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diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt index ff7c71d4fb..0b88a51d0b 100644 --- a/Documentation/user-manual.txt +++ b/Documentation/user-manual.txt @@ -1,10 +1,10 @@ -Git User's Manual (for version 1.5.1 or newer) +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 +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 @@ -13,17 +13,27 @@ 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>>. +<<Developing-With-git>> and <<sharing-development>>. Further chapters cover more specialized topics. Comprehensive reference documentation is available through the man -pages. For a command such as "git clone", just use +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. @@ -42,42 +52,44 @@ How to get a git repository It will be useful to have a git repository to experiment with as you read this manual. -The best way to get one is by using the gitlink:git-clone[1] command -to download a copy of an existing repository for a project that you -are interested in. If you don't already have a project in mind, here -are some interesting examples: +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. 10MB download): $ git clone git://git.kernel.org/pub/scm/git/git.git - # the linux kernel (approx. 150MB download): + # the Linux kernel (approx. 150MB download): $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git ------------------------------------------------ The initial clone may be time-consuming for a large project, but you will only need to clone once. -The clone command creates a new directory named after the project -("git" or "linux-2.6" in the examples above). After you cd into this +The clone command creates a new directory named after the project ("git" +or "linux-2.6" in the examples above). After you cd into this directory, you will see that it contains a copy of the project files, -together with a special top-level directory named ".git", which -contains all the information about the history of the project. - -In most of the following, examples will be taken from one of the two -repositories above. +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 (versions) of the project's -contents. +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>>. -A single git repository may contain multiple branches. It keeps track -of them by keeping a list of <<def_head,heads>> which reference the -latest version on each branch; the gitlink:git-branch[1] command shows +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: ------------------------------------------------ @@ -91,7 +103,7 @@ the project referred to by that branch head. Most projects also use <<def_tag,tags>>. Tags, like heads, are references into the project's history, and can be listed using the -gitlink:git-tag[1] command: +linkgit:git-tag[1] command: ------------------------------------------------ $ git tag -l @@ -111,14 +123,14 @@ Tags are expected to always point at the same version of a project, while heads are expected to advance as development progresses. Create a new branch head pointing to one of these versions and check it -out using gitlink:git-checkout[1]: +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 gitlink:git-branch[1] shows two +when it was tagged v2.6.13, and linkgit:git-branch[1] shows two branches, with an asterisk marking the currently checked-out branch: ------------------------------------------------ @@ -144,44 +156,39 @@ Understanding History: Commits ------------------------------ Every change in the history of a project is represented by a commit. -The gitlink:git-show[1] command shows the most recent commit on the +The linkgit:git-show[1] command shows the most recent commit on the current branch: ------------------------------------------------ $ git show -commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2 -Author: Jamal Hadi Salim <hadi@cyberus.ca> -Date: Sat Dec 2 22:22:25 2006 -0800 - - [XFRM]: Fix aevent structuring to be more complete. - - aevents can not uniquely identify an SA. We break the ABI with this - patch, but consensus is that since it is not yet utilized by any - (known) application then it is fine (better do it now than later). - - Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca> - Signed-off-by: David S. Miller <davem@davemloft.net> - -diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt -index 8be626f..d7aac9d 100644 ---- a/Documentation/networking/xfrm_sync.txt -+++ b/Documentation/networking/xfrm_sync.txt -@@ -47,10 +47,13 @@ aevent_id structure looks like: - - struct xfrm_aevent_id { - struct xfrm_usersa_id sa_id; -+ xfrm_address_t saddr; - __u32 flags; -+ __u32 reqid; - }; -... +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 -"SHA1 id", shown on the first line of the "git show" output. You can usually +"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 @@ -191,7 +198,7 @@ has that commit at all). Since the object name is computed as a hash over the contents of the commit, you are guaranteed that the commit can never change without its name also changing. -In fact, in <<git-internals>> we shall see that everything stored in git +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. @@ -211,13 +218,13 @@ representing a merge can therefore have more than one parent, with each parent representing the most recent commit on one of the lines of development leading to that point. -The best way to see how this works is using the gitlink:gitk[1] +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 descendent of X, or that there is a chain of parents +that Y is a descendant of X, or that there is a chain of parents leading from commit Y to commit X. [[history-diagrams]] @@ -300,7 +307,7 @@ ref: refs/heads/master Examining an old version without creating a new branch ------------------------------------------------------ -The git-checkout command normally expects a branch head, but will also +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: @@ -313,7 +320,7 @@ If you want to create a new branch from this checkout, you may do so HEAD is now at 427abfa... Linux v2.6.17 ------------------------------------------------ -The HEAD then refers to the SHA1 of the commit instead of to a branch, +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: ------------------------------------------------ @@ -338,7 +345,7 @@ The "master" branch that was created at the time you cloned is a copy of the HEAD in the repository that you cloned from. That repository may also have had other branches, though, and your local repository keeps branches which track each of those remote branches, which you -can view using the "-r" option to gitlink:git-branch[1]: +can view using the "-r" option to linkgit:git-branch[1]: ------------------------------------------------ $ git branch -r @@ -378,6 +385,11 @@ shorthand: 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". @@ -385,9 +397,9 @@ 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 gitlink:git-rev-parse[1]. +REVISIONS" section of linkgit:git-rev-parse[1]. -[[Updating-a-repository-with-git-fetch]] +[[Updating-a-repository-With-git-fetch]] Updating a repository with git fetch ------------------------------------ @@ -405,7 +417,7 @@ Fetching branches from other repositories ----------------------------------------- You can also track branches from repositories other than the one you -cloned from, using gitlink:git-remote[1]: +cloned from, using linkgit:git-remote[1]: ------------------------------------------------- $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git @@ -441,7 +453,7 @@ $ cat .git/config This is what causes git to track the remote's branches; you may modify or delete these configuration options by editing .git/config with a text editor. (See the "CONFIGURATION FILE" section of -gitlink:git-config[1] for details.) +linkgit:git-config[1] for details.) [[exploring-git-history]] Exploring git history @@ -449,7 +461,7 @@ Exploring git history Git is best thought of as a tool for storing the history of a collection of files. It does this by storing compressed snapshots of -the contents of a file heirarchy, together with "commits" which show +the 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 @@ -466,7 +478,7 @@ Suppose version 2.6.18 of your project worked, but the version at "master" crashes. Sometimes the best way to find the cause of such a regression is to perform a brute-force search through the project's history to find the particular commit that caused the problem. The -gitlink:git-bisect[1] command can help you do this: +linkgit:git-bisect[1] command can help you do this: ------------------------------------------------- $ git bisect start @@ -477,10 +489,10 @@ Bisecting: 3537 revisions left to test after this ------------------------------------------------- If you run "git branch" at this point, you'll see that git has -temporarily moved you to a new branch named "bisect". This branch -points to a commit (with commit id 65934...) that is reachable from -v2.6.19 but not from v2.6.18. Compile and test it, and see whether -it crashes. Assume it does crash. Then: +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 @@ -495,17 +507,16 @@ half each time. After about 13 tests (in this case), it will output the commit id of the guilty commit. You can then examine the commit with -gitlink:git-show[1], find out who wrote it, and mail them your bug +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 and delete the -temporary "bisect" branch. +to return you to the