2 Title: Collecting information about git
5 Author: Oleg Broytman <phd@phdru.name>
8 Content-Type: text/x-rst
15 This Informational PEP collects information about git. There is, of
16 course, a lot of documentation for git, so the PEP concentrates on
17 more complex issues, scenarios and topics.
19 The plan is to extend the PEP in the future collecting information
20 about equivalence of Mercurial and git scenarios to help migrating
21 Python development from Mercurial to git.
23 The author of the PEP doesn't currently plan to write a Process PEP on
24 migration from Mercurial to git.
30 Git is accompanied with a lot of documentation, both online and
33 Documentation for starters
34 --------------------------
37 <https://www.kernel.org/pub/software/scm/git/docs/gittutorial.html>`_,
39 <https://www.kernel.org/pub/software/scm/git/docs/gittutorial-2.html>`_.
42 <https://www.kernel.org/pub/software/scm/git/docs/user-manual.html>`_.
43 `Everyday GIT With 20 Commands Or So
44 <https://www.kernel.org/pub/software/scm/git/docs/everyday.html>`_.
46 <https://www.kernel.org/pub/software/scm/git/docs/gitworkflows.html>`_.
48 Advanced documentation
49 ----------------------
52 <http://www-cs-students.stanford.edu/~blynn/gitmagic/index.html>`_,
53 also with a number of translations.
55 `Pro Git <https://git-scm.com/book>`_. The Book about git. Buy it at
56 Amazon or download in PDF, mobi, or ePub form. Has translations to
57 many different languages. Download Russian translation from `GArik
58 <https://github.com/GArik/progit/wiki>`_.
60 `Git Wiki <https://git.wiki.kernel.org/index.php/Main_Page>`_.
65 Git has builtin help: run ``git help $TOPIC``. For example, run
66 ``git help git`` or ``git help help``.
72 Download and installation
73 -------------------------
75 Unix users: download and install using your package manager.
77 Microsoft Windows: download `git-for-windows
78 <https://github.com/git-for-windows/git/releases>`_ or `msysGit
79 <https://github.com/msysgit/msysgit/releases>`_.
81 MacOS X: use git installed with `XCode
82 <https://developer.apple.com/xcode/downloads/>`_ or download from
83 `MacPorts <https://www.macports.org/ports.php?by=name&substr=git>`_ or
85 <http://sourceforge.net/projects/git-osx-installer/files/>`_ or
86 install git with `Homebrew <http://brew.sh/>`_: ``brew install git``.
88 `git-cola <https://git-cola.github.io/index.html>`_ is a Git GUI
89 written in Python and GPL licensed. Linux, Windows, MacOS X.
91 `TortoiseGit <https://tortoisegit.org/>`_ is a Windows Shell Interface
92 to Git based on TortoiseSVN; open source.
97 This simple code is often appears in documentation, but it is
98 important so let repeat it here. Git stores author and committer
99 names/emails in every commit, so configure your real name and
102 $ git config --global user.name "User Name"
103 $ git config --global user.email user.name@example.org
109 Examples of git commands in this PEP use the following approach. It is
110 supposed that you, the user, works with a local repository named
111 ``python`` that has an upstream remote repo named ``origin``. Your
112 local repo has two branches ``v1`` and ``v2``. For most examples the
113 currently checked out branch is ``v2``. That is, it's assumed you have
114 done something like that::
116 $ git clone -b v2 http://git.python.org/python.git
118 $ git branch v1 origin/v1
120 The first command clones remote repository into local directory
121 `python``, creates a new local branch v2, sets remotes/origin/v2 as
122 its upstream remote-tracking branch and checks it out into the working
125 The last command creates a new local branch v1 and sets
126 remotes/origin/v1 as its upstream remote-tracking branch.
