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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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GITTUTORIAL(7) Git Manual GITTUTORIAL(7)
gittutorial - A tutorial introduction to Git
git *
This tutorial explains how to import a new project into Git, make
changes to it, and share changes with other developers.
If you are instead primarily interested in using Git to fetch a
project, for example, to test the latest version, you may prefer
to start with the first two chapters of The Git User’s Manual[1].
First, note that you can get documentation for a command such as
git log --graph with:
$ man git-log
or:
$ git help log
With the latter, you can use the manual viewer of your choice;
see git-help(1) for more information.
It is a good idea to introduce yourself to Git with your name and
public email address before doing any operation. The easiest way
to do so is:
$ git config --global user.name "Your Name Comes Here"
$ git config --global user.email [email protected]
Assume you have a tarball project.tar.gz with your initial work.
You can place it under Git revision control as follows.
$ tar xzf project.tar.gz
$ cd project
$ git init
Git will reply
Initialized empty Git repository in .git/
You’ve now initialized the working directory—you may notice a new
directory created, named .git.
Next, tell Git to take a snapshot of the contents of all files
under the current directory (note the .), with git add:
$ git add .
This snapshot is now stored in a temporary staging area which Git
calls the "index". You can permanently store the contents of the
index in the repository with git commit:
$ git commit
This will prompt you for a commit message. You’ve now stored the
first version of your project in Git.
Modify some files, then add their updated contents to the index:
$ git add file1 file2 file3
You are now ready to commit. You can see what is about to be
committed using git diff with the --cached option:
$ git diff --cached
(Without --cached, git diff will show you any changes that you’ve
made but not yet added to the index.) You can also get a brief
summary of the situation with git status:
$ git status
On branch master
Changes to be committed:
(use "git restore --staged <file>..." to unstage)
modified: file1
modified: file2
modified: file3
If you need to make any further adjustments, do so now, and then
add any newly modified content to the index. Finally, commit your
changes with:
$ git commit
This will again prompt you for a message describing the change,
and then record a new version of the project.
Alternatively, instead of running git add beforehand, you can use
$ git commit -a
which will automatically notice any modified (but not new) files,
add them to the index, and commit, all in one step.
A note on commit messages: Though not required, it’s a good idea
to begin the commit message with a single short (no more than 50
characters) line summarizing the change, followed by a blank line
and then a more thorough description. The text up to the first
blank line in a commit message is treated as the commit title,
and that title is used throughout Git. For example,
git-format-patch(1) turns a commit into email, and it uses the
title on the Subject line and the rest of the commit in the body.
Many revision control systems provide an add command that tells
the system to start tracking changes to a new file. Git’s add
command does something simpler and more powerful: git add is used
both for new and newly modified files, and in both cases it takes
a snapshot of the given files and stages that content in the
index, ready for inclusion in the next commit.
At any point you can view the history of your changes using
$ git log
If you also want to see complete diffs at each step, use
$ git log -p
Often the overview of the change is useful to get a feel of each
step
$ git log --stat --summary
A single Git repository can maintain multiple branches of
development. To create a new branch named experimental, use
$ git branch experimental
If you now run
$ git branch
you’ll get a list of all existing branches:
experimental
* master
The experimental branch is the one you just created, and the
master branch is a default branch that was created for you
automatically. The asterisk marks the branch you are currently
on; type
$ git switch experimental
to switch to the experimental branch. Now edit a file, commit the
change, and switch back to the master branch:
(edit file)
$ git commit -a
$ git switch master
Check that the change you made is no longer visible, since it was
made on the experimental branch and you’re back on the master
branch.
You can make a different change on the master branch:
(edit file)
$ git commit -a
at this point the two branches have diverged, with different
changes made in each. To merge the changes made in experimental
into master, run
$ git merge experimental
If the changes don’t conflict, you’re done. If there are
conflicts, markers will be left in the problematic files showing
the conflict;
$ git diff
will show this. Once you’ve edited the files to resolve the
conflicts,
$ git commit -a
will commit the result of the merge. Finally,
$ gitk
will show a nice graphical representation of the resulting
history.
At this point you could delete the experimental branch with
$ git branch -d experimental
This command ensures that the changes in the experimental branch
are already in the current branch.
If you develop on a branch crazy-idea, then regret it, you can
always delete the branch with
$ git branch -D crazy-idea
Branches are cheap and easy, so this is a good way to try
something out.
Suppose that Alice has started a new project with a Git
repository in /home/alice/project, and that Bob, who has a home
directory on the same machine, wants to contribute.
Bob begins with:
bob$ git clone /home/alice/project myrepo
This creates a new directory myrepo containing a clone of Alice’s
repository. The clone is on an equal footing with the original
project, possessing its own copy of the original project’s
history.