branch you were on before. -Note that the version which git-bisect checks out for you at each +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; @@ -516,7 +527,7 @@ $ git bisect visualize ------------------------------------------------- which will run gitk and label the commit it chose with a marker that -says "bisect". Chose a safe-looking commit nearby, note its commit +says "bisect". Choose a safe-looking commit nearby, note its commit id, and check it out with: ------------------------------------------------- @@ -526,6 +537,22 @@ $ 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 -------------- @@ -541,7 +568,7 @@ We have seen several ways of naming commits already: - HEAD: refers to the head of the current branch There are many more; see the "SPECIFYING REVISIONS" section of the -gitlink:git-rev-parse[1] man page for the complete list of ways to +linkgit:git-rev-parse[1] man page for the complete list of ways to name revisions. Some examples: ------------------------------------------------- @@ -565,11 +592,11 @@ 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 +`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 +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 ------------------------------------------------- @@ -582,7 +609,7 @@ When we discuss merges we'll also see the special name MERGE_HEAD, which refers to the other branch that we're merging in to the current branch. -The gitlink:git-rev-parse[1] command is a low-level command that is +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: @@ -606,14 +633,14 @@ 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 gitlink:git-tag[1] man page +should create a tag object instead; see the linkgit:git-tag[1] man page for details. [[browsing-revisions]] Browsing revisions ------------------ -The gitlink:git-log[1] command can show lists of commits. On its +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: @@ -643,7 +670,7 @@ You can also ask git log to show patches: $ git log -p ------------------------------------------------- -See the "--pretty" option in the gitlink:git-log[1] man page for more +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 @@ -656,22 +683,29 @@ Generating diffs ---------------- You can generate diffs between any two versions using -gitlink:git-diff[1]: +linkgit:git-diff[1]: ------------------------------------------------- $ git diff master..test ------------------------------------------------- -Sometimes what you want instead is a set of patches: +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. Note that if master also has commits which are -not reachable from test, then the combined result of these patches -will not be the same as the diff produced by the git-diff example. +but not from master. [[viewing-old-file-versions]] Viewing old file versions @@ -705,7 +739,7 @@ $ git log --pretty=oneline origin..mybranch | wc -l ------------------------------------------------- Alternatively, you may often see this sort of thing done with the -lower-level command gitlink:git-rev-list[1], which just lists the SHA1's +lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's of all the given commits: ------------------------------------------------- @@ -763,7 +797,7 @@ You could just visually inspect the commits since e05db0fd: $ gitk e05db0fd.. ------------------------------------------------- -Or you can use gitlink:git-name-rev[1], which will give the commit a +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: @@ -772,7 +806,7 @@ $ git name-rev --tags e05db0fd e05db0fd tags/v1.5.0-rc1^0~23 ------------------------------------------------- -The gitlink:git-describe[1] command does the opposite, naming the +The linkgit:git-describe[1] command does the opposite, naming the revision using a tag on which the given commit is based: ------------------------------------------------- @@ -784,7 +818,7 @@ but that may sometimes help you guess which tags might come after the given commit. If you just want to verify whether a given tagged version contains a -given commit, you could use gitlink:git-merge-base[1]: +given commit, you could use linkgit:git-merge-base[1]: ------------------------------------------------- $ git merge-base e05db0fd v1.5.0-rc1 @@ -805,7 +839,7 @@ $ git log v1.5.0-rc1..e05db0fd will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, because it outputs only commits that are not reachable from v1.5.0-rc1. -As yet another alternative, the gitlink:git-show-branch[1] command lists +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 @@ -838,7 +872,7 @@ 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 -gitlink:git-show-ref[1]: +linkgit:git-show-ref[1]: ------------------------------------------------- $ git show-ref --heads @@ -875,14 +909,14 @@ commits reachable from some head but not from any tag in the repository: $ gitk $( git show-ref --heads ) --not $( git show-ref --tags ) ------------------------------------------------- -(See gitlink:git-rev-parse[1] for explanations of commit-selecting +(See linkgit:git-rev-parse[1] for explanations of commit-selecting syntax such as `--not`.) [[making-a-release]] Creating a changelog and tarball for a software release ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The gitlink:git-archive[1] command can create a tar or zip archive from +The linkgit:git-archive[1] command can create a tar or zip archive from any version of a project; for example: ------------------------------------------------- @@ -890,7 +924,7 @@ $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz ------------------------------------------------- will use HEAD to produce a tar archive in which each filename is -preceded by "prefix/". +preceded by "project/". If you're releasing a new version of a software project, you may want to simultaneously make a changelog to include in the release @@ -921,24 +955,24 @@ echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new" and then he just cut-and-pastes the output commands after verifying that they look OK. -[[Finding-comments-with-given-content]] +[[Finding-comments-With-given-Content]] Finding commits referencing a file with given content ------------------------------------------------------ +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Somebody hands you a copy of a file, and asks which commits modified a file such that it contained the given content either before or after the commit. You can find out with this: ------------------------------------------------- -$ git log --raw -r --abbrev=40 --pretty=oneline -- filename | +$ 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 gitlink:git-log[1], gitlink:git-diff-tree[1], and -gitlink:git-hash-object[1] man pages may prove helpful. +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]] Developing with git =================== @@ -956,7 +990,7 @@ file named .gitconfig in your home directory: email = you@yourdomain.example.com ------------------------------------------------ -(See the "CONFIGURATION FILE" section of gitlink:git-config[1] for +(See the "CONFIGURATION FILE" section of linkgit:git-config[1] for details on the configuration file.) @@ -975,7 +1009,7 @@ $ git init If you have some initial content (say, a tarball): ------------------------------------------------- -$ tar -xzvf project.tar.gz +$ tar xzvf project.tar.gz $ cd project $ git init $ git add . # include everything below ./ in the first commit: @@ -1041,7 +1075,7 @@ 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. +you run `git add` on the file again. When you're ready, just run @@ -1070,7 +1104,7 @@ about to commit: ------------------------------------------------- $ git diff --cached # difference between HEAD and the index; what - # would be commited if you ran "commit" now. + # 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. @@ -1079,6 +1113,11 @@ $ git diff HEAD # difference between HEAD and working tree; what $ 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 ----------------------------- @@ -1097,23 +1136,17 @@ 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 +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 .`" and "`git commit -a`" practically useless, and they keep -showing up in the output of "`git status`", etc. +`git add .` practically useless, and they keep showing up in the output of +`git status`. -Git therefore provides "exclude patterns" for telling git which files to -actively ignore. Exclude patterns are thoroughly explained in the -gitlink:gitignore[5] manual page, but the heart of the concept is simply -a list of files which git should ignore. Entries in the list may contain -globs to specify multiple files, or may be prefixed by "`!`" to -explicitly include (un-ignore) a previously excluded (ignored) file -(i.e. later exclude patterns override earlier ones). The following -example should illustrate such patterns: +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 foo.txt. +# Ignore any file named foo.txt. foo.txt # Ignore (generated) html files, *.html @@ -1123,48 +1156,27 @@ foo.txt *.