You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
3071 lines
112 KiB
3071 lines
112 KiB
Git User's Manual |
|
_________________ |
|
|
|
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 |
|
------------------------------------------------ |
|
|
|
Git Quick Start |
|
=============== |
|
|
|
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 |
|
$ 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" |
|
$ git branch new v2.6.15 # tag named v2.6.15 |
|
$ git branch new HEAD^ # commit before the most recent |
|
$ git branch new HEAD^^ # commit before that |
|
$ git branch new test~10 # ten commits before tip of branch "test" |
|
----------------------------------------------- |
|
|
|
Create and switch to a new branch at the same time: |
|
|
|
----------------------------------------------- |
|
$ git checkout -b new v2.6.15 |
|
----------------------------------------------- |
|
|
|
Update and examine branches from the repository you cloned from: |
|
|
|
----------------------------------------------- |
|
$ git fetch # update |
|
$ git branch -r # list |
|
origin/master |
|
origin/next |
|
... |
|
$ git branch checkout -b masterwork origin/master |
|
----------------------------------------------- |
|
|
|
Fetch a branch from a different repository, and give it a new |
|
name in your repository: |
|
|
|
----------------------------------------------- |
|
$ git fetch git://example.com/project.git theirbranch:mybranch |
|
$ git fetch git://example.com/project.git v2.6.15:mybranch |
|
----------------------------------------------- |
|
|
|
Keep a list of repositories you work with regularly: |
|
|
|
----------------------------------------------- |
|
$ git remote add example git://example.com/project.git |
|
$ git remote # list remote repositories |
|
example |
|
origin |
|
$ git remote show example # get details |
|
* remote example |
|
URL: git://example.com/project.git |
|
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 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 |
|
$ git log master..test # ...in branch test, not in branch master |
|
$ git log test..master # ...in branch master, but not in test |
|
$ git log test...master # ...in one branch, not in both |
|
$ git log -S'foo()' # ...where difference contain "foo()" |
|
$ git log --since="2 weeks ago" |
|
$ git log -p # show patches as well |
|
$ git show # most recent commit |
|
$ git diff v2.6.15..v2.6.16 # diff between two tagged versions |
|
$ git diff v2.6.15..HEAD # diff with current head |
|
$ git grep "foo()" # search working directory for "foo()" |
|
$ git grep v2.6.15 "foo()" # search old tree for "foo()" |
|
$ git show v2.6.15:a.txt # look at old version of a.txt |
|
----------------------------------------------- |
|
|
|
Search for regressions: |
|
|
|
----------------------------------------------- |
|
$ git bisect start |
|
$ git bisect bad # current version is bad |
|
$ git bisect good v2.6.13-rc2 # last known good revision |
|
Bisecting: 675 revisions left to test after this |
|
# 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 |
|
[user] |
|
name = Your Name Comes Here |
|
email = you@yourdomain.example.com |
|
EOF |
|
------------------------------------------------ |
|
|
|
Select file contents to include in the next commit, then make the |
|
commit: |
|
|
|
----------------------------------------------- |
|
$ git add a.txt # updated file |
|
$ 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 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 |
|
# 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 |
|
----------------------------------------------- |
|
|
|
Repositories and Branches |
|
========================= |
|
|
|
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 gitlink: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 |
|
are some interesting examples: |
|
|
|
------------------------------------------------ |
|
# git itself (approx. 10MB download): |
|
$ git clone git://git.kernel.org/pub/scm/git/git.git |
|
# the linux kernel (approx. 150MB download): |
|
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git |
|
------------------------------------------------ |
|
|
|
The initial clone may be time-consuming for a large project, but you |
|
will only need to clone once. |
|
|
|
The clone command creates a new directory named after the project |
|
("git" or "linux-2.6" in the examples above). After you cd into this |
|
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 |
|
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 |
|
is a bookmark referencing a particular point in the project history. |
|
The gitlink:git-branch[1] command shows you the list of branches: |
|
|
|
------------------------------------------------ |
|
$ 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. |
|
|
|
Most projects also use tags. Tags, like branches, are references |
|
into the project's history, and can be listed using the |
|
gitlink:git-tag[1] command: |
|
|
|
------------------------------------------------ |
|
$ git tag -l |
|
v2.6.11 |
|
v2.6.11-tree |
|
v2.6.12 |
|
v2.6.12-rc2 |
|
v2.6.12-rc3 |
|
v2.6.12-rc4 |
|
v2.6.12-rc5 |
|
v2.6.12-rc6 |
|
v2.6.13 |
|
... |
|
------------------------------------------------ |
|
|
|
Tags are expected to always point at the same version of a project, |
|
while branches are expected to advance as development progresses. |
|
|
|
Create a new branch pointing to one of these versions and check it |
|
out using gitlink:git-checkout[1]: |
|
|
|
------------------------------------------------ |
|
$ git checkout -b new v2.6.13 |
|
------------------------------------------------ |
|
|
|
The working directory then reflects the contents that the project had |
|
when it was tagged v2.6.13, and gitlink:git-branch[1] shows two |
|
branches, with an asterisk marking the currently checked-out branch: |
|
|
|
------------------------------------------------ |
|
$ git branch |
|
master |
|
* new |
|
