Version: $Revision$
Last-Modified: $Date$
Author: Oleg Broytman <phd@phdru.name>
-Status: Active
+Status: Draft
Type: Informational
Content-Type: text/x-rst
Created: 01-Jun-2015
This Informational PEP collects information about git. There is, of
course, a lot of documentation for git, so the PEP concentrates on
-more complex issues, topics and scenarios.
+more complex issues, scenarios and topics.
The plan is to extend the PEP in the future collecting information
about equivalence of Mercurial and git scenarios to help migrating
The author of the PEP doesn't currently plan to write a Process PEP on
migration from Mercurial to git.
+
Documentation
=============
`Git workflows
<https://www.kernel.org/pub/software/scm/git/docs/gitworkflows.html>`_.
+Advanced documentation
+----------------------
+
`Git Magic
<http://www-cs-students.stanford.edu/~blynn/gitmagic/index.html>`_,
also with a number of translations.
-Advanced documentation
-----------------------
-
`Pro Git <https://git-scm.com/book>`_. The Book about git. Buy it at
Amazon or download in PDF, mobi, or ePub form. Has translations to
many different languages. Download Russian translation from `GArik
Offline documentation
---------------------
-Git has builtin help: run ``git help TOPIC``. For example, run
+Git has builtin help: run ``git help $TOPIC``. For example, run
``git help git`` or ``git help help``.
+
+Quick start
+===========
+
+Download and installation
+-------------------------
+
+Unix users: download and install using your package manager.
+
+Microsoft Windows: download `git-for-windows
+<https://github.com/git-for-windows/git/releases>`_ or `msysGit
+<https://github.com/msysgit/msysgit/releases>`_.
+
+MacOS X: use git installed with `XCode
+<https://developer.apple.com/xcode/downloads/>`_ or download from
+`MacPorts <https://www.macports.org/ports.php?by=name&substr=git>`_ or
+`git-osx-installer
+<http://sourceforge.net/projects/git-osx-installer/files/>`_ or
+install git with `Homebrew <http://brew.sh/>`_: ``brew install git``.
+
+`git-cola <https://git-cola.github.io/index.html>`_ is a Git GUI
+written in Python and GPL licensed. Linux, Windows, MacOS X.
+
+`TortoiseGit <https://tortoisegit.org/>`_ is a Windows Shell Interface
+to Git based on TortoiseSVN; open source.
+
+Initial configuration
+---------------------
+
+This simple code is often appears in documentation, but it is
+important so let repeat it here. Git stores author and committer
+names/emails in every commit, so configure your real name and
+preferred email::
+
+ $ git config --global user.name "User Name"
+ $ git config --global user.email user.name@example.org
+
+
+Examples in this PEP
+====================
+
+Examples of git commands in this PEP use the following approach. It is
+supposed that you, the user, works with a local repository named
+``python`` that has an upstream remote repo named ``origin``. Your
+local repo has two branches ``v1`` and ``v2``. For most examples the
+currently checked out branch is ``v2``. That is, it's assumed you have
+done something like that::
+
+ $ git clone -b v2 http://git.python.org/python.git
+ $ cd python
+ $ git branch v1 origin/v1
+
+The first command clones remote repository into local directory
+`python``, creates a new local branch v2, sets remotes/origin/v2 as
+its upstream remote-tracking branch and checks it out into the working
+directory.
+
+The last command creates a new local branch v1 and sets
+remotes/origin/v1 as its upstream remote-tracking branch.
+
+The same result can be achieved with commands::
+
+ $ git clone -b v1 http://git.python.org/python.git
+ $ cd python
+ $ git checkout --track origin/v2
+
+The last command creates a new local branch v2, sets remotes/origin/v2
+as its upstream remote-tracking branch and checks it out into the
+working directory.
+
+
+Branches and branches
+=====================
+
+Git terminology can be a bit misleading. Take, for example, the term
+"branch". In git it has two meanings. A branch is a directed line of
+commits (possibly with merges). And a branch is a label or a pointer
+assigned to a line of commits. It is important to distinguish when you
+talk about commits and when about their labels. Lines of commits are
+by itself unnamed and are usually only lengthening and merging.
