origin/master
origin/next
...
-$ git branch checkout -b masterwork origin/master
+$ git checkout -b masterwork origin/master
-----------------------------------------------
Fetch a branch from a different repository, and give it a new
------------------------------------------------
$ cat >~/.gitconfig <<\EOF
[user]
-name = Your Name Comes Here
-email = you@yourdomain.example.com
+ name = Your Name Comes Here
+ email = you@yourdomain.example.com
EOF
------------------------------------------------
-----------------------------------------------
$ 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"
+$ git am mbox # import patches from the mailbox "mbox"
-----------------------------------------------
Fetch a branch in a different git repository, then merge into the
collection of interrelated snapshots (versions) of the project's
contents.
-A single git repository may contain multiple branches. Each branch
-is a bookmark referencing a particular point in the project history.
-The gitlink:git-branch[1] command shows you the list of branches:
+A single git repository may contain multiple branches. It keeps track
+of them by keeping a list of <<def_head,heads>> which reference the
+latest version on each branch; the gitlink:git-branch[1] command shows
+you the list of branch heads:
------------------------------------------------
$ git branch
* master
------------------------------------------------
-A freshly cloned repository contains a single branch, named "master",
-and the working directory contains the version of the project
-referred to by the master branch.
+A freshly cloned repository contains a single branch head, by default
+named "master", with the working directory initialized to the state of
+the project referred to by that branch head.
-Most projects also use tags. Tags, like branches, are references
-into the project's history, and can be listed using the
+Most projects also use <<def_tag,tags>>. Tags, like heads, are
+references into the project's history, and can be listed using the
gitlink:git-tag[1] command:
------------------------------------------------
------------------------------------------------
Tags are expected to always point at the same version of a project,
-while branches are expected to advance as development progresses.
+while heads are expected to advance as development progresses.
-Create a new branch pointing to one of these versions and check it
+Create a new branch head pointing to one of these versions and check it
out using gitlink:git-checkout[1]:
------------------------------------------------
$ git reset --hard v2.6.17
------------------------------------------------
-Note that if the current branch was your only reference to a
+Note that if the current branch head 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.
+with no way to find the history it used to point to; so use this command
+carefully.
Understanding History: Commits
------------------------------
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).
+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 <<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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
-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
-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
+When we need to be precise, we will use the word "branch" to mean a line
+of development, and "branch head" (or just "head") to mean a reference
+to the most recent commit on a branch. In the example above, the branch
+head named "A" is a pointer to one particular commit, but we refer 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.
+However, when no confusion will result, we often just use the term
+"branch" both for branches and for branch heads.
Manipulating branches
---------------------
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.
+The special symbol "HEAD" can always be used to refer to the current
+branch. In fact, git uses a file named "HEAD" in the .git directory to
+remember which branch is current:
+
+------------------------------------------------
+$ cat .git/HEAD
+ref: refs/heads/master
+------------------------------------------------
+
+[[detached-head]]
+Examining an old version without creating a new branch
+------------------------------------------------------
+
+The git-checkout command normally expects a branch head, but will also
+accept an arbitrary commit; for example, you can check out the commit
+referenced by a tag:
+
+------------------------------------------------
+$ git checkout v2.6.17
+Note: moving to "v2.6.17" which isn't a local branch
+If you want to create a new branch from this checkout, you may do so
+(now or later) by using -b with the checkout command again. Example:
+ git checkout -b <new_branch_name>
+HEAD is now at 427abfa... Linux v2.6.17
+------------------------------------------------
+
+The HEAD then refers to the SHA1 of the commit instead of to a branch,
+and git branch shows that you are no longer on a branch:
+
+------------------------------------------------
+$ cat .git/HEAD
+427abfa28afedffadfca9dd8b067eb6d36bac53f
+git branch
+* (no branch)
+ master
+------------------------------------------------
+
+In this case we say that the HEAD is "detached".
+
+This can be an easy way to check out a particular version without having
+to make up a name for a new branch. However, keep in mind that when you
+switch away from the (for example, by checking out something else), you
+can lose track of what the HEAD used to point to.
Examining branches from a remote repository
-------------------------------------------
-------------------------------------------------
$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
-$ git fetch
+$ git fetch linux-nfs
* refs/remotes/linux-nfs/master: storing branch 'master' ...
commit: bf81b46
-------------------------------------------------
$ cat .git/config
...
[remote "linux-nfs"]
- url = git://linux-nfs.org/~bfields/git.git
- fetch = +refs/heads/*:refs/remotes/linux-nfs-read/*
+ url = git://linux-nfs.org/pub/nfs-2.6.git
+ fetch = +refs/heads/*:refs/remotes/linux-nfs/*
...
