Git: Difference between revisions

Latest revision as of 20:30, 27 February 2024

"I've met people who thought git is a front-end to GitHub. They were wrong, git is a front-end to the AUR." — Linus T.

Git is the version control system (VCS) designed and developed by Linus Torvalds, the creator of the Linux kernel. Git is now used to maintain AUR packages, as well as many other projects, including sources for the Linux kernel.

Installation

Install the git package. For the development version, install the git-git^AUR package. Check the optional dependencies when using tools such as git svn, git gui and gitk.

Graphical front-ends

Configuration

In order to use Git you need to set at least a name and email:

$ git config --global user.name  "John Doe"
$ git config --global user.email "johndoe@example.com"

See Getting Started - First-Time Git Setup.

See #Tips and tricks for more settings.

Usage

A Git repository is contained in a .git directory, which holds the revision history and other metadata. The directory tracked by the repository, by default the parent directory, is called the working directory. Changes in the working tree need to be staged before they can be recorded (committed) to the repository. Git also lets you restore, previously committed, working tree files.

See Getting Started - Git Basics.

This article or section is being considered for removal.

Reason: Entire section regurgitates the upstream documentation, either remove the sections entirely or link to the upstream docs in each subsection. (Discuss in Talk:Git#Deletion/editing of regurgitated docs)

This article or section needs language, wiki syntax or style improvements. See Help:Style for reference.

Reason: Use subsections instead of unordered lists, subsections allow people to link directly to the section within the wiki, and spaces out the page better, this can not be done with unordered lists. (Discuss in Talk:Git)

Getting a Git repository

Initialize a repository

git init, see git-init(1)

Clone an existing repository

git clone repository, see git-clone(1) (also explains the Git URLs)

Recording changes

Git projects have a staging area, which is an index file in your Git directory, that stores the changes that will go into your next commit. To record a modified file you therefore firstly need to add it to the index (stage it). The git commit command then stores the current index in a new commit.

Staging changes

Add working tree changes to the index

git add pathspec, see git-add(1)

Remove changes from the index

git reset pathspec, see git-reset(1)

Show changes to be committed, unstaged changes and untracked files

git status, see git-status(1)

You can tell Git to ignore certain untracked files using .gitignore files, see gitignore(5).

Git does not track file movement. Move detection during merges is based only on content similarity. The git mv command is just there for convenience and is equivalent to:

$ mv -i foo bar
$ git reset -- foo
$ git add bar

Committing changes

The git commit command records the staged changes to the repository, see git-commit(1).

-m – supply the commit message as an argument, instead of composing it in your default text editor
-a – automatically stage files that have been modified or deleted (does not add untracked files)
--amend – redo the last commit, amending the commit message or the committed files

Tip: Always commit small changes frequently and with meaningful messages.

Revision selection

Git offers multiple ways to specify revisions, see gitrevisions(7) and Revision Selection.

Many Git commands take revisions as arguments. A commit can be identified by any of the following:

SHA-1 hash of the commit (the first 7 digits are usually sufficient to identify it uniquely)
Any commit label such as a branch or tag name
The label HEAD always refers to the currently checked-out commit (usually the head of the branch, unless you used git checkout to jump back in history to an old commit)
Any of the above plus ~ to refer to previous commits. For example, HEAD~ refers to one commit before HEAD and HEAD~5 refers to five commits before HEAD.

Viewing changes

Show differences between commits:

$ git diff HEAD HEAD~3

or between staging area and working tree:

$ git diff

View history of changes (where "-N" is the number of latest commits):

$ git log -p (-N)

Undoing things

git checkout - to restore working tree files, see git-checkout(1)
git reset - reset current HEAD to the specified state, see git-reset(1)
git revert - revert some existing commits, see git-revert(1)

These, along with few others, are further explained at undoing-changes.

For more complex modifications of history, such as git commit --amend and git rebase see, for example, rewriting-history. It is highly advised not to use such rewrites for commits that were collaborated with other users. Or, at the very least, highly coordinate it in advance.

