Git User's Manual

How to check out a different version of a project

Understanding history: commits, parents, and reachability
Understanding history: History diagrams
Understanding history: What is a branch?

3. Exploring git history

4. Developing with git

Check whether two branches point at the same history
Find first tagged version including a given fix

Fixing a mistake with a new commit
Fixing a mistake by editing history
Checking out an old version of a file

5. Sharing development with others

Checking the repository for corruption
Recovering lost changes

Getting updates with git pull
Submitting patches to a project
Importing patches to a project
Setting up a public repository
Exporting a git repository via http
Exporting a git repository via the git protocol
Pushing changes to a public repository
Setting up a shared repository
Allow web browsing of a repository
Examples

6. Rewriting history and maintaining patch series

Creating the perfect patch series
Keeping a patch series up to date using git-rebase
Reordering or selecting from a patch series
Other tools
Problems with rewriting history

7. Advanced branch management

Fetching individual branches
Understanding git history: fast-forwards
Forcing git fetch to do non-fast-forward updates
Configuring remote branches

8. Git internals

working directory -> index
index -> object database
object database -> index
index -> working directory
Tying it all together

9. Glossary of git terms

10. Notes and todo list for this manual

Preface

This manual is designed to be readable by someone with basic unix +Git User's Manual

Git User's Manual

Table of Contents

Preface

1. Git Quick Start

Creating a new repository
Managing branches
Exploring history
Making changes
Merging
Sharing your changes
Repository maintenance

2. Repositories and Branches

How to check out a different version of a project

Understanding history: commits, parents, and reachability
Understanding history: History diagrams
Understanding history: What is a branch?

3. Exploring git history

4. Developing with git

Check whether two branches point at the same history
Find first tagged version including a given fix

Getting conflict-resolution help during a merge

Fixing a mistake with a new commit
Fixing a mistake by editing history
Checking out an old version of a file

5. Sharing development with others

Checking the repository for corruption
Recovering lost changes

Getting updates with git pull
Submitting patches to a project
Importing patches to a project
Setting up a public repository
Exporting a git repository via http
Exporting a git repository via the git protocol
Pushing changes to a public repository
Setting up a shared repository
Allow web browsing of a repository
Examples

6. Rewriting history and maintaining patch series

Creating the perfect patch series
Keeping a patch series up to date using git-rebase
Modifying a single commit
Reordering or selecting from a patch series
Other tools
Problems with rewriting history

7. Advanced branch management

Fetching individual branches
Understanding git history: fast-forwards
Forcing git fetch to do non-fast-forward updates
Configuring remote branches

8. Git internals

working directory -> index
index -> object database
object database -> index
index -> working directory
Tying it all together

9. Glossary of git terms

10. Notes and todo list for this manual

Preface

This manual is designed to be readable by someone with basic unix command-line skills, but no previous knowledge of git.

Chapter 1 gives a brief overview of git commands, without any explanation; you may prefer to skip to chapter 2 on a first reading.

Chapters 2 and 3 explain how to fetch and study a project using git—the tools you'd need to build and test a particular version of a software project, to search for regressions, and so on.

Chapter 4 explains how to do development with git, and chapter 5 how to share that development with others.

Further chapters cover more specialized topics.

Comprehensive reference documentation is available through the man -pages. For a command such as "git clone", just use

$ man git-clone

Chapter 1. Git Quick Start

Table of Contents

Creating a new repository
Managing branches
Exploring history
Making changes
Merging
Sharing your changes
Repository maintenance

This is a quick summary of the major commands; the following chapters -will explain how these work in more detail.

Creating a new repository

From a tarball:

$ tar xzf project.tar.gz
+pages. For a command such as "git clone", just use

$ man git-clone

Chapter 1. Git Quick Start

Table of Contents

Creating a new repository
Managing branches
Exploring history
Making changes
Merging
Sharing your changes
Repository maintenance

This is a quick summary of the major commands; the following chapters +will explain how these work in more detail.

Creating a new repository

From a tarball:

$ tar xzf project.tar.gz
$ cd project
$ git init
Initialized empty Git repository in .git/
$ git add .
$ git commit

From a remote repository:

$ git clone git://example.com/pub/project.git
-$ cd project

Managing branches

$ git branch # list all branches in this repo
+$ cd project

Managing branches

$ git branch         # list all branches in this repo
$ git checkout test  # switch working directory to branch "test"
$ git branch new     # create branch "new" starting at current HEAD
$ git branch -d new  # delete branch "new"

Instead of basing new branch on current HEAD (the default), use:

$ git branch new test    # branch named "test"
@@ -35,7 +35,7 @@ $   Tracked remote branches
    master next ...
$ git fetch example             # update branches from example
-$ git branch -r                 # list all remote branches

Exploring history

$ gitk # visualize and browse history
+$ git branch -r # list all remote branches

Exploring history

$ gitk                      # visualize and browse history
$ git log                   # list all commits
$ git log src/              # ...modifying src/
$ git log v2.6.15..v2.6.16  # ...in v2.6.16, not in v2.6.15
@@ -57,7 +57,7 @@ Bisecting:                                 # test here, then:
$ git bisect good               # if this revision is good, or
$ git bisect bad                # if this revision is bad.
-                                # repeat until done.