Bob then makes some changes and commits them:
(edit files)
bob$ git commit -a
(repeat as necessary)
When he’s ready, he tells Alice to pull changes from the
repository at /home/bob/myrepo. She does this with:
alice$ cd /home/alice/project
alice$ git pull /home/bob/myrepo master
This merges the changes from Bob’s master branch into Alice’s
current branch. If Alice has made her own changes in the
meantime, then she may need to manually fix any conflicts.
The pull command thus performs two operations: it fetches changes
from a remote branch, then merges them into the current branch.
Note that in general, Alice would want her local changes
committed before initiating this pull. If Bob’s work conflicts
with what Alice did since their histories forked, Alice will use
her working tree and the index to resolve conflicts, and existing
local changes will interfere with the conflict resolution process
(Git will still perform the fetch but will refuse to merge —
Alice will have to get rid of her local changes in some way and
pull again when this happens).
Alice can peek at what Bob did without merging first, using the
fetch command; this allows Alice to inspect what Bob did, using a
special symbol FETCH_HEAD, in order to determine if he has
anything worth pulling, like this:
alice$ git fetch /home/bob/myrepo master
alice$ git log -p HEAD..FETCH_HEAD
This operation is safe even if Alice has uncommitted local
changes. The range notation HEAD..FETCH_HEAD means "show
everything that is reachable from the FETCH_HEAD but exclude
anything that is reachable from HEAD". Alice already knows
everything that leads to her current state (HEAD), and reviews
what Bob has in his state (FETCH_HEAD) that she has not seen with
this command.
If Alice wants to visualize what Bob did since their histories
forked she can issue the following command:
$ gitk HEAD..FETCH_HEAD
This uses the same two-dot range notation we saw earlier with git
log.
Alice may want to view what both of them did since they forked.
She can use three-dot form instead of the two-dot form:
$ gitk HEAD...FETCH_HEAD
This means "show everything that is reachable from either one,
but exclude anything that is reachable from both of them".
Please note that these range notation can be used with both gitk
and git log.
After inspecting what Bob did, if there is nothing urgent, Alice
may decide to continue working without pulling from Bob. If Bob’s
history does have something Alice would immediately need, Alice
may choose to stash her work-in-progress first, do a pull, and
then finally unstash her work-in-progress on top of the resulting
history.
When you are working in a small closely knit group, it is not
unusual to interact with the same repository over and over again.
By defining remote repository shorthand, you can make it easier:
alice$ git remote add bob /home/bob/myrepo
With this, Alice can perform the first part of the pull operation
alone using the git fetch command without merging them with her
own branch, using:
alice$ git fetch bob
Unlike the longhand form, when Alice fetches from Bob using a
remote repository shorthand set up with git remote, what was
fetched is stored in a remote-tracking branch, in this case
bob/master. So after this:
alice$ git log -p master..bob/master
shows a list of all the changes that Bob made since he branched
from Alice’s master branch.
After examining those changes, Alice could merge the changes into
her master branch:
alice$ git merge bob/master
This merge can also be done by pulling from her own
remote-tracking branch, like this:
alice$ git pull . remotes/bob/master
Note that git pull always merges into the current branch,
regardless of what else is given on the command line.
Later, Bob can update his repo with Alice’s latest changes using
bob$ git pull
Note that he doesn’t need to give the path to Alice’s repository;
when Bob cloned Alice’s repository, Git stored the location of
her repository in the repository configuration, and that location
is used for pulls:
bob$ git config --get remote.origin.url
/home/alice/project
(The complete configuration created by git clone is visible using
git config -l, and the git-config(1) man page explains the
meaning of each option.)
Git also keeps a pristine copy of Alice’s master branch under the
name origin/master:
bob$ git branch -r
origin/master
If Bob later decides to work from a different host, he can still
perform clones and pulls using the ssh protocol:
bob$ git clone alice.org:/home/alice/project myrepo
Alternatively, Git has a native protocol, or can use http; see
git-pull(1) for details.
Git can also be used in a CVS-like mode, with a central
repository that various users push changes to; see git-push(1)
and gitcvs-migration(7).
Git history is represented as a series of interrelated commits.
We have already seen that the git log command can list those
commits. Note that first line of each git log entry also gives a
name for the commit:
$ git log
commit c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
Author: Junio C Hamano <[email protected]>
Date: Tue May 16 17:18:22 2006 -0700
merge-base: Clarify the comments on post processing.
We can give this name to git show to see the details about this
commit.