+Labels, on the other hand, can be created, moved, renamed and deleted
+freely.
+
+
+Remote repositories and remote branches
+=======================================
+
+Remote-tracking branches are branches (pointers to commits) in your
+local repository. They are there for you to remember what branches and
+commits have been pulled from and pushed to what remote repos (you can
+pull from and push to many remotes). Remote-tracking branches live
+under ``remotes/$REMOTE`` namespaces, e.g. ``remotes/origin/v2``.
+
+To see the status of remote-tracking branches run::
+
+ $ git branch -rv
+
+To see local and remote-tracking branches (and tags) pointing to
+commits::
+
+ $ git log --decorate
+
+You never do your own development on remote-tracking branches. You
+create a local branch that has a remote branch as upstream and do
+development on that local branch. On push git pushes commits to the
+remote repo and updates remote-tracking branches, on pull git fetches
+commits from the remote repo, updates remote-tracking branches and
+fast-forwards, merges or rebases local branches.
+
+When you do an initial clone like this::
+
+ $ git clone -b v1 http://git.python.org/python.git
+
+git clones remote repository ``http://git.python.org/python.git`` to
+directory ``python``, creates remote-tracking branches, creates a
+local branch ``v1``, configure it to track upstream remotes/origin/v1
+branch and checks out ``v1`` into the working directory.
+
+Updating local and remote-tracking branches
+-------------------------------------------
+
+There is a major difference between
+
+::
+
+ $ git fetch $REMOTE $BRANCH
+
+and
+
+::
+
+ $ git fetch $REMOTE $BRANCH:$BRANCH
+
+The first command fetches commits from the named $BRANCH in the
+$REMOTE repository that are not in your repository and leaves the id
+(the hash) of the head commit in file .git/FETCH_HEAD and updates
+remote-tracking branch.
+
+The second command fetches commits from the named $BRANCH in the
+$REMOTE repository that are not in your repository and updates both
+the local branch $BRANCH and its upstream remote-tracking branch. But
+it refuses to update branches in case of non-fast-forward. And it
+refuses to update the current branch.
+
+The first command is used internally by ``git pull``.
+
+::
+
+ $ git pull $REMOTE $BRANCH
+
+is equivalent to
+
+::
+
+ $ git fetch $REMOTE $BRANCH
+ $ git merge FETCH_HEAD
+
+Certainly, $BRANCH in that case should be your current branch. If you
+want to merge a different branch into your current branch first update
+that non-current branch and then merge::
+
+ $ git fetch origin v1:v1 # Update v1
+ $ git pull --rebase origin v2 # Update the current branch v2 using
+ # rebase instead of merge
+ $ git merge v1
+
+If you have not yet pushed commits on ``v1``, though, the scenario has
+to become a bit more complex. Git refuses to update
+non-fast-forwardable branch, and you don't want to do force-pull
+because that would remove your non-pushed commits and you would need
+to recover. So you want to rebase ``v1`` but you cannot rebase
+non-current branch. Hence, checkout ``v1`` and rebase it before
+merging::
+
+ $ git checkout v1
+ $ git pull --rebase origin v1
+ $ git checkout v2
+ $ git pull --rebase origin v2
+ $ git merge v1
+
+It is possible to configure git to make it fetch/pull a few branches
+or all branches at once, so you can simply run
+
+::
+
+ $ git pull origin
+
+or even
+
+::
+
+ $ git pull
+
+Default remote repository for fetching/pulling is origin. Default set
+of references to fetch is calculated using matching algorithm: git
+fetches all branches having the same name on both ends.
+
+Push
+''''
+
+Pushing is a bit simpler. There is only one command ``push``. When you
+run
+
+::
+
+ $ git push origin v1 v2
+
+git pushes local v1 to remote v1 and local v2 to remote v2. The same
+as::
+
+ $ git push origin v1:v1 v2:v2
+
+Git pushes commits to the remote repo and updates remote-tracking
+branches. Git refuses to push commits that aren't fast-forwardable.
+You can force-push anyway, but please remember - you can force-push to
+your own repositories but don't force-push to public or shared repos.