Making changes

Make sure git knows who to blame:

$ cat >~/.gitconfig <<\EOF
+ # repeat until done.

Making changes

Make sure git knows who to blame:

$ cat >~/.gitconfig <<\EOF
[user]
name = Your Name Comes Here
email = you@yourdomain.example.com
@@ -66,16 +66,16 @@ commit:

$ $ git add b.txt # new file
$ git rm c.txt # old file
$ git commit

Or, prepare and create the commit in one step:

$ git commit d.txt # use latest content only of d.txt
-$ git commit -a # use latest content of all tracked files

Merging

$ git merge test # merge branch "test" into the current branch
+$ git commit -a # use latest content of all tracked files

Merging

$ git merge test   # merge branch "test" into the current branch
$ git pull git://example.com/project.git master
                   # fetch and merge in remote branch
-$ git pull . test  # equivalent to git merge test

Sharing your changes

Importing or exporting patches:

$ git format-patch origin..HEAD # format a patch for each commit
+$ git pull . test # equivalent to git merge test

Sharing your changes

Importing or exporting patches:

$ git format-patch origin..HEAD # format a patch for each commit
# in HEAD but not in origin
$ git-am mbox # import patches from the mailbox "mbox"

Fetch a branch in a different git repository, then merge into the current branch:

$ git pull git://example.com/project.git theirbranch

Store the fetched branch into a local branch before merging into the current branch:

$ git pull git://example.com/project.git theirbranch:mybranch

After creating commits on a local branch, update the remote branch with your commits:

$ git push ssh://example.com/project.git mybranch:theirbranch

When remote and local branch are both named "test":

$ git push ssh://example.com/project.git test

Shortcut version for a frequently used remote repository:

$ git remote add example ssh://example.com/project.git
-$ git push example test

Repository maintenance

Check for corruption:

$ git fsck

Recompress, remove unused cruft:

$ git gc

Chapter 2. Repositories and Branches

Table of Contents

How to check out a different version of a project

Understanding history: commits, parents, and reachability
Understanding history: History diagrams
Understanding history: What is a branch?

How to get a git repository

It will be useful to have a git repository to experiment with as you +$ git push example test

Repository maintenance

Check for corruption:

$ git fsck

Recompress, remove unused cruft:

$ git gc

Chapter 2. Repositories and Branches

Table of Contents

How to check out a different version of a project

Understanding history: commits, parents, and reachability
Understanding history: History diagrams
Understanding history: What is a branch?

How to get a git repository

It will be useful to have a git repository to experiment with as you read this manual.

The best way to get one is by using the git-clone(1) command to download a copy of an existing repository for a project that you are interested in. If you don't already have a project in mind, here @@ -88,7 +88,7 @@ will only need to clone once.

The clone command creates a new directory na directory, you will see that it contains a copy of the project files, together with a special top-level directory named ".git", which contains all the information about the history of the project.

In most of the following, examples will be taken from one of the two -repositories above.

How to check out a different version of a project

Git is best thought of as a tool for storing the history of a +repositories above.

How to check out a different version of a project

Git is best thought of as a tool for storing the history of a collection of files. It stores the history as a compressed collection of interrelated snapshots (versions) of the project's contents.

A single git repository may contain multiple branches. Each branch @@ -118,7 +118,7 @@ branches, with an asterisk marking the currently checked-out branch:

$ git reset --hard v2.6.17

Note that if the current branch was your only reference to a particular point in history, then resetting that branch may leave you with no way to find the history it used to point to; so use this -command carefully.

Understanding History: Commits

Every change in the history of a project is represented by a commit. +command carefully.

Understanding History: Commits

Every change in the history of a project is represented by a commit. The git-show(1) command shows the most recent commit on the current branch:

$ git show
commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2
@@ -147,15 +147,18 @@ index + __u32 reqid;
};
...

As you can see, a commit shows who made the latest change, what they -did, and why.

Every commit has a 40-hexdigit id, sometimes called the "object name" -or the "SHA1 id", shown on the first line of the "git show" output. -You can usually refer to a commit by a shorter name, such as a tag or a -branch name, but this longer name can also be useful. Most -importantly, it is a globally unique name for this commit: so if you -tell somebody else the object name (for example in email), then you are -guaranteed that name will refer to the same commit in their repository -that it does in yours (assuming their repository has that commit at -all).

Understanding history: commits, parents, and reachability

Every commit (except the very first commit in a project) also has a +did, and why.

Every commit has a 40-hexdigit id, sometimes called the "object name" or the +"SHA1 id", shown on the first line of the "git show" output. You can usually +refer to a commit by a shorter name, such as a tag or a branch name, but this +longer name can also be useful. Most importantly, it is a globally unique +name for this commit: so if you tell somebody else the object name (for +example in email), then you are guaranteed that name will refer to the same +commit in their repository that it does in yours (assuming their repository +has that commit at all). Since the object name is computed as a hash over the +contents of the commit, you are guaranteed that the commit can never change +without its name also changing.

In fact, in Chapter 8, Git internals we shall see that everything stored in git +history, including file data and directory contents, is stored in an object +with a name that is a hash of its contents.

Understanding history: commits, parents, and reachability

Every commit (except the very first commit in a project) also has a parent commit which shows what happened before this commit. Following the chain of parents will eventually take you back to the beginning of the project.

