viewing-old-file-versions]] |
| 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. |
| |
| [[history-examples]] |
| Examples |
| -------- |
| |
| [[counting-commits-on-a-branch]] |
| Counting the number of commits on a branch |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Suppose you want to know how many commits you've made on `mybranch` |
| since it diverged from `origin`: |
| |
| ------------------------------------------------- |
| $ git log --pretty=oneline origin..mybranch | wc -l |
| ------------------------------------------------- |
| |
| Alternatively, you may often see this sort of thing done with the |
| lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's |
| of all the given commits: |
| |
| ------------------------------------------------- |
| $ git rev-list origin..mybranch | wc -l |
| ------------------------------------------------- |
| |
| [[checking-for-equal-branches]] |
| 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. |
| |
| [[finding-tagged-descendants]] |
| 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 linkgit: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 linkgit: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 linkgit: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 linkgit: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. |
| |
| [[showing-commits-unique-to-a-branch]] |
| Showing commits unique to a given branch |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Suppose you would like to see all the commits reachable from the branch |
| head named `master` but not from any other head in your repository. |
| |
| We can list all the heads in this repository with |
| linkgit:git-show-ref[1]: |
| |
| ------------------------------------------------- |
| $ git show-ref --heads |
| bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial |
| db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint |
| a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master |
| 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2 |
| 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes |
| ------------------------------------------------- |
| |
| We can get just the branch-head names, and remove `master`, with |
| the help of the standard utilities cut and grep: |
| |
| ------------------------------------------------- |
| $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' |
| refs/heads/core-tutorial |
| refs/heads/maint |
| refs/heads/tutorial-2 |
| refs/heads/tutorial-fixes |
| ------------------------------------------------- |
| |
| And then we can ask to see all the commits reachable from master |
| but not from these other heads: |
| |
| ------------------------------------------------- |
| $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 | |
| grep -v '^refs/heads/master' ) |
| ------------------------------------------------- |
| |
| Obviously, endless variations are possible; for example, to see all |
| commits reachable from some head but not from any tag in the repository: |
| |
| ------------------------------------------------- |
| $ gitk $( git show-ref --heads ) --not $( git show-ref --tags ) |
| ------------------------------------------------- |
| |
| (See linkgit:gitrevisions[7] for explanations of commit-selecting |
| syntax such as `--not`.) |
| |
| [[making-a-release]] |
| Creating a changelog and tarball for a software release |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| The linkgit:git-archive[1] command can create a tar or zip archive from |
| any version of a project; for example: |
| |
| ------------------------------------------------- |
| $ git archive -o latest.tar.gz --prefix=project/ HEAD |
| ------------------------------------------------- |
| |
| will use HEAD to produce a gzipped tar archive in which each filename |
| is preceded by `project/`. The output file format is inferred from |
| the output file extension if possible, see linkgit:git-archive[1] for |
| details. |
| |
| Versions of Git older than 1.7.7 don't know about the `tar.gz` format, |
| you'll need to use gzip explicitly: |
| |
| ------------------------------------------------- |
| $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz |
| ------------------------------------------------- |
| |
| If you're releasing a new version of a software project, you may want |
| to simultaneously make a changelog to include in the release |
| announcement. |
| |
| Linus Torvalds, for example, makes new kernel releases by tagging them, |
| then running: |
| |
| ------------------------------------------------- |
| $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7 |
| ------------------------------------------------- |
| |
| where release-script is a shell script that looks like: |
| |
| ------------------------------------------------- |
| #!/bin/sh |
| stable="$1" |
| last="$2" |
| new="$3" |
| echo "# git tag v$new" |
| echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz" |
| echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz" |
| echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new" |
| echo "git shortlog --no-merges v$new ^v$last > ../ShortLog" |
| echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new" |
| ------------------------------------------------- |
| |
| and then he just cut-and-pastes the output commands after verifying that |
| they look OK. |
| |
| [[Finding-commits-With-given-Content]] |
| Finding commits referencing a file with given content |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Somebody hands you a copy of a file, and asks which commits modified a |
| file such that it contained the given content either before or after the |
| commit. You can find out with this: |
| |
| ------------------------------------------------- |
| $ git log --raw --abbrev=40 --pretty=oneline | |
| grep -B 1 `git hash-object filename` |
| ------------------------------------------------- |
| |
| Figuring out why this works is left as an exercise to the (advanced) |
| student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and |
| linkgit:git-hash-object[1] man pages may prove helpful. |
| |
| [[Developing-With-git]] |
| Developing with Git |
| =================== |
| |
| [[telling-git-your-name]] |
| Telling Git your name |
| --------------------- |
| |
| Before creating any commits, you should introduce yourself to Git. |
| The easiest way to do so is to use linkgit:git-config[1]: |
| |
| ------------------------------------------------ |
| $ git config --global user.name 'Your Name Comes Here' |
| $ git config --global user.email 'you@yourdomain.example.com' |
| ------------------------------------------------ |
| |
| Which will add the following to a file named `.gitconfig` in your |
| home directory: |
| |
| ------------------------------------------------ |
| [user] |
| name = Your Name Comes Here |
| email = you@yourdomain.example.com |
| ------------------------------------------------ |
| |
| See the "CONFIGURATION FILE" section of linkgit:git-config[1] for |
| details on the configuration file. The file is plain text, so you can |
| also edit it with your favorite editor. |
| |
| |
| [[creating-a-new-repository]] |
| 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 committed 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 diff HEAD # difference between HEAD and working tree; what |
| # would be committed if you ran "commit -a" now. |
| $ git status # a brief per-file summary of the above. |
| ------------------------------------------------- |
| |
| You can also use linkgit:git-gui[1] to create commits, view changes in |
| the index and the working tree files, and individually select diff hunks |
| for inclusion in the index (by right-clicking on the diff hunk and |
| choosing "Stage Hunk For Commit"). |
| |
| [[creating-good-commit-messages]] |
| 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. The text up to the first blank line in a commit |
| message is treated as the commit title, and that title is used |
| throughout Git. For example, linkgit:git-format-patch[1] turns a |
| commit into email, and it uses the title on the Subject line and the |
| rest of the commit in the body. |
| |
| |
| [[ignoring-files]] |
| Ignoring files |
| -------------- |
| |
| A project will often generate files that you do 'not' want to track with Git. |
| This typically includes files generated by a build process or temporary |
| backup files made by your editor. Of course, 'not' tracking files with Git |
| is just a matter of 'not' calling `git add` on them. But it quickly becomes |
| annoying to have these untracked files lying around; e.g. they make |
| `git add .` practically useless, and they keep showing up in the output of |
| `git status`. |
| |
| You can tell Git to ignore certain files by creating a file called |
| `.gitignore` in the top level of your working directory, with contents |
| such as: |
| |
| ------------------------------------------------- |
| # Lines starting with '#' are considered comments. |
| # Ignore any file named foo.txt. |
| foo.txt |
| # Ignore (generated) html files, |
| *.html |
| # except foo.html which is maintained by hand. |
| !foo.html |
| # Ignore objects and archives. |
| *.[oa] |
| ------------------------------------------------- |
| |
| See linkgit:gitignore[5] for a detailed explanation of the syntax. You can |
| also place .gitignore files in other directories in your working tree, and they |
| will apply to those directories and their subdirectories. The `.gitignore` |
| files can be added to your repository like any other files (just run `git add |
| .gitignore` and `git commit`, as usual), which is convenient when the exclude |
| patterns (such as patterns matching build output files) would also make sense |
| for other users who clone your repository. |
| |
| If you wish the exclude patterns to affect only certain repositories |
| (instead of every repository for a given project), you may instead put |
| them in a file in your repository named `.git/info/exclude`, or in any |
| file specified by the `core.excludesfile` configuration variable. |
| Some Git commands can also take exclude patterns directly on the |
| command line. See linkgit:gitignore[5] for the details. |
| |
| [[how-to-merge]] |
| How to merge |
| ------------ |
| |
| You can rejoin two diverging branches of development using |
| linkgit:git-merge[1]: |
| |
| ------------------------------------------------- |
| $ git merge branchname |
| ------------------------------------------------- |
| |
| merges the development in the branch `branchname` into the current |
| branch. |
| |
| A merge is made by combining the changes made in `branchname` and the |
| changes made up to the latest commit in your current branch since |
| their histories forked. The work tree is overwritten by the result of |
| the merge when this combining is done cleanly, or overwritten by a |
| half-merged results when this combining results in conflicts. |