-------------------------------------------------
run
-------------------------------------------------
-$ git bisect-visualize
+$ git bisect visualize
-------------------------------------------------
which will run gitk and label the commit it chose with a marker that
running
-------------------------------------------------
-$ git-tag stable-1 1b2e1d63ff
+$ git tag stable-1 1b2e1d63ff
-------------------------------------------------
You can use stable-1 to refer to the commit 1b2e1d63ff.
descendants:
-------------------------------------------------
-$ git name-rev e05db0fd
+$ git name-rev --tags e05db0fd
e05db0fd tags/v1.5.0-rc1^0~23
-------------------------------------------------
-------------------------------------------------
$ git describe e05db0fd
-v1.5.0-rc0-ge05db0f
+v1.5.0-rc0-260-ge05db0f
-------------------------------------------------
but that may sometimes help you guess which tags might come after the
-------------------------------------------------
[[how-to-make-a-commit]]
-how to make a commit
+How to make a commit
--------------------
Creating a new commit takes three steps:
$ git status # a brief per-file summary of the above.
-------------------------------------------------
-creating good commit messages
+Creating good commit messages
-----------------------------
Though not required, it's a good idea to begin the commit message
the first line on the Subject line and the rest of the commit in the
body.
-how to merge
+How to merge
------------
You can rejoin two diverging branches of development using
branch--then you are warned; the output may look something like this:
-------------------------------------------------
-$ git pull . next
-Trying really trivial in-index merge...
-fatal: Merge requires file-level merging
-Nope.
-Merging HEAD with 77976da35a11db4580b80ae27e8d65caf5208086
-Merging:
-15e2162 world
-77976da goodbye
-found 1 common ancestor(s):
-d122ed4 initial
-Auto-merging file.txt
+$ git merge next
+ 100% (4/4) done
+Auto-merged file.txt
CONFLICT (content): Merge conflict in file.txt
Automatic merge failed; fix conflicts and then commit the result.
-------------------------------------------------
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:
+resolve the problem and update the index, gitlink:git-commit[1] will
+fail:
-------------------------------------------------
$ git commit
file.txt: needs merge
-------------------------------------------------
-Also, git status will list those files as "unmerged".
+Also, gitlink: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 gitlink:git-diff[1] shows only
-the conflicts. Also, it uses a somewhat unusual syntax:
+the conflicts. It uses an unusual syntax:
-------------------------------------------------
$ git diff
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:
+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 gitlink: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 gitlink: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
first parent, deleted "Goodbye" from the second parent, and added
"Goodbye world", which was previously absent from both.
-The gitlink:git-log[1] command also provides special help for merges:
+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 gitlink:git-log[1] and gitk[1] commands also provide special help
+for merges:
-------------------------------------------------
$ git log --merge
+$ gitk --merge
-------------------------------------------------
-This will list all commits which exist only on HEAD or on MERGE_HEAD,
-and which touch an unmerged file.
+These will display 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:
+Each time you resolve the conflicts in a file and update the index:
-------------------------------------------------
$ 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 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]]
-undoing a merge
+Undoing a merge
---------------
If you get stuck and decide to just give up and throw the whole mess
Or, if you've already commited the merge that you want to throw away,
-------------------------------------------------
-$ git reset --hard HEAD^
+$ git reset --hard ORIG_HEAD
-------------------------------------------------
However, this last command can be dangerous in some cases--never
conflicts manually, just as in the case of <<resolving-a-merge,
resolving a merge>>.
+[[fixing-a-mistake-by-editing-history]]
Fixing a mistake by editing history
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gitlink:git-show[1]:
-------------------------------------------------
-$ git show HEAD^ path/to/file
+$ git show HEAD^:path/to/file
-------------------------------------------------
which will display the given version of the file.
then you can just pull changes from each other's repositories
directly; note that all of the commands (gitlink:git-clone[1],
git-fetch[1], git-pull[1], etc.) that accept a URL as an argument
-will also accept a local file patch; so, for example, you can
+will also accept a local directory name; so, for example, you can
use
-------------------------------------------------
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.
+gitweb/INSTALL in the git source tree for instructions on setting it up.
Examples
--------
You have performed no merges into mywork, so it is just a simple linear
sequence of patches on top of "origin":
-
+................................................
o--o--o <-- origin
\
o--o--o <-- mywork
+................................................
Some more interesting work has been done in the upstream project, and
"origin" has advanced:
+................................................
o--o--O--o--o--o <-- origin
\
a--b--c <-- mywork
+................................................
At this point, you could use "pull" to merge your changes back in;
the result would create a new merge commit, like this:
-
+................................................
o--o--O--o--o--o <-- origin
\ \
a--b--c--m <-- mywork
+................................................
However, if you prefer to keep the history in mywork a simple series of
commits without any merges, you may instead choose to use
patches to the new mywork. The result will look like:
+................................................
o--o--O--o--o--o <-- origin
\
a'--b'--c' <-- mywork
+................................................
