X-Git-Url: https://git.phdru.name/?p=git-wiki.git;a=blobdiff_plain;f=pep-git.txt;h=4684b1e739eb1859be92dda50b52e1aa382b5098;hp=d995d2456fe367ceaa1d0fa0a8081274497d2e2c;hb=2df5f521d793c523e8d281ab7922db3b4f44e9ce;hpb=021099ec5db6e77e41c480d68c3c0312d7cabffa diff --git a/pep-git.txt b/pep-git.txt index d995d24..4684b1e 100644 --- a/pep-git.txt +++ b/pep-git.txt @@ -3,7 +3,7 @@ Title: Collecting information about git Version: $Revision$ Last-Modified: $Date$ Author: Oleg Broytman -Status: Active +Status: Draft Type: Informational Content-Type: text/x-rst Created: 01-Jun-2015 @@ -14,7 +14,7 @@ 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, 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 @@ -45,13 +45,13 @@ Git Tutorial: `part 1 `Git workflows `_. +Advanced documentation +---------------------- + `Git Magic `_, also with a number of translations. -Advanced documentation ----------------------- - `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 @@ -62,7 +62,7 @@ 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``. @@ -72,21 +72,33 @@ Quick start Download and installation ------------------------- -Unix users: download and install using your package manager. +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 +`_ or download from +`MacPorts `_ or `git-osx-installer -`_. +`_ or +install git with `Homebrew `_: ``brew install git``. + +`git-cola `_ is a 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:: +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 @@ -98,26 +110,284 @@ 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``. Usually the currently -checked out branch is ``v2``. +local repo has two branches ``v1`` and ``master``. For most examples +the currently checked out branch is ``master``. That is, it's assumed +you have done something like that:: + + $ git clone 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 master, sets +remotes/origin/master 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/master + +The last command creates a new local branch master, sets +remotes/origin/master 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/master``. + +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, updates +remote-tracking branch and leaves the id (the hash) of the head commit +in file .git/FETCH_HEAD. + +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 master # Update the current branch master + # 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 master + $ git pull --rebase origin master + $ 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 master + +git pushes local v1 to remote v1 and local master to remote master. +The same as:: + + $ git push origin v1:v1 master:master + +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. + +That changed in git 2.3, but see `the blog post +`_ +for caveats; in 2.4 the push-to-deploy feature was `further improved +`_. + +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 + $ git fetch origin v1:v1 tag 2.1.7 + +Git doesn't automatically pushes tags. That allows you to have private +tags. To push tags list them explicitly:: + + $ git push origin tag 1.4.2 + $ git push origin v1 master tag 2.1.7 + +Don't move tags with ``git tag -f`` or remove tags with ``git tag -d`` +after they have been published. + +Private information +''''''''''''''''''' + +When cloning/fetching/pulling/pushing git copies only database objects +(commits, trees, files and tags) and symbolic references (branches and +lightweight tags). Everything else is private to the repository and +never cloned, updated or pushed. It's your config, your hooks, your +private exclude file. + +If you want to distribute hooks, copy them to the working tree, add, +commit, push and instruct the team to update ind install the hook +manually. Commit editing and caveats ========================== A warning not to edit published (pushed) commits also appears in -documentation but it's also repeated here as it's very important. +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 see the head of the -remote branch:: +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/master.. + $ git log origin/v1..v1 -For every branch that has an upstream remote branch git maintains an -alias @{upstream} (short version @{u}):: +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 @@ -126,14 +396,364 @@ 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 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. +safely edit, remove, reorder, combine and split commits that haven'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 have +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 +`_ 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 +`_ 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 ``master`` back to the +original commit but preserve two commits created in the current branch +do something like:: + + $ git branch save-master # create a new branch saving master + $ git reflog # find the original place of master + $ git reset $COMMIT_ID + $ git cherry-pick save-master~ save-master + $ git branch -D save-master # 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 revert(s) 