| Therefore, if you have uncommitted changes touching the same files as |
| the ones impacted by the merge, Git will refuse to proceed. Most of |
| the time, you will want to commit your changes before you can merge, |
| and if you don't, then linkgit:git-stash[1] can take these changes |
| away while you're doing the merge, and reapply them afterwards. |
| |
| If the changes are independent enough, Git will automatically complete |
| the merge and commit the result (or reuse an existing commit in case |
| of <<fast-forwards,fast-forward>>, see below). On the other hand, |
| 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. |
| |
| [[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, linkgit:git-commit[1] will |
| fail: |
| |
| ------------------------------------------------- |
| $ git commit |
| file.txt: needs merge |
| ------------------------------------------------- |
| |
| Also, linkgit: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: |
| |
| [[conflict-resolution]] |
| 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 linkgit: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 committed 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. |
| $ git show :3:file.txt # the version from MERGE_HEAD. |
| ------------------------------------------------- |
| |
| When you ask linkgit:git-diff[1] to show the conflicts, it runs a |
| three-way diff between the conflicted merge results in the work tree with |
| stages 2 and 3 to show only hunks whose contents come from both sides, |
| mixed (in other words, when a hunk's merge results come only from stage 2, |
| that part is not conflicting and is not shown. Same for stage 3). |
| |
| 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 linkgit: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 linkgit:git-log[1] and linkgit: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. |
| |
| You may also use linkgit:git-mergetool[1], which lets you merge the |
| unmerged files using external tools such as Emacs or kdiff3. |
| |
| 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 committed 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-forwards]] |
| 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 the current branch is a descendant of the other--so every |
| commit present in the one is already contained in the other--then Git |
| just performs a "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]] |
| 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 old 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. |
| |
| [[reverting-a-commit]] |
| Fixing a mistake with a new commit |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Creating a new commit that reverts an earlier change is very easy; |
| just pass the linkgit: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-rewriting-history]] |
| Fixing a mistake by rewriting 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 linkgit:git-revert[1] instead in |
| that case. |
| |
| It is also possible to replace commits further back in the history, but |
| this is an advanced topic to be left for |
| <<cleaning-up-history,another chapter>>. |
| |
| [[checkout-of-path]] |
| 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 |
| linkgit: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 |
| linkgit:git-show[1]: |
| |
| ------------------------------------------------- |
| $ git show HEAD^:path/to/file |
| ------------------------------------------------- |
| |
| which will display the given version of the file. |
| |
| [[interrupted-work]] |
| Temporarily setting aside work in progress |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| While you are in the middle of working on something complicated, you |
| find an unrelated but obvious and trivial bug. You would like to fix it |
| before continuing. You can use linkgit:git-stash[1] to save the current |
| state of your work, and after fixing the bug (or, optionally after doing |
| so on a different branch and then coming back), unstash the |
| work-in-progress changes. |
| |
| ------------------------------------------------ |
| $ git stash save "work in progress for foo feature" |
| ------------------------------------------------ |
| |
| This command will save your changes away to the `stash`, and |
| reset your working tree and the index to match the tip of your |
| current branch. Then you can make your fix as usual. |
| |
| ------------------------------------------------ |
| ... edit and test ... |
| $ git commit -a -m "blorpl: typofix" |
| ------------------------------------------------ |
| |
| After that, you can go back to what you were working on with |
| `git stash pop`: |
| |
| ------------------------------------------------ |
| $ git stash pop |
| ------------------------------------------------ |
| |
| |
| [[ensuring-good-performance]] |
| Ensuring good performance |
| ------------------------- |
| |
| On large repositories, Git depends on compression to keep the history |
| information from taking up too much space on disk or in memory. Some |
| Git commands may automatically run linkgit:git-gc[1], so you don't |
| have to worry about running it manually. However, compressing a large |
| repository may take a while, so you may want to call `gc` explicitly |
| to avoid automatic compression kicking in when it is not convenient. |
| |
| |
| [[ensuring-reliability]] |
| Ensuring reliability |
| -------------------- |
| |
| [[checking-for-corruption]] |
| Checking the repository for corruption |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| The linkgit:git-fsck[1] command runs a number of self-consistency checks |
| on the repository, and reports on any problems. This may take some |
| time. |
| |
| ------------------------------------------------- |
| $ 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 |
| ... |
| ------------------------------------------------- |
| |
| You will see informational messages on dangling objects. They are objects |
| that still exist in the repository but are no longer referenced by any of |
| your branches, and can (and will) be removed after a while with `gc`. |
| You can run `git fsck --no-dangling` to suppress these messages, and still |
| view real errors. |
| |
| [[recovering-lost-changes]] |
| Recovering lost changes |
| ~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| [[reflogs]] |
| Reflogs |
| ^^^^^^^ |
| |
| Say you modify a branch with <<fixing-mistakes,`git reset --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 |
| `master` branch head. This syntax can be used 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 |
| $ git log --walk-reflogs master # show reflog entries for master |
| ------------------------------------------------- |
| |
| A separate reflog is kept for the HEAD, so |
| |
| ------------------------------------------------- |
| $ git show HEAD@{"1 week ago"} |
| ------------------------------------------------- |
| |
| will show what HEAD pointed to one week ago, not what the current branch |
| pointed to one week ago. This allows you to see the history of what |
| you've checked out. |
| |
| The reflogs are kept by default for 30 days, after which they may be |
| pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn |
| how to control this pruning, and see the "SPECIFYING REVISIONS" |
| section of linkgit:gitrevisions[7] 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. |
| |
| [[dangling-object-recovery]] |
| 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 in the dangling objects that `git fsck` reports. See |
| <<dangling-objects>> for the details. |
| |
| ------------------------------------------------- |
| $ 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 |
| ------------------------------------------------ |
| |
| Other types of dangling objects (blobs and trees) are also possible, and |
| dangling objects can arise in other situations. |
| |
| |
| [[sharing-development]] |
| Sharing development with others |
| =============================== |
| |
| [[getting-updates-With-git-pull]] |
| Getting updates with git pull |
| ----------------------------- |
| |
| After you clone a repository and commit 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 linkgit: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 linkgit:git-pull[1] command provides a way to do this in |
| one step: |
| |
| ------------------------------------------------- |
| $ git pull origin master |
| ------------------------------------------------- |
| |
| In fact, if you have `master` checked out, then this branch has been |
| configured by `git clone` to get changes from the HEAD branch of the |
| origin repository. So often you can |
| accomplish the above with just a simple |
| |
| ------------------------------------------------- |
| $ git pull |
| ------------------------------------------------- |
| |
| This command will fetch changes from the remote branches to your |
| remote-tracking branches `origin/*`, and merge the default branch into |
| the current branch. |
| |
| More generally, a branch that is created from a remote-tracking branch |
| will pull |
| by default from that branch. See the descriptions of the |
| `branch.<name>.remote` and `branch.<name>.merge` options in |
| linkgit:git-config[1], and the discussion of the `--track` option in |
| linkgit:git-checkout[1], to learn how to control these defaults. |
| |
| 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]] |
| 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 linkgit: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`. |
| |
| `git format-patch` can include an initial "cover letter". You can insert |
| commentary on individual patches after the three dash line which |
| `format-patch` places after the commit message but before the patch |
| itself. If you use `git notes` to track your cover letter material, |
| `git format-patch --notes` will include the commit's notes in a similar |
| manner. |
| |
| 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 linkgit: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]] |
| Importing patches to a project |
| ------------------------------ |
| |
| Git also provides a tool called linkgit: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 --continue |
| ------------------------------------------------- |
| |
| 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. |
| |
| [[public-repositories]] |
| Public Git repositories |
| ----------------------- |
| |
| Another way to submit changes to a project is to tell the maintainer |
| of that project to pull the changes from your repository using |
| linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull, |
| Getting updates with `git pull`>>" we described this as a way to get |
| updates from the "main" repository, but it works just as well in the |
| other direction. |
| |
| If you and the maintainer both have accounts on the same machine, then |
