PEP: 103 Title: Collecting information about git Author: Oleg Broytman
<phd@phdru.name> Status: Withdrawn Type: Informational Created:
01-Jun-2015 Post-History: 12-Sep-2015

It is too generic and doesn't really deal with Python development. It is
no longer updated.

The content was moved to Python Wiki. Make further updates in the wiki.

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 (and more related to Python development) issues, scenarios and
examples.

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 Python development 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, with a number of translations.

Pro Git. The Book about git. Buy it at Amazon or download in PDF, mobi,
or ePub form. It has translations to many different languages. Download
Russian translation from GArik.

Git Wiki.

Git Buch (German).

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.

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 (repository) 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. 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 master. For most examples the currently checked out
branch is master. That is, it's assumed you have done something like
that:

    $ git clone https://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 https://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 git (and 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 https://git.python.org/python.git

git clones remote repository https://git.python.org/python.git to
directory python, creates a remote named origin, 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.

Some commands, like git status --branch and git branch --verbose, report
the difference between local and remote branches. Please remember they
only do comparison with remote-tracking branches in your local
repository, and the state of those remote-tracking branches can be
outdated. To update remote-tracking branches you either fetch and merge
(or rebase) commits from the remote repository or update remote-tracking
branches without updating local branches.

Updating local and remote-tracking branches

To update remote-tracking branches without updating local branches run
git remote update [$REMOTE...]. For example:

    $ git remote update
    $ git remote update origin

Fetch and pull

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 (currently checked out branch, where HEAD is pointing
to).

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 doesn't allow 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

Or push all tags at once:

    $ git push --tags origin

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 and install the hooks
manually.

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 a 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/master..  # from origin/master to HEAD (of master)
    $ git log origin/v1..v1  # from origin/v1 to the head of 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. It is in git help rebase.

On the other hand, don't be too afraid about commit editing. You can
safely edit, reorder, remove, 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 doesn't allow you to switch
branches with git checkout. It stops 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 - edit commit messages,
change commits, reorder, combine, split, 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. To preserve the beauty of
linear history it's recommended to use rebase when pulling, i.e. 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.

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.

But even that small amount of rebasing could be too big in case of
long-lived merged branches. Imagine you're doing work in both v1 and
master branches, regularly merging v1 into master. After some time you
will have a lot of merge and non-merge commits in master. Then you want
to push your finished work to a shared repository and find someone has
pushed a few commits to v1. Now you have a choice of two equally bad
alternatives: either you fetch and rebase v1 and then have to recreate
all you work in master (reset master to the origin, merge v1 and
cherry-pick all non-merge commits from the old master); or merge the new
v1 and loose the beauty of linear history.

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

Branching models

Git doesn't assume any particular development model regarding branching
and merging. Some projects prefer to graduate patches from the oldest
branch to the newest, some prefer to cherry-pick commits backwards, some
use squashing (combining a number of commits into one). Anything is
possible.

There are a few examples to start with. git help workflows describes how
the very git authors develop git.

ProGit book has a few chapters devoted to branch management in different
projects: Git Branching - Branching Workflows and Distributed Git -
Contributing to a Project.

There is also a well-known article A successful Git branching model by
Vincent Driessen. It recommends a set of very detailed rules on creating
and managing mainline, topic and bugfix branches. To support the model
the author implemented git flow extension.

Advanced configuration

Line endings

Git has builtin mechanisms to handle line endings between platforms with
different end-of-line styles. To allow git to do CRLF conversion assign
text attribute to files using .gitattributes. For files that have to
have specific line endings 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

Useful assets

GitAlias (repository) is a big collection of aliases. A careful
selection of aliases for frequently used commands could save you a lot
of keystrokes!

GitIgnore and https://github.com/github/gitignore are collections of
.gitignore files for all kinds of IDEs and programming languages. Python
included!

pre-commit (repositories) is a framework for managing and maintaining
multi-language pre-commit hooks. The framework is written in Python and
has a lot of plugins for many programming languages.