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 +`_. + +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.master.rebase true + +After that ``git pull origin master`` becomes equivalent to ``git pull +--rebase origin master``. + +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 master + $ git pull --rebase origin master # update master from the upstream + $ git merge issue-42 + $ git branch -d issue-42 # delete the topic branch + $ git push origin master + +When the topic branch is deleted only the label is removed, commits +are stayed in the database, they are now merged into master:: + + o--o--o--o--o--M--< master - 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 master + + +Advanced configuration +====================== + +Line endings +------------ + +Git has builtin mechanisms to handle line endings between platforms +with different EOL styles. To allow git to do CRLF conversion assign +``text`` attribute to files using `.gitattributes +`_. +For files that have to have specific line ending assign ``eol`` +attribute. For binary files the attribute is, naturally, ``binary``. + +For example:: + + $ cat .gitattributes + *.py text + *.txt text + *.png binary + /readme.txt eol=CRLF + +To check what attributes git uses for files use ``git check-attr`` +command. For example:: + +$ git check-attr -a -- \*.py + + +Advanced topics +=============== + +Staging area +------------ + +Staging area aka index aka cache is a distinguishing feature of git. +Staging area is where git collects patches before committing them. +Separation between collecting patches and commit phases provides a +very useful feature of git: one can review collected patches before +commit and even edit them - remove some hunks, add new hunks and +review again. + +To add files to the index use ``git add``. Collecting patches before +committing means you need to do that for every change, not only to add +new (untracked) files. To simplify committing in case you just want to +commit everything without reviewing run ``git commit --all`` (or just +``-a``) - the command adds every changed tracked file to the index and +then commit. To commit a file or files regardless of patches collected +in the index run ``git commit [--only|-o] -- $FILE...``. + +To add hunks of patches to the index use ``git add --patch`` (or just +``-p``). To remove collected files from the index use ``git reset HEAD +-- $FILE...`` To add/inspect/remove collected hunks use ``git add +--interactive`` (``-i``). + +To see the diff between the index and the last commit (i.e., collected +patches) use ``git diff --cached``. To see the diff between the +working tree and the index (i.e., uncollected patches) use just ``git +diff``. To see the diff between the working tree and the last commit +(i.e., both collected and uncollected patches) run ``git diff HEAD``. + +See `WhatIsTheIndex +`_ and +`IndexCommandQuickref +`_ in Git +Wiki. + + +ReReRe +====== + +https://git-scm.com/book/en/Git-Tools-Rerere + + +Database maintenance +==================== + +Git object database and other files/directories under ``.git`` require +periodic maintenance and cleanup. For example, commit editing left +unreferenced objects (dangling objects, in git terminology) and these +objects should be pruned to avoid collecting cruft in the DB. The +command ``git gc`` is used for maintenance. Git automatically runs +``git gc --auto`` as a part of some commands to do quick maintenance. +Users are recommended to run ``git gc --aggressive`` from time to +time; ``git help gc`` recommends to run it every few hundred +changesets; for more intensive projects it should be something like +once a week and less frequently (biweekly or monthly) for lesser +active projects. + +``git gc --aggressive`` not only removes dangling objects, it also +repacks object database into indexed and better optimized pack(s); it +also packs symbolic references (branches and tags). Another way to do +it is to run ``git repack``. + +There is a well-known `message +`_ from Linus +Torvalds regarding "stupidity" of ``git gc --aggressive``. The message +can safely be ignored now. It is old and outdated, ``git gc +--aggressive`` became much better since that time. + +For those who still prefer ``git repack`` over ``git gc --aggressive`` +the recommended parameters are ``git repack -a -d -f --depth=20 +--window=250``. See `this detailed experiment +`_ +for explanation on the effects of these parameters. + +From time to time run ``git fsck [--strict]`` to verify integrity of +the database. ``git fsck`` could report dangling objects; that's not +an error, just a reminder to perform regular maintenance. + + +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 daemon``); git over ssh; gitolite; +gitweb; cgit; Kallithea; pagure; gogs and gitea; gitlab. + +http://gitolite.com/gitolite/index.html + +https://git.kernel.org/cgit/git/git.git/tree/gitweb + +http://git.zx2c4.com/cgit/ + +https://kallithea-scm.org/ + +https://pagure.io/ + +http://gogs.io/ and http://gitea.io/ + +https://about.gitlab.com/ + + +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