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 differentiate when
146 you talk about commits and when about their labels. Lines of commits
147 are 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 REMOTE
202 repository that are not in your repository and leaves the id (the
203 hash) of the head commit in file .git/FETCH_HEAD. But it doesn't
204 update any branch (doesn't move any pointer).
206 The second command fetches commits from the named BRANCH in the REMOTE
207 repository that are not in your repository and updates both the local
208 branch BRANCH and its upstream remote-tracking branch. But it refuses
209 to update branches in case of non-fast-forward. And it refuses to
210 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 # FETCH_HEAD is a literal here
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
264 Pushing is a bit simpler. There is only one command ``push``. When you
269 $ git push origin v1 v2
271 git guesses (knowing upstream remote branches) that you really want
275 $ git push origin v1:v1 v2:v2
277 Git pushes commits to the remote repo and updates remote-tracking
278 branches. Git refuses to push commits that aren't fast-forwardable.
279 You can force-push anyway, but please remember - you can force-push to
280 your own repositories but don't force-push to public or shared repos.
281 If you find git refuses to push commits that aren't fast-forwardable,
282 better fetch and merge commits from the remote repo (or rebase your
283 commits on top of the fetched commits), then push. Only force-push if
284 you know what you do and why you do it. See the section `Commit
285 editing and caveats`_ below.
287 It is possible to configure git to make it push a few branches or all
288 branches at once, so you can simply run
300 Git refuses to push a branch if it's the current branch in the remote
301 non-bare repository: git refuses to update remote working directory.
302 You really should push only to bare repositories. For non-bare
303 repositories git prefers pull-based workflow.
305 When you want to deploy code on a remote host and can only use push
306 (because your workstation is behind a firewall and you cannot pull
307 from it) you do that in two steps using two repositories: you push
308 from the workstation to a bare repo on the remote host, ssh to the
309 remote host and pull from the bare repo to a non-bare deployment repo.
314 Git automatically fetches tags that point to commits being fetched
315 during fetch/pull. To fetch all tags (and commits they point to) run
316 ``git fetch --tags origin``. To fetch some specific tags fetch them
319 $ git fetch origin tag TAG1 tag TAG2...
323 $ git fetch origin tag 1.4.2 tag 2.1.7
325 Git doesn't automatically pushes tags. That allows you to have private
326 tags (lightweight tags are also private for a repo, they cannot be
327 pushed). To push tags list them explicitly::
329 $ git push origin tag 1.4.2
330 $ git push origin v1 v2 tag 2.1.7
332 Don't move tags with ``git tag -f`` after they have been published.
335 Commit editing and caveats
336 ==========================
338 A warning not to edit published (pushed) commits also appears in
339 documentation but it's repeated here anyway as it's very important.
341 It is possible to recover from forced push but it's PITA for the
342 entire team. Please avoid it.
344 To see what commits have not been published yet compare the head of the
345 branch with its upstream remote-tracking branch::
347 $ git log origin/v2..
348 $ git log origin/v1..v1
350 For every branch that has an upstream remote-tracking branch git
351 maintains an alias @{upstream} (short version @{u}), so the commands
352 above can be given as::
357 To see the status of all branches::
361 To compare the status of local branches with a remote repo::
363 $ git remote show origin
365 Read `how to recover from upstream rebase
366 <https://git-scm.com/docs/git-rebase#_recovering_from_upstream_rebase>`_.
367 It is in ``git help rebase``.
369 On the other hand don't be too afraid about commit editing. You can
370 safely edit, remove, reorder, combine and split commits that hasn't
371 been pushed yet. You can even push commits to your own (backup) repo,
372 edit them later and force-push edited commits to replace what has
373 already been pushed. Not a problem until commits are in a public
374 or shared repository.
380 Whatever you do, don't panic. Almost anything in git can be undone.
381 ``git checkout``, for example, can be used to restore the content of
382 file(s) to that one of a commit. Like this::
384 git checkout HEAD~ README
386 The commands restores the contente of README file to the last but one
387 commit in the current branch. By default a commit ID is simple HEAD;
388 i.e. ``git checkout README`` restores README to the latest commit.
390 (Do not use ``git checkout`` to view a content of a file in a commit,
391 use ``git cat-file -p``; e.g. ``git cat-file -p HEAD~:path/to/README``).
