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 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 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
135 remotes/origin/v2 as its upstream remote branch and checks it out into
136 the working directory.
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 Another example of slightly misleading terminology. Remote
156 repositories are really remote, you access them via network (well, a
157 remote repository can be on your local disk, but it's still remote
158 because it's not the current repo).
160 Remote branches, on the other hand, are branches (pointers to commits)
161 in your local repository. They are there for you to remember what
162 branches and commits have been pulled from and pushed to what remote
163 repos (you can pull from and push to many remotes). Remote branches
164 live under ``remotes/REMOTE`` namespaces, e.g. ``remotes/origin/v2``.
166 To see the status of remote branches run::
170 To see local and remote branches (and tags) pointing to commits::
174 You never do your own development on remote branches. You create a
175 local branch that has a remote branch as upstream and do development
176 on that local branch. On push git updates remote branches, and on pull
177 git updates remote branches and fast-forwards, merges or rebases local
180 When you do an initial clone like this::
182 $ git clone -b v1 http://git.python.org/python.git
184 git clones remote repository ``http://git.python.org/python.git`` to
185 directory ``python``, creates remote branches, creates a local branch
186 ``v1``, configure it to track upstream remotes/origin/v1 branch and
187 checks out ``v1`` into the working directory.
189 Updating local and remote branches
190 ----------------------------------
192 There is a major difference between
196 $ git fetch REMOTE BRANCH
202 $ git fetch REMOTE BRANCH:BRANCH
204 The first command fetches commits from the named BRANCH in the REMOTE
205 repository that are not in your repository and leaves the id (the
206 hash) of the head commit in file .git/FETCH_HEAD. But it doesn't
207 update any branch (doesn't move any pointer).
209 The second command fetches commits from the named BRANCH in the REMOTE
210 repository that are not in your repository and updates both the local
211 branch BRANCH and its upstream remote branch. But it refuses to update
212 branches in case of non-fast-forward. And it refuses to update the
215 The first command is used internally by ``git pull``.
219 $ git pull REMOTE BRANCH
225 $ git fetch REMOTE BRANCH
226 $ git merge FETCH_HEAD # FETCH_HEAD is a literal here
228 Certainly, BRANCH in that case should be your current branch. If you
229 want to merge a different branch into your current branch first update
230 that non-current branch and then merge::
232 $ git fetch origin v1:v1 # Update v1
233 $ git pull --rebase origin v2 # Update the current branch v2 using
234 # rebase instead of merge
237 If you have not yet pushed commits on ``v1``, though, the scenario has
238 to become a bit more complex. Git refuses to update
239 non-fast-forwardable branch, and you don't want to do force-pull
240 because that would remove your non-pushed commits and you would need
241 to recover. So you want to rebase ``v1`` but you cannot rebase
242 non-current branch. Hence, checkout ``v1`` and rebase it before
246 $ git pull --rebase origin v1
248 $ git pull --rebase origin v2
251 It is possible to configure git to make it fetch/pull a few branches
252 or all branches at once, so you can simply run
267 Pushing is a bit simpler. There is only one command ``push``. When you
272 $ git push origin v1 v2
274 git guesses (knowing upstream remote branches) that you really want
278 $ git push origin v1:v1 v2:v2
280 Git pushes commits to the remote repo and updates remote branches. Git
281 refuses to push commits that aren't fast-forwardable. You can
282 force-push anyway, but please remember - you can force-push to your
283 own repositories but don't force-push to public or shared repos. If
284 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 Git refuses to push a branch if it's the current branch in the remote
304 non-bare repository: git refuses to update remote working directory.
305 You really should push only to bare repositories. For non-bare
306 repositories git prefers pull-based workflow.
308 When you want to deploy code on a remote host and can only use push
309 (because your workstation is behind a firewall and you cannot pull
310 from it) you do that in two steps using two repositories: you push
311 from the workstation to a bare repo on the remote host, ssh to the
312 remote host and pull from the bare repo to a non-bare deployment repo.
317 Git automatically fetches tags that point to commits being fetched
318 during fetch/pull. To fetch all tags (and commits they point to) run
319 ``git fetch --tags origin``. To fetch some specific tags fetch them
322 $ git fetch origin tag TAG1 tag TAG2...
326 $ git fetch origin tag 1.4.2 tag 2.1.7
328 Git doesn't automatically pushes tags. That allows you to have private
329 tags (lightweight tags are also private for a repo, they cannot be
330 pushed). To push tags list them explicitly::
332 $ git push origin tag 1.4.2
333 $ git push origin v1 v2 tag 2.1.7
335 Don't move tags with ``git tag -f`` after they have been published.
338 Commit editing and caveats
339 ==========================
341 A warning not to edit published (pushed) commits also appears in
342 documentation but it's repeated here anyway as it's very important.
344 It is possible to recover from forced push but it's PITA for the
345 entire team. Please avoid it.
347 To see what commits have not been published yet compare the head of the
348 branch with its upstream remote branch::
350 $ git log origin/v2..