+If you find git refuses to push commits that aren't fast-forwardable,
+better fetch and merge commits from the remote repo (or rebase your
+commits on top of the fetched commits), then push. Only force-push if
+you know what you do and why you do it. See the section `Commit
+editing and caveats`_ below.
+
+It is possible to configure git to make it push a few branches or all
+branches at once, so you can simply run
+
+::
+
+ $ git push origin
+
+or even
+
+::
+
+ $ git push
+
+Default remote repository for pushing is origin. Default set
+of references to push in git before 2.0 is calculated using matching
+algorithm: git pushes all branches having the same name on both ends.
+Default set of references to push in git 2.0+ is calculated using
+simple algorithm: git pushes the current branch back to its
+@{upstream}.
+
+To configure git before 2.0 to the new behaviour run::
+
+$ git config push.default simple
+
+To configure git 2.0+ to the old behaviour run::
+
+$ git config push.default matching
+
+Git refuses to push a branch if it's the current branch in the remote
+non-bare repository: git refuses to update remote working directory.
+You really should push only to bare repositories. For non-bare
+repositories git prefers pull-based workflow.
+
+When you want to deploy code on a remote host and can only use push
+(because your workstation is behind a firewall and you cannot pull
+from it) you do that in two steps using two repositories: you push
+from the workstation to a bare repo on the remote host, ssh to the
+remote host and pull from the bare repo to a non-bare deployment repo.
+
+Tags
+''''
+
+Git automatically fetches tags that point to commits being fetched
+during fetch/pull. To fetch all tags (and commits they point to) run
+``git fetch --tags origin``. To fetch some specific tags fetch them
+explicitly::
+
+ $ git fetch origin tag $TAG1 tag $TAG2...
+
+For example::
+
+ $ git fetch origin tag 1.4.2 tag 2.1.7
+
+Git doesn't automatically pushes tags. That allows you to have private
+tags (lightweight tags are also private for a repo, they cannot be
+pushed). To push tags list them explicitly::
+
+ $ git push origin tag 1.4.2
+ $ git push origin v1 v2 tag 2.1.7
+
+Don't move tags with ``git tag -f`` or remove tags with ``git tag -d``
+after they have been published.
+
+
+Commit editing and caveats
+==========================
+
+A warning not to edit published (pushed) commits also appears in
+documentation but it's repeated here anyway as it's very important.
+
+It is possible to recover from forced push but it's PITA for the
+entire team. Please avoid it.
+
+To see what commits have not been published yet compare the head of the
+branch with its upstream remote-tracking branch::
+
+ $ git log origin/v2..
+ $ git log origin/v1..v1
+
+For every branch that has an upstream remote-tracking branch git
+maintains an alias @{upstream} (short version @{u}), so the commands
+above can be given as::
+
+ $ git log @{u}..
+ $ git log v1@{u}..v1
+
+To see the status of all branches::
+
+ $ git branch -avv
+
+To compare the status of local branches with a remote repo::
+
+ $ git remote show origin
+
+Read `how to recover from upstream rebase
+<https://git-scm.com/docs/git-rebase#_recovering_from_upstream_rebase>`_.
+It is in ``git help rebase``.
+
+On the other hand don't be too afraid about commit editing. You can
+safely edit, remove, reorder, combine and split commits that hasn't
+been pushed yet. You can even push commits to your own (backup) repo,
+edit them later and force-push edited commits to replace what has
+already been pushed. Not a problem until commits are in a public
+or shared repository.
+
+
+Undo
+====
+
+Whatever you do, don't panic. Almost anything in git can be undone.
+
+git checkout: restore file's content
+------------------------------------
+
+``git checkout``, for example, can be used to restore the content of
+file(s) to that one of a commit. Like this::
+
+ git checkout HEAD~ README
+
+The commands restores the contents of README file to the last but one
+commit in the current branch. By default the commit ID is simply HEAD;
+i.e. ``git checkout README`` restores README to the latest commit.
+
+(Do not use ``git checkout`` to view a content of a file in a commit,
+use ``git cat-file -p``; e.g. ``git cat-file -p HEAD~:path/to/README``).