$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
But there are other ways to refer to commits. You can use any
initial part of the name that is long enough to uniquely identify
the commit:
$ git show c82a22c39c # the first few characters of the name are
# usually enough
$ git show HEAD # the tip of the current branch
$ git show experimental # the tip of the "experimental" branch
Every commit usually has one "parent" commit which points to the
previous state of the project:
$ git show HEAD^ # to see the parent of HEAD
$ git show HEAD^^ # to see the grandparent of HEAD
$ git show HEAD~4 # to see the great-great grandparent of HEAD
Note that merge commits may have more than one parent:
$ git show HEAD^1 # show the first parent of HEAD (same as HEAD^)
$ git show HEAD^2 # show the second parent of HEAD
You can also give commits names of your own; after running
$ git tag v2.5 1b2e1d63ff
you can refer to 1b2e1d63ff by the name v2.5. If you intend to
share this name with other people (for example, to identify a
release version), you should create a "tag" object, and perhaps
sign it; see git-tag(1) for details.
Any Git command that needs to know a commit can take any of these
names. For example:
$ git diff v2.5 HEAD # compare the current HEAD to v2.5
$ git branch stable v2.5 # start a new branch named "stable" based
# at v2.5
$ git reset --hard HEAD^ # reset your current branch and working
# directory to its state at HEAD^
Be careful with that last command: in addition to losing any
changes in the working directory, it will also remove all later
commits from this branch. If this branch is the only branch
containing those commits, they will be lost. Also, don’t use git
reset on a publicly-visible branch that other developers pull
from, as it will force needless merges on other developers to
clean up the history. If you need to undo changes that you have
pushed, use git revert instead.
The git grep command can search for strings in any version of
your project, so
$ git grep "hello" v2.5
searches for all occurrences of "hello" in v2.5.
If you leave out the commit name, git grep will search any of the
files it manages in your current directory. So
$ git grep "hello"
is a quick way to search just the files that are tracked by Git.
Many Git commands also take sets of commits, which can be
specified in a number of ways. Here are some examples with git
log:
$ git log v2.5..v2.6 # commits between v2.5 and v2.6
$ git log v2.5.. # commits since v2.5
$ git log --since="2 weeks ago" # commits from the last 2 weeks
$ git log v2.5.. Makefile # commits since v2.5 which modify
# Makefile
You can also give git log a "range" of commits where the first is
not necessarily an ancestor of the second; for example, if the
tips of the branches stable and master diverged from a common
commit some time ago, then
$ git log stable..master
will list commits made in the master branch but not in the stable
branch, while
$ git log master..stable
will show the list of commits made on the stable branch but not
the master branch.
The git log command has a weakness: it must present commits in a
list. When the history has lines of development that diverged and
then merged back together, the order in which git log presents
those commits is meaningless.
Most projects with multiple contributors (such as the Linux
kernel, or Git itself) have frequent merges, and gitk does a
better job of visualizing their history. For example,
$ gitk --since="2 weeks ago" drivers/
allows you to browse any commits from the last 2 weeks of commits
that modified files under the drivers directory. (Note: you can
adjust gitk’s fonts by holding down the control key while
pressing "-" or "+".)
Finally, most commands that take filenames will optionally allow
you to precede any filename by a commit, to specify a particular
version of the file:
$ git diff v2.5:Makefile HEAD:Makefile.in
You can also use git show to see any such file:
$ git show v2.5:Makefile
This tutorial should be enough to perform basic distributed
revision control for your projects. However, to fully understand
the depth and power of Git you need to understand two simple
ideas on which it is based:
• The object database is the rather elegant system used to
store the history of your project—files, directories, and
commits.
• The index file is a cache of the state of a directory tree,
used to create commits, check out working directories, and
hold the various trees involved in a merge.
Part two of this tutorial explains the object database, the index
file, and a few other odds and ends that you’ll need to make the
most of Git. You can find it at gittutorial-2(7).
If you don’t want to continue with that right away, a few other
digressions that may be interesting at this point are:
• git-format-patch(1), git-am(1): These convert series of git
commits into emailed patches, and vice versa, useful for
projects such as the Linux kernel which rely heavily on
emailed patches.
• git-bisect(1): When there is a regression in your project,
one way to track down the bug is by searching through the
history to find the exact commit that’s to blame. git bisect
can help you perform a binary search for that commit. It is
smart enough to perform a close-to-optimal search even in the
case of complex non-linear history with lots of merged
branches.
• gitworkflows(7): Gives an overview of recommended workflows.
• giteveryday(7): Everyday Git with 20 Commands Or So.
• gitcvs-migration(7): Git for CVS users.
gittutorial-2(7), gitcvs-migration(7), gitcore-tutorial(7),
gitglossary(7), git-help(1), gitworkflows(7), giteveryday(7), The
Git User’s Manual[1]
Part of the git(1) suite
1. The Git User’s Manual
file:///home/mtk/share/doc/git-doc/user-manual.html
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Git 2.45.2.492.gd63586 2024-06-12 GITTUTORIAL(7)
Pages that refer to this page: git(1), gitcore-tutorial(7), gitcvs-migration(7), gitglossary(7), gittutorial-2(7), gitworkflows(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|