as promised, docs: git for the confused

As I mentioned with all my questions, I was writing up the answers I got. Here's the current status. If anyone would like to comment on its accuracy or usefulness, feedback is appreciated. I've tried to omit or skim very lightly over subjects I think are adequately explained in existing docs, unless that would leave an uncomfortable hole in the explanation. TODO: Describe the config file. It's a recent invention, and I haven't found a good description of its contents. "I Don't Git It" Git for the confused Git is hardly lacking in documentation, but coming at it fresh, I found it somewhat confusing. Git is a toolkit in the Unix tradition. There are a number of primitives written in C, which are made friendly by a layer of shell scripts. These are known in git-speak, as the "plumbing" and the "porcelain", respectively. The porcelain should work and look nice. The plumbing should just deal with lots of crap efficiently. Much of git's documentation was first written to explain the plumbing to the people writing the porcelain. Since then, although the essentials haven't changed, porcelain has been added and conventions have been established that make it a lot more pleasant to deal with. Some commands have been changed or replaced, and it's not quite the same. Using the original low-level commands is now most likely more difficult than necessary, unless you want to do something not supported by the existing porcelain. This document retraces (with fewer false turns) how I learned my way around git. There are some concepts I didn't understand so well the first time through, and an overview of all the git commands, grouped by application. A good rule of thumb is that the commands with one-word names (git-diff, git-commit, git-merge, git-push, git-pull, git-status, git-tag, etc.) are designed for end-user use. Multi-word names (git-count-objects, git-write-tree, git-cat-file) are generally designed for use from a script. This isn't ironclad. The first command to start using git is git-init-db, and git-show-branch is pure porcelain, while git-mktag is a primitive. And you don't often run git-daemon by hand. But still, it's a useful guideline. * Background material. To start with, read "man git". Or Documentation/git.txt in the git source tree, which is the same thing. Particularly note the description of the index, which is where all the action in git happens. One thing that's confusing is why git allows you to have one version of a file in the current HEAD, a second version in the index, and possibly a third in the working directory. Why doesn't the index just contain a copy of the current HEAD until you commit a new one? The answer is merging, which does all its work in the index. Neither the object database nor the working directory let you have multiple files with the same name. The index is really very simple. It's a series of structures, each describing one file. There's an object ID (SHA1) of the contents, some file metadata to detect changes (time-stamps, inode number, size, permissions, owner, etc.), and the path name relative to the root of the working directory. It's always stored sorted by path name, for efficient merging. At (almost) any time, you can take a snapshot of the index and write it as a tree object. The only interesting feature is that each entry has a 2-bit stage number. Normally, this is always zero, but each path name is allowed up to three different versions (object IDs) in the index at once. This is used to represent an incomplete merge, and an unmerged index entry (with more than one version) prevents committing the index to the object database. * Terminology - heads, branches, refs, and revisions (This is a supplement to what's already in "man git".) The most common object needed by git primitives is a tree. Since a commit points to a tree and a tag points to a commit, both of these are acceptable "tree-ish" objects and can be used interchangeably. Likewise, a tag is "commit-ish" and can be used where a commit is required. As soon as you get to the porcelain, the most commonly used object is a commit. Also known as a revision, this is a tree plus a history. While you can always use the full object ID, you can also use a reference. A reference is a file that contains a 40-character hex SHA1 object ID (and a trailing newline). When you specify the name of a reference, it is searched for in one of the directories: .git/ (or $GIT_DIR) .git/refs/ (or $GIT_DIR/refs/) .git/refs/heads/ (or $GIT_DIR/refs/heads/) .git/refs/tags/ (or $GIT_DIR/refs/tags/) You may use subdirectories by including slashes in the reference name. There is no search order; if searching the above four path prefixes produces more than one match for the reference name (it's ambiguous), then the name is not valid. There is additional syntax (which looks like "commit~3^2~17") for specifying an ancestor of a given commit (or tag). This is documented in detail in the documentation for git-rev-parse. Briefly, commit^ is the parent of the given commit. commit^^ is the grandparent, etc.. If there is more than one ancestor (a merge), then they can be referenced as commit^1 (a synonym for commit^), commit^2, commit^3, etc. (commit^0 gives the commit object itself. A no-op if you're starting from a commit, but it lets you get the commit object from a tag object.) As long strings of ^ can be annoying, they can be abbreviated using ~ syntax. commit^^^ is the same as commit~3, ^^^^ is the same as ~4, etc. You can see lots of examples in the output of "git-show-branch". Now, the although the most primitive git tools don't care, a convention among all the porcelain is that the current head of development is .git/HEAD, a symbolic link to a reference under refs/heads/. git-init-db creates HEAD pointing to refs/heads/master, and that is traditionally the name used for the "main trunk" of development. Note that initially refs/heads/master doesn't exist - HEAD is a dangling symlink! This is okay, and will cause the initial commit to have zero parents. A "head" is mostly synonymous with a "branch", but the terms have different emphasis. The "head" is particularly the tip of the branch, where future development will be appended. A "branch" is the entire development history leading to the head. However, as far as git is concerned, they're both references to commit objects, referred to from refs/heads/. When you actually do more (with git-commit, or git-merge), then the current HEAD reference is overwritten with the new commit's id, and the old HEAD becomes HEAD^. Since HEAD is a symlink, it's the file in refs/heads/ that's actually overwritten. (See the git-update-ref documentation for further details.) The git-checkout command actually changes the HEAD symlink. git-checkout enforces the rule that it will only check out a branch under refs/heads. You can use refs/tags as a source for git-diff or any other command that only examines the revision, but if you want to check it out, you have to copy it to refs/heads. * Resetting The "undo" command for commits to the object database is git-reset. Like all deletion-type commands, be careful or you'll hurt yourself. Given a commit (using any of the