| you can just pull changes from each other's repositories directly; |
| commands that accept repository URLs as arguments will also accept a |
| local directory name: |
| |
| ------------------------------------------------- |
| $ git clone /path/to/repository |
| $ git pull /path/to/other/repository |
| ------------------------------------------------- |
| |
| or an ssh URL: |
| |
| ------------------------------------------------- |
| $ git clone ssh://yourhost/~you/repository |
| ------------------------------------------------- |
| |
| For projects with few developers, or for synchronizing a few private |
| repositories, this may be all you need. |
| |
| However, the more common way to do this is to maintain a separate public |
| repository (usually on a different host) for others to pull changes |
| from. This is usually more convenient, and 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 |
| |
| We explain how to do this in the following sections. |
| |
| [[setting-up-a-public-repository]] |
| Setting up a public repository |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Assume your personal repository is in the directory `~/proj`. We |
| first create a new clone of the repository and tell `git daemon` that it |
| is meant to be public: |
| |
| ------------------------------------------------- |
| $ git clone --bare ~/proj proj.git |
| $ touch proj.git/git-daemon-export-ok |
| ------------------------------------------------- |
| |
| The resulting directory proj.git contains a "bare" git repository--it is |
| just the contents of the `.git` directory, without any files checked out |
| around it. |
| |
| Next, copy `proj.git` to the server where you plan to host the |
| public repository. You can use scp, rsync, or whatever is most |
| convenient. |
| |
| [[exporting-via-git]] |
| Exporting a Git repository via the Git protocol |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| This is the preferred method. |
| |
| If someone else administers the server, they should tell you what |
| directory to put the repository in, and what `git://` URL it will |
| appear at. You can then skip to the section |
| "<<pushing-changes-to-a-public-repository,Pushing changes to a public |
| repository>>", below. |
| |
| Otherwise, all you need to do is start linkgit:git-daemon[1]; it will |
| listen on port 9418. By default, it will allow access to any directory |
| that looks like a Git directory and contains the magic file |
| git-daemon-export-ok. Passing some directory paths as `git daemon` |
| arguments will further restrict the exports to those paths. |
| |
| You can also run `git daemon` as an inetd service; see the |
| linkgit:git-daemon[1] man page for details. (See especially the |
| examples section.) |
| |
| [[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 --bare update-server-info |
| $ mv hooks/post-update.sample hooks/post-update |
| ------------------------------------------------- |
| |
| (For an explanation of the last two lines, see |
| linkgit:git-update-server-info[1] and linkgit:githooks[5].) |
| |
| Advertise the URL of `proj.git`. Anybody else should then be able to |
| clone or pull from that URL, for example with a command line 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.) |
| |
| [[pushing-changes-to-a-public-repository]] |
| Pushing changes to a public repository |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Note that the two techniques outlined 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 linkgit: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>>; see the following section for details on |
| handling this case. |
| |
| Note that the target of a `push` is normally a |
| <<def_bare_repository,bare>> repository. You can also push to a |
| repository that has a checked-out working tree, but a push to update the |
| currently checked-out branch is denied by default to prevent confusion. |
| See the description of the receive.denyCurrentBranch option |
| in linkgit:git-config[1] for details. |
| |
| As with `git fetch`, you may also set up configuration options to |
| save typing; so, for example: |
| |
| ------------------------------------------------- |
| $ git remote add public-repo ssh://yourserver.com/~you/proj.git |
| ------------------------------------------------- |
| |
| adds the following to `.git/config`: |
| |
| ------------------------------------------------- |
| [remote "public-repo"] |
| url = yourserver.com:proj.git |
| fetch = +refs/heads/*:refs/remotes/example/* |
| ------------------------------------------------- |
| |
| which lets you do the same 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 |
| linkgit:git-config[1] for details. |
| |
| [[forcing-push]] |
| What to do when a push fails |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| If a push would not result in a <<fast-forwards,fast-forward>> of the |
| remote branch, then it will fail with an error like: |
| |
| ------------------------------------------------- |
| error: remote 'refs/heads/master' is not an ancestor of |
| local 'refs/heads/master'. |
| Maybe you are not up-to-date and need to pull first? |
| error: failed to push to 'ssh://yourserver.com/~you/proj.git' |
| ------------------------------------------------- |
| |
| This can happen, for example, if you: |
| |
| - use `git reset --hard` to remove already-published commits, or |
| - use `git commit --amend` to replace already-published commits |
| (as in <<fixing-a-mistake-by-rewriting-history>>), or |
| - use `git rebase` to rebase any already-published commits (as |
| in <<using-git-rebase>>). |
| |
| You may force `git push` to perform the update anyway by preceding the |
| branch name with a plus sign: |
| |
| ------------------------------------------------- |
| $ git push ssh://yourserver.com/~you/proj.git +master |
| ------------------------------------------------- |
| |
| Note the addition of the `+` sign. Alternatively, you can use the |
| `-f` flag to force the remote update, as in: |
| |
| ------------------------------------------------- |
| $ git push -f ssh://yourserver.com/~you/proj.git master |
| ------------------------------------------------- |
| |
| Normally whenever a branch head in a public repository is modified, it |
| is modified to point to a descendant of the commit that it pointed to |
| before. By forcing a push in this situation, you break that convention. |
| (See <<problems-With-rewriting-history>>.) |
| |
| Nevertheless, this is a common practice for people that need a simple |
| way to publish a work-in-progress patch series, and it is an acceptable |
| compromise as long as you warn other developers that this is how you |
| intend to manage the branch. |
| |
| It's also possible for a push to fail in this way when other people have |
| the right to push to the same repository. In that case, the correct |
| solution is to retry the push after first updating your work: either by a |
| pull, or by a fetch followed by a rebase; see the |
| <<setting-up-a-shared-repository,next section>> and |
| linkgit:gitcvs-migration[7] for more. |
| |
| [[setting-up-a-shared-repository]] |
| 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 |
| linkgit:gitcvs-migration[7] for instructions on how to |
| set this up. |
| |
| However, while there is nothing wrong with Git's support for shared |
| repositories, this mode of operation is not generally recommended, |
| simply because the mode of collaboration that Git supports--by |
| exchanging patches and pulling from public repositories--has so many |
| advantages over the central shared repository: |
| |
| - Git's ability to quickly import and merge patches allows a |
| single maintainer to process incoming changes even at very |
| high rates. And when that becomes too much, `git pull` provides |
| an easy way for that maintainer to delegate this job to other |
| maintainers while still allowing optional review of incoming |
| changes. |
| - Since every developer's repository has the same complete copy |
| of the project history, no repository is special, and it is |
| trivial for another developer to take over maintenance of a |
| project, either by mutual agreement, or because a maintainer |
| becomes unresponsive or difficult to work with. |
| - The lack of a central group of "committers" means there is |
| less need for formal decisions about who is "in" and who is |
| "out". |
| |
| [[setting-up-gitweb]] |
| Allowing 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. |
| |
| [[sharing-development-examples]] |
| Examples |
| -------- |
| |
| [[maintaining-topic-branches]] |
| Maintaining topic branches for a Linux subsystem maintainer |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| This describes how Tony Luck uses Git in his role as maintainer of the |
| IA64 architecture for the Linux kernel. |
| |
| He uses two public branches: |
| |
| - A "test" tree into which patches are initially placed so that they |
| can get some exposure when integrated with other ongoing development. |
| This tree is available to Andrew for pulling into -mm whenever he |
| wants. |
| |
| - A "release" tree into which tested patches are moved for final sanity |
| checking, and as a vehicle to send them upstream to Linus (by sending |
| him a "please pull" request.) |
| |
| He also uses a set of temporary branches ("topic branches"), each |
| containing a logical grouping of patches. |
| |
| To set this up, first create your work tree by cloning Linus's public |
| tree: |
| |
| ------------------------------------------------- |
| $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git work |
| $ cd work |
| ------------------------------------------------- |
| |
| Linus's tree will be stored in the remote-tracking branch named origin/master, |
| and can be updated using linkgit:git-fetch[1]; you can track other |
| public trees using linkgit:git-remote[1] to set up a "remote" and |
| linkgit:git-fetch[1] to keep them up-to-date; see |
| <<repositories-and-branches>>. |
| |
| Now create the branches in which you are going to work; these start out |
| at the current tip of origin/master branch, and should be set up (using |
| the `--track` option to linkgit:git-branch[1]) to merge changes in from |
| Linus by default. |
| |
| ------------------------------------------------- |
| $ git branch --track test origin/master |
| $ git branch --track release origin/master |
| ------------------------------------------------- |
| |
| These can be easily kept up to date using linkgit:git-pull[1]. |
| |
| ------------------------------------------------- |
| $ git checkout test && git pull |
| $ git checkout release && git pull |
| ------------------------------------------------- |
| |
| Important note! If you have any local changes in these branches, then |
| this merge will create a commit object in the history (with no local |
| changes Git will simply do a "fast-forward" merge). Many people dislike |