Branching

This article or section needs expansion.

Reason: Add links for some common branching models. (Discuss in Talk:Git)

Fixes and new features are usually tested in branches. When changes are satisfactory they can merged back into the default (master) branch.

Create a branch, whose name accurately reflects its purpose:

$ git branch help-section-addition

List branches:

$ git branch

Switch branches:

$ git checkout branch

Create and switch:

$ git checkout -b branch

Merge a branch back to the master branch:

$ git checkout master
$ git merge branch

The changes will be merged if they do not conflict. Otherwise, Git will print an error message, and annotate files in the working tree to record the conflicts. The annotations can be displayed with git diff. Conflicts are resolved by editing the files to remove the annotations, and committing the final version. See #Dealing with merges below.

When done with a branch, delete it with:

$ git branch -d branch

Collaboration

A typical Git work-flow is:

Create a new repository or clone a remote one.
Create a branch to make changes; then commit those changes.
Consolidate commits for better organization/understanding.
Merge commits back into the main branch.
(Optional) Push changes to a remote server.

Pull requests

After making and committing some changes, the contributor can ask the original author to merge them. This is called a pull request.

To pull:

$ git pull location master

The pull command combines both fetching and merging. If there are conflicts (e.g. the original author made changes in the same time span), then it will be necessary to manually fix them.

Alternatively, the original author can pick the changes wanting to be incorporated. Using the fetch option (and log option with a special FETCH_HEAD symbol), the contents of the pull request can be viewed before deciding what to do:

$ git fetch location master
$ git log -p HEAD..FETCH_HEAD
$ git merge location master

Using remotes

Remotes are aliases for tracked remote repositories. A label is created defining a location. These labels are used to identify frequently accessed repositories.

Create a remote:

$ git remote add label location

Fetch a remote:

$ git fetch label

Show differences between master and a remote master:

$ git log -p master..label/master

View remotes for the current repository:

$ git remote -v

When defining a remote that is a parent of the fork (the project lead), it is defined as upstream.

Push to a repository

After being given rights from the original authors, push changes with:

$ git push location branch

When git clone is performed, it records the original location and gives it a remote name of origin.

So what typically is done is this:

$ git push origin master

If the -u (--set-upstream) option is used, the location is recorded so the next time just a git push is necessary.

Dealing with merges

See Basic Merge Conflicts in the Git Book for a detailed explanation on how to resolve merge conflicts. Merges are generally reversible. If wanting to back out of a merge one can usually use the --abort command (e.g. git merge --abort or git pull --abort).

History and versioning

Searching the history

git log will give the history with a commit checksum, author, date, and the short message. The checksum is the "object name" of a commit object, typically a 40-character SHA-1 hash.

For history with a long message (where the "checksum" can be truncated, as long as it is unique):

$ git show (checksum)

Search for pattern in tracked files:

$ git grep pattern

Search in .c and .h files:

$ git grep pattern -- '*.[ch]'

Tagging

Tag commits for versioning:

$ git tag 2.14 checksum

Tagging is generally done for releasing/versioning but it can be any string. Generally annotated tags are used, because they get added to the Git database.

Tag the current commit with:

$ git tag -a 2.14 -m "Version 2.14"

List tags:

$ git tag -l

Delete a tag:

$ git tag -d 2.08

Update remote tags:

$ git push --tags

Organizing commits

Before submitting a pull request it may be desirable to consolidate/organize the commits. This is done with the git rebase --interactive option:

$ git rebase -i checksum

This will open the editor with a summary of all the commits in the range specified; in this case including the newest (HEAD) back to, but excluding, commit checksum. Or to use a number notation, use for example HEAD~3, which will rebase the last three commits:

pick d146cc7 Mountpoint test.
pick 4f47712 Explain -o option in readme.
pick 8a4d479 Rename documentation.