syntaxes mentioned above), this sets the current HEAD to refer to the given commit. This does NOT alter the HEAD symlink (as git-checkout <branch> will do), but actually changes the reference pointed to by HEAD (e.g. refs/heads/master) to contain a new object ID. The classic example is to undo an erroneous commit, use "git-reset HEAD^". There are actually three kinds of git-reset: git-reset --soft: Only overwrite the reference. If you can find the old object ID, you can put everything back with a second git-reset --soft OLD_HEAD. git-reset --mixed: This is the default, which I always think of as "--medium". Overwrite the reference, and (using git-read-tree) read the commit into the index. The working directory is unchanged. git-reset --hard: Do everything --mixed does, and also check out the index into the working directory. This really erases all traces of the previous version. (One caveat: this will not delete any files in the working directory that were added as part of the changes being undone.) The space taken up by the abandoned commit won't actually be reclaimed until you collect garbage with git-prune. git-reset with no commit specified is "git-reset HEAD", which is much safer because the object reference is not actually changed. This can be used to undo changes in the index or working directory that you did not intend. Note, however, that it is not selective. "git-commit" has options for doing this selectively. Like being sure what directory you're in when typing "rm -r", think carefully about what branch you're on when typing "git-reset <commit>". There is an undelete: git-reset stores the previous HEAD commit in OLD_HEAD. And git-lost-found can find leftover commits until you do a git-prune. * Merging Merging is central to git operations. Indeed, a big difference between git and other version control systems is that git assumes that a change will be merged more often than it's written, as it's passed around different developers' repositories. Even "git checkout" is a merge. The heart of merging is git-read-tree, but if you can understand it from the man page, you're doing better than me. As mentioned, the index and the working directory versions of a file could both be different from the HEAD. Git lets you merge "under" your current working directory edits, as long as the merge doesn't change the files you're editing. There are some special cases of merging, but let me start with the procedure for the general 3-way merge case: merging branch B into branch A (the current HEAD). 1) Given two commits, find a common ancestor O to server as the origin of the merge. The basic "resolve" algorithm uses git-merge-base for the task, but the "recursive" merge strategy gets more clever in the case where there are multiple candidates. I won't got into what it does, but it does a pretty good job. 2) Add all three input trees (the Origin, A, and B) to the index by "git-read-tree -m O A B". The index now contains up to three copies of every file. (Four, including the original, but that is discarded before git-read-tree returns.) Then, for each file in the index, git-read-tree does the following: 2a) For each file, git-merge-tree tries to collapse the various versions into one using the "trivial in-index merge". This just uses the file blob object names to see if the file contents are identical, and if two or more of the three trees contain an identical copy of this file, it is merged. A missing (deleted) file matches another missing file. Note that this is NOT a majority vote. If A and B agree on the contents of the file, that's what is used. (Whether O agrees is irrelevant in this case.) But if O and A agree, then the change made in B is taken as the final value. Likewise, if O and B agree, then A is used. 2b) If this is possible, then a check is made to see if the merge would conflict with any uncommitted work in the index or change the index out from under a modified working directory file. If either of those cases happen, the entire merge is backed out and fails. (In the git source, the test "t/t1000-read-tree-m-3way.sh" has a particularly detailed description of the various cases.) If the merge is possible and safe, the versions are collapsed into one final result version. 2c) If all three versions differ, the trivial in-index merge is not possible, and the three source versions are left in the index unmerged. Again, if there was uncommitted work in the index or the working directory, the entire merge fails. 3) Use git-merge-index to iterate over the remaining unmerged files, and apply an intra-file merge. The intra-file merge is usually done with git-merge-one-file, which does a standard RCS-style three-way merge (see "man merge"). 4) Check out all the successfully merged files into the working directory. 5) If automatic merging was successful on every file, commit the merged version immediately and stop. 6) If automatic merging was not complete, then replace the working directory copies of any remaining unmerged files with a merged copy with conflict markers (again, just like RCS or CVS) in the working directory. All three source versions are available in the index for diffing against. (We have not destroyed anything, because in step 2c), we checked to make sure the working directory file didn't have anything not in the repository.) 7) Manually edit the conflicts and resolve the merge. As long as an unmerged, multi-version file exists in the index, committing the index is forbidden. (You can use the options to git-diff to see the changes.) 8) Commit the final merged version of the conflicting file(s), replacing the unmerged versions with the single finished version. Note that if the merge is simple, with no one file edited on both branches, git never has to open a single file. It reads three tree objects (recursively) and stat(2)s some working directory files to verify that they haven't changed. Also note that this aborts and backs out rather than overwrite anything not committed. You can merge "under" uncommitted edits only if those edits are to files not affected by the merge. * 2-way merging A "2-way merge" is basically a 3-way merge with the contents of the index as the "current HEAD", and the original HEAD as the Origin. However, this merge is designed only for simple cases and only supports the "trivial merge" cases. It does not fall back to an intra-file merge. [[ I'm not sure why it couldn't, I confess. For reversibility? Or just because it's likely to be too confusing. ]] This merge is used by git-checkout to switch between two branches, while preserving any changes in the working directory and index. Like the 3-way case, if a particular file hasn't changed between the two heads, then git will preserve any uncommitted edits. If the file has changed in any way, git doesn't try to perform any sort of intra-file merge, it just fails. * 1-way merging This is not actually used by the git-core porcelain, and so is only useful to someone writing more porcelain, but I'll describe it for completeness. Plain (non-merging) git-read-tree will overwrite the index entries with those from the tree. This invalidates the cached stat data, causing git to think all the working directory files are "potentially changed" until you do a git-update-index --refresh. By specifying a 1-way merge, any index entry whose contents (object ID) matches the incoming tree will have its cached stat data preserved. Thus, git will know if the working directory file is not changed, and will not overwrite if you execute git-checkout-index. This is purely an efficiency hack. * Special merges - already up to date, and fast-forward There are two cases of 3-way or 2-way merging that are special. Recall that the basic merge pattern is B--------> A+B / / / / O -----> A The two special cases arise if one of A or B is a direct ancestor of the other. In that case, the common ancestor of both A and B is the older of the two commits. And the merged result is simply the newer of the two, unchanged. Recalling that we are merging B into A, if B is a direct ancestor of A, then A already includes all of B. A is "already up to date" and not changed at all by the merge. The other case you'll hear mentioned, because it happens a lot when pulling, is when A is a direct ancestor of B. In this case, the result of the merge is a "fast-forward" to B. Both of these cases are handled very efficiently by the in-index merge done by git-read-tree. * Deleted files during merges There is one small wrinkle in git's merge algorithm that will probably never bite you, but I ought to explain anyway, just because it's so rare that it's difficult to discover it by experiment. The index contains a list of all files that git is tracking. If the index file is empty or missing and you do a commit, you write an empty tree with no files. When merging, if git finds no pre-existing index entry for a path it is trying to merge, it considers that to mean "status unknown" rather than "modified by being deleted". Thus, this is not uncommitted work in the index file, and does not block the merge. Instead, the file will reappear in the merge. This is because it is possible to blow away the index file (rm .git/index will do it quite nicely), and if this was considered a modification to be preserved, it would cause all sorts of conflicts. So the one change to the index that will NOT be preserved by a merge is the removal of a file. A missing index entry is treated the same as an unmodified index entry. The index will be updated, and when you check out the revision, the working directory file will be (re-)created. Note that none of this affects you in the usual case where you make changes in the working directory only, and leave the index equal to HEAD until you're ready to commit. * Packs Originally, git stored every object in its own file, and used rsync to share repositories. It was quickly discovered that this brought mighty servers to their knees. It's great for retrieving a small subset of the database the way git usually does, but rsync scans the whole .git/objects tree every time. So packs were developed. A pack is a file, built all at once, which contains many delta-compressed objects. With each .pack file, there's an accompanying .idx file that indexes the pack so that individual objects can be retrieved quickly. You can reduce the disk space used by your repositories by periodically repacking them with git-repack. Normally, this makes a new incremental pack of everything not already packed. With the -a flag, this repacks everything for even greater compression (but takes longer). The git wire protocol basically consists of negotiation over what objects needs to be transferred followed by sending a custom-built pack. The .idx file can be reconstructed from the .pack file, so it's never transferred. [[ Is once every few hundred commits a good rule of thumb for repacking? When .git/objects/?? reaches X megabytes? I think too many packs is itself a bad thing, since they all have to be searched. ]] * Raw diffs A major source of git's speed is that it tries to avoid accessing files unnecessarily. In particular, files can be compared based on their object IDs without needing to open and read them. As part of this, the responsibility for finding file differences (printing diffs) is divided into finding what files have changed, and finding the changes within those files. This is all explained in the Documentation/diffcore.txt in the git distribution, but the basics is that many of the primitives spit out a line like this: :100755 100755 68838f3fad1d22ab4f14977434e9ce73365fb304 0000000000000000000000000000000000000000 M git-bisect.sh when asked for a diff. This is known as a "raw diff". They can be told to generate a human-readable diff with the "-p" (patch) flag. The git-diff command includes this by default. * Advice on using git If you're used to CVS, where branches and merges are "advanced" features that you can go a long time, you need to learn to use branches in git a lot more. Branch early and often. Every time you think about developing a feature or fixing a bug, create a branch to do it on. In fact, avoid doing any development on the master branch. Merges only. A branch is the git equivalent of a patch, and merging a branch is the equivalent of applying that patch. A branch gives it a name that you can use to refer to it. This is particularly useful if you're sharing your changes. Once you're done with a branch, you can delete it. This is basically just removing the refs/heads/<branch> file, but "git-branch -d" adds a few extra safety checks. Assuming you merged the branch in, you can still find all the commits in the history, it's just the name that's been deleted. You can also rename a branch by renaming the refs/heads/branch file. There's no git command to do this, but as long as you update the HEAD symlink if necessary, you don't need one. Periodically merge all of the branches you're working on into a testing branch to see if everything works. Blow away and re-create the testing branch whenever you do this. When you like the result, merge them into the master. * The .git directory There are a number of files in the .git directory used by the porcelain. In case you're curious (I was), this is what they are: index - The actual index file. objects/ - The object database. Can be overridden by $GIT_OBJECT_DIRECTORY hooks/ - where the hook scripts are kept. The standard git template includes examples, but disabled by being marked non-executable. info/exclude - Default project-wide list of file patterns to exclude from notice. To this is added the per-directory list in .gitignore. See the git-ls-files docs for full details. refs/ - References to development heads (branches) and tags. remotes/ - Short names of remote repositories we pull from or push to. Details are in the "git-fetch" man page. HEAD - The current default development head. - Created by git-init-db and never deleted - Changed by git-checkout - Used by git-commit and any other command that commits changes. - May be a dangling pointer, in which case git-commit does an "initial checkin" with no parent. COMMIT_EDITMSG - Temp used by git-commit to edit a commit message. COMMIT_MSG - Temp used by git-commit to form a commit message, post-processed from COMMIT_EDITMSG. FETCH_HEAD - Just-fetched commits, to be merged into the local trunk. - Created by git-fetch. - Used by git-pull as the source