393 ``git reset`` moves the head of the current branch. The head can be
394 moved to point to any commit but it's often used to remove a commit or
395 a few (preferably, non-pushed ones) from the top of the branch - that
396 is, to move the branch backward in order to undo a few non-pushed
399 ``git reset`` has three modes of operation - soft, hard and mixed.
400 Default is mixed. ProGit `explains
401 <https://git-scm.com/book/en/Git-Tools-Reset-Demystified>`_ the
402 difference very clearly. Bare repositories don't have indices or
403 working trees so in a bare repo only soft reset is possible.
405 Mixed mode reset with a path or paths can be used to unstage changes -
406 that is, to remove changes added with ``git add`` for committing. See
407 `The Book <https://git-scm.com/book/en/v2/Git-Basics-Undoing-Things>`_
408 for details about unstaging and other undo tricks.
410 TODO: describe undo strategies: git reflog, git revert.
411 "Commit early, commit often".
414 https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html
420 Internet is full of heated discussions on the topic: "merge or
421 rebase?" Most of them are meaningless. When a DVCS is being used in a
422 big team with a big and complex project with many branches there is
423 simply no way to avoid merges. So the question's diminished to
424 "whether to use rebase, and if yes - when to use rebase?" Considering
425 that it is very much recommended not to rebase published commits the
426 question's diminished even further: "whether to use rebase on
429 That small question is for the team to decide. The author of the PEP
430 recommends to use rebase when pulling, i.e. always do ``git pull
431 --rebase`` or even configure automatic setup of rebase for every new
434 $ git config branch.autosetuprebase always
436 and configure rebase for existing branches::
438 $ git config branch.NAME.rebase true
442 $ git config branch.v1.rebase true
443 $ git config branch.v2.rebase true
445 After that ``git pull origin v2`` becomes equivalent to ``git pull
446 --rebase origin v2``.
448 In case when merge is preferred it is recommended to create new
449 commits in a separate feature or topic branch while using rebase to
450 update the mainline branch. When the topic branch is ready merge it
451 into mainline. To avoid a tedious task of resolving large number of
452 conflicts at once you can merge the topic branch to the mainline from
453 time to time and switch back to the topic branch to continue working
454 on it. The entire workflow would be something like::
456 $ git checkout -b issue-42 # create a new issue branch and switch to it
457 ...edit/test/commit...
459 $ git pull --rebase origin v2 # update v2 from the upstream
461 $ git branch -d issue-42 # delete the topic branch
464 When the topic branch is deleted only the label is removed, commits
465 are stayed in the database, they are now merged into v2::
467 o--o--o--o--o--M--< v2 - the mainline branch
469 --*--*--* - the topic branch, now unnamed
471 The topic branch is deleted to avoid cluttering branch namespace with
472 small topic branches. Information on what issue was fixed or what
473 feature was implemented should be in the commit messages.
479 Git has a builtin merge strategy for what Python core developers call
482 $ git merge -s ours v1 # null-merge v1 into v2
488 https://git-scm.com/book/en/Git-Tools-Rerere
497 Staging area aka index is a distinguishing feature of git. See
499 <https://git.wiki.kernel.org/index.php/WhatIsTheIndex>`_ and
500 `IndexCommandQuickref
501 <https://git.wiki.kernel.org/index.php/IndexCommandQuickref>`_ in Git
505 Advanced configuration
506 ======================
511 Git has builtin mechanisms to handle line endings.
513 TODO: describe crlf configuration and .gitattributes.
519 TODO: dangling objects, git gc, git repack.
520 https://gcc.gnu.org/ml/gcc/2007-12/msg00165.html
526 TODO: sticky options; example: git grep -O.
528 TODO: tricky options; example: git log -p3.
530 TODO: bash/zsh completion, bash/zsh prompt.
531 https://git.kernel.org/cgit/git/git.git/tree/contrib/completion
537 TODO: anonymous access; git over ssh; gitolite; gitweb; cgit; gitlab.
539 http://gitolite.com/gitolite/index.html
541 https://git.kernel.org/cgit/git/git.git/tree/gitweb
543 http://git.zx2c4.com/cgit/
545 From Mercurial to git
546 =====================
548 Mercurial for Git users https://mercurial.selenic.com/wiki/GitConcepts
550 https://github.com/felipec/git-remote-hg
552 https://hg-git.github.io/
564 This document has been placed in the public domain.
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