Editing the action in the first column will dictate how the rebase will be done. The options are:

pick — Apply this commit as is (the default).
edit — Edit files and/or commit message.
reword — Edit commit message.
squash — Merge/fold into previous commit.
fixup — Merge/fold into previous commit discarding its message.

The commits can be re-ordered or erased from the history (but be very careful with these). After editing the file, Git will perform the specified actions; if prompted to resolve merge problems, fix them and continue with git rebase --continue or back out with the git rebase --abort command.

Note: Squashing commits is only used for local commits, it will cause troubles on a repository that is shared by other people.

Tips and tricks

Using git-config

Git reads its configuration from four INI-type configuration files:

/etc/gitconfig for system-wide defaults
~/.gitconfig and ~/.config/git/config (since 1.7.12) for user-specific configuration
.git/config for repository-specific configuration

These files can be edited directly, but the usual method is to use git config, as shown in the examples below.

List the currently set variables:

$ git config {--local,--global,--system} --list

Set the default editor from vim to nano:

$ git config --global core.editor "nano -w"

Set the default push action:

$ git config --global push.default simple

Set a different tool for git difftool (meld by default):

$ git config --global diff.tool vimdiff

See git-config(1) and Git Configuration for more information.

Adopting a good etiquette

When considering contributing to an existing project, read and understand its license, as it may excessively limit your ability to change the code. Some licenses can generate disputes over the ownership of the code.
Think about the project's community and how well you can fit into it. To get a feeling of the direction of the project, read any documentation and even the log of the repository.
When requesting to pull a commit, or submit a patch, keep it small and well documented; this will help the maintainers understand your changes and decide whether to merge them or ask you to make some amendments.
If a contribution is rejected, do not get discouraged, it is their project after all. If it is important, discuss the reasoning for the contribution as clearly and as patiently as possible: with such an approach a resolution may eventually be possible.

Speeding up authentication

You may wish to avoid the hassle of authenticating interactively at every push to the Git server.

If you are authenticating with SSH keys, use an SSH agent. See also OpenSSH#Speeding up SSH and OpenSSH#Keep alive.
If you are authenticating with username and password, switch to SSH keys if the server supports SSH, otherwise use git-credential-libsecret credential helper, or try git-credential-cache or git-credential-store.

Using git-credential-libsecret as credential-helper

Git may fetch your credentials from a org.freedesktop.secrets compatible keyring like GNOME/Keyring or KeePassXC. Therefore set up one compatible keyring and check if a keyring is registered to dbus using:

$ dbus-send --session --print-reply --dest=org.freedesktop.DBus / \
    org.freedesktop.DBus.GetConnectionUnixProcessID \
    string:org.freedesktop.secrets

then run

$ git config --global credential.helper /usr/lib/git-core/git-credential-libsecret

to set up git.

Using git-credential-netrc as credential-helper

Git can read the netrc file to access credentials. First, direct Git to the netrc helper script:

$ git config --global credential.helper /usr/share/git/credential/netrc/git-credential-netrc.perl

Then, create a .netrc file:

~/.netrc

machine git-host
login username
password password

The credential helper also supports gpg-encrypted files (~/.netrc.gpg) if you like to keep your secrets safe.

Protocol defaults

If you are running a multiplexed SSH connection as shown above, Git over SSH might be faster than HTTPS. Also, some servers (like the AUR) only allow pushing via SSH. For example, the following configuration will set Git over SSH for any repository hosted on the AUR.

~/.gitconfig

[url "ssh://aur@aur.archlinux.org/"]
	insteadOf = https://aur.archlinux.org/
	insteadOf = http://aur.archlinux.org/
	insteadOf = git://aur.archlinux.org/

Bash completion

In order to enable Bash completion, source /usr/share/git/completion/git-completion.bash in a Bash startup file. Alternatively, install bash-completion.