of data to merge. MERGE_HEAD - Keeps track of what heads are currently being merged into HEAD. - Created by git-merge --no-commit with the heads used - Deleted by git-checkout and git-reset (since you're abandoning the merge) - Used by git-commit to supply additional parents to the current commit. (And deleted when done.) MERGE_MSG - Generated by git-merge --no-commit. - Used by git-commit as the commit message for a merge (If present, git-commit doesn't prompt.) MERGE_SAVE - cpio archive of all locally modified files created by "git-merge" before starting to do anything, if multiple merge strategies are being attempted. Used to rewind the tree in case a merge fails. ORIG_HEAD - Previous HEAD commit prior to a merge or reset operation. LAST_MERGE - Set by the "resolve" strategy to the most recently merged-in branch. Basically, a copy of MERGE_HEAD. Not used by the other merge strategies, and resolve is no longer the default, so its utility is very limited. BISECT_LOG - History of a git-bisect operation. - Can be replayed (or, more usefully, a prefix can) by "git-bisect replay" BISECT_NAMES - The list of files to be modified by git-bisect. - Set by "git-bisect start" TMP_HEAD (used by git-fetch) TMP_ALT (used by git-fetch) * Git command summary There are slightly over a hundred git commands. This section tries to classify them by purpose, so you can know which commands are intended to be used for what. You can always use the low-level plumbing directly, but that's inconvenient and error-prone. Helper programs (not for direct use) for a specific utility are shown indented under the program they help. Note that all of these can be invoked using the "git" wrapper by replacing the leading "git-" with "git ". The results are exactly the same. There is a suggestion to reduce the clutter in /usr/bin and move all the git binaries to their own directory, leaving just the git wrapper in /usr/bin. so you'll have to use it or adjust your $PATH. But that hasn't happened yet. In the meantime, including the hyphen makes tab-completion work. I include ".sh", ".perl", etc. suffixes to show what the programs are written in, so you can read those scripts written in languages you're familiar with. These are the names in the git source tree, but the suffix is not included in the /usr/bin copies. + Administrative commands git-init-db + Object database maintenance: git-convert-objects git-fsck-objects git-lost-found.sh git-prune.sh git-relink.perl + Pack maintenance git-count-objects.sh git-index-pack git-pack-objects git-pack-redundant git-prune-packed git-repack.sh git-show-index git-unpack-objects git-verify-pack + Important primitives git-commit-tree git-rev-list git-rev-parse + Useful primitives git-ls-files git-update-index + General script helpers (used only by scripts) git-cat-file git-check-ref-format git-checkout-index git-fmt-merge-msg.perl git-hash-object git-ls-tree git-repo-config git-unpack-file git-update-ref git-sh-setup.sh git-stripspace git-symbolic-ref git-var git-write-tree + Oddballs git-mv.perl + Code browsing git-diff.sh git-diff-files git-diff-index git-diff-tree git-diff-stages git-grep.sh git-log.sh git-name-rev git-shortlog.perl git-show-branch git-whatchanged.sh + Making local changes git-add.sh git-bisect.sh git-branch.sh git-checkout.sh git-commit.sh git-reset.sh git-status.sh + Cherry-picking git-cherry.sh git-patch-id git-cherry-pick.sh git-rebase.sh git-revert.sh + Accepting changes by e-mail git-apply git-am.sh git-mailinfo git-mailsplit git-applypatch.sh git-applymbox.sh + Publishing changes by e-mail git-format-patch.sh git-send-email.perl + Merging git-merge.sh git-merge-base git-merge-index git-merge-one-file.sh git-merge-octopus.sh git-merge-ours.sh git-merge-recursive.py git-merge-resolve.sh git-merge-stupid.sh git-read-tree git-resolve.sh git-octopus.sh + Making releases git-get-tar-commit-id git-tag.sh git-mktag git-tar-tree git-verify-tag.sh + Accepting changes by network git-clone.sh git-clone-pack git-fetch.sh git-fetch-pack git-local-fetch git-http-fetch git-ssh-fetch git-ls-remote.sh git-peek-remote git-parse-remote.sh git-pull.sh git-ssh-pull git-shell git-receive-pack + Publishing changes by network git-daemon git-push.sh git-http-push git-ssh-push git-ssh-upload git-request-pull.sh git-send-pack git-update-server-info git-upload-pack All of the basic git commands are designed to be scripted. When scripting, use the "--" option to ensure that files beginning with "-" won't be interpreted as options, and the "-z" option to output NUL-terminated file names so embedded newlines won't break things. (A person who'd do either of these on purpose is probably crazy, but it's not actually illegal.) Looking at existing shell scripts can be very informative. * Detailed list Here's a repeat, including descriptions. I don't try to include every detail you can find on the man page, but to explain when you'd want to use a command. + Administrative commands git-init-db This creates an empty git repository in ./.git (or $GIT_DIR if that is non-null) using a system-wide template. It won't hurt an existing repository. + Object database maintenance: git-convert-objects You will *never* need to use this command. The git repository format has undergone some revision since its first release. If you have an ancient and crufty git repository from the very very early days, this will convert it for you. But as you're new to git, it doesn't apply. git-fsck-objects Validate the object database. Checks that all references point somewhere, all the SHA1 hashes are correct, and that sort of thing. This walks the entire repository, uncompressing and hashing every object, so it takes a while. Note that by default, it skips over packs, which can make it seem misleadingly fast. git-lost-found.sh Find (using git-fsck-objects) any unreferenced commits and tags in the object database, and place them in a .git/lost-found directory. This can be used to recover from accidentally deleting a tag or branch reference that you wanted to keep. This is the opposite of git-prune. git-prune.sh Delete all unreachable objects from the object database. It deletes useless packs, but does not remove useless objects from the middle of partially useful packs. Git leaks objects in a number of cases, such as unsuccessful merges. The leak rate is generally a small fraction of the rate at which the desired history grows, so it's not very alarming, but occasionally running git-prune will eliminate the If you deliberately throw away a development branch, you will need to run this command to fully reclaim the disk space. On something like the full Linux repository, this takes a while. git-relink.perl Merge the objects stores of multiple git repositories by making hard links between them. Useful to save space if duplicate copies are accidentally created on one machine. + Pack maintenance The classic git format is to compress and store each object separately. This is still used for all newly created changes. However, objects can also be stored en masse in "packs" which contain many objects and tan take advantage of delta-compressing. Repacking your repositories periodically can save space. (Repacking is pretty quick but not quick