However, the commits do not form a simple list; git allows lines of @@ -168,13 +171,13 @@ command; running gitk now on a git repository and looking for merge commits will help understand how the git organizes history.

In the following, we say that commit X is "reachable" from commit Y if commit X is an ancestor of commit Y. Equivalently, you could say that Y is a descendent of X, or that there is a chain of parents -leading from commit Y to commit X.

Understanding history: History diagrams

We will sometimes represent git history using diagrams like the one +leading from commit Y to commit X.

Understanding history: History diagrams

We will sometimes represent git history using diagrams like the one below. Commits are shown as "o", and the links between them with lines drawn with - / and \. Time goes left to right:

        o--o--o <-- Branch A
        /
 o--o--o <-- master
                 o--o--o <-- Branch B

If we need to talk about a particular commit, the character "o" may -be replaced with another letter or number.

Understanding history: What is a branch?

Though we've been using the word "branch" to mean a kind of reference +be replaced with another letter or number.

Understanding history: What is a branch?

Though we've been using the word "branch" to mean a kind of reference to a particular commit, the word branch is also commonly used to refer to the line of commits leading up to that point. In the example above, git may think of the branch named "A" as just a @@ -182,7 +185,7 @@ pointer to one particular commit, but we may refer informally to the line of three commits leading up to that point as all being part of "branch A".

If we need to make it clear that we're just talking about the most recent commit on the branch, we may refer to that commit as the -"head" of the branch.

Manipulating branches

Creating, deleting, and modifying branches is quick and easy; here's +"head" of the branch.

Manipulating branches

Creating, deleting, and modifying branches is quick and easy; here's a summary of the commands:

git branch: @@ -223,7 +226,7 @@ git checkout -b <new> <start-point> create a new branch <new> referencing <start-point>, and check it out.

It is also useful to know that the special symbol "HEAD" can always -be used to refer to the current branch.

Examining branches from a remote repository

The "master" branch that was created at the time you cloned is a copy +be used to refer to the current branch.

Examining branches from a remote repository

The "master" branch that was created at the time you cloned is a copy of the HEAD in the repository that you cloned from. That repository may also have had other branches, though, and your local repository keeps branches which track each of those remote branches, which you @@ -259,7 +262,7 @@ repository, creating new commits and advancing the branches to point at the new commits.

The command "git fetch", with no arguments, will update all of the remote-tracking branches to the latest version found in her repository. It will not touch any of your own branches—not even the -"master" branch that was created for you on clone.

Fetching branches from other repositories

You can also track branches from repositories other than the one you +"master" branch that was created for you on clone.

Fetching branches from other repositories

You can also track branches from repositories other than the one you cloned from, using git-remote(1):

$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
$ git fetch
* refs/remotes/linux-nfs/master: storing branch 'master' ...
@@ -276,12 +279,12 @@ a new stanza:

$ ...

This is what causes git to track the remote's branches; you may modify or delete these configuration options by editing .git/config with a text editor. (See the "CONFIGURATION FILE" section of -git-config(1) for details.)

Chapter 3. Exploring git history

Table of Contents

Check whether two branches point at the same history
Find first tagged version including a given fix

Git is best thought of as a tool for storing the history of a +git-config(1) for details.)

Chapter 3. Exploring git history

Table of Contents

Check whether two branches point at the same history
Find first tagged version including a given fix

Git is best thought of as a tool for storing the history of a collection of files. It does this by storing compressed snapshots of the contents of a file heirarchy, together with "commits" which show the relationships between these snapshots.

Git provides extremely flexible and fast tools for exploring the history of a project.

We start with one specialized tool that is useful for finding the -commit that introduced a bug into a project.

How to use bisect to find a regression

Suppose version 2.6.18 of your project worked, but the version at +commit that introduced a bug into a project.

How to use bisect to find a regression

Suppose version 2.6.18 of your project worked, but the version at "master" crashes. Sometimes the best way to find the cause of such a regression is to perform a brute-force search through the project's history to find the particular commit that caused the problem. The @@ -309,7 +312,7 @@ occasionally you may land on a commit that broke something unrelated; run

$ git bisect-visualize

which will run gitk and label the commit it chose with a marker that says "bisect". Chose a safe-looking commit nearby, note its commit id, and check it out with:

$ git reset --hard fb47ddb2db...

then test, run "bisect good" or "bisect bad" as appropriate, and -continue.

Naming commits

We have seen several ways of naming commits already:

+continue.

Naming commits

We have seen several ways of naming commits already:

40-hexdigit object name
branch name: refers to the commit at the head of the given @@ -339,11 +342,11 @@ which refers to the other branch that we're merging in to the current branch.
The git-rev-parse(1) command is a low-level command that is occasionally useful for translating some name for a commit to the object name for that commit:
$ git rev-parse origin
-e05db0fd4f31dde7005f075a84f96b360d05984b

Creating tags

We can also create a tag to refer to a particular commit; after +e05db0fd4f31dde7005f075a84f96b360d05984b

Creating tags

We can also create a tag to refer to a particular commit; after running

$ git-tag stable-1 1b2e1d63ff

You can use stable-1 to refer to the commit 1b2e1d63ff.