Git prompt

The Git package comes with a prompt script. To enable it, source the /usr/share/git/completion/git-prompt.sh and set a custom prompt with the %s parameter:

For Bash: PS1='[\u@\h \W$(__git_ps1 " (%s)")]\$ '
For zsh: setopt PROMPT_SUBST ; PS1='[%n@%m %c$(__git_ps1 " (%s)")]\$ '

Note that the command substitution must be escaped, see Bash/Prompt customization#Embedding commands for details. See Command-line shell#Configuration files for persistent configuration.

When changing to a directory of a Git repository, the prompt will change to show the branch name. Extra details can be set to be shown by the prompt by setting the corresponding environment variable:


Shell variable	Information
GIT_PS1_SHOWDIRTYSTATE	`+` for staged, `*` if unstaged.
GIT_PS1_SHOWSTASHSTATE	`$` if something is stashed.
GIT_PS1_SHOWUNTRACKEDFILES	`%` if there are untracked files.
GIT_PS1_SHOWUPSTREAM	`<`, `>`, `<>` behind, ahead, or diverged from upstream.
GIT_PS1_STATESEPARATOR	separator between branch name and state symbols
GIT_PS1_DESCRIBE_STYLE	show commit relative to tag or branch, when detached HEAD
GIT_PS1_SHOWCOLORHINTS	display in color

The full documentation for the environment variables is available in the comments of the script.

Note:

If you experience that $(__git_ps1) returns ((unknown)), then there is a .git folder in your current directory which does not contain any repository, and therefore Git does not recognize it. This can, for example, happen if you mistake Git's configuration file to be ~/.git/config instead of ~/.gitconfig.
If your prompt is experiencing delays with very large repositories, it is likely due to the GIT_PS1_SHOWUNTRACKEDFILES option, which triggers a full directory tree scan every time to detect new files, causing noticeable performance impact. To disable this option locally for those repositories, you can use the command git config --local bash.showUntrackedFiles false.

Alternatively, you can use one of git shell prompt customization packages from AUR such as bash-git-prompt^AUR or gittify^AUR.

Visual representation

To get an idea of the amount of work done:

$ git diff --stat

git log with forking representation:

$ git log --graph --oneline --decorate

git log graph alias (i.e. git graph will show a decorated version):

$ git config --global alias.graph 'log --graph --oneline --decorate'

Commit tips

Reset to previous commit (very dangerous, erases everything to specified commit):

$ git reset --hard HEAD^

If a repository address gets changed, its remote location will need to be updated:

$ git remote set-url origin git@address:user/repo.git

Alternatively, edit .git/config with the new location.

Signed-off-by line append (a name-email signature is added to the commit which is required by some projects):

$ git commit -s

Signed-off-by automatically append to patches (when using git format-patch commit):

$ git config --local format.signoff true

Commit specific parts of files that have changed. This is useful if there are a large number of changes made that would be best split into several commits:

$ git add -p

Signing commits

Git allows commits and tags to be signed using GnuPG, see Signing Your Work.

Note: To use pinentry curses for GPG signing make sure to export GPG_TTY=$(tty) (alternatively use pinentry-tty) otherwise the signing step will fail if GPG is currently in a locked state (since it cannot prompt for pin).

To configure Git to automatically sign commits:

$ git config --global commit.gpgSign true

Working with a non-master branch

Occasionally a maintainer will ask that work be done on a branch. These branches are often called devel or testing. Begin by cloning the repository.

To enter another branch beside master (git clone only shows master branch but others still exist, git branch -a to show):

$ git checkout -b branch origin/branch

Now edit normally; however to keep the repository tree in sync be sure to use both:

$ git pull --all
$ git push --all

Directly sending patches to a mailing list

If you want to send patches directly to a mailing list, you have to install the following packages: perl-authen-sasl and perl-io-socket-ssl.

Make sure you have configured your username and e-mail address, see #Configuration.