| the "noise" that this creates in the Linux history, so you should avoid |
| doing this capriciously in the `release` branch, as these noisy commits |
| will become part of the permanent history when you ask Linus to pull |
| from the release branch. |
| |
| A few configuration variables (see linkgit:git-config[1]) can |
| make it easy to push both branches to your public tree. (See |
| <<setting-up-a-public-repository>>.) |
| |
| ------------------------------------------------- |
| $ cat >> .git/config <<EOF |
| [remote "mytree"] |
| url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux.git |
| push = release |
| push = test |
| EOF |
| ------------------------------------------------- |
| |
| Then you can push both the test and release trees using |
| linkgit:git-push[1]: |
| |
| ------------------------------------------------- |
| $ git push mytree |
| ------------------------------------------------- |
| |
| or push just one of the test and release branches using: |
| |
| ------------------------------------------------- |
| $ git push mytree test |
| ------------------------------------------------- |
| |
| or |
| |
| ------------------------------------------------- |
| $ git push mytree release |
| ------------------------------------------------- |
| |
| Now to apply some patches from the community. Think of a short |
| snappy name for a branch to hold this patch (or related group of |
| patches), and create a new branch from a recent stable tag of |
| Linus's branch. Picking a stable base for your branch will: |
| 1) help you: by avoiding inclusion of unrelated and perhaps lightly |
| tested changes |
| 2) help future bug hunters that use `git bisect` to find problems |
| |
| ------------------------------------------------- |
| $ git checkout -b speed-up-spinlocks v2.6.35 |
| ------------------------------------------------- |
| |
| Now you apply the patch(es), run some tests, and commit the change(s). If |
| the patch is a multi-part series, then you should apply each as a separate |
| commit to this branch. |
| |
| ------------------------------------------------- |
| $ ... patch ... test ... commit [ ... patch ... test ... commit ]* |
| ------------------------------------------------- |
| |
| When you are happy with the state of this change, you can pull it into the |
| "test" branch in preparation to make it public: |
| |
| ------------------------------------------------- |
| $ git checkout test && git pull . speed-up-spinlocks |
| ------------------------------------------------- |
| |
| It is unlikely that you would have any conflicts here ... but you might if you |
| spent a while on this step and had also pulled new versions from upstream. |
| |
| Some time later when enough time has passed and testing done, you can pull the |
| same branch into the `release` tree ready to go upstream. This is where you |
| see the value of keeping each patch (or patch series) in its own branch. It |
| means that the patches can be moved into the `release` tree in any order. |
| |
| ------------------------------------------------- |
| $ git checkout release && git pull . speed-up-spinlocks |
| ------------------------------------------------- |
| |
| After a while, you will have a number of branches, and despite the |
| well chosen names you picked for each of them, you may forget what |
| they are for, or what status they are in. To get a reminder of what |
| changes are in a specific branch, use: |
| |
| ------------------------------------------------- |
| $ git log linux..branchname | git shortlog |
| ------------------------------------------------- |
| |
| To see whether it has already been merged into the test or release branches, |
| use: |
| |
| ------------------------------------------------- |
| $ git log test..branchname |
| ------------------------------------------------- |
| |
| or |
| |
| ------------------------------------------------- |
| $ git log release..branchname |
| ------------------------------------------------- |
| |
| (If this branch has not yet been merged, you will see some log entries. |
| If it has been merged, then there will be no output.) |
| |
| Once a patch completes the great cycle (moving from test to release, |
| then pulled by Linus, and finally coming back into your local |
| `origin/master` branch), the branch for this change is no longer needed. |
| You detect this when the output from: |
| |
| ------------------------------------------------- |
| $ git log origin..branchname |
| ------------------------------------------------- |
| |
| is empty. At this point the branch can be deleted: |
| |
| ------------------------------------------------- |
| $ git branch -d branchname |
| ------------------------------------------------- |
| |
| Some changes are so trivial that it is not necessary to create a separate |
| branch and then merge into each of the test and release branches. For |
| these changes, just apply directly to the `release` branch, and then |
| merge that into the `test` branch. |
| |
| After pushing your work to `mytree`, you can use |
| linkgit:git-request-pull[1] to prepare a "please pull" request message |
| to send to Linus: |
| |
| ------------------------------------------------- |
| $ git push mytree |
| $ git request-pull origin mytree release |
| ------------------------------------------------- |
| |
| Here are some of the scripts that simplify all this even further. |
| |
| ------------------------------------------------- |
| ==== update script ==== |
| # Update a branch in my Git tree. If the branch to be updated |
| # is origin, then pull from kernel.org. Otherwise merge |
| # origin/master branch into test|release branch |
| |
| case "$1" in |
| test|release) |
| git checkout $1 && git pull . origin |
| ;; |
| origin) |
| before=$(git rev-parse refs/remotes/origin/master) |
| git fetch origin |
| after=$(git rev-parse refs/remotes/origin/master) |
| if [ $before != $after ] |
| then |
| git log $before..$after | git shortlog |
| fi |
| ;; |
| *) |
| echo "usage: $0 origin|test|release" 1>&2 |
| exit 1 |
| ;; |
| esac |
| ------------------------------------------------- |
| |
| ------------------------------------------------- |
| ==== merge script ==== |
| # Merge a branch into either the test or release branch |
| |
| pname=$0 |
| |
| usage() |
| { |
| echo "usage: $pname branch test|release" 1>&2 |
| exit 1 |
| } |
| |
| git show-ref -q --verify -- refs/heads/"$1" || { |
| echo "Can't see branch <$1>" 1>&2 |
| usage |
| } |
| |
| case "$2" in |
| test|release) |
| if [ $(git log $2..$1 | wc -c) -eq 0 ] |
| then |
| echo $1 already merged into $2 1>&2 |
| exit 1 |
| fi |
| git checkout $2 && git pull . $1 |
| ;; |
| *) |
| usage |
| ;; |
| esac |
| ------------------------------------------------- |
| |
| ------------------------------------------------- |
| ==== status script ==== |
| # report on status of my ia64 Git tree |
| |
| gb=$(tput setab 2) |
| rb=$(tput setab 1) |
| restore=$(tput setab 9) |
| |
| if [ `git rev-list test..release | wc -c` -gt 0 ] |
| then |
| echo $rb Warning: commits in release that are not in test $restore |
| git log test..release |
| fi |
| |
| for branch in `git show-ref --heads | sed 's|^.*/||'` |
| do |
| if [ $branch = test -o $branch = release ] |
| then |
| continue |
| fi |
| |
| echo -n $gb ======= $branch ====== $restore " " |
| status= |
| for ref in test release origin/master |
| do |
| if [ `git rev-list $ref..$branch | wc -c` -gt 0 ] |
| then |
| status=$status${ref:0:1} |
| fi |
| done |
| case $status in |
| trl) |
| echo $rb Need to pull into test $restore |
| ;; |
| rl) |
| echo "In test" |
| ;; |
| l) |
| echo "Waiting for linus" |
| ;; |
| "") |
| echo $rb All done $restore |
| ;; |
| *) |
| echo $rb "<$status>" $restore |
| ;; |
| esac |
| git log origin/master..$branch | git shortlog |
| done |
| ------------------------------------------------- |
| |
| |
| [[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. |
| |
| [[patch-series]] |
| 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. |
| |
| [[using-git-rebase]] |
| 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 |
| \ |
| a--b--c <-- 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 |
| linkgit: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 `.git/rebase-apply`), 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 |
| ------------------------------------------------- |
| |
| If you need to reorder or edit a number of commits in a branch, it may |
| be easier to use `git rebase -i`, which allows you to reorder and |
| squash commits, as well as marking them for individual editing during |
| the rebase. See <<interactive-rebase>> for details, and |
| <<reordering-patch-series>> for alternatives. |
| |
| [[rewriting-one-commit]] |
| Rewriting a single commit |
| ------------------------- |
| |
| We saw in <<fixing-a-mistake-by-rewriting-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. |
| This is useful for fixing typos in your last commit, or for adjusting |
| the patch contents of a poorly staged commit. |
| |
| If you need to amend commits from deeper in your history, you can |
| use <<interactive-rebase,interactive rebase's `edit` instruction>>. |
| |
| [[reordering-patch-series]] |
| Reordering or selecting from a patch series |
| ------------------------------------------- |
| |
| Sometimes you want to edit a commit deeper in your history. One |
| approach is to use `git format-patch` to create a series of patches |
| and then reset the state to before the patches: |
| |
| ------------------------------------------------- |
| $ git format-patch origin |
| $ git reset --hard origin |
| ------------------------------------------------- |
| |
| Then modify, reorder, or eliminate patches as needed before applying |
| them again with linkgit:git-am[1]: |
| |
| ------------------------------------------------- |
| $ git am *.patch |
| ------------------------------------------------- |
| |
| [[interactive-rebase]] |
| Using interactive rebases |
| ------------------------- |
| |
| You can also edit a patch series with an interactive rebase. This is |
| the same as <<reordering-patch-series,reordering a patch series using |
| `format-patch`>>, so use whichever interface you like best. |
| |
| Rebase your current HEAD on the last commit you want to retain as-is. |
| For example, if you want to reorder the last 5 commits, use: |
| |
| ------------------------------------------------- |
| $ git rebase -i HEAD~5 |
| ------------------------------------------------- |
| |
| This will open your editor with a list of steps to be taken to perform |
| your rebase. |
| |
| ------------------------------------------------- |
| pick deadbee The oneline of this commit |
| pick fa1afe1 The oneline of the next commit |
| ... |
| |
| # Rebase c0ffeee..deadbee onto c0ffeee |
| # |
| # Commands: |
| # p, pick = use commit |
| # r, reword = use commit, but edit the commit message |