This creates a "lightweight" tag. If the tag is a tag you wish to share with others, and possibly sign cryptographically, then you should create a tag object instead; see the git-tag(1) man -page for details.

Browsing revisions

The git-log(1) command can show lists of commits. On its +page for details.

Browsing revisions

The git-log(1) command can show lists of commits. On its own, it shows all commits reachable from the parent commit; but you can also make more specific requests:

$ git log v2.5.. # commits since (not reachable from) v2.5
$ git log test..master # commits reachable from master but not test
@@ -359,15 +362,15 @@ commits since v2.5 which touch the Makefile or any file under fs:

Note that git log starts with the most recent commit and works backwards through the parents; however, since git history can contain multiple independent lines of development, the particular order that -commits are listed in may be somewhat arbitrary.

Generating diffs

You can generate diffs between any two versions using +commits are listed in may be somewhat arbitrary.

Generating diffs

You can generate diffs between any two versions using git-diff(1):

$ git diff master..test

Sometimes what you want instead is a set of patches:

$ git format-patch master..test

will generate a file with a patch for each commit reachable from test but not from master. Note that if master also has commits which are not reachable from test, then the combined result of these patches -will not be the same as the diff produced by the git-diff example.

Viewing old file versions

You can always view an old version of a file by just checking out the +will not be the same as the diff produced by the git-diff example.

Viewing old file versions

You can always view an old version of a file by just checking out the correct revision first. But sometimes it is more convenient to be able to view an old version of a single file without checking anything out; this command does that:

$ git show v2.5:fs/locks.c

Before the colon may be anything that names a commit, and after it -may be any path to a file tracked by git.

Examples

Check whether two branches point at the same history

Suppose you want to check whether two branches point at the same point +may be any path to a file tracked by git.

Examples

Check whether two branches point at the same history

Suppose you want to check whether two branches point at the same point in history.

$ git diff origin..master

will tell you whether the contents of the project are the same at the two branches; in theory, however, it's possible that the same project contents could have been arrived at by two different historical @@ -376,7 +379,7 @@ e05db0fd4f31dde7005f075a84f96b360d05984b
$ git rev-list master
e05db0fd4f31dde7005f075a84f96b360d05984b

Or you could recall that the … operator selects all commits contained reachable from either one reference or the other but not -both: so

$ git log origin...master

will return no commits when the two branches are equal.

Find first tagged version including a given fix

Suppose you know that the commit e05db0fd fixed a certain problem. +both: so

$ git log origin...master

will return no commits when the two branches are equal.

Find first tagged version including a given fix

Suppose you know that the commit e05db0fd fixed a certain problem. You'd like to find the earliest tagged release that contains that fix.

Of course, there may be more than one answer—if the history branched after commit e05db0fd, then there could be multiple "earliest" tagged @@ -403,13 +406,13 @@ available
! [v1.5.0-rc2] GIT v1.5.0-rc2
...

then search for a line that looks like

+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
available

Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and -from v1.5.0-rc2, but not from v1.5.0-rc0.

Chapter 4. Developing with git

Table of Contents

Fixing a mistake with a new commit
Fixing a mistake by editing history
Checking out an old version of a file

Checking the repository for corruption
Recovering lost changes

Telling git your name

Before creating any commits, you should introduce yourself to git. The +from v1.5.0-rc2, but not from v1.5.0-rc0.

Chapter 4. Developing with git

Table of Contents

Getting conflict-resolution help during a merge

Fixing a mistake with a new commit
Fixing a mistake by editing history
Checking out an old version of a file

Checking the repository for corruption
Recovering lost changes

Telling git your name

Before creating any commits, you should introduce yourself to git. The easiest way to do so is:

$ cat >~/.gitconfig <<\EOF
[user]
name = Your Name Comes Here
email = you@yourdomain.example.com
EOF

(See the "CONFIGURATION FILE" section of git-config(1) for -details on the configuration file.)

Creating a new repository

Creating a new repository from scratch is very easy:

$ mkdir project
+details on the configuration file.)

Creating a new repository

Creating a new repository from scratch is very easy:

$ mkdir project
$ cd project
$ git init

If you have some initial content (say, a tarball):

$ tar -xzvf project.tar.gz
$ cd project
@@ -440,12 +443,12 @@ about to commit:

$ $ git diff          # difference between the index file and your
                    # working directory; changes that would not
                    # be included if you ran "commit" now.
-$ git status        # a brief per-file summary of the above.

creating good commit messages

Though not required, it's a good idea to begin the commit message +$ git status # a brief per-file summary of the above.

creating good commit messages

Though not required, it's a good idea to begin the commit message with a single short (less than 50 character) line summarizing the change, followed by a blank line and then a more thorough description. Tools that turn commits into email, for example, use the first line on the Subject line and the rest of the commit in the -body.

how to merge

You can rejoin two diverging branches of development using +body.

how to merge

You can rejoin two diverging branches of development using git-merge(1):

$ git merge branchname

merges the development in the branch "branchname" into the current branch. If there are conflicts—for example, if the same file is modified in two different ways in the remote branch and the local @@ -469,10 +472,21 @@ has two parents, one pointing to the top of the current branch, and one to the top of the other branch.

In more detail:

Resolving a merge

When a merge isn't resolved automatically, git leaves the index and the working tree in a special state that gives you all the information you need to help resolve the merge.