[oa] ------------------------------------------------- -The next question is where to put these exclude patterns so that git can -find them. Git looks for exclude patterns in the following files: - -`.gitignore` files in your working tree::: - You may store multiple `.gitignore` files at various locations in your - working tree. Each `.gitignore` file is applied to the directory where - it's located, including its subdirectories. Furthermore, the - `.gitignore` files can be tracked like any other files in your working - tree; just do a "`git add .gitignore`" and commit. `.gitignore` is - therefore the right place to put exclude patterns that are meant to - be shared between all project participants, such as build output files - (e.g. `\*.o`), etc. -`.git/info/exclude` in your repo::: - Exclude patterns in this file are applied to the working tree as a - whole. Since the file is not located in your working tree, it does - not follow push/pull/clone like `.gitignore` can do. This is therefore - the place to put exclude patterns that are local to your copy of the - repo (i.e. 'not' shared between project participants), such as - temporary backup files made by your editor (e.g. `\*~`), etc. -The file specified by the `core.excludesfile` config directive::: - By setting the `core.excludesfile` config directive you can tell git - where to find more exclude patterns (see gitlink:git-config[1] for - more information on configuration options). This config directive - can be set in the per-repo `.git/config` file, in which case the - exclude patterns will apply to that repo only. Alternatively, you - can set the directive in the global `~/.gitconfig` file to apply - the exclude pattern to all your git repos. As with the above - `.git/info/exclude` (and, indeed, with git config directives in - general), this directive does not follow push/pull/clone, but remain - local to your repo(s). - -[NOTE] -In addition to the above alternatives, there are git commands that can take -exclude patterns directly on the command line. See gitlink:git-ls-files[1] -for an example of this. +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 -gitlink:git-merge[1]: +linkgit:git-merge[1]: ------------------------------------------------- $ git merge branchname @@ -1201,7 +1213,7 @@ the working tree in a special state that gives you all the information you need to help resolve the merge. Files with conflicts are marked specially in the index, so until you -resolve the problem and update the index, gitlink:git-commit[1] will +resolve the problem and update the index, linkgit:git-commit[1] will fail: ------------------------------------------------- @@ -1209,7 +1221,7 @@ $ git commit file.txt: needs merge ------------------------------------------------- -Also, gitlink:git-status[1] will list those files as "unmerged", and the +Also, linkgit:git-status[1] will list those files as "unmerged", and the files with conflicts will have conflict markers added, like this: ------------------------------------------------- @@ -1240,7 +1252,7 @@ Getting conflict-resolution help during a merge ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ All of the changes that git was able to merge automatically are -already added to the index file, so gitlink:git-diff[1] shows only +already added to the index file, so linkgit:git-diff[1] shows only the conflicts. It uses an unusual syntax: ------------------------------------------------- @@ -1257,7 +1269,7 @@ index 802992c,2b60207..0000000 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt ------------------------------------------------- -Recall that the commit which will be commited after we resolve this +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. @@ -1267,16 +1279,15 @@ these three "file stages" represents a different version of the file: ------------------------------------------------- $ git show :1:file.txt # the file in a common ancestor of both branches -$ git show :2:file.txt # the version from HEAD, but including any - # nonconflicting changes from MERGE_HEAD -$ git show :3:file.txt # the version from MERGE_HEAD, but including any - # nonconflicting changes from HEAD. +$ git show :2:file.txt # the version from HEAD. +$ git show :3:file.txt # the version from MERGE_HEAD. ------------------------------------------------- -Since the stage 2 and stage 3 versions have already been updated with -nonconflicting changes, the only remaining differences between them are -the important ones; thus gitlink:git-diff[1] can use the information in -the index to show only those conflicts. +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 @@ -1284,7 +1295,7 @@ each line by a single "+" or "-", it now uses two columns: the first column is used for differences between the first parent and the working directory copy, and the second for differences between the second parent and the working directory copy. (See the "COMBINED DIFF FORMAT" section -of gitlink:git-diff-files[1] for a details of the format.) +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: @@ -1317,7 +1328,7 @@ $ git diff -3 file.txt # diff against stage 3 $ git diff --theirs file.txt # same as the above. ------------------------------------------------- -The gitlink:git-log[1] and gitk[1] commands also provide special help +The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help for merges: ------------------------------------------------- @@ -1328,8 +1339,8 @@ $ 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 gitlink:git-mergetool[1], which lets you merge the -unmerged files using external tools such as emacs or kdiff3. +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: @@ -1338,7 +1349,7 @@ $ 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. +`git diff` will (by default) no longer show diffs for that file. [[undoing-a-merge]] Undoing a merge @@ -1351,7 +1362,7 @@ away, you can always return to the pre-merge state with $ git reset --hard HEAD ------------------------------------------------- -Or, if you've already commited the merge that you want to throw away, +Or, if you've already committed the merge that you want to throw away, ------------------------------------------------- $ git reset --hard ORIG_HEAD @@ -1393,7 +1404,7 @@ If you make a commit that you later wish you hadn't, there are two fundamentally different ways to fix the problem: 1. You can create a new commit that undoes whatever was done - by the previous commit. This is the correct thing if your + 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 @@ -1407,7 +1418,7 @@ Fixing a mistake with a new commit ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Creating a new commit that reverts an earlier change is very easy; -just pass the gitlink:git-revert[1] command a reference to the bad +just pass the linkgit:git-revert[1] command a reference to the bad commit; for example, to revert the most recent commit: ------------------------------------------------- @@ -1429,13 +1440,13 @@ with the changes to be reverted, then you will be asked to fix conflicts manually, just as in the case of <<resolving-a-merge, resolving a merge>>. -[[fixing-a-mistake-by-editing-history]] -Fixing a mistake by editing history +[[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>>. +<<undoing-a-merge,destroy it using `git reset`>>. Alternatively, you can edit the working directory and update the index to fix your @@ -1450,10 +1461,10 @@ which will replace the old commit by a new commit incorporating your changes, giving you a chance to edit the old commit message first. Again, you should never do this to a commit that may already have -been merged into another branch; use gitlink:git-revert[1] instead in +been merged into another branch; use linkgit:git-revert[1] instead in that case. -It is also possible to edit commits further back in the history, but +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>>. @@ -1463,7 +1474,7 @@ Checking out an old version of a file In the process of undoing a previous bad change, you may find it useful to check out an older version of a particular file using -gitlink:git-checkout[1]. We've used git checkout before to switch +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 @@ -1476,7 +1487,7 @@ also updates the index to match. It does not change branches. If you just want to look at an old version of the file, without modifying the working directory, you can do that with -gitlink:git-show[1]: +linkgit:git-show[1]: ------------------------------------------------- $ git show HEAD^:path/to/file @@ -1484,22 +1495,54 @@ $ 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 to much space on disk or in memory. +information from taking up too much space on disk or in memory. This compression is not performed automatically. Therefore you -should occasionally run gitlink:git-gc[1]: +should occasionally run linkgit:git-gc[1]: ------------------------------------------------- $ git gc ------------------------------------------------- to recompress the archive. This can be very time-consuming, so -you may prefer to run git-gc when you are not doing other work. +you may prefer to run `git gc` when you are not doing other work. [[ensuring-reliability]] @@ -1510,7 +1553,7 @@ Ensuring reliability Checking the repository for corruption ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The gitlink:git-fsck[1] command runs a number of self-consistency checks +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. The most common warning by far is about "dangling" objects: @@ -1528,18 +1571,8 @@ dangling tree b24c2473f1fd3d91352a624795be026d64c8841f ------------------------------------------------- Dangling objects are not a problem. At worst they may take up a little -extra disk space. They can sometimes provide a last-resort method of -recovery lost work--see <<dangling-objects>> for details. However, if -you want, you may remove them with gitlink:git-prune[1] or the --prune -option to gitlink:git-gc[1]: - -------------------------------------------------- -$ git gc --prune -------------------------------------------------- - -This may be time-consuming. Unlike most other git operations (including -git-gc when run without any options), it is not safe to prune while -other git operations are in progress in the same repository. +extra disk space. They can sometimes provide a last-resort method for +recovering lost work--see <<dangling-objects>> for details. [[recovering-lost-changes]] Recovering lost changes @@ -1549,7 +1582,7 @@ Recovering lost changes Reflogs ^^^^^^^ -Say you modify a branch with gitlink:git-reset[1] --hard, and then +Say you modify a branch with `linkgit:git-reset[1] --hard`, and then realize that the branch was the only reference you had to that point in history. @@ -1561,9 +1594,9 @@ old history using, for example, $ git log master@{1} ------------------------------------------------- -This lists the commits reachable from the previous version of the head. -This syntax can be used to with any git command that accepts a commit, -not just with git log. Some other examples: +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, @@ -1584,9 +1617,9 @@ 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 gitlink:git-reflog[1] and gitlink:git-gc[1] to learn +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 gitlink:git-rev-parse[1] for details. +section of linkgit:git-rev-parse[1] for details. Note that the reflog history is very different from normal git history. While normal history is shared by every repository that works on the @@ -1601,7 +1634,7 @@ 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 +commits in the dangling objects that `git fsck` reports. See <<dangling-objects>> for the details. ------------------------------------------------- @@ -1642,7 +1675,7 @@ dangling objects can arise in other situations. Sharing development with others =============================== -[[getting-updates-with-git-pull]] +[[getting-updates-With-git-pull]] Getting updates with git pull ----------------------------- @@ -1650,8 +1683,8 @@ After you clone a repository and make a few changes of your own, you may wish to check the original repository for updates and merge them into your own work. -We have already seen <<Updating-a-repository-with-git-fetch,how to -keep remote tracking branches up to date>> with gitlink:git-fetch[1], +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: @@ -1660,31 +1693,26 @@ $ git fetch $ git merge origin/master ------------------------------------------------- -However, the gitlink:git-pull[1] command provides a way to do this in +However, the linkgit:git-pull[1] command provides a way to do this in one step: ------------------------------------------------- $ git pull origin master ------------------------------------------------- -In fact, "origin" is normally the default repository to pull from, -and the default branch is normally the HEAD of the remote repository, -so often you can accomplish the above with just +In fact, if you have "master" checked out, then by default "git pull" +merges from the HEAD branch of the origin repository. So often you can +accomplish the above with just a simple ------------------------------------------------- $ git pull ------------------------------------------------- -See the descriptions of the branch.<name>.remote and branch.<name>.merge -options in gitlink:git-config[1] to learn how to control these defaults -depending on the current branch. Also note that the --track option to -gitlink:git-branch[1] and gitlink:git-checkout[1] can be used to -automatically set the default remote branch to pull from at the time -that a branch is created: - -------------------------------------------------- -$ git checkout --track -b maint origin/maint -------------------------------------------------- +More generally, a branch that is created from a remote 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 @@ -1694,7 +1722,7 @@ repository that you pulled from. <<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, +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 @@ -1712,7 +1740,7 @@ Submitting patches to a project If you just have a few changes, the simplest way to submit them may just be to send them as patches in email: -First, use gitlink:git-format-patch[1]; for example: +First, use linkgit:git-format-patch[1]; for example: ------------------------------------------------- $ git format-patch origin @@ -1723,7 +1751,7 @@ for each patch in the current branch but not in origin/HEAD. You can then import these into your mail client and send them by hand. However, if you have a lot to send at once, you may prefer to -use the gitlink:git-send-email[1] script to automate the process. +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. @@ -1731,7 +1759,7 @@ prefer such patches be handled. Importing patches to a project ------------------------------ -Git also provides a tool called gitlink:git-am[1] (am stands for +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 @@ -1764,15 +1792,16 @@ taken from the message containing each patch. 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 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. +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 accepts repository URLs as arguments will also accept a +commands that accept repository URLs as arguments will also accept a local directory name: ------------------------------------------------- @@ -1780,6 +1809,15 @@ $ 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 @@ -1802,12 +1840,14 @@ like this: | 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 +first create a new clone of the repository and tell `git daemon` that it is meant to be public: ------------------------------------------------- @@ -1830,19 +1870,19 @@ 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 +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 gitlink:git-daemon[1]; it will +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 +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 -gitlink:git-daemon[1] man page for details. (See especially the +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]] @@ -1860,15 +1900,14 @@ 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 -$ chmod a+x hooks/post-update +$ mv hooks/post-update.sample hooks/post-update ------------------------------------------------- (For an explanation of the last two lines, see -gitlink:git-update-server-info[1], and the documentation -link:hooks.html[Hooks used by git].) +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 commandline like: +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 @@ -1889,7 +1928,7 @@ maintainers to fetch your latest changes, but they do not allow write access, which you will need to update the public repository with the latest changes created in your private repository. -The simplest way to do this is using gitlink:git-push[1] and ssh; to +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 @@ -1903,17 +1942,17 @@ or just $ git push ssh://yourserver.com/~you/proj.git master ------------------------------------------------- -As with git-fetch, git-push will complain if this does not result in -a <<fast-forwards,fast forward>>. Normally this is a sign of -something wrong. However, if you are sure you know what you're -doing, you may force git-push to perform the update anyway by -proceeding the branch name by a plus sign: +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. -------------------------------------------------- -$ git push ssh://yourserver.com/~you/proj.git +master -------------------------------------------------- +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 the working tree +will not be updated by the push. This may lead to unexpected results if +the branch you push to is the currently checked-out branch! -As with git-fetch, you may also set up configuration options to +As with `git fetch`, you may also set up configuration options to save typing; so, for example, after ------------------------------------------------- @@ -1930,9 +1969,55 @@ $ git push public-repo master ------------------------------------------------- See the explanations of the remote.<name>.url, branch.<name>.remote, -and remote.