| # e, edit = use commit, but stop for amending |
| # s, squash = use commit, but meld into previous commit |
| # f, fixup = like "squash", but discard this commit's log message |
| # x, exec = run command (the rest of the line) using shell |
| # |
| # These lines can be re-ordered; they are executed from top to bottom. |
| # |
| # If you remove a line here THAT COMMIT WILL BE LOST. |
| # |
| # However, if you remove everything, the rebase will be aborted. |
| # |
| # Note that empty commits are commented out |
| ------------------------------------------------- |
| |
| As explained in the comments, you can reorder commits, squash them |
| together, edit commit messages, etc. by editing the list. Once you |
| are satisfied, save the list and close your editor, and the rebase |
| will begin. |
| |
| The rebase will stop where `pick` has been replaced with `edit` or |
| when a step in the list fails to mechanically resolve conflicts and |
| needs your help. When you are done editing and/or resolving conflicts |
| you can continue with `git rebase --continue`. If you decide that |
| things are getting too hairy, you can always bail out with `git rebase |
| --abort`. Even after the rebase is complete, you can still recover |
| the original branch by using the <<reflogs,reflog>>. |
| |
| For a more detailed discussion of the procedure and additional tips, |
| see the "INTERACTIVE MODE" section of linkgit:git-rebase[1]. |
| |
| [[patch-series-tools]] |
| 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]] |
| 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. |
| |
| [[bisect-merges]] |
| Why bisecting merge commits can be harder than bisecting linear history |
| ----------------------------------------------------------------------- |
| |
| The linkgit:git-bisect[1] command correctly handles history that |
| includes merge commits. However, when the commit that it finds is a |
| merge commit, the user may need to work harder than usual to figure out |
| why that commit introduced a problem. |
| |
| Imagine this history: |
| |
| ................................................ |
| ---Z---o---X---...---o---A---C---D |
| \ / |
| o---o---Y---...---o---B |
| ................................................ |
| |
| Suppose that on the upper line of development, the meaning of one |
| of the functions that exists at Z is changed at commit X. The |
| commits from Z leading to A change both the function's |
| implementation and all calling sites that exist at Z, as well |
| as new calling sites they add, to be consistent. There is no |
| bug at A. |
| |
| Suppose that in the meantime on the lower line of development somebody |
| adds a new calling site for that function at commit Y. The |
| commits from Z leading to B all assume the old semantics of that |
| function and the callers and the callee are consistent with each |
| other. There is no bug at B, either. |
| |
| Suppose further that the two development lines merge cleanly at C, |
| so no conflict resolution is required. |
| |
| Nevertheless, the code at C is broken, because the callers added |
| on the lower line of development have not been converted to the new |
| semantics introduced on the upper line of development. So if all |
| you know is that D is bad, that Z is good, and that |
| linkgit:git-bisect[1] identifies C as the culprit, how will you |
| figure out that the problem is due to this change in semantics? |
| |
| When the result of a `git bisect` is a non-merge commit, you should |
| normally be able to discover the problem by examining just that commit. |
| Developers can make this easy by breaking their changes into small |
| self-contained commits. That won't help in the case above, however, |
| because the problem isn't obvious from examination of any single |
| commit; instead, a global view of the development is required. To |
| make matters worse, the change in semantics in the problematic |
| function may be just one small part of the changes in the upper |
| line of development. |
| |
| On the other hand, if instead of merging at C you had rebased the |
| history between Z to B on top of A, you would have gotten this |
| linear history: |
| |
| ................................................................ |
| ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D* |
| ................................................................ |
| |
| Bisecting between Z and D* would hit a single culprit commit Y*, |
| and understanding why Y* was broken would probably be easier. |
| |
| Partly for this reason, many experienced Git users, even when |
| working on an otherwise merge-heavy project, keep the history |
| linear by rebasing against the latest upstream version before |
| publishing. |
| |
| [[advanced-branch-management]] |
| Advanced branch management |
| ========================== |
| |
| [[fetching-individual-branches]] |
| Fetching individual branches |
| ---------------------------- |
| |
| Instead of using linkgit: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-forwards,fast-forward>> to the commit given by example.com's |
| master branch. In more detail: |
| |
| [[fetch-fast-forwards]] |
| git fetch and 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-forwards,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-fetch]] |
| 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. Alternatively, you can use the `-f` |
| flag to force updates of all the fetched branches, as in: |
| |
| ------------------------------------------------- |
| $ git fetch -f origin |
| ------------------------------------------------- |
| |
| Be aware that commits that the old version of example/master pointed at |
| may be lost, as we saw in the previous section. |
| |
| [[remote-branch-configuration]] |
| Configuring remote-tracking 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 |
| linkgit: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, |
| |
| ------------------------------------------------- |
| $ git remote add example git://example.com/proj.git |
| ------------------------------------------------- |
| |
| adds the following to `.git/config`: |
| |
| ------------------------------------------------- |
| [remote "example"] |
| url = git://example.com/proj.git |
| fetch = +refs/heads/*:refs/remotes/example/* |
| ------------------------------------------------- |
| |
| Also note that the above configuration can be performed by directly |
| editing the file `.git/config` instead of using linkgit:git-remote[1]. |
| |
| After configuring the remote, the following three commands will do the |
| same thing: |
| |
| ------------------------------------------------- |
| $ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/* |
| $ git fetch example +refs/heads/*:refs/remotes/example/* |
| $ git fetch example |
| ------------------------------------------------- |
| |
| See linkgit:git-config[1] for more details on the configuration |
| options mentioned above and linkgit:git-fetch[1] for more details on |
| the refspec syntax. |
| |
| |
| [[git-concepts]] |
| Git concepts |
| ============ |
| |
| Git is built on a small number of simple but powerful ideas. While it |
| is possible to get things done without understanding them, you will find |
| Git much more intuitive if you do. |
| |
| We start with the most important, the <<def_object_database,object |
| database>> and the <<def_index,index>>. |
| |
| [[the-object-database]] |
| The Object Database |
| ------------------- |
| |
| |
| We already saw in <<understanding-commits>> that all commits are stored |
| under a 40-digit "object name". In fact, all the information needed to |
| represent the history of a project is stored in objects with such names. |
| In each case the name is calculated by taking the SHA-1 hash of the |
| contents of the object. The SHA-1 hash is a cryptographic hash function. |
| What that means to us is that it is impossible to find two different |
| objects with the same name. This has a number of advantages; among |
| others: |
| |
| - Git can quickly determine whether two objects are identical or not, |
| just by comparing names. |
| - Since object names are computed the same way in every repository, the |
| same content stored in two repositories will always be stored under |
| the same name. |
| - Git can detect errors when it reads an object, by checking that the |
| object's name is still the SHA-1 hash of its contents. |
| |
| (See <<object-details>> for the details of the object formatting and |
| SHA-1 calculation.) |
| |
| There are four different types of objects: "blob", "tree", "commit", and |
| "tag". |
| |
| - A <<def_blob_object,"blob" object>> is used to store file data. |
| - A <<def_tree_object,"tree" object>> 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 contains the object name of exactly one tree designating the |
| directory hierarchy at the time of the commit. In addition, a commit |
| refers to "parent" commit objects that describe the history of how we |
| arrived at that directory hierarchy. |
| - A <<def_tag_object,"tag" object>> symbolically identifies and can be |
| used to sign other objects. It contains the object name and type of |
| another object, a symbolic name (of course!) and, optionally, a |
| signature. |
| |
| The object types in some more detail: |
| |
| [[commit-object]] |
| Commit Object |
| ~~~~~~~~~~~~~ |
| |
| The "commit" object links a physical state of a tree with a description |
| of how we got there and why. Use the `--pretty=raw` option to |
| linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite |
| commit: |
| |
| ------------------------------------------------ |
| $ git show -s --pretty=raw 2be7fcb476 |
| commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4 |
| tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf |
| parent 257a84d9d02e90447b149af58b271c19405edb6a |
| author Dave Watson <dwatson@mimvista.com> 1187576872 -0400 |
| committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700 |
| |
| Fix misspelling of 'suppress' in docs |
| |
| Signed-off-by: Junio C Hamano <gitster@pobox.com> |
| ------------------------------------------------ |
| |
| As you can see, a commit is defined by: |
| |
| - a tree: The SHA-1 name of a tree object (as defined below), representing |
| the contents of a directory at a certain point in time. |
| - parent(s): The SHA-1 name(s) of some number of commits which represent the |
| immediately previous step(s) in the history of the project. The |
| example above has one parent; merge commits may have more than |
| one. A commit with no parents is called a "root" commit, and |
| represents the initial revision of a project. Each project must have |
| at least one root. A project can also have multiple roots, though |
| that isn't common (or necessarily a good idea). |
| - an author: The name of the person responsible for this change, together |
| with its date. |