Files with conflicts are marked specially in the index, so until you -resolve the problem and update the index, git commit will fail:

$ git commit
-file.txt: needs merge

Also, git status will list those files as "unmerged".

All of the changes that git was able to merge automatically are +resolve the problem and update the index, git-commit(1) will +fail:

$ git commit
+file.txt: needs merge

Also, git-status(1) will list those files as "unmerged", and the +files with conflicts will have conflict markers added, like this:

<<<<<<< HEAD:file.txt
+Hello world
+=======
+Goodbye
+>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt

All you need to do is edit the files to resolve the conflicts, and then

$ git add file.txt
+$ git commit

Note that the commit message will already be filled in for you with +some information about the merge. Normally you can just use this +default message unchanged, but you may add additional commentary of +your own if desired.

The above is all you need to know to resolve a simple merge. But git +also provides more information to help resolve conflicts:

Getting conflict-resolution help during a merge

All of the changes that git was able to merge automatically are already added to the index file, so git-diff(1) shows only -the conflicts. Also, it uses a somewhat unusual syntax:

$ git diff
+the conflicts. It uses an unusual syntax:

$ git diff
diff --cc file.txt
index 802992c,2b60207..0000000
--- a/file.txt
@@ -485,14 +499,22 @@ index ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt

Recall that the commit which will be commited after we resolve this conflict will have two parents instead of the usual one: one parent will be HEAD, the tip of the current branch; the other will be the -tip of the other branch, which is stored temporarily in MERGE_HEAD.

The diff above shows the differences between the working-tree version -of file.txt and two previous versions: one version from HEAD, and one -from MERGE_HEAD. So instead of preceding each line by a single "+" -or "-", it now uses two columns: the first column is used for -differences between the first parent and the working directory copy, -and the second for differences between the second parent and the -working directory copy. Thus after resolving the conflict in the -obvious way, the diff will look like:

$ git diff
+tip of the other branch, which is stored temporarily in MERGE_HEAD.

During the merge, the index holds three versions of each file. Each of +these three "file stages" represents a different version of the file:

$ git show :1:file.txt  # the file in a common ancestor of both branches
+$ git show :2:file.txt  # the version from HEAD, but including any
+                        # nonconflicting changes from MERGE_HEAD
+$ git show :3:file.txt  # the version from MERGE_HEAD, but including any
+                        # nonconflicting changes from HEAD.

Since the stage 2 and stage 3 versions have already been updated with +nonconflicting changes, the only remaining differences between them are +the important ones; thus git-diff(1) can use the information in +the index to show only those conflicts.

The diff above shows the differences between the working-tree version of +file.txt and the stage 2 and stage 3 versions. So instead of preceding +each line by a single "+" or "-", it now uses two columns: the first +column is used for differences between the first parent and the working +directory copy, and the second for differences between the second parent +and the working directory copy. (See the "COMBINED DIFF FORMAT" section +of git-diff-files(1) for a details of the format.)

After resolving the conflict in the obvious way (but before updating the +index), the diff will look like:

$ git diff
diff --cc file.txt
index 802992c,2b60207..0000000
--- a/file.txt
@@ -502,16 +524,21 @@ index -Goodbye
++Goodbye world

This shows that our resolved version deleted "Hello world" from the first parent, deleted "Goodbye" from the second parent, and added -"Goodbye world", which was previously absent from both.

The git-log(1) command also provides special help for merges:

$ git log --merge

This will list all commits which exist only on HEAD or on MERGE_HEAD, -and which touch an unmerged file.

We can now add the resolved version to the index and commit:

$ git add file.txt
-$ git commit

Note that the commit message will already be filled in for you with -some information about the merge. Normally you can just use this -default message unchanged, but you may add additional commentary of -your own if desired.

undoing a merge

If you get stuck and decide to just give up and throw the whole mess -away, you can always return to the pre-merge state with

$ git reset --hard HEAD

Or, if you've already commited the merge that you want to throw away,

$ git reset --hard HEAD^

However, this last command can be dangerous in some cases—never +"Goodbye world", which was previously absent from both.

Some special diff options allow diffing the working directory against +any of these stages:

$ git diff -1 file.txt          # diff against stage 1
+$ git diff --base file.txt      # same as the above
+$ git diff -2 file.txt          # diff against stage 2
+$ git diff --ours file.txt      # same as the above
+$ git diff -3 file.txt          # diff against stage 3
+$ git diff --theirs file.txt    # same as the above.

The git-log(1) and gitk[1] commands also provide special help +for merges:

$ git log --merge
+$ gitk --merge

These will display all commits which exist only on HEAD or on +MERGE_HEAD, and which touch an unmerged file.

Each time you resolve the conflicts in a file and update the index:

$ git add file.txt

the different stages of that file will be "collapsed", after which +git-diff will (by default) no longer show diffs for that file.

undoing a merge

If you get stuck and decide to just give up and throw the whole mess +away, you can always return to the pre-merge state with

$ git reset --hard HEAD

Or, if you've already commited the merge that you want to throw away,

$ git reset --hard ORIG_HEAD

However, this last command can be dangerous in some cases—never throw away a commit you have already committed if that commit may itself have been merged into another branch, as doing so may confuse -further merges.

Fast-forward merges

There is one special case not mentioned above, which is treated +further merges.