enough to be comfortable doing every commit.) git-count-objects.sh Print the number and total size of unpacked objects in the repository, to help you decide when is a good time to repack. git-index-pack A pack file has an accompanying .idx file to allow rapid lookup. This regenerates the .idx file from the .pack. This is almost never needed directly, but can be used after transferring a .pack file between machines. git-pack-objects Given a list of objects on stdin, build a pack file. This is a helper used by the various network communication scripts. git-pack-redundant Produce a list of redundant packs, for feeding to "xargs rm". A helper for git-prune. git-prune-packed Delete unpacked object files that are duplicated in packs. (With -n, only lists them.) A helper for git-prune. git-repack.sh Make a new pack with all the unpacked objects. With -a, include already-packed objects in the new pack. With -d as well, deletes all the old packs thereby made redundant. git-show-index Dump the contents of a pack's .idx file. Mostly for debugging git itself. git-unpack-objects Unpack a .pack file, the opposite of git-pack-objects. With -n, doesn't actually create the files. With -q, suppresses the progress indicator. git-verify-pack Validate a pack file. Useful when debugging git, and when downloading from a remote source. A helper for git-clone. + Important primitives Although these primitives are not used directly very frequently, understanding them will help you understand other git commands that wrap them. git-commit-tree Create a new commit object from a tree and a list of parent commits. This is the primitive that's the heart of git-commit. (It's also used by git-am, git-applypatch, git-merge, etc.) git-rev-list Print a list of commits (revisions), in reverse chronological order. This is the heart of git-log and other history examination commands, and the options for specifying parts of history are shared by all of them. In particular, it takes an arbitrary number of revisions as arguments, some of which may be prefixed with ^ to negate them. These make up "include" and "exclude" sets. git-rev-list lists all revisions that are ancestors of the "include" set but not ancestors of the "exclude" set. For this purpose, a revision is considered an ancestor of itself. Thus, "git-rev-list ^v1.1 v1.2" will list all revisions from the v1.2 release back to (but not including) the v1.1 release. Because this is so convenient, a special syntax, "v1.1..v1.2" is allowed as an equivalent. However, occasionally the general form is useful. For example, adding ^branch will show the trunk (including merges from the branch), but exclude the branch itself. Similarly, "branch ^trunk", a.k.a. trunk..branch, will show all work on the branch that hasn't been merged to the trunk. This works even though trunk is not a direct ancestor of branch. Git-rev-list has a variety of flags to control it output format. The default is to just print the raw SHA1 object IDs of the commits, but --pretty produces a human-readable log. You can also specify a set of files names (or directories), in which case output will be limited to commits that modified those files. This command is used extensively by the git:// protocol to compute a set of objects to send to update a repository. git-rev-parse This is a very widely used command line canonicalizer for git scripts. It converts relative commit references (e.g. master~3) to absolute SHA1 hashes, and can also pass through arguments not recognizable as references, so the script can interpret them. It is important because it defines the <rev> syntax. This takes a variety of options to specify how to prepare the command line for the script's use. --verify is a particularly important one. + Useful primitives These primitives are potentially useful directly. git-ls-files List files in the index and/or working directory. A variety of options control which files to list, based on whether they are the same in both places or have been modified. This command is the start of most check-in scripts. git-update-index Copy the given files from the working directory into the index. This create the blob objects, but no trees yet. (Note that editing a file executing this multiple times without creating a commit will generate orphaned objects. Harmless.) One common safe option is "git-update-index --refresh". This looks for files whose metadata (modification time etc.) has changed, but not their contents, and updates the metadata in the index so the file contents won't have to be examined again. + General script helpers (used only by scripts) These are almost exclusively helpers for use in porcelain scripts and have little use by themselves from the command line. git-cat-file Extract a file from the object database. You can ask for an object's type or size given only an object ID, but to get its contents, you have to specify the type. This is a deliberate safety measure. git-check-ref-format Verify that the reference specified on the command line is syntactically valid for a new reference name under $GIT_DIR/refs. A number of characters (^, ~, :, and ..) are reserved; see the man page for the full list of rules. git-checkout-index Copy files from the index to the working directory, or to a specified directory. Most important as a helper for git-checkout, this is also used by git-merge and git-reset. git-fmt-merge-msg.perl Generate a reasonable default commit message for a merge. Used by git-pull and git-octopus. git-hash-object Very primitive helper to turn an arbitrary file into an object, returning just the ID or actually adding it to the database. Used by the cvs-to-git and svn-to-git import filters. git-ls-tree List the contents of a tree object. Will tell you all the files in a commit. Used by the checkout scripts git-checkout and git-reset. git-repo-config Get and set options in .git/config. The .git/config format is designed to be human-readable. This gives programmatic access to the settings. This currently has a lot of overlap with the function of git-var. git-unpack-file Write the contents of the given block to a temporary file, and return the name of that temp file. Used most often by merging scripts. git-update-ref Rewrite a reference (in .git/refs/) to point to a new object. "echo $sha1 > $file" is mostly equivalent, but this adds locking so two people don't update the same reference at once. git-sh-setup.sh This is a general prefix script that sets up $GIT_DIR and $GIT_OBJECT_DIRECTORY for a script, or errors out if the git control files can't be found. git-stripspace Remove unnecessary whitespace. Used mostly on commit messages received by e-mail. git-symbolic-ref This queries or creates symlinks to references such as HEAD. Basically equivalent to readlink(1) or ln -s, this also works on platforms that don't have symlinks. See the man page. git-var Provide access to the GIT_AUTHOR_IDENT and/or GIT_COMMITTER_IDENT values, used in various commit scripts. This currently has a lot of overlap with the function of git-repo-config. git-write-tree Generate a tree object reflecting the current index. The output is the tree object; if you don't remember it somewhere (usually, pass it to git-commit-tree), it'll