<name>.push options in gitlink:git-config[1] for +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 +------------------------------------------------- + +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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -1940,7 +2025,7 @@ Setting up a shared repository Another way to collaborate is by using a model similar to that commonly used in CVS, where several developers with special rights all push to and pull from a single shared repository. See -link:cvs-migration.html[git for CVS users] for instructions on how to +linkgit:gitcvs-migration[7] for instructions on how to set this up. However, while there is nothing wrong with git's support for shared @@ -1951,7 +2036,7 @@ 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 + 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. @@ -2006,13 +2091,14 @@ $ cd work ------------------------------------------------- Linus's tree will be stored in the remote branch named origin/master, -and can be updated using gitlink:git-fetch[1]; you can track other -public trees using gitlink:git-remote[1] to set up a "remote" and -git-fetch[1] to keep them up-to-date; see <<repositories-and-branches>>. +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 gitlink:git-branch[1]) to merge changes in from +the --track option to linkgit:git-branch[1]) to merge changes in from Linus by default. ------------------------------------------------- @@ -2020,7 +2106,7 @@ $ git branch --track test origin/master $ git branch --track release origin/master ------------------------------------------------- -These can be easily kept up to date using gitlink:git-pull[1] +These can be easily kept up to date using linkgit:git-pull[1]. ------------------------------------------------- $ git checkout test && git pull @@ -2035,7 +2121,7 @@ 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 gitlink:git-config[1]) can +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>>.) @@ -2049,7 +2135,7 @@ EOF ------------------------------------------------- Then you can push both the test and release trees using -gitlink:git-push[1]: +linkgit:git-push[1]: ------------------------------------------------- $ git push mytree @@ -2109,10 +2195,10 @@ 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 +$ git log linux..branchname | git shortlog ------------------------------------------------- -To see whether it has already been merged into the test or release branches +To see whether it has already been merged into the test or release branches, use: ------------------------------------------------- @@ -2125,12 +2211,12 @@ or $ git log release..branchname ------------------------------------------------- -(If this branch has not yet been merged you will see some log entries. +(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. +"origin/master" branch), the branch for this change is no longer needed. You detect this when the output from: ------------------------------------------------- @@ -2174,9 +2260,9 @@ test|release) git checkout $1 && git pull . origin ;; origin) - before=$(cat .git/refs/remotes/origin/master) + before=$(git rev-parse refs/remotes/origin/master) git fetch origin - after=$(cat .git/refs/remotes/origin/master) + after=$(git rev-parse refs/remotes/origin/master) if [ $before != $after ] then git log $before..$after | git shortlog @@ -2201,11 +2287,10 @@ usage() exit 1 } -if [ ! -f .git/refs/heads/"$1" ] -then +git show-ref -q --verify -- refs/heads/"$1" || { echo "Can't see branch <$1>" 1>&2 usage -fi +} case "$2" in test|release) @@ -2236,7 +2321,7 @@ then git log test..release fi -for branch in `ls .git/refs/heads` +for branch in `git show-ref --heads | sed 's|^.*/||'` do if [ $branch = test -o $branch = release ] then @@ -2319,7 +2404,7 @@ 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 +Keeping a patch series up to date using git rebase -------------------------------------------------- Suppose that you create a branch "mywork" on a remote-tracking branch @@ -2363,7 +2448,7 @@ the result would create a new merge commit, like this: However, if you prefer to keep the history in mywork a simple series of commits without any merges, you may instead choose to use -gitlink:git-rebase[1]: +linkgit:git-rebase[1]: ------------------------------------------------- $ git checkout mywork @@ -2371,7 +2456,7 @@ $ git rebase origin ------------------------------------------------- This will remove each of your commits from mywork, temporarily saving -them as patches (in a directory named ".dotest"), update mywork to +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: @@ -2383,9 +2468,9 @@ patches to the new mywork. The result will look like: ................................................ 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 +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 @@ -2393,18 +2478,18 @@ $ 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 +At any point you may use the `--abort` option to abort this process and return mywork to the state it had before you started the rebase: ------------------------------------------------- $ git rebase --abort ------------------------------------------------- -[[modifying-one-commit]] -Modifying a single commit +[[rewriting-one-commit]] +Rewriting a single commit ------------------------- -We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the +We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the most recent commit using ------------------------------------------------- @@ -2414,14 +2499,16 @@ $ git commit --amend which will replace the old commit by a new commit incorporating your changes, giving you a chance to edit the old commit message first. -You can also use a combination of this and gitlink:git-rebase[1] to edit -commits further back in your history. First, tag the problematic commit with +You can also use a combination of this and linkgit:git-rebase[1] to +replace a commit further back in your history and recreate the +intervening changes on top of it. First, tag the problematic commit +with ------------------------------------------------- $ git tag bad mywork~5 ------------------------------------------------- -(Either gitk or git-log may be useful for finding the commit.) +(Either gitk or `git log` may be useful for finding the commit.) Then check out that commit, edit it, and rebase the rest of the series on top of it (note that we could check out the commit on a temporary @@ -2450,7 +2537,7 @@ new commits having new object names. Reordering or selecting from a patch series ------------------------------------------- -Given one existing commit, the gitlink:git-cherry-pick[1] command +Given one existing commit, the linkgit:git-cherry-pick[1] command allows you to apply the change introduced by that commit and create a new commit that records it. So, for example, if "mywork" points to a series of patches on top of "origin", you might do something like: @@ -2460,12 +2547,14 @@ $ git checkout -b mywork-new origin $ gitk origin..mywork & ------------------------------------------------- -And browse through the list of patches in the mywork branch using gitk, +and browse through the list of patches in the mywork branch using gitk, applying them (possibly in a different order) to mywork-new using -cherry-pick, and possibly modifying them as you go using commit ---amend. +cherry-pick, and possibly modifying them as you go using `git commit --amend`. +The linkgit:git-gui[1] command may also help as it allows you to +individually select diff hunks for inclusion in the index (by +right-clicking on the diff hunk and choosing "Stage Hunk for Commit"). -Another technique is to use git-format-patch to create a series of +Another technique is to use `git format-patch` to create a series of patches, then reset the state to before the patches: ------------------------------------------------- @@ -2474,17 +2563,17 @@ $ git reset --hard origin ------------------------------------------------- Then modify, reorder, or eliminate patches as preferred before applying -them again with gitlink:git-am[1]. +them again with linkgit:git-am[1]. [[patch-series-tools]] Other tools ----------- -There are numerous other tools, such as stgit, which exist for the +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]] Problems with rewriting history ------------------------------- @@ -2533,6 +2622,72 @@ 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 ========================== @@ -2541,7 +2696,7 @@ Advanced branch management Fetching individual branches ---------------------------- -Instead of using gitlink:git-remote[1], you can also choose just +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: @@ -2570,8 +2725,8 @@ master branch. In more detail: 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 +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>>. @@ -2632,7 +2787,7 @@ Configuring remote branches We saw above that "origin" is just a shortcut to refer to the repository that you originally cloned from. This information is stored in git configuration variables, which you can see using -gitlink:git-config[1]: +linkgit:git-config[1]: ------------------------------------------------- $ git config -l @@ -2681,200 +2836,211 @@ $ git config remote.example.fetch +master:ref/remotes/example/master ------------------------------------------------- Don't do this unless you're sure you won't mind "git fetch" possibly -throwing away commits on mybranch. +throwing away commits on 'example/master'. Also note that all of the above configuration can be performed by directly editing the file .git/config instead of using -gitlink:git-config[1]. +linkgit:git-config[1]. -See gitlink:git-config[1] for more details on the configuration +See linkgit:git-config[1] for more details on the configuration options mentioned above. -[[git-internals]] -Git internals -============= +[[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. -Git depends on two fundamental abstractions: the "object database", and -the "current directory cache" aka "index". +We start with the most important, the <<def_object_database,object +database>> and the <<def_index,index>>. [[the-object-database]] The Object Database ------------------- -The object database is literally just a content-addressable collection -of objects. All objects are named by their content, which is -approximated by the SHA1 hash of the object itself. Objects may refer -to other objects (by referencing their SHA1 hash), and so you can -build up a hierarchy of objects. -All objects have a statically determined "type" which is -determined at object creation time, and which identifies the format of -the object (i.e. how it is used, and how it can refer to other -objects). There are currently four different object types: "blob", -"tree", "commit", and "tag". +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. -A <<def_blob_object,"blob" object>> cannot refer to any other object, -and is, as the name implies, a pure storage object containing some -user data. It is used to actually store the file data, i.e. a blob -object is associated with some particular version of some file. - -A <<def_tree_object,"tree" object>> is an object that ties one or more -"blob" objects into a directory structure. In addition, a tree object -can refer to other tree objects, thus creating a directory hierarchy. - -A <<def_commit_object,"commit" object>> ties such directory hierarchies -together into a <<def_DAG,directed acyclic graph>> of revisions - each -"commit" is associated with exactly one tree (the directory hierarchy at -the time of the commit). In addition, a "commit" refers to one or more -"parent" commit objects that describe the history of how we arrived at -that directory hierarchy. - -As a special case, a commit object with no parents is called the "root" -commit, and is the point of an initial project commit. Each project -must have at least one root, and while you can tie several different -root objects together into one project by creating a commit object which -has two or more separate roots as its ultimate parents, that's probably -just going to confuse people. So aim for the notion of "one root object -per project", even if git itself does not enforce that. - -A <<def_tag_object,"tag" object>> symbolically identifies and can be -used to sign other objects. It contains the identifier and type of -another object, a symbolic name (of course!) and, optionally, a -signature. +The object types in some more detail: -Regardless of object type, all objects share the following -characteristics: they are all deflated with zlib, and have a header -that not only specifies their type, but also provides size information -about the data in the object. It's worth noting that the SHA1 hash -that is used to name the object is the hash of the original data -plus this header, so `sha1sum` 'file' does not match the object name -for 'file'. -(Historical note: in the dawn of the age of git the hash -was the sha1 of the 'compressed' object.) +[[commit-object]] +Commit 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> {plus} <space> {plus} <ascii decimal -size> {plus} <byte\0> {plus} <binary object data>. +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: -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). +------------------------------------------------ +$ 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 -The object types in some more detail: + 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 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 ------------ +~~~~~~~~~~~ -A "blob" object is nothing but a binary blob of data, and doesn't -refer to anything else. There is no signature or any other -verification of the data, so while the object is consistent (it 'is' -indexed by its sha1 hash, so the data itself is certainly correct), it -has absolutely no other attributes. No name associations, no -permissions. It is purely a blob of data (i.e. normally "file -contents"). +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: -In particular, since the blob is entirely defined by its data, if two -files in a directory tree (or in multiple different versions of the -repository) have the same contents, they will share the same blob -object. The object is totally independent of its location in the -directory tree, and renaming a file does not change the object that -file is associated with in any way. +------------------------------------------------ +$ git show 6ff87c4664 -A blob is typically created when gitlink:git-update-index[1] -is run, and its data can be accessed by gitlink:git-cat-file[1]. + 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. +... +------------------------------------------------ -[[tree-object]] -Tree Object ------------ +A "blob" object is nothing but a binary blob of data. It doesn't refer +to anything else or have attributes of any kind. -The next hierarchical object type is the "tree" object. A tree object -is a list of mode/name/blob data, sorted by name. Alternatively, the -mode data may specify a directory mode, in which case instead of -naming a blob, that name is associated with another TREE object. - -Like the "blob" object, a tree object is uniquely determined by the -set contents, and so two separate but identical trees will always -share the exact same object. This is true at all levels, i.e. it's -true for a "leaf" tree (which does not refer to any other trees, only -blobs) as well as for a whole subdirectory. - -For that reason a "tree" object is just a pure data abstraction: it -has no history, no signatures, no verification of validity, except -that since the contents are again protected by the hash itself, we can -trust that the tree is immutable and its contents never change. - -So you can trust the contents of a tree to be valid, the same way you -can trust the contents of a blob, but you don't know where those -contents 'came' from. - -Side note on trees: since a "tree" object is a sorted list of -"filename+content", you can create a diff between two trees without -actually having to unpack two trees. Just ignore all common parts, -and your diff will look right. In other words, you can effectively -(and efficiently) tell the difference between any two random trees by -O(n) where "n" is the size of the difference, rather than the size of -the tree. - -Side note 2 on trees: since the name of a "blob" depends entirely and -exclusively on its contents (i.e. there are no names or permissions -involved), you can see trivial renames or permission changes by -noticing that the blob stayed the same. However, renames with data -changes need a smarter "diff" implementation. - -A tree is created with gitlink:git-write-tree[1] and -its data can be accessed by gitlink:git-ls-tree[1]. -Two trees can be compared with gitlink:git-diff-tree[1]. +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. -[[commit-object]] -Commit Object -------------- - -The "commit" object is an object that introduces the notion of -history into the picture. In contrast to the other objects, it -doesn't just describe the physical state of a tree, it describes how -we got there, and why. - -A "commit" is defined by the tree-object that it results in, the -parent commits (zero, one or more) that led up to that point, and a -comment on what happened. Again, a commit is not trusted per se: -the contents are well-defined and "safe" due to the cryptographically -strong signatures at all levels, but there is no reason to believe -that the tree is "good" or that the merge information makes sense. -The parents do not have to actually have any relationship with the -result, for example. - -Note on commits: unlike some SCM's, commits do not contain -rename information or file mode change information. All of that is -implicit in the trees involved (the result tree, and the result trees -of the parents), and describing that makes no sense in this idiotic -file manager. - -A commit is created with gitlink:git-commit-tree[1] and -its data can be accessed by gitlink:git-cat-file[1]. +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 ------ +~~~~~ -An aside on the notion of "trust". Trust is really outside the scope -of "git", but it's worth noting a few things. First off, since -everything is hashed with SHA1, you 'can' trust that an object is -intact and has not been messed with by external sources. So the name -of an object uniquely identifies a known state - just not a state that -you may want to trust. +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. -Furthermore, since the SHA1 signature of a commit refers to the -SHA1 signatures of the tree it is associated with and the signatures -of the parent, a single named commit specifies uniquely a whole set -of history, with full contents. You can't later fake any step of the -way once you have the name of a commit. +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 @@ -2883,7 +3049,7 @@ that you trust that commit, and the immutability of the history of commits tells others that they can trust the whole history. In other words, you can easily validate a whole archive by just -sending out a single email that tells the people the name (SHA1 hash) +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. @@ -2891,103 +3057,651 @@ 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. -Git provides the "tag" object to simplify creating, managing and -exchanging symbolic and signed tokens. The "tag" object at its -simplest simply symbolically identifies another object by containing -the sha1, type and symbolic name. +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. -However it can optionally contain additional signature information -(which git doesn't care about as long as there's less than 8k of -it). This can then be verified externally to git. +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). -Note that despite the tag features, "git" itself only handles content -integrity; the trust framework (and signature provision and -verification) has to come from outside. +Before starting, verify that there is corruption, and figure out where +it is with linkgit:git-fsck[1]; this may be time-consuming. -A tag is created with gitlink:git-mktag[1], -its data can be accessed by gitlink:git-cat-file[1], -and the signature