| - a committer: The name of the person who actually created the commit, |
| with the date it was done. This may be different from the author, for |
| example, if the author was someone who wrote a patch and emailed it |
| to the person who used it to create the commit. |
| - a comment describing this commit. |
| |
| Note that a commit does not itself contain any information about what |
| actually changed; all changes are calculated by comparing the contents |
| of the tree referred to by this commit with the trees associated with |
| its parents. In particular, Git does not attempt to record file renames |
| explicitly, though it can identify cases where the existence of the same |
| file data at changing paths suggests a rename. (See, for example, the |
| `-M` option to linkgit:git-diff[1]). |
| |
| A commit is usually created by linkgit:git-commit[1], which creates a |
| commit whose parent is normally the current HEAD, and whose tree is |
| taken from the content currently stored in the index. |
| |
| [[tree-object]] |
| Tree Object |
| ~~~~~~~~~~~ |
| |
| The ever-versatile linkgit:git-show[1] command can also be used to |
| examine tree objects, but linkgit:git-ls-tree[1] will give you more |
| details: |
| |
| ------------------------------------------------ |
| $ git ls-tree fb3a8bdd0ce |
| 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore |
| 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap |
| 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING |
| 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation |
| 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN |
| 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL |
| 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile |
| 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README |
| ... |
| ------------------------------------------------ |
| |
| As you can see, a tree object contains a list of entries, each with a |
| mode, object type, SHA-1 name, and name, sorted by name. It represents |
| the contents of a single directory tree. |
| |
| The object type may be a blob, representing the contents of a file, or |
| another tree, representing the contents of a subdirectory. Since trees |
| and blobs, like all other objects, are named by the SHA-1 hash of their |
| contents, two trees have the same SHA-1 name if and only if their |
| contents (including, recursively, the contents of all subdirectories) |
| are identical. This allows Git to quickly determine the differences |
| between two related tree objects, since it can ignore any entries with |
| identical object names. |
| |
| (Note: in the presence of submodules, trees may also have commits as |
| entries. See <<submodules>> for documentation.) |
| |
| Note that the files all have mode 644 or 755: Git actually only pays |
| attention to the executable bit. |
| |
| [[blob-object]] |
| Blob Object |
| ~~~~~~~~~~~ |
| |
| You can use linkgit:git-show[1] to examine the contents of a blob; take, |
| for example, the blob in the entry for `COPYING` from the tree above: |
| |
| ------------------------------------------------ |
| $ git show 6ff87c4664 |
| |
| Note that the only valid version of the GPL as far as this project |
| is concerned is _this_ particular version of the license (ie v2, not |
| v2.2 or v3.x or whatever), unless explicitly otherwise stated. |
| ... |
| ------------------------------------------------ |
| |
| A "blob" object is nothing but a binary blob of data. It doesn't refer |
| to anything else or have attributes of any kind. |
| |
| 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. |
| |
| Note that any tree or blob object can be examined using |
| linkgit:git-show[1] with the <revision>:<path> syntax. This can |
| sometimes be useful for browsing the contents of a tree that is not |
| currently checked out. |
| |
| [[trust]] |
| Trust |
| ~~~~~ |
| |
| If you receive the SHA-1 name of a blob from one source, and its contents |
| from another (possibly untrusted) source, you can still trust that those |
| contents are correct as long as the SHA-1 name agrees. This is because |
| the SHA-1 is designed so that it is infeasible to find different contents |
| that produce the same hash. |
| |
| Similarly, you need only trust the SHA-1 name of a top-level tree object |
| to trust the contents of the entire directory that it refers to, and if |
| you receive the SHA-1 name of a commit from a trusted source, then you |
| can easily verify the entire history of commits reachable through |
| parents of that commit, and all of those contents of the trees referred |
| to by those commits. |
| |
| 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 (SHA-1 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]] |
| Tag Object |
| ~~~~~~~~~~ |
| |
| A tag object contains an object, object type, tag name, the name of the |
| person ("tagger") who created the tag, and a message, which may contain |
| a signature, as can be seen using linkgit:git-cat-file[1]: |
| |
| ------------------------------------------------ |
| $ git cat-file tag v1.5.0 |
| object 437b1b20df4b356c9342dac8d38849f24ef44f27 |
| type commit |
| tag v1.5.0 |
| tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000 |
| |
| GIT 1.5.0 |
| -----BEGIN PGP SIGNATURE----- |
| Version: GnuPG v1.4.6 (GNU/Linux) |
| |
| iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui |
| nLE/L9aUXdWeTFPron96DLA= |
| =2E+0 |
| -----END PGP SIGNATURE----- |
| ------------------------------------------------ |
| |
| See the linkgit:git-tag[1] command to learn how to create and verify tag |
| objects. (Note that linkgit:git-tag[1] can also be used to create |
| "lightweight tags", which are not tag objects at all, but just simple |
| references whose names begin with `refs/tags/`). |
| |
| [[pack-files]] |
| How Git stores objects efficiently: pack files |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| Newly created objects are initially created in a file named after the |
| object's SHA-1 hash (stored in `.git/objects`). |
| |
| 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 linkgit: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 linkgit: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 everything it pointed to. The branch |
| pointer itself just doesn't, since you replaced it with another one. |
| |
| There are also other situations 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, you can just use: |
| |
| ------------------------------------------------ |
| $ gitk <dangling-commit-sha-goes-here> --not --all |
| ------------------------------------------------ |
| |
| This asks for all the history reachable from the given commit but not |
| from any branch, tag, or other reference. If you decide it's something |
| you want, you can always create a new reference to it, e.g., |
| |
| ------------------------------------------------ |
| $ git branch recovered-branch <dangling-commit-sha-goes-here> |
| ------------------------------------------------ |
| |
| For blobs and trees, you can't do the same, but you can still 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). |
| |
| [[recovering-from-repository-corruption]] |
| Recovering from repository corruption |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| By design, Git treats data trusted to it with caution. However, even in |
| the absence of bugs in Git itself, it is still possible that hardware or |
| operating system errors could corrupt data. |
| |
| The first defense against such problems is backups. You can back up a |
| Git directory using clone, or just using cp, tar, or any other backup |
| mechanism. |
| |
| As a last resort, you can search for the corrupted objects and attempt |
| to replace them by hand. Back up your repository before attempting this |
| in case you corrupt things even more in the process. |
| |
| We'll assume that the problem is a single missing or corrupted blob, |
| which is sometimes a solvable problem. (Recovering missing trees and |
| especially commits is *much* harder). |
| |
| Before starting, verify that there is corruption, and figure out where |
| it is with linkgit:git-fsck[1]; this may be time-consuming. |
| |
| Assume the output looks like this: |
| |
| ------------------------------------------------ |
| $ git fsck --full --no-dangling |
| broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 |
| to blob 4b9458b3786228369c63936db65827de3cc06200 |
| missing blob 4b9458b3786228369c63936db65827de3cc06200 |
| ------------------------------------------------ |
| |
| Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6 |
| points to it. If you could find just one copy of that missing blob |
| object, possibly in some other repository, you could move it into |
| `.git/objects/4b/9458b3...` and be done. Suppose you can't. You can |
| still examine the tree that pointed to it with linkgit:git-ls-tree[1], |
| which might output something like: |
| |
| ------------------------------------------------ |
| $ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 |
| 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore |
| 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap |
| 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING |
| ... |
| 100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile |
| ... |
| ------------------------------------------------ |
| |
| So now you know that the missing blob was the data for a file named |
| `myfile`. And chances are you can also identify the directory--let's |
| say it's in `somedirectory`. If you're lucky the missing copy might be |
| the same as the copy you have checked out in your working tree at |
| `somedirectory/myfile`; you can test whether that's right with |
| linkgit:git-hash-object[1]: |
| |
| ------------------------------------------------ |
| $ git hash-object -w somedirectory/myfile |
| ------------------------------------------------ |
| |
| which will create and store a blob object with the contents of |
| somedirectory/myfile, and output the SHA-1 of that object. if you're |
| extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in |
| which case you've guessed right, and the corruption is fixed! |
| |
| Otherwise, you need more information. How do you tell which version of |
| the file has been lost? |
| |
| The easiest way to do this is with: |
| |
| ------------------------------------------------ |
| $ git log --raw --all --full-history -- somedirectory/myfile |
| ------------------------------------------------ |
| |
| Because you're asking for raw output, you'll now get something like |
| |
| ------------------------------------------------ |
| commit abc |
| Author: |
| Date: |
| ... |
| :100644 100644 4b9458b... newsha... M somedirectory/myfile |
| |
| |
| commit xyz |
| Author: |
| Date: |
| |
| ... |
| :100644 100644 oldsha... 4b9458b... M somedirectory/myfile |
| ------------------------------------------------ |
| |
