PEP: XXX Title: Collecting information about git Version: $Revision$ Last-Modified: $Date$ Author: Oleg Broytman Status: Draft Type: Informational Content-Type: text/x-rst Created: 01-Jun-2015 Post-History: Abstract ======== 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, 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 Python development from Mercurial to git. The author of the PEP doesn't currently plan to write a Process PEP on migration from Mercurial to git. Documentation ============= Git is accompanied with a lot of documentation, both online and offline. Documentation for starters -------------------------- Git Tutorial: `part 1 `_, `part 2 `_. `Git User's manual `_. `Everyday GIT With 20 Commands Or So `_. `Git workflows `_. Advanced documentation ---------------------- `Git Magic `_, also with a number of translations. `Pro Git `_. 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 `_. `Git Wiki `_. Offline documentation --------------------- 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 `_ or `msysGit `_. MacOS X: use git installed with `XCode `_ or download from `MacPorts `_ or `git-osx-installer `_ or install git with `Homebrew `_: ``brew install git``. `git-cola `_ is a sleek and powerful Git GUI written in Python and GPL licensed. Linux, Windows, MacOS X. `TortoiseGit `_ 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 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 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 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 differentiate 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 repository and remote branches ===================================== Another example of slightly misleading terminology. Remote repositories are really remote, you access them via network (well, a remote repository can be on your local disk, but it's still remote because it's not the current repo). Remote branches, on the other hand, 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 branches live under ``remotes/REMOTE`` namespaces, e.g. ``remotes/origin/v2``. To see the status of remote branches run:: $ git branch -rv To see local and remote branches (and tags) pointing to commits:: $ git log --decorate You never do your own development on remote branches. You create a local branch that has a remote branch as upstream and do development on that local branch. On push git updates remote branches, and on pull git updates remote 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 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 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. But it doesn't update any branch (doesn't move any pointer). 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 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 # FETCH_HEAD is a literal here 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 Push '''' Pushing is a bit simpler. There is only one command ``push``. When you run :: $ git push origin v1 v2 git guesses (knowing upstream remote branches) that you really want :: $ git push origin v1:v1 v2:v2 Git pushes commits to the remote repo and updates remote 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 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`` 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 branch:: $ git log origin/v2.. $ git log origin/v1..v1 For every branch that has an upstream remote 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 `_. 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 ==== TODO: describe undo strategies: git reset, git revert, git checkout, git reflog. "Commit early, commit often". How to undo a merge https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html 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 true 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 and switch to a new branch ...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 - it is the mainline branch \ / --*--*--* - it is 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 strategy for what Python core developers call "null-merge":: $ git merge -s ours v1 # null-merge v1 into v2 ReReRe ====== https://git-scm.com/book/en/Git-Tools-Rerere Advanced topics =============== Staging area ------------ Staging area aka index is a distinguishing feature of git. See `WhatIsTheIndex `_ and `IndexCommandQuickref `_ in Git Wiki. Advanced configuration ====================== Line endings ------------ Git has builtin mechanisms to handle line endings. TODO: describe crlf configuration and .gitattributes. Database maintenance ==================== TODO: dangling objects, git gc, git repack. https://gcc.gnu.org/ml/gcc/2007-12/msg00165.html Tips and tricks =============== TODO: sticky options; example: git grep -O. 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. 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 ========== .. [] Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End: vim: set fenc=us-ascii tw=70 :