Fast-forward merges

There is one special case not mentioned above, which is treated differently. Normally, a merge results in a merge commit, with two parents, one pointing at each of the two lines of development that were merged.

However, if one of the two lines of development is completely @@ -519,7 +546,7 @@ contained within the other—so every commit present in the one is already contained in the other—then git just performs a fast forward; the head of the current branch is moved forward to point at the head of the merged-in branch, without -any new commits being created.

Fixing mistakes

If you've messed up the working tree, but haven't yet committed your +any new commits being created.

Fixing mistakes

If you've messed up the working tree, but haven't yet committed your mistake, you can return the entire working tree to the last committed state with

$ git reset --hard HEAD

If you make a commit that you later wish you hadn't, there are two fundamentally different ways to fix the problem:

@@ -532,13 +559,13 @@ You can go back and modify the old commit. You should git does not normally expect the "history" of a project to change, and cannot correctly perform repeated merges from a branch that has had its history changed. -

Fixing a mistake with a new commit

Creating a new commit that reverts an earlier change is very easy; +

Fixing a mistake with a new commit

Creating a new commit that reverts an earlier change is very easy; just pass the git-revert(1) command a reference to the bad commit; for example, to revert the most recent commit:

$ git revert HEAD

This will create a new commit which undoes the change in HEAD. You will be given a chance to edit the commit message for the new commit.

You can also revert an earlier change, for example, the next-to-last:

$ git revert HEAD^

In this case git will attempt to undo the old change while leaving intact any changes made since then. If more recent changes overlap with the changes to be reverted, then you will be asked to fix -conflicts manually, just as in the case of resolving a merge.

Fixing a mistake by editing history

If the problematic commit is the most recent commit, and you have not +conflicts manually, just as in the case of resolving a merge.

Fixing a mistake by editing history

If the problematic commit is the most recent commit, and you have not yet made that commit public, then you may just destroy it using git-reset.

Alternatively, you can edit the working directory and update the index to fix your @@ -547,17 +574,17 @@ changes, giving you a chance to edit the old commit message first.

Again, been merged into another branch; use git-revert(1) instead in that case.

It is also possible to edit commits further back in the history, but this is an advanced topic to be left for -another chapter.

Checking out an old version of a file

In the process of undoing a previous bad change, you may find it +another chapter.

Checking out an old version of a file

In the process of undoing a previous bad change, you may find it useful to check out an older version of a particular file using git-checkout(1). We've used git checkout before to switch branches, but it has quite different behavior if it is given a path name: the command

$ git checkout HEAD^ path/to/file

replaces path/to/file by the contents it had in the commit HEAD^, and also updates the index to match. It does not change branches.

If you just want to look at an old version of the file, without modifying the working directory, you can do that with -git-show(1):

$ git show HEAD^ path/to/file

which will display the given version of the file.

Ensuring good performance

On large repositories, git depends on compression to keep the history +git-show(1):

$ git show HEAD^ path/to/file

which will display the given version of the file.

Ensuring good performance

On large repositories, git depends on compression to keep the history information from taking up to much space on disk or in memory.

This compression is not performed automatically. Therefore you should occasionally run git-gc(1):

$ git gc

to recompress the archive. This can be very time-consuming, so -you may prefer to run git-gc when you are not doing other work.

Ensuring reliability

Checking the repository for corruption

The git-fsck(1) command runs a number of self-consistency checks +you may prefer to run git-gc when you are not doing other work.

Ensuring reliability

Checking the repository for corruption

The git-fsck(1) command runs a number of self-consistency checks on the repository, and reports on any problems. This may take some time. The most common warning by far is about "dangling" objects:

$ git fsck
dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
@@ -572,7 +599,7 @@ dangling you can remove them at any time with git-prune(1) or the —prune option to git-gc(1):

$ git gc --prune

This may be time-consuming. Unlike most other git operations (including git-gc when run without any options), it is not safe to prune while -other git operations are in progress in the same repository.

For more about dangling objects, see the section called “Dangling objects”.

Recovering lost changes

Reflogs

Say you modify a branch with git-reset(1) —hard, and then +other git operations are in progress in the same repository.

For more about dangling objects, see the section called “Dangling objects”.

Recovering lost changes

Reflogs

Say you modify a branch with git-reset(1) —hard, and then realize that the branch was the only reference you had to that point in history.

Fortunately, git also keeps a log, called a "reflog", of all the previous values of each branch. So in this case you can still find the @@ -587,7 +614,7 @@ how to control this pruning, and see the "SPECIFYING REVISIONS" section of git-rev-parse(1) for details.

Note that the reflog history is very different from normal git history. While normal history is shared by every repository that works on the same project, the reflog history is not shared: it tells you only about -how the branches in your local repository have changed over time.

Examining dangling objects

In some situations the reflog may not be able to save you. For +how the branches in your local repository have changed over time.

Examining dangling objects

In some situations the reflog may not be able to save you. For example, suppose you delete a branch, then realize you need the history it contained. The reflog is also deleted; however, if you have not yet pruned the repository, then you may still be able to find @@ -604,7 +631,7 @@ you get exactly the history reachable from that commit that is lost. (And notice that it might not be just one commit: we only report the "tip of the line" as being dangling, but there might be a whole deep and complex commit history that was dropped.)