128 The same result can be achieved with commands::
130 $ git clone -b v1 http://git.python.org/python.git
132 $ git checkout --track origin/v2
134 The last command creates a new local branch v2, sets remotes/origin/v2
135 as its upstream remote-tracking branch and checks it out into the
139 Branches and branches
140 =====================
142 Git terminology can be a bit misleading. Take, for example, the term
143 "branch". In git it has two meanings. A branch is a directed line of
144 commits (possibly with merges). And a branch is a label or a pointer
145 assigned to a line of commits. It is important to distinguish when you
146 talk about commits and when about their labels. Lines of commits are
147 by itself unnamed and are usually only lengthening and merging.
148 Labels, on the other hand, can be created, moved, renamed and deleted
152 Remote repositories and remote branches
153 =======================================
155 Remote-tracking branches are branches (pointers to commits) in your
156 local repository. They are there for you to remember what branches and
157 commits have been pulled from and pushed to what remote repos (you can
158 pull from and push to many remotes). Remote-tracking branches live
159 under ``remotes/$REMOTE`` namespaces, e.g. ``remotes/origin/v2``.
161 To see the status of remote-tracking branches run::
165 To see local and remote-tracking branches (and tags) pointing to
170 You never do your own development on remote-tracking branches. You
171 create a local branch that has a remote branch as upstream and do
172 development on that local branch. On push git pushes commits to the
173 remote repo and updates remote-tracking branches, on pull git fetches
174 commits from the remote repo, updates remote-tracking branches and
175 fast-forwards, merges or rebases local branches.
177 When you do an initial clone like this::
179 $ git clone -b v1 http://git.python.org/python.git
181 git clones remote repository ``http://git.python.org/python.git`` to
182 directory ``python``, creates remote-tracking branches, creates a
183 local branch ``v1``, configure it to track upstream remotes/origin/v1
184 branch and checks out ``v1`` into the working directory.
186 Updating local and remote-tracking branches
187 -------------------------------------------
189 There is a major difference between
193 $ git fetch $REMOTE $BRANCH
199 $ git fetch $REMOTE $BRANCH:$BRANCH
201 The first command fetches commits from the named $BRANCH in the
202 $REMOTE repository that are not in your repository and leaves the id
203 (the hash) of the head commit in file .git/FETCH_HEAD and updates
204 remote-tracking branch.
206 The second command fetches commits from the named $BRANCH in the
207 $REMOTE repository that are not in your repository and updates both
208 the local branch $BRANCH and its upstream remote-tracking branch. But
209 it refuses to update branches in case of non-fast-forward. And it
210 refuses to update the current branch.
212 The first command is used internally by ``git pull``.
216 $ git pull $REMOTE $BRANCH
222 $ git fetch $REMOTE $BRANCH
223 $ git merge FETCH_HEAD
225 Certainly, $BRANCH in that case should be your current branch. If you
226 want to merge a different branch into your current branch first update
227 that non-current branch and then merge::
229 $ git fetch origin v1:v1 # Update v1
230 $ git pull --rebase origin v2 # Update the current branch v2 using
231 # rebase instead of merge
234 If you have not yet pushed commits on ``v1``, though, the scenario has
235 to become a bit more complex. Git refuses to update
236 non-fast-forwardable branch, and you don't want to do force-pull
237 because that would remove your non-pushed commits and you would need
238 to recover. So you want to rebase ``v1`` but you cannot rebase
239 non-current branch. Hence, checkout ``v1`` and rebase it before
243 $ git pull --rebase origin v1
245 $ git pull --rebase origin v2
248 It is possible to configure git to make it fetch/pull a few branches
249 or all branches at once, so you can simply run
261 Default remote repository for fetching/pulling is origin. Default set
262 of references to fetch is calculated using matching algorithm: git
263 fetches all branches having the same name on both ends.
268 Pushing is a bit simpler. There is only one command ``push``. When you
273 $ git push origin v1 v2
275 git pushes local v1 to remote v1 and local v2 to remote v2. The same
278 $ git push origin v1:v1 v2:v2
280 Git pushes commits to the remote repo and updates remote-tracking
281 branches. Git refuses to push commits that aren't fast-forwardable.