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: you 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.

Root

Git switches to the root (top-level directory of the project where .git
subdirectory exists) before running any command. Git remembers though
the directory that was current before the switch. Some programs take
into account the current directory. E.g., git status shows file paths of
changed and unknown files relative to the current directory; git grep
searches below the current directory; git apply applies only those hunks
from the patch that touch files below the current directory.

But most commands run from the root and ignore the current directory.
Imagine, for example, that you have two work trees, one for the branch
v1 and the other for master. If you want to merge v1 from a subdirectory
inside the second work tree you must write commands as if you're in the
top-level dir. Let take two work trees, project-v1 and project, for
example:

    $ cd project/subdirectory
    $ git fetch ../project-v1 v1:v1
    $ git merge v1

Please note the path in git fetch ../project-v1 v1:v1 is ../project-v1
and not ../../project-v1 despite the fact that we run the commands from
a subdirectory, not from the root.

ReReRe

Rerere is a mechanism that helps to resolve repeated merge conflicts.
The most frequent source of recurring merge conflicts are topic branches
that are merged into mainline and then the merge commits are removed;
that's often performed to test the topic branches and train rerere;
merge commits are removed to have clean linear history and finish the
topic branch with only one last merge commit.

Rerere works by remembering the states of tree before and after a
successful commit. That way rerere can automatically resolve conflicts
if they appear in the same files.

Rerere can be used manually with git rerere command but most often it's
used automatically. Enable rerere with these commands in a working tree:

    $ git config rerere.enabled true
    $ git config rerere.autoupdate true

You don't need to turn rerere on globally - you don't want rerere in
bare repositories or single-branch repositories; you only need rerere in
repos where you often perform merges and resolve merge conflicts.

See Rerere in The Book.

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 of the effects of these
parameters.

From time to time run git fsck [--strict] to verify integrity of the
database. git fsck may produce a list of dangling objects; that's not an
error, just a reminder to perform regular maintenance.

Tips and tricks

Command-line options and arguments

git help cli recommends not to combine short options/flags. Most of the
times combining works: git commit -av works perfectly, but there are
situations when it doesn't. E.g., git log -p -5 cannot be combined as
git log -p5.

Some options have arguments, some even have default arguments. In that
case the argument for such option must be spelled in a sticky way:
-Oarg, never -O arg because for an option that has a default argument
the latter means "use default value for option -O and pass arg further
to the option parser". For example, git grep has an option -O that
passes a list of names of the found files to a program; default program
for -O is a pager (usually less), but you can use your editor:

    $ git grep -Ovim  # but not -O vim

BTW, if git is instructed to use less as the pager (i.e., if pager is
not configured in git at all it uses less by default, or if it gets less
from GIT_PAGER or PAGER environment variables, or if it was configured
with git config [--global] core.pager less, or less is used in the
command git grep -Oless) git grep passes +/$pattern option to less which
is quite convenient. Unfortunately, git grep doesn't pass the pattern if
the pager is not exactly less, even if it's less with parameters
(something like git config [--global] core.pager less -FRSXgimq);
fortunately, git grep -Oless always passes the pattern.

bash/zsh completion

It's a bit hard to type
git rebase --interactive --preserve-merges HEAD~5 manually even for
those who are happy to use command-line, and this is where shell
completion is of great help. Bash/zsh come with programmable completion,
often automatically installed and enabled, so if you have bash/zsh and
git installed, chances are you are already done - just go and use it at
the command-line.

If you don't have necessary bits installed, install and enable
bash_completion package. If you want to upgrade your git completion to
the latest and greatest download necessary file from git contrib.

Git-for-windows comes with git-bash for which bash completion is
installed and enabled.

bash/zsh prompt

For command-line lovers shell prompt can carry a lot of useful
information. To include git information in the prompt use git-prompt.sh.
Read the detailed instructions in the file.

Search the Net for "git prompt" to find other prompt variants.