If you decide you want the history back, you can always create a new -reference pointing to it, for example, a new branch:

$ git branch recovered-branch 7281251ddd

Chapter 5. Sharing development with others

Table of Contents

Getting updates with git pull
Submitting patches to a project
Importing patches to a project
Setting up a public repository
Exporting a git repository via http
Exporting a git repository via the git protocol
Pushing changes to a public repository
Setting up a shared repository
Allow web browsing of a repository
Examples

Getting updates with git pull

After you clone a repository and make a few changes of your own, you +reference pointing to it, for example, a new branch:

$ git branch recovered-branch 7281251ddd

Chapter 5. Sharing development with others

Table of Contents

Getting updates with git pull
Submitting patches to a project
Importing patches to a project
Setting up a public repository
Exporting a git repository via http
Exporting a git repository via the git protocol
Pushing changes to a public repository
Setting up a shared repository
Allow web browsing of a repository
Examples

Getting updates with git pull

After you clone a repository and make a few changes of your own, you may wish to check the original repository for updates and merge them into your own work.

We have already seen how to keep remote tracking branches up to date with git-fetch(1), and how to merge two branches. So you can merge in changes from the @@ -621,13 +648,13 @@ repository that you pulled from.

(But note that no such commit will be cre updated to point to the latest commit from the upstream branch.)

The git-pull command can also be given "." as the "remote" repository, in which case it just merges in a branch from the current repository; so the commands

$ git pull . branch
-$ git merge branch

are roughly equivalent. The former is actually very commonly used.

Submitting patches to a project

If you just have a few changes, the simplest way to submit them may +$ git merge branch

are roughly equivalent. The former is actually very commonly used.

Submitting patches to a project

If you just have a few changes, the simplest way to submit them may just be to send them as patches in email:

First, use git-format-patch(1); for example:

$ git format-patch origin

will produce a numbered series of files in the current directory, one for each patch in the current branch but not in origin/HEAD.

You can then import these into your mail client and send them by hand. However, if you have a lot to send at once, you may prefer to use the git-send-email(1) script to automate the process. Consult the mailing list for your project first to determine how they -prefer such patches be handled.

Importing patches to a project

Git also provides a tool called git-am(1) (am stands for +prefer such patches be handled.

Importing patches to a project

Git also provides a tool called git-am(1) (am stands for "apply mailbox"), for importing such an emailed series of patches. Just save all of the patch-containing messages, in order, into a single mailbox file, say "patches.mbox", then run

$ git am -3 patches.mbox

Git will apply each patch in order; if any conflicts are found, it @@ -699,16 +726,16 @@ save typing; so, for example, after

$ url = ssh://yourserver.com/~you/proj.git
EOF

you should be able to perform the above push with just

$ git push public-repo master

See the explanations of the remote.<name>.url, branch.<name>.remote, and remote.<name>.push options in git-config(1) for -details.

Setting up a shared repository

Another way to collaborate is by using a model similar to that +details.

Setting up a shared repository

Another way to collaborate is by using a model similar to that commonly used in CVS, where several developers with special rights all push to and pull from a single shared repository. See git for CVS users for instructions on how to -set this up.

Allow web browsing of a repository

The gitweb cgi script provides users an easy way to browse your +set this up.

Allow web browsing of a repository

The gitweb cgi script provides users an easy way to browse your project's files and history without having to install git; see the file -gitweb/README in the git source tree for instructions on setting it up.

Examples

TODO: topic branches, typical roles as in everyday.txt, ?

Chapter 6. Rewriting history and maintaining patch series

Table of Contents

Creating the perfect patch series
Keeping a patch series up to date using git-rebase
Reordering or selecting from a patch series
Other tools
Problems with rewriting history

Normally commits are only added to a project, never taken away or +gitweb/README in the git source tree for instructions on setting it up.

Examples

TODO: topic branches, typical roles as in everyday.txt, ?

Chapter 6. Rewriting history and maintaining patch series

Table of Contents

Creating the perfect patch series
Keeping a patch series up to date using git-rebase
Modifying a single commit
Reordering or selecting from a patch series
Other tools
Problems with rewriting history

Normally commits are only added to a project, never taken away or replaced. Git is designed with this assumption, and violating it will cause git's merge machinery (for example) to do the wrong thing.

However, there is a situation in which it can be useful to violate this -assumption.

Creating the perfect patch series

Suppose you are a contributor to a large project, and you want to add a +assumption.

Creating the perfect patch series

Suppose you are a contributor to a large project, and you want to add a complicated feature, and to present it to the other developers in a way that makes it easy for them to read your changes, verify that they are correct, and understand why you made each change.

If you present all of your changes as a single patch (or commit), they @@ -727,7 +754,7 @@ The complete series produces the same end result as your own (probably much messier!) development process did.

We will introduce some tools that can help you do this, explain how to use them, and then explain some of the problems that can arise because -you are rewriting history.

Keeping a patch series up to date using git-rebase

Suppose that you create a branch "mywork" on a remote-tracking branch +you are rewriting history.