351 $ git log origin/v1..v1
353 For every branch that has an upstream remote branch git maintains an
354 alias @{upstream} (short version @{u}), so the commands above can be
360 To see the status of all branches::
364 To compare the status of local branches with a remote repo::
366 $ git remote show origin
368 Read `how to recover from upstream rebase
369 <https://git-scm.com/docs/git-rebase#_recovering_from_upstream_rebase>`_.
370 It is in ``git help rebase``.
372 On the other hand don't be too afraid about commit editing. You can
373 safely edit, remove, reorder, combine and split commits that hasn't
374 been pushed yet. You can even push commits to your own (backup) repo,
375 edit them later and force-push edited commits to replace what has
376 already been pushed. Not a problem until commits are in a public
377 or shared repository.
383 Whatever you do, don't panic. Almost anything in git can be undone.
384 ``git checkout``, for example, can be used to restore the content of
385 file(s) to that one of a commit. Like this::
387 git checkout HEAD~ README
389 The commands restores the contente of README file to the last but one
390 commit in the current branch. By default a commit ID is simple HEAD;
391 i.e. ``git checkout README`` restores README to the latest commit.
393 (Do not use ``git checkout`` to view a content of a file in a commit,
394 use ``git cat-file -p``; e.g. ``git cat-file -p HEAD~:path/to/README``).
396 TODO: describe undo strategies: git reset, git reflog, git revert.
397 "Commit early, commit often".
400 https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html
406 Internet is full of heated discussions on the topic: "merge or
407 rebase?" Most of them are meaningless. When a DVCS is being used in a
408 big team with a big and complex project with many branches there is
409 simply no way to avoid merges. So the question's diminished to
410 "whether to use rebase, and if yes - when to use rebase?" Considering
411 that it is very much recommended not to rebase published commits the
412 question's diminished even further: "whether to use rebase on
415 That small question is for the team to decide. The author of the PEP
416 recommends to use rebase when pulling, i.e. always do ``git pull
417 --rebase`` or even configure automatic setup of rebase for every new
420 $ git config branch.autosetuprebase true
422 and configure rebase for existing branches::
424 $ git config branch.NAME.rebase true
428 $ git config branch.v1.rebase true
429 $ git config branch.v2.rebase true
431 After that ``git pull origin v2`` becomes equivalent to ``git pull
432 --rebase origin v2``.
434 In case when merge is preferred it is recommended to create new
435 commits in a separate feature or topic branch while using rebase to
436 update the mainline branch. When the topic branch is ready merge it
437 into mainline. To avoid a tedious task of resolving large number of
438 conflicts at once you can merge the topic branch to the mainline from
439 time to time and switch back to the topic branch to continue working
440 on it. The entire workflow would be something like::
442 $ git checkout -b issue-42 # create a new issue branch and switch to it
443 ...edit/test/commit...
445 $ git pull --rebase origin v2 # update v2 from the upstream
447 $ git branch -d issue-42 # delete the topic branch
450 When the topic branch is deleted only the label is removed, commits
451 are stayed in the database, they are now merged into v2::
453 o--o--o--o--o--M--< v2 - the mainline branch
455 --*--*--* - the topic branch, now unnamed
457 The topic branch is deleted to avoid cluttering branch namespace with
458 small topic branches. Information on what issue was fixed or what
459 feature was implemented should be in the commit messages.
465 Git has a builtin merge strategy for what Python core developers call
468 $ git merge -s ours v1 # null-merge v1 into v2
474 https://git-scm.com/book/en/Git-Tools-Rerere
483 Staging area aka index is a distinguishing feature of git. See
485 <https://git.wiki.kernel.org/index.php/WhatIsTheIndex>`_ and
486 `IndexCommandQuickref
487 <https://git.wiki.kernel.org/index.php/IndexCommandQuickref>`_ in Git
491 Advanced configuration
492 ======================
497 Git has builtin mechanisms to handle line endings.
499 TODO: describe crlf configuration and .gitattributes.
505 TODO: dangling objects, git gc, git repack.
506 https://gcc.gnu.org/ml/gcc/2007-12/msg00165.html
512 TODO: sticky options; example: git grep -O.
514 TODO: tricky options; example: git log -p3.
516 TODO: bash/zsh completion, bash/zsh prompt.
517 https://git.kernel.org/cgit/git/git.git/tree/contrib/completion
523 TODO: anonymous access; git over ssh; gitolite; gitweb; cgit; gitlab.
525 http://gitolite.com/gitolite/index.html
527 https://git.kernel.org/cgit/git/git.git/tree/gitweb
529 http://git.zx2c4.com/cgit/
531 From Mercurial to git
532 =====================
534 Mercurial for Git users https://mercurial.selenic.com/wiki/GitConcepts
536 https://github.com/felipec/git-remote-hg
538 https://hg-git.github.io/
550 This document has been placed in the public domain.
557 indent-tabs-mode: nil
558 sentence-end-double-space: t
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