SSH connection sharing

SSH connection sharing is a feature of OpenSSH and perhaps derivatives
like PuTTY. SSH connection sharing is a way to decrease ssh client
startup time by establishing one connection and reusing it for all
subsequent clients connecting to the same server. SSH connection sharing
can be used to speedup a lot of short ssh sessions like scp, sftp, rsync
and of course git over ssh. If you regularly fetch/pull/push from/to
remote repositories accessible over ssh then using ssh connection
sharing is recommended.

To turn on ssh connection sharing add something like this to your
~/.ssh/config:

    Host *
    ControlMaster auto
    ControlPath ~/.ssh/mux-%r@%h:%p
    ControlPersist 600

See OpenSSH wikibook and search for more information.

SSH connection sharing can be used at GitHub, GitLab and SourceForge
repositories, but please be advised that BitBucket doesn't allow it and
forcibly closes master connection after a short inactivity period so you
will see errors like this from ssh: "Connection to bitbucket.org closed
by remote host."

git on server

The simplest way to publish a repository or a group of repositories is
git daemon. The daemon provides anonymous access, by default it is
read-only. The repositories are accessible by git protocol (git://
URLs). Write access can be enabled but the protocol lacks any
authentication means, so it should be enabled only within a trusted LAN.
See git help daemon for details.

Git over ssh provides authentication and repo-level authorisation as
repositories can be made user- or group-writeable (see parameter
core.sharedRepository in git help config). If that's too permissive or
too restrictive for some project's needs there is a wrapper gitolite
that can be configured to allow access with great granularity; gitolite
is written in Perl and has a lot of documentation.

Web interface to browse repositories can be created using gitweb or
cgit. Both are CGI scripts (written in Perl and C). In addition to web
interface both provide read-only dumb http access for git (http(s)://
URLs). Klaus is a small and simple WSGI web server that implements both
web interface and git smart HTTP transport; supports Python 2 and Python
3, performs syntax highlighting.

There are also more advanced web-based development environments that
include ability to manage users, groups and projects; private,
group-accessible and public repositories; they often include issue
trackers, wiki pages, pull requests and other tools for development and
communication. Among these environments are Kallithea and pagure, both
are written in Python; pagure was written by Fedora developers and is
being used to develop some Fedora projects. GitPrep is yet another
GitHub clone, written in Perl. Gogs is written in Go. GitBucket is
written in Scala.

And last but not least, GitLab. It's perhaps the most advanced web-based
development environment for git. Written in Ruby, community edition is
free and open source (MIT license).

From Mercurial to git

There are many tools to convert Mercurial repositories to git. The most
famous are, probably, hg-git and fast-export (many years ago it was
known under the name hg2git).

But a better tool, perhaps the best, is git-remote-hg. It provides
transparent bidirectional (pull and push) access to Mercurial
repositories from git. Its author wrote a comparison of alternatives
that seems to be mostly objective.

To use git-remote-hg, install or clone it, add to your PATH (or copy
script git-remote-hg to a directory that's already in PATH) and prepend
hg:: to Mercurial URLs. For example:

    $ git clone https://github.com/felipec/git-remote-hg.git
    $ PATH=$PATH:"`pwd`"/git-remote-hg
    $ git clone hg::https://hg.python.org/peps/ PEPs

To work with the repository just use regular git commands including
git fetch/pull/push.

To start converting your Mercurial habits to git see the page Mercurial
for Git users at Mercurial wiki. At the second half of the page there is
a table that lists corresponding Mercurial and git commands. Should work
perfectly in both directions.

Python Developer's Guide also has a chapter Mercurial for git developers
that documents a few differences between git and hg.

Git and GitHub

gitsome - Git/GitHub command line interface (CLI). Written in Python,
work on MacOS, Unix, Windows. Git/GitHub CLI with autocomplete, includes
many GitHub integrated commands that work with all shells, builtin xonsh
with Python REPL to run Python commands alongside shell commands,
command history, customizable highlighting, thoroughly documented.

Copyright

This document has been placed in the public domain.