be lost. This requires that the index be fully merged. If any incomplete merges are present in the index (files in stages 1, 2 or 3), git-write-tree will fail. + Oddballs git-mv.perl I have to admit, I'm not quite sure what advantages this is supposed to have over plain "mv" followed by "git-update-index", or why it's complex enough to need perl. Basically, this renames a file, deleting its old name and adding its new name to the index. Otherwise, it's a two-step process to rename a file: - Rename the file - git-add the new name Followed by which you must commit both the old and new names + Code browsing git-diff.sh Show changes between various trees. Takes up to two tree specifications, and shows the difference between the versions. Zero arguments: index vs. working directory (git-diff-files) One: tree vs. working directory (git-diff-index) One, --cached: tree vs. index (git-diff-index) Two: tree vs. tree (git-diff-tree) This wrapper always produces human-readable patch output. The helpers all produce "diff-raw" format unless you supply the -p option. There are some interesting options. Unfortunately, the git-diff man page is annoyingly sparse, and refers to the helper scripts' documentation rather than describing the many useful options they all have in common. Please do read the man pages of the helpers to see what's available. In particular, although git does not explicitly record file renames, it has some pretty good heuristics to notice things. -M tries to detect renamed files by matching up deleted files with similar newly created files. -C tries to detect copies as well. By default, -C only looks among the modified files for the copy source. For common cases like splitting a file in two, this works well. The --find-copies-harder searches ALL files in the tree for the copy source. This can be slow on large trees! See Documentation/diffcore.txt for an explanation of how all this works. git-diff-files Compare the index and the working directory. git-diff-index Compare the working directory and a given tree. This is the git equivalent of the single-operand form of "cvs diff". If "--cached" is specified, uses the index rather than the working directory. git-diff-tree Compare two trees. This is the git equivalent of the two-operand form of "cvs diff". This command is sometimes useful by itself to see the changes made by a single commit. If you give it only one commit on the command line, it shows the diff between that commit and its first parent. If the commit specification is long and awkward to type, using "git-diff-tree -p <commit>" can be easier than "git-diff <commit>^ <commit>". git-diff-stages Although not called by git-diff, there is a fourth diff helper routine, used to compare the various versions of an unmerged file in the index. It is intended for use by merging porcelain. git-grep.sh A very simple wrapper that runs git-ls-files and greps the output looking for a file name. Does nothing fancy except saves typing. git-log.sh Wrapper around git-rev-list --pretty. Shows a history of changes made to the repository. Takes all of git-rev-list's options for specifying which revisions to list. git-name-rev Find a symbolic name for the commit specified on the command line, and returns a symbolic name of the form "maint~404^2~7". Basically, this does a breadth-first search from all the heads in .git/refs looking for the given commit. git-shortlog.perl This is a filter for the output of "git-log --pretty=short" to generate a one-line-per-change "shortlog" as Linus likes. git-show-branch Visually show the merge history of the references given as arguments. Prints one column per reference and one line per commit showing whether that commit is an ancestor of each reference. git-whatchanged.sh A simple wrapper around git-rev-list and git-diff-tree, this shows the change history of a repository. Specify a directory or file on the command line to limit the output to changes affecting those files. This isn't the same as "cvs annotate", but it serves a similar purpose among git folks. You can add the -p option to include patches as well as log comments. You can also add the -M or -C option to follow history back through file renames. -S is interesting: it's the "pickaxe" option. Given a string, this limits the output to changes that make that string appear or disappear. This is for "digging through history" to see when a piece of code was introduced. The string may (and often does) contain embedded newlines. See Documentation/cvs-migration.txt. + Making local changes All of these are examples of "porcelain" scripts. Reading the scripts themselves can be informative; they're generally not too confusing. git-add.sh A simple wrapper around "git-ls-files | git-update-index --add" to add new files to the index. You may specify directories. You need to invoke this for every new file you want git to track. git-bisect.sh Utility to do a binary search to find the change that broke something. The heart of this is in "git-rev-list --bisect" A very handy little utility! Kernel developers love it when you tell them exactly which patch broke something. NOTE: this uses the head named "bisect", and will blow away any existing branch by that name. Try not to create a branch with that name. There are three steps: git-bisect start [<files>] - Reset to start bisecting. If any files are specified, only they will be checked out as bisection proceeds. git-bisect good [<revision>] - Record the revision as "good". The change being sought must be after this revision. git-bisect bad [<revision>] - Record the revision as "bad". The change being sought must be before or equal to this revision. As soon as you have specified one good version and one bad version, git-bisect will find a halfway point and check out that revision. Build and test it, then report it as good or bad, and git-bisect will narrow the search. Finally, git-bisect will tell you exactly which change caused the problem. git-bisect log - Show a history of revisions. git-bisect replay - Replay (part of) a git-bisect log. Generally used to recover from a mistake, you can truncate the log before the mistake and replay it to continue. If git-bisect chooses a version that cannot build, or you are otherwise unable to determine whether it is good or bad, you can change revisions with "git-reset --hard <revision>" to another checkout between the current good and bad limits, and continue from there. "git-reset --hard <revision>" is generally dangerous, but you are on a scratch branch. This can, of course, be used to look for any change, even one for the better, if you can avoid being confused by the terms "good" and "bad". git-branch.sh Most commonly used bare, to show the available branches. Show, create, or delete a branch. The current branches are simply the contents of .git/refs/heads/. Note that this does NOT switch to the created branch! For the common case of creating a branch and immediately switching to it, "git-checkout -b <branch>" is simpler. git-checkout.sh This does two superficially similar but very different things depending on whether any files or paths are specified on the command line. git-checkout [-f] [-b <new-branch>] <branch> This switches (changes the HEAD symlink to) the specified branch, updating the index and working directory to reflect the change. This preserves changes in the working directory unless -f is specified. If -b is specified, a new branch is started from the specified point and switched to. If <branch> is omitted, it defaults to HEAD. This is the usual way to start a new branch. git-checkout [<branch>] [--] <paths>... This replaces the files specified by the given paths with the versions from the index or the specified branch. It does NOT affect the HEAD symlink, just replaces the specified paths. This form is like a selective form of "git-reset". Normally, this can guess whether the first argument is a branch name or a path, but you can use "--" to force the latter interpretation. With no branch, this is used to revert a botched edit of a particular file. Both forms use git-read-tree internally, but the net effect is quite different. git-commit.sh Commit changes to the revision history. In terms of primitives, this does three things: 1) Updates the index file with the working directory files specified on the command line, or -a for all (using git-diff-files --name-only | git-update_index), 2) Prompts for or generates a commit message, and then 3) Creates a commit object with the current index contents. This also executes the pre-commit, commit-msg, and post-commit hooks if present. This will remove deleted files from the index, but will not add new files to the index, even if explicitly specified on the command line; you must use git-add for that. git-reset.sh Explained in detail in "resetting", above. This modifies the current branch head reference (as pointed to by .git/HEAD) to refer to the given commit. It does not modify .git/HEAD Reset the current HEAD to the specified commit, so that future checkins will be relative to it. There are three variations: --soft: Just move the HEAD link. The index is unchanged. --mixed (default): Move the HEAD link and update the index file. Any local changes will appear not checked in. --hard: Move the HEAD links, update the index file, and check out the index, overwriting the working directory. Like "cvs update -C". In case of accidents, this copies the previous head object ID to ORIG_HEAD (which is NOT a symlink). git-status.sh Show all files in the directory not current with respect to the git HEAD. The basic categories are: 1) Changed in the index, will be included in the next commit. 2) Changed in the working directory but NOT in the index; will be committed only if added via git-update-index or the git-commit command line. 3) Not tracked by git. + Cherry-picking Cherry-picking is the process of taking part of the changes introduced on one tree and applying those changes to another. This doesn't produce a parent/descendant relationship in the commit history. To produce that relationship, there's a special type of merge you can do if you've taken everything you want off a branch and want to show it in the merge history without actually importing any changes from it: ours. "git-merge -s ours" will generate a commit that shows some branches were merged in, but not actually alter the current HEAD source code in any way. One thing cherry-picking is sometimes used for is taking a development branch and re-organizing the changes into a patch series for submission to the Linux kernel. git-cherry.sh This searches a branch for patches which have not been applied to another. Basically, it finds the unpicked cherries. It searches back to the common ancestor of the named branch and the current head using git-patch-id to identify similarity in patches. git-patch-id Generate a hash of a patch, ignoring whitespace and line numbers so that "the same" patch, even relative to a different code base, probably has the same hash, and different patches probably have different ones. git-cherry looks for patch hashes which are present on the branch (source branch) that are not present on the trunk (destination branch). git-cherry-pick.sh Given a commit (on a different branch), compute a diff between it and its immediate parent, and apply it to the current HEAD. This is actually the same script as "git revert", but works forward. git-cherry finds the patches, this merges them. Handles failures gracefully. git-rebase.sh Move a branch to a more recent "base" release. This just extracts all the patches applied on the local head since the last merge with upstream (using git-format-patch) and re-applies them relative to the current upstream with git-am (explained under "accepting changes by e-mail"). Finally, it deletes the old branch and gives its name to the new one, so your branch now contains all the same changes, but relative to a different base. Basically the same as cherry-picking an entire branch. git-revert.sh Undo a commit. Basically "patch -R" followed by a commit. This is actually the same script as "git-cherry-pick", just applies the patch in reverse, undoing a change that you don't wish to back up to using git-reset. Handles failures gracefully by telling the user what to do. + Accepting changes by e-mail git-apply Apply a (git-style extended) patch to the current index and working directory. git-am.sh The new and improved "apply an mbox" script. Takes an mbox-style concatenation of e-mails as input and batch-applies them, generating one commit per message. Can resume after stopping on a patch problem. (Invoke it as "git-am --skip" or "git-am --resolved" to deal with the problematic patch and continue.) git-mailinfo Given a single mail message on stdin (in the Linux standard SubmittingPatches format), extract a commit message and the patch proper. git-mailsplit Split an mbox into separate files. git-applypatch.sh Tries simple git-apply, then tries a few other clever merge strategies to get a patch to apply. Used in the main loop of git-am and git-applymbox. git-applymbox.sh This is Linus's original apply-mbox script. Mostly superseded by git-am (which is friendlier and has more features), but he still uses it, so it's maintained. This is so old it was originally a test of the git core called "dotest", and that name is still lurking in the temp file names. + Publishing changes by e-mail git-format-patch.sh Generate a series of patches, in the preferred Linux kernel (Documentation/SubmittingPatches) format, for posting to lkml or the like. This formats every commit on a branch as a separate patch. git-send-email.perl Actually e-mail the output of git-format-patch. (This uses direct SMTP, a matter of some controversy. Others feel that /bin/mail is the correct local mail-sending interface.) + Merging git-merge.sh Merge one or more "remote" heads into the current head. Some changes, when there has been change only on one branch or the same change has been made to all branches, can be resolved by the "trivial in-index" merge done by git-read-tree. For more complex cases, git provides a number of different merge strategies (with reasonable defaults). Note that merges are done on a filename basis. While git tries to detect renames when generating diffs, most merge strategies don't track them by renaming. (The "recursive" strategy, which recently became the default, is a notable