282 You can force-push anyway, but please remember - you can force-push to
283 your own repositories but don't force-push to public or shared repos.
284 If you find git refuses to push commits that aren't fast-forwardable,
285 better fetch and merge commits from the remote repo (or rebase your
286 commits on top of the fetched commits), then push. Only force-push if
287 you know what you do and why you do it. See the section `Commit
288 editing and caveats`_ below.
290 It is possible to configure git to make it push a few branches or all
291 branches at once, so you can simply run
303 Default remote repository for pushing is origin. Default set
304 of references to push in git before 2.0 is calculated using matching
305 algorithm: git pushes all branches having the same name on both ends.
306 Default set of references to push in git 2.0+ is calculated using
307 simple algorithm: git pushes the current branch back to its
310 To configure git before 2.0 to the new behaviour run::
312 $ git config push.default simple
314 To configure git 2.0+ to the old behaviour run::
316 $ git config push.default matching
318 Git refuses to push a branch if it's the current branch in the remote
319 non-bare repository: git refuses to update remote working directory.
320 You really should push only to bare repositories. For non-bare
321 repositories git prefers pull-based workflow.
323 When you want to deploy code on a remote host and can only use push
324 (because your workstation is behind a firewall and you cannot pull
325 from it) you do that in two steps using two repositories: you push
326 from the workstation to a bare repo on the remote host, ssh to the
327 remote host and pull from the bare repo to a non-bare deployment repo.
332 Git automatically fetches tags that point to commits being fetched
333 during fetch/pull. To fetch all tags (and commits they point to) run
334 ``git fetch --tags origin``. To fetch some specific tags fetch them
337 $ git fetch origin tag $TAG1 tag $TAG2...
341 $ git fetch origin tag 1.4.2 tag 2.1.7
343 Git doesn't automatically pushes tags. That allows you to have private
344 tags (lightweight tags are also private for a repo, they cannot be
345 pushed). To push tags list them explicitly::
347 $ git push origin tag 1.4.2
348 $ git push origin v1 v2 tag 2.1.7
350 Don't move tags with ``git tag -f`` or remove tags with ``git tag -d``
351 after they have been published.
354 Commit editing and caveats
355 ==========================
357 A warning not to edit published (pushed) commits also appears in
358 documentation but it's repeated here anyway as it's very important.
360 It is possible to recover from forced push but it's PITA for the
361 entire team. Please avoid it.
363 To see what commits have not been published yet compare the head of the
364 branch with its upstream remote-tracking branch::
366 $ git log origin/v2..
367 $ git log origin/v1..v1
369 For every branch that has an upstream remote-tracking branch git
370 maintains an alias @{upstream} (short version @{u}), so the commands
371 above can be given as::
376 To see the status of all branches::
380 To compare the status of local branches with a remote repo::
382 $ git remote show origin
384 Read `how to recover from upstream rebase
385 <https://git-scm.com/docs/git-rebase#_recovering_from_upstream_rebase>`_.
386 It is in ``git help rebase``.
388 On the other hand don't be too afraid about commit editing. You can
389 safely edit, remove, reorder, combine and split commits that hasn't
390 been pushed yet. You can even push commits to your own (backup) repo,
391 edit them later and force-push edited commits to replace what has
392 already been pushed. Not a problem until commits are in a public
393 or shared repository.
399 Whatever you do, don't panic. Almost anything in git can be undone.
401 git checkout: restore file's content
402 ------------------------------------
404 ``git checkout``, for example, can be used to restore the content of
405 file(s) to that one of a commit. Like this::
407 git checkout HEAD~ README
409 The commands restores the contents of README file to the last but one
410 commit in the current branch. By default the commit ID is simply HEAD;
411 i.e. ``git checkout README`` restores README to the latest commit.
413 (Do not use ``git checkout`` to view a content of a file in a commit,
414 use ``git cat-file -p``; e.g. ``git cat-file -p HEAD~:path/to/README``).