+
+git reset: remove (non-pushed) commits
+--------------------------------------
+
+``git reset`` moves the head of the current branch. The head can be
+moved to point to any commit but it's often used to remove a commit or
+a few (preferably, non-pushed ones) from the top of the branch - that
+is, to move the branch backward in order to undo a few (non-pushed)
+commits.
+
+``git reset`` has three modes of operation - soft, hard and mixed.
+Default is mixed. ProGit `explains
+<https://git-scm.com/book/en/Git-Tools-Reset-Demystified>`_ the
+difference very clearly. Bare repositories don't have indices or
+working trees so in a bare repo only soft reset is possible.
+
+Unstaging
+'''''''''
+
+Mixed mode reset with a path or paths can be used to unstage changes -
+that is, to remove from index changes added with ``git add`` for
+committing. See `The Book
+<https://git-scm.com/book/en/Git-Basics-Undoing-Things>`_ for details
+about unstaging and other undo tricks.
+
+git reflog: reference log
+-------------------------
+
+Removing commits with ``git reset`` or moving the head of a branch
+sounds dangerous and it is. But there is a way to undo: another
+reset back to the original commit. Git doesn't remove commits
+immediately; unreferenced commits (in git terminology they are called
+"dangling commits") stay in the database for some time (default is two
+weeks) so you can reset back to it or create a new branch pointing to
+the original commit.
+
+For every move of a branch's head - with ``git commit``, ``git
+checkout``, ``git fetch``, ``git pull``, ``git rebase``, ``git reset``
+and so on - git stores a reference log (reflog for short). For every
+move git stores where the head was. Command ``git reflog`` can be used
+to view (and manipulate) the log.
+
+In addition to the moves of the head of every branch git stores the
+moves of the HEAD - a symbolic reference that (usually) names the
+current branch. HEAD is changed with ``git checkout $BRANCH``.
+
+By default ``git reflog`` shows the moves of the HEAD, i.e. the
+command is equivalent to ``git reflog HEAD``. To show the moves of the
+head of a branch use the command ``git reflog $BRANCH``.
+
+So to undo a ``git reset`` lookup the original commit in ``git
+reflog``, verify it with ``git show`` or ``git log`` and run ``git
+reset $COMMIT_ID``. Git stores the move of the branch's head in
+reflog, so you can undo that undo later again.
+
+In a more complex situation you'd want to move some commits along with
+resetting the head of the branch. Cherry-pick them to the new branch.
+For example, if you want to reset the branch ``v2`` back to the
+original commit but preserve two commits created in the current branch
+do something like::
+
+ $ git branch save-v2 # create a new branch saving v2
+ $ git reflog # find the original place of v2
+ $ git reset $COMMIT_ID
+ $ git cherry-pick save-v2~ save-v2
+ $ git branch -D save-v2 # remove temporary branch
+
+git revert: revert a commit
+---------------------------
+
+``git revert`` reverts a commit or commits, that is, it creates a new
+commit or commits that reverts the effects of the given commits. It's
+the only way to undo published commits (``git commit --amend``, ``git
+rebase`` and ``git reset`` change the branch in non-fast-forwardable
+ways so they should only be used for non-pushed commits.)
+
+There is a problem with reverting a merge commit. ``git revert`` can
+undo the code created by the merge commit but it cannot undo the fact
+of merge. See the discussion `How to revert a faulty merge
+<https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html>`_.
+
+One thing that cannot be undone
+-------------------------------
+
+Whatever you undo, there is one thing that cannot be undone -
+overwritten uncommitted changes. Uncommitted changes don't belong to
+git so git cannot help preserving them.
+
+Most of the time git warns you when you're going to execute a command
+that overwrites uncommitted changes. Git warns you when you try to
+switch branches with ``git checkout``. It warns you when you're going
+to rebase with non-clean working tree. It refuses to pull new commits
+over non-committed files.
+
+But there are commands that do exactly that - overwrite files in the
+working tree. Commands like ``git checkout $PATHs`` or ``git reset
+--hard`` silently overwrite files including your uncommitted changes.
+
+With that in mind you can understand the stance "commit early, commit
+often". Commit as often as possible. Commit on every save in your
+editor or IDE. You can edit your commits before pushing - change,
+reorder, combine, remove. But save your changes in git database,
+either commit changes or at least stash them with ``git stash``.