In the process, it may discover conflicts. In that case it will stop
and allow you to fix the conflicts; after fixing conflicts, use "git
$ git rebase --abort
-------------------------------------------------
+Modifying a single commit
+-------------------------
+
+We saw in <<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 gitlink: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 that commit, edit it, and rebase the rest of the series
+on top of it (note that we could check out the commit on a temporary
+branch, but instead we're using a <<detached-head,detached head>>):
+
+-------------------------------------------------
+$ git checkout bad
+$ # make changes here and update the index
+$ git commit --amend
+$ git rebase --onto HEAD bad mywork
+-------------------------------------------------
+
+When you're done, you'll be left with mywork checked out, with the top
+patches on mywork reapplied on top of your modified commit. You can
+then clean up with
+
+-------------------------------------------------
+$ 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
-------------------------------------------
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
/
o--o--O--o--o--o <-- old head of origin
+................................................
If we examined all this history together in one repository, it will
look like:
+................................................
o--o--o <-- new head of origin
/
o--o--O--o--o--o <-- old head of origin
\ \
t--t--t--m <-- their branch:
+................................................
Git has no way of knowing that the new head is an updated version of
the old head; it treats this situation exactly the same as it would if
A fast forward looks something like this:
+................................................
o--o--o--o <-- old head of the branch
\
o--o--o <-- new head of the branch
+................................................
In some cases it is possible that the new head will *not* actually be
realized she made a serious mistake, and decided to backtrack,
resulting in a situation like:
+................................................
o--o--o--o--a--b <-- old head of the branch
\
o--o--o <-- new head of the branch
-
-
+................................................
In this case, "git fetch" will fail, and print out a warning.
options mentioned above.
+[[git-internals]]
Git internals
=============
-There are two object abstractions: the "object database", and the
-"current directory cache" aka "index".
+Git depends on two fundamental abstractions: the "object database", and
+the "current directory cache" aka "index".
The Object Database
-------------------
determined at object creation time, and which identifies the format of
the object (i.e. how it is used, and how it can refer to other
objects). There are currently four different object types: "blob",
-"tree", "commit" and "tag".
+"tree", "commit", and "tag".
-A "blob" object cannot refer to any other object, and is, like the type
-implies, a pure storage object containing some user data. It is used to
-actually store the file data, i.e. a blob object is associated with some
-particular version of some file.
+A <<def_blob_object,"blob" object>> cannot refer to any other object,
+and is, as the name implies, a pure storage object containing some
+user data. It is used to actually store the file data, i.e. a blob
+object is associated with some particular version of some file.
-A "tree" object is an object that ties one or more "blob" objects into a
-directory structure. In addition, a tree object can refer to other tree
-objects, thus creating a directory hierarchy.
+A <<def_tree_object,"tree" object>> is an object that ties one or more
+"blob" objects into a directory structure. In addition, a tree object
+can refer to other tree objects, thus creating a directory hierarchy.
-A "commit" object ties such directory hierarchies together into
-a DAG of revisions - each "commit" is associated with exactly one tree
-(the directory hierarchy at the time of the commit). In addition, a
-"commit" refers to one or more "parent" commit objects that describe the
-history of how we arrived at that directory hierarchy.
+A <<def_commit_object,"commit" object>> ties such directory hierarchies
+together into a <<def_DAG,directed acyclic graph>> of revisions - each
+"commit" is associated with exactly one tree (the directory hierarchy at
+the time of the commit). In addition, a "commit" refers to one or more
+"parent" commit objects that describe the history of how we arrived at
+that directory hierarchy.
As a special case, a commit object with no parents is called the "root"
object, and is the point of an initial project commit. Each project
just going to confuse people. So aim for the notion of "one root object
per project", even if git itself does not enforce that.
-A "tag" object symbolically identifies and can be used to sign other
-objects. It contains the identifier and type of another object, a
-symbolic name (of course!) and, optionally, a signature.
+A <<def_tag_object,"tag" object>> symbolically identifies and can be
+used to sign other objects. It contains the identifier and type of
+another object, a symbolic name (of course!) and, optionally, a
+signature.
Regardless of object type, all objects share the following
characteristics: they are all deflated with zlib, and have a header
contrast, running "git prune" while somebody is actively changing the
repository is a *BAD* idea).
-Glossary of git terms
-=====================
-
include::glossary.txt[]
Notes and todo list for this manual
Simplify beginning by suggesting disconnected head instead of
temporary branch creation?
-Explain how to refer to file stages in the "how to resolve a merge"
-section: diff -1, -2, -3, --ours, --theirs :1:/path notation. The
-"git ls-files --unmerged --stage" thing is sorta useful too,
-actually. And note gitk --merge.
-
Add more good examples. Entire sections of just cookbook examples
might be a good idea; maybe make an "advanced examples" section a
standard end-of-chapter section?