can be verified by -gitlink:git-verify-tag[1]. +Assume the output looks like this: +------------------------------------------------ +$ git fsck --full +broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 + to blob 4b9458b3786228369c63936db65827de3cc06200 +missing blob 4b9458b3786228369c63936db65827de3cc06200 +------------------------------------------------ + +(Typically there will be some "dangling object" messages too, but they +aren't interesting.) + +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 preceding version of the file was +"newsha", and that the immediately following 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" aka "Current Directory Cache" ------------------------------------------ +The index +----------- -The index is a simple binary file, which contains an efficient -representation of the contents of a virtual directory. It -does so by a simple array that associates a set of names, dates, -permissions and content (aka "blob") objects together. The cache is -always kept ordered by name, and names are unique (with a few very -specific rules) at any point in time, but the cache has no long-term -meaning, and can be partially updated at any time. - -In particular, the index certainly does not need to be consistent with -the current directory contents (in fact, most operations will depend on -different ways to make the index 'not' be consistent with the directory -hierarchy), but it has three very important attributes: - -'(a) it can re-generate the full state it caches (not just the -directory structure: it contains pointers to the "blob" objects so -that it can regenerate the data too)' - -As a special case, there is a clear and unambiguous one-way mapping -from a current directory cache to a "tree object", which can be -efficiently created from just the current directory cache without -actually looking at any other data. So a directory cache at any one -time uniquely specifies one and only one "tree" object (but has -additional data to make it easy to match up that tree object with what -has happened in the directory) - -'(b) it has efficient methods for finding inconsistencies between that -cached state ("tree object waiting to be instantiated") and the -current state.' - -'(c) it can additionally efficiently represent information about merge -conflicts between different tree objects, allowing each pathname to be +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.' +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 +------------------------------------------------- -Those are the ONLY three things that the directory cache does. It's a -cache, and the normal operation is to re-generate it completely from a -known tree object, or update/compare it with a live tree that is being -developed. If you blow the directory cache away entirely, you generally -haven't lost any information as long as you have the name of the tree -that it described. +Now use `git submodule update` to clone the repositories and check out the +commits specified in the superproject: -At the same time, the index is at the same time also the -staging area for creating new trees, and creating a new tree always -involves a controlled modification of the index file. In particular, -the index file can have the representation of an intermediate tree that -has not yet been instantiated. So the index can be thought of as a -write-back cache, which can contain dirty information that has not yet -been written back to the backing store. +------------------------------------------------- +$ 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' +------------------------------------------------- + +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. + +This is not the case if you did not commit your changes. + +[[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 to and from the index file. Either -from the database or from the working directory. Thus there are four -main combinations: +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 ~~~~~~~~~~~~~~~~~~~~~~~~~~ -You update the index with information from the working directory with -the gitlink:git-update-index[1] command. You -generally update the index information by just specifying the filename -you want to update, like so: +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 +$ git update-index filename ------------------------------------------------- but to avoid common mistakes with filename globbing etc, the command @@ -3001,16 +3715,19 @@ should use the `--remove` and `--add` flags respectively. NOTE! A `--remove` flag does 'not' mean that subsequent filenames will necessarily be removed: if the files still exist in your directory structure, the index will be updated with their new status, not -removed. The only thing `--remove` means is that update-cache will be +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 +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 ~~~~~~~~~~~~~~~~~~~~~~~~ @@ -3018,10 +3735,10 @@ index -> object database You write your current index file to a "tree" object with the program ------------------------------------------------- -$ git-write-tree +$ git write-tree ------------------------------------------------- -that doesn't come with any options - it will just write out the +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 @@ -3032,12 +3749,12 @@ 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 +populate (and overwrite--don't do this if your index contains any unsaved state that you might want to restore later!) your current index. Normal operation is just ------------------------------------------------- -$ git-read-tree <sha1 of tree> +$ git read-tree <SHA-1 of tree> ------------------------------------------------- and your index file will now be equivalent to the tree that you saved @@ -3052,7 +3769,7 @@ 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`). +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 @@ -3060,12 +3777,12 @@ index file with read-tree, and then you need to check out the result with ------------------------------------------------- -$ git-checkout-index filename +$ 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 +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. @@ -3078,9 +3795,9 @@ from one representation to the other: Tying it all together ~~~~~~~~~~~~~~~~~~~~~ -To commit a tree you have instantiated with "git-write-tree", you'd +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 +behind it--most notably the "parent" commits that preceded it in history. Normally a "commit" has one parent: the previous state of the tree @@ -3097,13 +3814,13 @@ 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> ..] +$ 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 +`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 @@ -3156,23 +3873,23 @@ Examining the data You can examine the data represented in the object database and the index with various helper tools. For every object, you can use -gitlink:git-cat-file[1] to examine details about the +linkgit:git-cat-file[1] to examine details about the object: ------------------------------------------------- -$ git-cat-file -t <objectname> +$ 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> +$ 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 +`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 @@ -3181,7 +3898,7 @@ follow the convention of having the top commit name in `.git/HEAD`, you can do ------------------------------------------------- -$ git-cat-file commit HEAD +$ git cat-file commit HEAD ------------------------------------------------- to see what the top commit was. @@ -3205,7 +3922,7 @@ To get the "base" for the merge, you first look up the common parent of two commits with ------------------------------------------------- -$ git-merge-base <commit1> <commit2> +$ git merge-base <commit1> <commit2> ------------------------------------------------- which will return you the commit they are both based on. You should @@ -3213,7 +3930,7 @@ now look up the "tree" objects of those commits, which you can easily do with (for example) ------------------------------------------------- -$ git-cat-file commit <commitname> | head -1 +$ git cat-file commit <commitname> | head -1 ------------------------------------------------- since the tree object information is always the first line in a commit @@ -3223,19 +3940,19 @@ 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 +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> +$ 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`. +`git write-tree`. [[merging-multiple-trees-2]] @@ -3243,31 +3960,31 @@ 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 +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` +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 +$ git read-tree -m $orig HEAD $target +$ git ls-files --unmerged 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c ------------------------------------------------ -Each line of the `git-ls-files --unmerged` output begins with -the blob mode bits, blob SHA1, 'stage number', and the +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 `$orig` tree, stage 2 `HEAD` tree, and stage3 `$target` tree. Earlier we said that trivial merges are done inside -`git-read-tree -m`. For example, if the file did not change +`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 `$target` the same way, obviously the final outcome is what is in `HEAD`. What the @@ -3278,9 +3995,9 @@ program, e.g. `diff3`, `merge`, or git's own