+
+
+Merge or rebase?
+================
+
+Internet is full of heated discussions on the topic: "merge or
+rebase?" Most of them are meaningless. When a DVCS is being used in a
+big team with a big and complex project with many branches there is
+simply no way to avoid merges. So the question's diminished to
+"whether to use rebase, and if yes - when to use rebase?" Considering
+that it is very much recommended not to rebase published commits the
+question's diminished even further: "whether to use rebase on
+non-pushed commits?"
+
+That small question is for the team to decide. The author of the PEP
+recommends to use rebase when pulling, i.e. always do ``git pull
+--rebase`` or even configure automatic setup of rebase for every new
+branch::
+
+ $ git config branch.autosetuprebase always
+
+and configure rebase for existing branches::
+
+ $ git config branch.$NAME.rebase true
+
+For example::
+
+ $ git config branch.v1.rebase true
+ $ git config branch.v2.rebase true
+
+After that ``git pull origin v2`` becomes equivalent to ``git pull
+--rebase origin v2``.
+
+In case when merge is preferred it is recommended to create new
+commits in a separate feature or topic branch while using rebase to
+update the mainline branch. When the topic branch is ready merge it
+into mainline. To avoid a tedious task of resolving large number of
+conflicts at once you can merge the topic branch to the mainline from
+time to time and switch back to the topic branch to continue working
+on it. The entire workflow would be something like::
+
+ $ git checkout -b issue-42 # create a new issue branch and switch to it
+ ...edit/test/commit...
+ $ git checkout v2
+ $ git pull --rebase origin v2 # update v2 from the upstream
+ $ git merge issue-42
+ $ git branch -d issue-42 # delete the topic branch
+ $ git push origin v2
+
+When the topic branch is deleted only the label is removed, commits
+are stayed in the database, they are now merged into v2::
+
+ o--o--o--o--o--M--< v2 - the mainline branch
+ \ /
+ --*--*--* - the topic branch, now unnamed
+
+The topic branch is deleted to avoid cluttering branch namespace with
+small topic branches. Information on what issue was fixed or what
+feature was implemented should be in the commit messages.
+
+
+Null-merges
+===========
+
+Git has a builtin merge strategy for what Python core developers call
+"null-merge"::
+
+ $ git merge -s ours v1 # null-merge v1 into v2
+
+
+Advanced configuration
+======================
+
+Line endings
+------------
+
+Git has builtin mechanisms to handle line endings.
+
+TODO: describe crlf configuration and .gitattributes.
+
+
+Advanced topics
+===============
+
+Staging area
+------------
+
+Staging area aka index is a distinguishing feature of git. See
+`WhatIsTheIndex
+<https://git.wiki.kernel.org/index.php/WhatIsTheIndex>`_ and
+`IndexCommandQuickref
+<https://git.wiki.kernel.org/index.php/IndexCommandQuickref>`_ in Git
+Wiki.
+
+
+ReReRe
+======
+
+https://git-scm.com/book/en/Git-Tools-Rerere
+
+
+Database maintenance
+====================
+
+TODO: dangling objects, git gc, git repack.
+
+https://gcc.gnu.org/ml/gcc/2007-12/msg00165.html
+
+http://vcscompare.blogspot.ru/2008/06/git-repack-parameters.html
+
+
+Tips and tricks
+===============
+
+TODO: sticky options; example: git grep -O.
+
+TODO: tricky options; example: git log -p3.
+
+TODO: bash/zsh completion, bash/zsh prompt.
+https://git.kernel.org/cgit/git/git.git/tree/contrib/completion
+
+
+git on server
+=============
+
+TODO: anonymous access; git over ssh; gitolite; gitweb; cgit; gitlab.
+
+http://gitolite.com/gitolite/index.html
+
+https://git.kernel.org/cgit/git/git.git/tree/gitweb
+
+http://git.zx2c4.com/cgit/
+
+From Mercurial to git
+=====================
+
+Mercurial for Git users https://mercurial.selenic.com/wiki/GitConcepts
+
+https://github.com/felipec/git-remote-hg
+
+https://hg-git.github.io/
+
+
References
==========
projects / git-wiki.git / blobdiff