| This tells you that the immediately following version of the file was |
| "newsha", and that the immediately preceding version was "oldsha". |
| You also know the commit messages that went with the change from oldsha |
| to 4b9458b and with the change from 4b9458b to newsha. |
| |
| If you've been committing small enough changes, you may now have a good |
| shot at reconstructing the contents of the in-between state 4b9458b. |
| |
| If you can do that, you can now recreate the missing object with |
| |
| ------------------------------------------------ |
| $ git hash-object -w <recreated-file> |
| ------------------------------------------------ |
| |
| and your repository is good again! |
| |
| (Btw, you could have ignored the `fsck`, and started with doing a |
| |
| ------------------------------------------------ |
| $ git log --raw --all |
| ------------------------------------------------ |
| |
| and just looked for the sha of the missing object (4b9458b..) in that |
| whole thing. It's up to you--Git does *have* a lot of information, it is |
| just missing one particular blob version. |
| |
| [[the-index]] |
| The index |
| ----------- |
| |
| The index is a binary file (generally kept in `.git/index`) containing a |
| sorted list of path names, each with permissions and the SHA-1 of a blob |
| object; linkgit:git-ls-files[1] can show you the contents of the index: |
| |
| ------------------------------------------------- |
| $ git ls-files --stage |
| 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore |
| 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap |
| 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING |
| 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore |
| 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile |
| ... |
| 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h |
| 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c |
| 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h |
| ------------------------------------------------- |
| |
| Note that in older documentation you may see the index called the |
| "current directory cache" or just the "cache". It has three important |
| properties: |
| |
| 1. The index contains all the information necessary to generate a single |
| (uniquely determined) tree object. |
| + |
| For example, running linkgit:git-commit[1] generates this tree object |
| from the index, stores it in the object database, and uses it as the |
| tree object associated with the new commit. |
| |
| 2. The index enables fast comparisons between the tree object it defines |
| and the working tree. |
| + |
| It does this by storing some additional data for each entry (such as |
| the last modified time). This data is not displayed above, and is not |
| stored in the created tree object, but it can be used to determine |
| quickly which files in the working directory differ from what was |
| stored in the index, and thus save Git from having to read all of the |
| data from such files to look for changes. |
| |
| 3. It can 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. |
| + |
| We saw in <<conflict-resolution>> that during a merge the index can |
| store multiple versions of a single file (called "stages"). The third |
| column in the linkgit:git-ls-files[1] output above is the stage |
| number, and will take on values other than 0 for files with merge |
| conflicts. |
| |
| The index is thus a sort of temporary staging area, which is filled with |
| a tree which you are in the process of working on. |
| |
| If you blow the index away entirely, you generally haven't lost any |
| information as long as you have the name of the tree that it described. |
| |
| [[submodules]] |
| Submodules |
| ========== |
| |
| Large projects are often composed of smaller, self-contained modules. For |
| example, an embedded Linux distribution's source tree would include every |
| piece of software in the distribution with some local modifications; a movie |
| player might need to build against a specific, known-working version of a |
| decompression library; several independent programs might all share the same |
| build scripts. |
| |
| With centralized revision control systems this is often accomplished by |
| including every module in one single repository. Developers can check out |
| all modules or only the modules they need to work with. They can even modify |
| files across several modules in a single commit while moving things around |
| or updating APIs and translations. |
| |
| Git does not allow partial checkouts, so duplicating this approach in Git |
| would force developers to keep a local copy of modules they are not |
| interested in touching. Commits in an enormous checkout would be slower |
| than you'd expect as Git would have to scan every directory for changes. |
| If modules have a lot of local history, clones would take forever. |
| |
| On the plus side, distributed revision control systems can much better |
| integrate with external sources. In a centralized model, a single arbitrary |
| snapshot of the external project is exported from its own revision control |
| and then imported into the local revision control on a vendor branch. All |
| the history is hidden. With distributed revision control you can clone the |
| entire external history and much more easily follow development and re-merge |
| local changes. |
| |
| Git's submodule support allows a repository to contain, as a subdirectory, a |
| checkout of an external project. Submodules maintain their own identity; |
| the submodule support just stores the submodule repository location and |
| commit ID, so other developers who clone the containing project |
| ("superproject") can easily clone all the submodules at the same revision. |
| Partial checkouts of the superproject are possible: you can tell Git to |
| clone none, some or all of the submodules. |
| |
| The linkgit:git-submodule[1] command is available since Git 1.5.3. Users |
| with Git 1.5.2 can look up the submodule commits in the repository and |
| manually check them out; earlier versions won't recognize the submodules at |
| all. |
| |
| To see how submodule support works, create (for example) four example |
| repositories that can be used later as a submodule: |
| |
| ------------------------------------------------- |
| $ mkdir ~/git |
| $ cd ~/git |
| $ for i in a b c d |
| do |
| mkdir $i |
| cd $i |
| git init |
| echo "module $i" > $i.txt |
| git add $i.txt |
| git commit -m "Initial commit, submodule $i" |
| cd .. |
| done |
| ------------------------------------------------- |
| |
| Now create the superproject and add all the submodules: |
| |
| ------------------------------------------------- |
| $ mkdir super |
| $ cd super |
| $ git init |
| $ for i in a b c d |
| do |
| git submodule add ~/git/$i $i |
| done |
| ------------------------------------------------- |
| |
| NOTE: Do not use local URLs here if you plan to publish your superproject! |
| |
| See what files `git submodule` created: |
| |
| ------------------------------------------------- |
| $ ls -a |
| . .. .git .gitmodules a b c d |
| ------------------------------------------------- |
| |
| The `git submodule add <repo> <path>` command does a couple of things: |
| |
| - It clones the submodule from `<repo>` to the given `<path>` under the |
| current directory and by default checks out the master branch. |
| - It adds the submodule's clone path to the linkgit:gitmodules[5] file and |
| adds this file to the index, ready to be committed. |
| - It adds the submodule's current commit ID to the index, ready to be |
| committed. |
| |
| Commit the superproject: |
| |
| ------------------------------------------------- |
| $ git commit -m "Add submodules a, b, c and d." |
| ------------------------------------------------- |
| |
| Now clone the superproject: |
| |
| ------------------------------------------------- |
| $ cd .. |
| $ git clone super cloned |
| $ cd cloned |
| ------------------------------------------------- |
| |
| The submodule directories are there, but they're empty: |
| |
| ------------------------------------------------- |
| $ ls -a a |
| . .. |
| $ git submodule status |
| -d266b9873ad50488163457f025db7cdd9683d88b a |
| -e81d457da15309b4fef4249aba9b50187999670d b |
| -c1536a972b9affea0f16e0680ba87332dc059146 c |
| -d96249ff5d57de5de093e6baff9e0aafa5276a74 d |
| ------------------------------------------------- |
| |
| NOTE: The commit object names shown above would be different for you, but they |
| should match the HEAD commit object names of your repositories. You can check |
| it by running `git ls-remote ../a`. |
| |
| Pulling down the submodules is a two-step process. First run `git submodule |
| init` to add the submodule repository URLs to `.git/config`: |
| |
| ------------------------------------------------- |
| $ git submodule init |
| ------------------------------------------------- |
| |
| Now use `git submodule update` to clone the repositories and check out the |
| commits specified in the superproject: |
| |
| ------------------------------------------------- |
| $ git submodule update |
| $ cd a |
| $ ls -a |
| . .. .git a.txt |
| ------------------------------------------------- |
| |
| One major difference between `git submodule update` and `git submodule add` is |
| that `git submodule update` checks out a specific commit, rather than the tip |
| of a branch. It's like checking out a tag: the head is detached, so you're not |
| working on a branch. |
| |
| ------------------------------------------------- |
| $ git branch |
| * (no branch) |
| master |
| ------------------------------------------------- |
| |
| If you want to make a change within a submodule and you have a detached head, |
| then you should create or checkout a branch, make your changes, publish the |
| change within the submodule, and then update the superproject to reference the |
| new commit: |
| |
| ------------------------------------------------- |
| $ git checkout master |
| ------------------------------------------------- |
| |
| or |
| |
| ------------------------------------------------- |
| $ git checkout -b fix-up |
| ------------------------------------------------- |
| |
| then |
| |
| ------------------------------------------------- |
| $ echo "adding a line again" >> a.txt |
| $ git commit -a -m "Updated the submodule from within the superproject." |
| $ git push |
| $ cd .. |
| $ git diff |
| diff --git a/a b/a |
| index d266b98..261dfac 160000 |
| --- a/a |
| +++ b/a |
| @@ -1 +1 @@ |
| -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b |
| +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24 |
| $ git add a |
| $ git commit -m "Updated submodule a." |
| $ git push |
| ------------------------------------------------- |
| |
| You have to run `git submodule update` after `git pull` if you want to update |
| submodules, too. |
| |
| Pitfalls with submodules |