exception.) git-merge-base Finds a common ancestor to use when comparing the changes made on two branches. The simple case is straightforward, but if there have been cross-merges between the branches, it gets somewhat hairy. The algorithm is not 100% final yet. (There's also --all, which lists all candidates.) git-merge-index This is the outer merging loop. It takes the name of a one-file merge executable as an argument, and runs it for every incomplete merge. git-merge-one-file.sh This is the standard git-merge-index helper, that tries to resolve a 3-way merge. A helper used by all the merge strategies. (Except "recursive" which has its own equivalent.) git-merge-octopus.sh Many-way merge. Overlaps should be negligible. git-merge-ours.sh A "dummy" merge strategy helper. Claims that we did the merge, but actually takes the current tree unmodified. This is used to cleanly terminate side branches that heve been cherry-picked in. git-merge-recursive.py A somewhat fancier 3-way merge. This handles multiple cross-merges better by using multiple common ancestors. git-merge-resolve.sh git-merge-stupid.sh Not actually used by git-merge, this is a simple example merge strategy. git-read-tree Read the given tree into the index. This is the difference between the "--soft" and "--mixed" modes of git-reset, but the important thing this command does is simple merging. If -m is specified, this can take up to three trees as arguments. git-resolve.sh OBSOLETE. Perform a merge using the "resolve" strategy. Has been superseded by the "-s resolve" option to git-merge and git-pull. git-octopus.sh OBSOLETE. Perform a merge using the "octopus" strategy. Has been superseded by the "-s octopus" option to git-merge and git-pull. + Making releases git-get-tar-commit-id Reads out the commit ID that git-tar-tree puts in its output. (Or fails if this isn't a git-generated tar file.) git-tag.sh Create a tag in the refs/tags directory. There are two kinds: "lightweight tags" are just references to commits. More serious tags are GPG-signed tag objects, and people receiving the git tree can verify that it is the version that you released. git-mktag Creates a tag object. Verifies syntactic correctness of its input. (If you want to cheat, use git-hash-object.) git-tar-tree Generate a tar archive of the named tree. Because git does NOT track file timestamps, this uses the timestamp of the commit, or the current time if you specify a tree. Also stores the commit ID in an extended tar header. git-verify-tag.sh Given a tag object, GPG-verify the embedded signature. + Accepting changes by network Pulling consists of two steps: retrieving the remote commit objects and everything they point to (including ancestors), then merging that into the desired tree. There are still separate fetch and merge commands, but it's more commonly done with a single "git-pull" command. git-fetch leaves the commit objects, one per line, in .git/FETCH_HEAD. git-merge will merge those in if that file exists when it is run. References to remote repositories can be made with long URLs, or with files in the .git/remotes/ directory. The latter also specifies the local branches to merge the fetched data into, making it very easy to track a remote repository. git-clone.sh Create a new local clone of a remote repository. (Can do a couple of space-sharing hacks when "remote" is on a local machine.) You only do this once. git-clone-pack Runs git-upload-pack remotely and places the resultant pack into the local repository. Supports a variety of network protocols, but "remote" can also be a different directory on the current machine. git-fetch.sh Fetch the named refs and all linked objects from a remote repository. The resultant refs (tags and commits) are stored in .git/FETCH_HEAD, which is used by a later git-resolve or git octopus. This is the first half of a "git pull" operation. git-fetch-pack Retrieve missing objects from a remote repository. git-local-fetch Duplicates a git repository from the local system. (Er... is this used anywhere???) git-http-fetch Do a fetch via http. Http requires some kludgery on the server (see git-update-server-info), but it works. git-ssh-fetch Do a fetch via ssh. git-ls-remote.sh Show the contents of the refs/heads/ and/or refs/tags/ directories of a remote repository. Useful to see what's available. git-peek-remote Helper C program for the git-ls-remote script. Implements the git protocol form of it. git-parse-remote.sh Helper script to parse a .git/remotes/ file. Used by a number of these programs. git-pull.sh Fetches specific commits from the given remote repository, and merges everything into the current branch. If a remote commit is named as src:dst, this merges the remote head "src" into the branch "dst" as well as the trunk. Typically, the "dst" branch is not modified locally, but is kept as a pristine copy of the remote branch. One very standard example of this contention is that a repository that is tracking another specifies "master:origin" to provide a pristine local copy of the remote "master" branch in the local branch named "origin". git-ssh-pull A helper program that pulls over ssh. git-shell A shell that can be used for git-only users. Allows git push (git-receive-pack) and pull (git-upload-pack) only. git-receive-pack Receive a pack from git-send-pack, validate it, and add it to the repository. Adding just the bare objects has no security implications, but this can also update branches and tags, which does have an effect. Runs pre-update and post-update hooks; the former may do permissions checking and disallow the upload. This is the command run remotely via ssh by git-push. + Publishing changes by network git-daemon A daemon that serves up the git native protocol so anonymous clients can fetch data. For it to allow export of a directory, the magic file name "git-daemon-export-ok" must exist in it. This does not accept (receive) data under any circumstances. git-push.sh Git-pull, only backwards. Send local changes to a remote repository. The same .git/remotes/ short-cuts can be used, and the same src:dst syntax. (But this time, the src is local and the dst is remote.) git-http-push A helper to git-push to implement the http: protocol. git-ssh-push A helper to git-push to push over ssh. git-ssh-upload Another helper. This just does the equivalent of "fetch" ("throw"?) and doesn't actually merge the result. Obsolete? git-request-pull.sh Generate an e-mail summarizing the changes between two commits, and request that the recipient pull them from your repository. Just a little helper to generate a consistent and informative format. git-send-pack Pack together a pile of objects missing at the destination and send them. This is the sending half that talks to a remote git-receive-pack. git-update-server-info To run git over http, auxiliary info files are required that describes what objects are in the repository (since git-upload-pack can't generate this on the fly). If you want to publish a repository via http, run this after every commit. (Typically via the hooks/post-update script.) git-upload-pack Like git-send-pack, but this is invoked by a remote git-fetch-pack. - To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html