416 git reset: remove (non-pushed) commits
417 --------------------------------------
419 ``git reset`` moves the head of the current branch. The head can be
420 moved to point to any commit but it's often used to remove a commit or
421 a few (preferably, non-pushed ones) from the top of the branch - that
422 is, to move the branch backward in order to undo a few (non-pushed)
425 ``git reset`` has three modes of operation - soft, hard and mixed.
426 Default is mixed. ProGit `explains
427 <https://git-scm.com/book/en/Git-Tools-Reset-Demystified>`_ the
428 difference very clearly. Bare repositories don't have indices or
429 working trees so in a bare repo only soft reset is possible.
434 Mixed mode reset with a path or paths can be used to unstage changes -
435 that is, to remove from index changes added with ``git add`` for
436 committing. See `The Book
437 <https://git-scm.com/book/en/Git-Basics-Undoing-Things>`_ for details
438 about unstaging and other undo tricks.
440 git reflog: reference log
441 -------------------------
443 Removing commits with ``git reset`` or moving the head of a branch
444 sounds dangerous and it is. But there is a way to undo: another
445 reset back to the original commit. Git doesn't remove commits
446 immediately; unreferenced commits (in git terminology they are called
447 "dangling commits") stay in the database for some time (default is two
448 weeks) so you can reset back to it or create a new branch pointing to
451 For every move of a branch's head - with ``git commit``, ``git
452 checkout``, ``git fetch``, ``git pull``, ``git rebase``, ``git reset``
453 and so on - git stores a reference log (reflog for short). For every
454 move git stores where the head was. Command ``git reflog`` can be used
455 to view (and manipulate) the log.
457 In addition to the moves of the head of every branch git stores the
458 moves of the HEAD - a symbolic reference that (usually) names the
459 current branch. HEAD is changed with ``git checkout $BRANCH``.
461 By default ``git reflog`` shows the moves of the HEAD, i.e. the
462 command is equivalent to ``git reflog HEAD``. To show the moves of the
463 head of a branch use the command ``git reflog $BRANCH``.
465 So to undo a ``git reset`` lookup the original commit in ``git
466 reflog``, verify it with ``git show`` or ``git log`` and run ``git
467 reset $COMMIT_ID``. Git stores the move of the branch's head in
468 reflog, so you can undo that undo later again.
470 In a more complex situation you'd want to move some commits along with
471 resetting the head of the branch. Cherry-pick them to the new branch.
472 For example, if you want to reset the branch ``v2`` back to the
473 original commit but preserve two commits created in the current branch
476 $ git branch save-v2 # create a new branch saving v2
477 $ git reflog # find the original place of v2
478 $ git reset $COMMIT_ID
479 $ git cherry-pick save-v2~ save-v2
480 $ git branch -D save-v2 # remove temporary branch
482 git revert: revert a commit
483 ---------------------------
485 ``git revert`` reverts a commit or commits, that is, it creates a new
486 commit or commits that reverts the effects of the given commits. It's
487 the only way to undo published commits (``git commit --amend``, ``git
488 rebase`` and ``git reset`` change the branch in non-fast-forwardable
489 ways so they should only be used for non-pushed commits.)
491 There is a problem with reverting a merge commit. ``git revert`` can
492 undo the code created by the merge commit but it cannot undo the fact
493 of merge. See the discussion `How to revert a faulty merge
494 <https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html>`_.
496 One thing that cannot be undone
497 -------------------------------
499 Whatever you undo, there is one thing that cannot be undone -
500 overwritten uncommitted changes. Uncommitted changes don't belong to
501 git so git cannot help with them - no way.