| ------------------------ |
| |
| Always publish the submodule change before publishing the change to the |
| superproject that references it. If you forget to publish the submodule change, |
| others won't be able to clone the repository: |
| |
| ------------------------------------------------- |
| $ cd ~/git/super/a |
| $ echo i added another line to this file >> a.txt |
| $ git commit -a -m "doing it wrong this time" |
| $ cd .. |
| $ git add a |
| $ git commit -m "Updated submodule a again." |
| $ git push |
| $ cd ~/git/cloned |
| $ git pull |
| $ git submodule update |
| error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git. |
| Did you forget to 'git add'? |
| Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a' |
| ------------------------------------------------- |
| |
| In older Git versions it could be easily forgotten to commit new or modified |
| files in a submodule, which silently leads to similar problems as not pushing |
| the submodule changes. Starting with Git 1.7.0 both `git status` and `git diff` |
| in the superproject show submodules as modified when they contain new or |
| modified files to protect against accidentally committing such a state. `git |
| diff` will also add a `-dirty` to the work tree side when generating patch |
| output or used with the `--submodule` option: |
| |
| ------------------------------------------------- |
| $ git diff |
| diff --git a/sub b/sub |
| --- a/sub |
| +++ b/sub |
| @@ -1 +1 @@ |
| -Subproject commit 3f356705649b5d566d97ff843cf193359229a453 |
| +Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty |
| $ git diff --submodule |
| Submodule sub 3f35670..3f35670-dirty: |
| ------------------------------------------------- |
| |
| You also should not rewind branches in a submodule beyond commits that were |
| ever recorded in any superproject. |
| |
| It's not safe to run `git submodule update` if you've made and committed |
| changes within a submodule without checking out a branch first. They will be |
| silently overwritten: |
| |
| ------------------------------------------------- |
| $ cat a.txt |
| module a |
| $ echo line added from private2 >> a.txt |
| $ git commit -a -m "line added inside private2" |
| $ cd .. |
| $ git submodule update |
| Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b' |
| $ cd a |
| $ cat a.txt |
| module a |
| ------------------------------------------------- |
| |
| NOTE: The changes are still visible in the submodule's reflog. |
| |
| If you have uncommitted changes in your submodule working tree, `git |
| submodule update` will not overwrite them. Instead, you get the usual |
| warning about not being able switch from a dirty branch. |
| |
| [[low-level-operations]] |
| Low-level Git operations |
| ======================== |
| |
| Many of the higher-level commands were originally implemented as shell |
| scripts using a smaller core of low-level Git commands. These can still |
| be useful when doing unusual things with Git, or just as a way to |
| understand its inner workings. |
| |
| [[object-manipulation]] |
| Object access and manipulation |
| ------------------------------ |
| |
| The linkgit:git-cat-file[1] command can show the contents of any object, |
| though the higher-level linkgit:git-show[1] is usually more useful. |
| |
| The linkgit:git-commit-tree[1] command allows constructing commits with |
| arbitrary parents and trees. |
| |
| A tree can be created with linkgit:git-write-tree[1] and its data can be |
| accessed by linkgit:git-ls-tree[1]. Two trees can be compared with |
| linkgit:git-diff-tree[1]. |
| |
| A tag is created with linkgit:git-mktag[1], and the signature can be |
| verified by linkgit:git-verify-tag[1], though it is normally simpler to |
| use linkgit:git-tag[1] for both. |
| |
| [[the-workflow]] |
| The Workflow |
| ------------ |
| |
| High-level operations such as linkgit:git-commit[1], |
| linkgit:git-checkout[1] and linkgit:git-reset[1] work by moving data |
| between the working tree, the index, and the object database. Git |
| provides low-level operations which perform each of these steps |
| individually. |
| |
| 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 between the index file and either |
| the database or the working directory. Thus there are four main |
| combinations: |
| |
| [[working-directory-to-index]] |
| working directory -> index |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| The linkgit:git-update-index[1] command updates the index with |
| information from the working directory. 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-index 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. |
| |
| The previously introduced linkgit:git-add[1] is just a wrapper for |
| linkgit:git-update-index[1]. |
| |
| [[index-to-object-database]] |
| 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-to-index]] |
| 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 <SHA-1 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-to-working-directory]] |
| 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]] |
| 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]] |
| 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 |
| linkgit: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]] |
| 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 tree, 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-2]] |
| 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 SHA-1, 'stage number', and the |
| filename. The 'stage number' is Git's way to say which tree it |
| came from: stage 1 corresponds to the `$orig` tree, stage 2 to |
| the `HEAD` tree, and stage 3 to the `$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`, `merge`, or Git's own merge-file, 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 |
| $ git merge-file 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 the "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, runs `git cat-file` three times |
| for this. There is a `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. |
| |
| [[hacking-git]] |
| Hacking Git |
| =========== |
| |
| This chapter covers internal details of the Git implementation which |
| probably only Git developers need to understand. |
| |
| [[object-details]] |
| Object storage format |
| --------------------- |
| |
| All objects have a statically determined "type" 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". |
| |
| 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 SHA-1 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 SHA-1 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). |
| |
| [[birdview-on-the-source-code]] |
| A birds-eye view of Git's source code |
| ------------------------------------- |
| |
| It is not always easy for new developers to find their way through Git's |
| source code. This section gives you a little guidance to show where to |
| start. |
| |
| A good place to start is with the contents of the initial commit, with: |
| |
| ---------------------------------------------------- |
| $ git checkout e83c5163 |
| ---------------------------------------------------- |
| |
| The initial revision lays the foundation for almost everything Git has |
| today, but is small enough to read in one sitting. |
| |
| Note that terminology has changed since that revision. For example, the |
| README in that revision uses the word "changeset" to describe what we |
| now call a <<def_commit_object,commit>>. |
| |
| Also, we do not call it "cache" any more, but rather "index"; however, the |
| file is still called `cache.h`. Remark: Not much reason to change it now, |
| especially since there is no good single name for it anyway, because it is |
| basically _the_ header file which is included by _all_ of Git's C sources. |
| |
| If you grasp the ideas in that initial commit, you should check out a |
| more recent version and skim `cache.h`, `object.h` and `commit.h`. |
| |
| In the early days, Git (in the tradition of UNIX) was a bunch of programs |
| which were extremely simple, and which you used in scripts, piping the |
| output of one into another. This turned out to be good for initial |
| development, since it was easier to test new things. However, recently |
| many of these parts have become builtins, and some of the core has been |
| "libified", i.e. put into libgit.a for performance, portability reasons, |
| and to avoid code duplication. |
| |
| By now, you know what the index is (and find the corresponding data |
| structures in `cache.h`), and that there are just a couple of object types |
| (blobs, trees, commits and tags) which inherit their common structure from |
| `struct object`, which is their first member (and thus, you can cast e.g. |
| `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e. |
| get at the object name and flags). |
| |
| Now is a good point to take a break to let this information sink in. |
| |
| Next step: get familiar with the object naming. Read <<naming-commits>>. |
| There are quite a few ways to name an object (and not only revisions!). |
| All of these are handled in `sha1_name.c`. Just have a quick look at |
| the function `get_sha1()`. A lot of the special handling is done by |
| functions like `get_sha1_basic()` or the likes. |
| |
| This is just to get you into the groove for the most libified part of Git: |
| the revision walker. |
| |
| Basically, the initial version of `git log` was a shell script: |
| |
| ---------------------------------------------------------------- |
| $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \ |
| LESS=-S ${PAGER:-less} |
| ---------------------------------------------------------------- |
| |
| What does this mean? |
| |
| `git rev-list` is the original version of the revision walker, which |
| _always_ printed a list of revisions to stdout. It is still functional, |
| and needs to, since most new Git commands start out as scripts using |
| `git rev-list`. |
| |
| `git rev-parse` is not as important any more; it was only used to filter out |
| options that were relevant for the different plumbing commands that were |
| called by the script. |
| |
| Most of what `git rev-list` did is contained in `revision.c` and |
| `revision.h`. It wraps the options in a struct named `rev_info`, which |
| controls how and what revisions are walked, and more. |
| |
| The original job of `git rev-parse` is now taken by the function |
| `setup_revisions()`, which parses the revisions and the common command line |
| options for the revision walker. This information is stored in the struct |
| `rev_info` for later consumption. You can do your own command line option |
| parsing after calling `setup_revisions()`. After that, you have to call |
| `prepare_revision_walk()` for initialization, and then you can get the |
| commits one by one with the function `get_revision()`. |
| |
| If you are interested in more details of the revision walking process, |
| just have a look at the first implementation o
|