merge-file, on the blob objects from these three stages yourself, like this: ------------------------------------------------ -$ 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 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 ------------------------------------------------ @@ -3291,171 +4008,62 @@ merge result for this file is by: ------------------------------------------------- $ mv -f hello.c~2 hello.c -$ git-update-index hello.c +$ git update-index hello.c ------------------------------------------------- -When a path is in unmerged state, running `git-update-index` for +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, uses three `git-cat-file` -for this. There is `git-merge-index` program that extracts the +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 +$ git merge-index git-merge-one-file hello.c ------------------------------------------------- and that is what higher level `git merge -s resolve` is implemented with. -[[pack-files]] -How git stores objects efficiently: pack files ----------------------------------------------- - -We've seen how git stores each object in a file named after the -object's SHA1 hash. - -Unfortunately this system becomes inefficient once a project has a -lot of objects. Try this on an old project: - ------------------------------------------------- -$ git count-objects -6930 objects, 47620 kilobytes ------------------------------------------------- - -The first number is the number of objects which are kept in -individual files. The second is the amount of space taken up by -those "loose" objects. - -You can save space and make git faster by moving these loose objects in -to a "pack file", which stores a group of objects in an efficient -compressed format; the details of how pack files are formatted can be -found in link:technical/pack-format.txt[technical/pack-format.txt]. - -To put the loose objects into a pack, just run git repack: - ------------------------------------------------- -$ git repack -Generating pack... -Done counting 6020 objects. -Deltifying 6020 objects. - 100% (6020/6020) done -Writing 6020 objects. - 100% (6020/6020) done -Total 6020, written 6020 (delta 4070), reused 0 (delta 0) -Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. ------------------------------------------------- - -You can then run - ------------------------------------------------- -$ git prune ------------------------------------------------- - -to remove any of the "loose" objects that are now contained in the -pack. This will also remove any unreferenced objects (which may be -created when, for example, you use "git reset" to remove a commit). -You can verify that the loose objects are gone by looking at the -.git/objects directory or by running - ------------------------------------------------- -$ git count-objects -0 objects, 0 kilobytes ------------------------------------------------- - -Although the object files are gone, any commands that refer to those -objects will work exactly as they did before. - -The gitlink:git-gc[1] command performs packing, pruning, and more for -you, so is normally the only high-level command you need. - -[[dangling-objects]] -Dangling objects ----------------- - -The gitlink:git-fsck[1] command will sometimes complain about dangling -objects. They are not a problem. - -The most common cause of dangling objects is that you've rebased a -branch, or you have pulled from somebody else who rebased a branch--see -<<cleaning-up-history>>. In that case, the old head of the original -branch still exists, as does 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 ------------------------------------------------- +[[hacking-git]] +Hacking git +=========== -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., +This chapter covers internal details of the git implementation which +probably only git developers need to understand. ------------------------------------------------- -$ 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. +[[object-details]] +Object storage format +--------------------- -Anyway, once you are sure that you're not interested in any dangling -state, you can just prune all unreachable objects: +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". ------------------------------------------------- -$ git prune ------------------------------------------------- +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.) -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. +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> {plus} <space> {plus} <ascii decimal +size> {plus} <byte\0> {plus} <binary object data>. -(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). +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 @@ -3478,7 +4086,7 @@ 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 "index", however, the +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. @@ -3521,20 +4129,20 @@ $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \ What does this mean? -`git-rev-list` is the original version of the revision walker, which +`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 programs start out as scripts using -`git-rev-list`. +`git rev-list`. -`git-rev-parse` is not as important any more; it was only used to filter out +`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 +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 +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 @@ -3544,7 +4152,7 @@ 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 of `cmd_log()`; call -`git-show v1.3.0~155^2~4` and scroll down to that function (note that you +`git show v1.3.0{tilde}155^2{tilde}4` and scroll down to that function (note that you no longer need to call `setup_pager()` directly). Nowadays, `git log` is a builtin, which means that it is _contained_ in the @@ -3590,7 +4198,7 @@ it does. ------------------------------------------------------------------ git_config(git_default_config); if (argc != 3) - usage("git-cat-file [-t|-s|-e|-p|<type>] <sha1>"); + usage("git cat-file [-t|-s|-e|-p|<type>] <sha1>"); if (get_sha1(argv[2], sha1)) die("Not a valid object name %s", argv[2]); ------------------------------------------------------------------ @@ -3604,7 +4212,7 @@ Two things are interesting here: - `get_sha1()` returns 0 on _success_. This might surprise some new Git hackers, but there is a long tradition in UNIX to return different - negative numbers in case of different errors -- and 0 on success. + negative numbers in case of different errors--and 0 on success. - the variable `sha1` in the function signature of `get_sha1()` is `unsigned char \*`, but is actually expected to be a pointer to `unsigned @@ -3667,7 +4275,10 @@ You see, Git is actually the best tool to find out about the source of Git itself! [[glossary]] -include::glossary.txt[] +GIT Glossary +============ + +include::glossary-content.txt[] [[git-quick-start]] Appendix A: Git Quick Reference @@ -3709,7 +4320,7 @@ $ git branch new # create branch "new" starting at current HEAD $ git branch -d new # delete branch "new" ----------------------------------------------- -Instead of basing new branch on current HEAD (the default), use: +Instead of basing a new branch on current HEAD (the default), use: ----------------------------------------------- $ git branch new test # branch named "test" @@ -3755,7 +4366,9 @@ $ git remote show example # get details * remote example URL: git://example.com/project.git Tracked remote branches - master next ... + master + next + ... $ git fetch example # update branches from example $ git branch -r # list all remote branches ----------------------------------------------- @@ -3909,25 +4522,26 @@ Appendix B: Notes and todo list for this manual This is a work in progress. The basic requirements: - - It must be readable in order, from beginning to end, by - someone intelligent with a basic grasp of the unix - commandline, but without any special knowledge of git. If - necessary, any other prerequisites should be specifically - mentioned as they arise. - - Whenever possible, section headings should clearly describe - the task they explain how to do, in language that requires - no more knowledge than necessary: for example, "importing - patches into a project" rather than "the git-am command" + +- It must be readable in order, from beginning to end, by someone + intelligent with a basic grasp of the UNIX command line, but without + any special knowledge of git. If necessary, any other prerequisites + should be specifically mentioned as they arise. +- Whenever possible, section headings should clearly describe the task + they explain how to do, in language that requires no more knowledge + than necessary: for example, "importing patches into a project" rather + than "the `git am` command" Think about how to create a clear chapter dependency graph that will allow people to get to important topics without necessarily reading everything in between. Scan Documentation/ for other stuff left out; in particular: - howto's - some of technical/? - hooks - list of commands in gitlink:git[1] + +- howto's +- some of technical/? +- hooks +- list of commands in linkgit:git[1] Scan email archives for other stuff left out @@ -3955,4 +4569,6 @@ Write a chapter on using plumbing and writing scripts. Alternates, clone -reference, etc. -git unpack-objects -r for recovery +More on recovery from repository corruption. See: + http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2 + http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2 |