Configure your e-mail settings:

$ git config --global sendemail.smtpserver smtp.example.com
$ git config --global sendemail.smtpserverport 465
$ git config --global sendemail.smtpencryption ssl
$ git config --global sendemail.smtpuser foobar@example.com

Now you should be able to send the patch to the mailing list (see also OpenEmbedded:How to submit a patch to OpenEmbedded#Sending patches and git-send-email.io):

$ git add filename
$ git commit -s
$ git send-email --to=pacman-contrib@lists.archlinux.org --confirm=always -M -1

Working with a large git repository

When working with a large remote repository, a significant amount of data has to be fetched. The following examples use the Linux kernel to illustrate how to work with such codebases.

Fetching the entire repository

The easiest solution is to get the entire repository:

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

Note: git clone cannot be resumed if interrupted.

You can update your repository by git pull.

Partially fetching the repository

To limit your local repository to a smaller subset of the origin, say after v4.14 to bisect a bug, use a shallow clone:

$ git clone --shallow-exclude v4.13 git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

You will get v4.14 and later, but not v4.13 and older.

If you only want the latest snapshot, ignoring all history. (If a tarball is available and it suffices, choose that. Downloading from a git repository needs more bandwidth.) You can get it with:

$ git clone --depth 1 git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

You can later obtain older commits, as the two following examples show:

$ git fetch --tags --shallow-exclude v4.1
$ git fetch --tags --shallow-since 2016-01-01

Note: Without --tags, tags will not be fetched.

Getting other branches

Your local repository tracks, in the above example, only the mainline kernel, i.e. in which the latest development is done. Suppose you want the latest LTS, for example the up-to-date 4.14 branch. You can get it by:

$ git remote set-branches --add origin linux-4.17.y
$ git fetch
$ git branch --track linux-4.17.y origin/linux-4.17.y

The last line is not mandatory, but probably wanted. (To know the name of the branch you want, there is no general rule. You can guess one by seeing the "ref" link in the gitweb interface.)

For the snapshot of linux-4.17.y, do

$ git checkout -b linux-4.17.y

Or to extract it in another directory,

$ mkdir /path/to/src-4.17; cd /path/to /src-4.17
$ git clone --no-local --depth 1 -b linux-4.17.y  ../linux-stable

As usual, do git pull to update your snapshot.

Possible alternative

Virtual File System for Git (VFS for Git), allows to access git repositories without a local one. (See this Microsoft blog or the Wikipedia article.)

It already has a successor : Scalar, which is available in git-vfs^AUR^{[broken link: package not found]}, Microsoft's fork of git including gvfs and scalar.

Filtering confidential information

Occasionally, software may keep plain-text passwords in configuration files, as opposed to hooking into a keyring. In these cases, git clean-filters may be handy to avoid accidentally commiting confidential information. E. g., the following file assigns a filter to the file “some-dotfile”:

.gitattributes

some-dotfile filter=remove-pass

Whenever the file “some-dotfile” is checked into git, git will invoke the filter “remove-pass” on the file before checking it in. The filter must be defined in the git-configuration file, e. g.:

.git/config

[filter "remove-pass"]
clean = "sed -e 's/^password=.*/#password=TODO/'"

Note: Escaping special characters for sed expressions can be a tricky task in this context. Remember that git is turning two backslashes into one, while the shell that git invokes to run commands will again turn two backslashes into one. For more details, see Git filter and sed fight over `\$`.

HTML help files

The git help documentation is also available in HTML form by installing git-htmldocs^AUR. After installing, the HTML docs can be accessed by passing the -w flag. For example:

$ git help -w merge

The HTML documentation can be loaded by default by setting a git config option:

$ git config --global help.format html

Extensions

gitflow-avh — Extend git with Vincent Driessen's branching model. The AVH Edition adds more functionality.

https://github.com/petervanderdoes/gitflow || gitflow-avh^AUR

git-extras — some utilities for git (repo summary, repl,changelog population, author commit percentages, etc.)

https://github.com/tj/git-extras || git-extras^AUR - If you're using oh-my-zsh, you may also enable git-extras plugin

gitmoji-cli — A gitmoji interactive NodeJS client for using gitmojis on commit messages.

https://github.com/carloscuesta/gitmoji-cli || nodejs-gitmoji-cli^AUR