Keeping a patch series up to date using git-rebase

Suppose that you create a branch "mywork" on a remote-tracking branch "origin", and create some commits on top of it:

$ git checkout -b mywork origin
$ vi file.txt
$ git commit
@@ -750,7 +777,19 @@ patches to the new mywork. The result will look like:

$ git rebase --continue
and git will continue applying the rest of the patches.
At any point you may use the —abort option to abort this process and
-return mywork to the state it had before you started the rebase:
$ git rebase --abort

Reordering or selecting from a patch series

Given one existing commit, the git-cherry-pick(1) command +return mywork to the state it had before you started the rebase:

$ git rebase --abort

Modifying a single commit

We saw in the section called “Fixing a mistake by editing history” that you can replace the +most recent commit using

$ git commit --amend

which will replace the old commit by a new commit incorporating your +changes, giving you a chance to edit the old commit message first.

You can also use a combination of this and git-rebase(1) to edit +commits further back in your history. First, tag the problematic commit with

$ git tag bad mywork~5

(Either gitk or git-log may be useful for finding the commit.)

Then check out a new branch at that commit, edit it, and rebase the rest of +the series on top of it:

$ git checkout -b TMP bad
+$ # make changes here and update the index
+$ git commit --amend
+$ git rebase --onto TMP bad mywork

When you're done, you'll be left with mywork checked out, with the top patches +on mywork reapplied on top of the modified commit you created in TMP. You can +then clean up with

$ git branch -d TMP
+$ git tag -d bad

Note that the immutable nature of git history means that you haven't really +"modified" existing commits; instead, you have replaced the old commits with +new commits having new object names.

Reordering or selecting from a patch series

Given one existing commit, the git-cherry-pick(1) command allows you to apply the change introduced by that commit and create a new commit that records it. So, for example, if "mywork" points to a series of patches on top of "origin", you might do something like:

$ git checkout -b mywork-new origin
@@ -760,9 +799,9 @@ cherry-pick, and possibly modifying them as you go using commit —amend.

Another technique is to use git-format-patch to create a series of patches, then reset the state to before the patches:

$ git format-patch origin
$ git reset --hard origin

Then modify, reorder, or eliminate patches as preferred before applying -them again with git-am(1).

Other tools

There are numerous other tools, such as stgit, which exist for the +them again with git-am(1).

Other tools

There are numerous other tools, such as stgit, which exist for the purpose of maintaining a patch series. These are outside of the scope of -this manual.

Problems with rewriting history

The primary problem with rewriting the history of a branch has to do +this manual.

Problems with rewriting history

The primary problem with rewriting the history of a branch has to do with merging. Suppose somebody fetches your branch and merges it into their branch, with a result something like this:

o--o--O--o--o--o <-- origin
        \                 t--t--t--m <-- their branch:

Then suppose you modify the last three commits:

        o--o--o <-- new head of origin
@@ -781,7 +820,7 @@ new.  The results are likely to be unexpected.
You may still choose to pub
 and it may be useful for others to be able to fetch those branches in
 order to examine or test them, but they should not attempt to pull such
 branches into their own work.
For true distributed development that supports proper merging,
-published branches should never be rewritten.

Chapter 7. Advanced branch management

Table of Contents

Fetching individual branches
Understanding git history: fast-forwards
Forcing git fetch to do non-fast-forward updates
Configuring remote branches

Fetching individual branches

Instead of using git-remote(1), you can also choose just +published branches should never be rewritten.

Chapter 7. Advanced branch management

Table of Contents

Fetching individual branches
Understanding git history: fast-forwards
Forcing git fetch to do non-fast-forward updates
Configuring remote branches

Fetching individual branches

Instead of using git-remote(1), you can also choose just to update one branch at a time, and to store it locally under an arbitrary name:

$ git fetch origin todo:my-todo-work

The first argument, "origin", just tells git to fetch from the repository you originally cloned from. The second argument tells git @@ -803,10 +842,10 @@ resulting in a situation like:

o--o--o--o--a--b &l described in the following section. However, note that in the situation above this may mean losing the commits labeled "a" and "b", unless you've already created a reference of your own pointing to -them.

Forcing git fetch to do non-fast-forward updates

If git fetch fails because the new head of a branch is not a +them.

Forcing git fetch to do non-fast-forward updates

If git fetch fails because the new head of a branch is not a descendant of the old head, you may force the update with:

$ git fetch git://example.com/proj.git +master:refs/remotes/example/master

Note the addition of the "+" sign. Be aware that commits that the old version of example/master pointed at may be lost, as we saw in -the previous section.

Configuring remote branches

We saw above that "origin" is just a shortcut to refer to the +the previous section.

Configuring remote branches

We saw above that "origin" is just a shortcut to refer to the repository that you originally cloned from. This information is stored in git configuration variables, which you can see using git-config(1):

$ git config -l
@@ -826,8 +865,8 @@ $ throwing away commits on mybranch.

Also note that all of the above configuration can be performed by directly editing the file .git/config instead of using git-config(1).

See git-config(1) for more details on the configuration -options mentioned above.

Chapter 8. Git internals

Table of Contents

working directory -> index
index -> object database
object database -> index
index -> working directory
Tying it all together

There are two object abstractions: the "object database", and the -"current directory cache" aka "index".

The Object Database

The object database is literally just a content-addressable collection +options mentioned above.

Chapter 8. Git internals

Table of Contents

working directory -> index
index -> object database
object database -> index
index -> working directory
Tying it all together