503 Most of the time git warns you when you're going to execute a command
504 that overwrites uncommitted changes. Git warns you when you try to
505 switch branches with ``git checkout``. It warns you when you're going
506 to rebase with non-clean working tree. It refuses to pull commits over
509 But there are commands that designed exactly for that - overwriting
510 files in the working tree. With commands like ``git checkout $PATHs``
511 or ``git reset --hard`` git silently overwrites files including your
514 With that in mind you can understand the stance "commit early, commit
515 often". Commit as often as possible. Commit on every save in your
516 editor or IDE. You can edit your commits before pushing - change,
517 reorder, combine. But save your changes in git database, either in
518 commits or at least in stashes.
524 Internet is full of heated discussions on the topic: "merge or
525 rebase?" Most of them are meaningless. When a DVCS is being used in a
526 big team with a big and complex project with many branches there is
527 simply no way to avoid merges. So the question's diminished to
528 "whether to use rebase, and if yes - when to use rebase?" Considering
529 that it is very much recommended not to rebase published commits the
530 question's diminished even further: "whether to use rebase on
533 That small question is for the team to decide. The author of the PEP
534 recommends to use rebase when pulling, i.e. always do ``git pull
535 --rebase`` or even configure automatic setup of rebase for every new
538 $ git config branch.autosetuprebase always
540 and configure rebase for existing branches::
542 $ git config branch.$NAME.rebase true
546 $ git config branch.v1.rebase true
547 $ git config branch.v2.rebase true
549 After that ``git pull origin v2`` becomes equivalent to ``git pull
550 --rebase origin v2``.
552 In case when merge is preferred it is recommended to create new
553 commits in a separate feature or topic branch while using rebase to
554 update the mainline branch. When the topic branch is ready merge it
555 into mainline. To avoid a tedious task of resolving large number of
556 conflicts at once you can merge the topic branch to the mainline from
557 time to time and switch back to the topic branch to continue working
558 on it. The entire workflow would be something like::
560 $ git checkout -b issue-42 # create a new issue branch and switch to it
561 ...edit/test/commit...
563 $ git pull --rebase origin v2 # update v2 from the upstream
565 $ git branch -d issue-42 # delete the topic branch
568 When the topic branch is deleted only the label is removed, commits
569 are stayed in the database, they are now merged into v2::
571 o--o--o--o--o--M--< v2 - the mainline branch
573 --*--*--* - the topic branch, now unnamed
575 The topic branch is deleted to avoid cluttering branch namespace with
576 small topic branches. Information on what issue was fixed or what
577 feature was implemented should be in the commit messages.
583 Git has a builtin merge strategy for what Python core developers call
586 $ git merge -s ours v1 # null-merge v1 into v2
592 https://git-scm.com/book/en/Git-Tools-Rerere
601 Staging area aka index is a distinguishing feature of git. See
603 <https://git.wiki.kernel.org/index.php/WhatIsTheIndex>`_ and
604 `IndexCommandQuickref
605 <https://git.wiki.kernel.org/index.php/IndexCommandQuickref>`_ in Git
609 Advanced configuration
610 ======================
615 Git has builtin mechanisms to handle line endings.
617 TODO: describe crlf configuration and .gitattributes.
623 TODO: dangling objects, git gc, git repack.
625 https://gcc.gnu.org/ml/gcc/2007-12/msg00165.html
627 http://vcscompare.blogspot.ru/2008/06/git-repack-parameters.html
633 TODO: sticky options; example: git grep -O.
635 TODO: tricky options; example: git log -p3.
637 TODO: bash/zsh completion, bash/zsh prompt.
638 https://git.kernel.org/cgit/git/git.git/tree/contrib/completion
644 TODO: anonymous access; git over ssh; gitolite; gitweb; cgit; gitlab.
646 http://gitolite.com/gitolite/index.html
648 https://git.kernel.org/cgit/git/git.git/tree/gitweb
650 http://git.zx2c4.com/cgit/
652 From Mercurial to git
653 =====================
655 Mercurial for Git users https://mercurial.selenic.com/wiki/GitConcepts
657 https://github.com/felipec/git-remote-hg
659 https://hg-git.github.io/
671 This document has been placed in the public domain.
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