------------------------------------------------ |
|
|
|
If you decide that you'd rather see version 2.6.17, you can modify |
|
the current branch to point at v2.6.17 instead, with |
|
|
|
------------------------------------------------ |
|
$ 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. |
|
The gitlink:git-show[1] command shows the most recent commit on the |
|
current branch: |
|
|
|
------------------------------------------------ |
|
$ git show |
|
commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2 |
|
Author: Jamal Hadi Salim <hadi@cyberus.ca> |
|
Date: Sat Dec 2 22:22:25 2006 -0800 |
|
|
|
[XFRM]: Fix aevent structuring to be more complete. |
|
|
|
aevents can not uniquely identify an SA. We break the ABI with this |
|
patch, but consensus is that since it is not yet utilized by any |
|
(known) application then it is fine (better do it now than later). |
|
|
|
Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca> |
|
Signed-off-by: David S. Miller <davem@davemloft.net> |
|
|
|
diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt |
|
index 8be626f..d7aac9d 100644 |
|
--- a/Documentation/networking/xfrm_sync.txt |
|
+++ b/Documentation/networking/xfrm_sync.txt |
|
@@ -47,10 +47,13 @@ aevent_id structure looks like: |
|
|
|
struct xfrm_aevent_id { |
|
struct xfrm_usersa_id sa_id; |
|
+ xfrm_address_t saddr; |
|
__u32 flags; |
|
+ __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). 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 |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
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 |
|
development to diverge and then reconverge, and the point where two |
|
lines of development reconverge is called a "merge". The commit |
|
representing a merge can therefore have more than one parent, with |
|
each parent representing the most recent commit on one of the lines |
|
of development leading to that point. |
|
|
|
The best way to see how this works is using the gitlink:gitk[1] |
|
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 |
|
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 |
|
"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 |
|
a summary of the commands: |
|
|
|
git branch:: |
|
list all branches |
|
git branch <branch>:: |
|
create a new branch named <branch>, referencing the same |
|
point in history as the current branch |
|
git branch <branch> <start-point>:: |
|
create a new branch named <branch>, referencing |
|
<start-point>, which may be specified any way you like, |
|
including using a branch name or a tag name |
|
git branch -d <branch>:: |
|
delete the branch <branch>; if the branch you are deleting |
|
points to a commit which is not reachable from this branch, |
|
this command will fail with a warning. |
|
git branch -D <branch>:: |
|
even if the branch points to a commit not reachable |
|
from the current branch, you may know that that commit |
|
is still reachable from some other branch or tag. In that |
|
case it is safe to use this command to force git to delete |
|
the branch. |
|
git checkout <branch>:: |
|
make the current branch <branch>, updating the working |
|
directory to reflect the version referenced by <branch> |
|
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 |
|
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 |
|
can view using the "-r" option to gitlink:git-branch[1]: |
|
|
|
------------------------------------------------ |
|
$ git branch -r |
|
origin/HEAD |
|
origin/html |
|
origin/maint |
|
origin/man |
|
origin/master |
|
origin/next |
|
origin/pu |
|
origin/todo |
|
------------------------------------------------ |
|
|
|
You cannot check out these remote-tracking branches, but you can |
|
examine them on a branch of your own, just as you would a tag: |
|
|
|
------------------------------------------------ |
|
$ git checkout -b my-todo-copy origin/todo |
|
------------------------------------------------ |
|
|
|
Note that the name "origin" is just the name that git uses by default |
|
to refer to the repository that you cloned from. |
|
|
|
[[how-git-stores-references]] |
|
Naming branches, tags, and other references |
|
------------------------------------------- |
|
|
|
Branches, remote-tracking branches, and tags are all references to |
|
commits. All references are named with a slash-separated path name |
|
starting with "refs"; the names we've been using so far are actually |
|
shorthand: |
|
|
|
- The branch "test" is short for "refs/heads/test". |
|
- The tag "v2.6.18" is short for "refs/tags/v2.6.18". |
|
- "origin/master" is short for "refs/remotes/origin/master". |
|
|
|
The full name is occasionally useful if, for example, there ever |
|
exists a tag and a branch with the same name. |
|
|
|
As another useful shortcut, if the repository "origin" posesses only |
|
a single branch, you can refer to that branch as just "origin". |
|
|
|
More generally, if you have defined a remote repository named |
|
"example", you can refer to the branch in that repository as |
|
"example". And for a repository with multiple branches, this will |
|
refer to the branch designated as the "HEAD" branch. |
|
|
|
For the complete list of paths which git checks for references, and |
|
the order it uses to decide which to choose when there are multiple |
|
references with the same shorthand name, see the "SPECIFYING |
|
REVISIONS" section of gitlink:git-rev-parse[1]. |
|
|
|
[[Updating-a-repository-with-git-fetch]] |
|
Updating a repository with git fetch |
|
------------------------------------ |
|
|
|
Eventually the developer cloned from will do additional work in her |
|
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 |
|
cloned from, using gitlink: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' ... |
|
commit: bf81b46 |
|
------------------------------------------------- |
|
|
|
New remote-tracking branches will be stored under the shorthand name |
|
that you gave "git remote add", in this case linux-nfs: |
|
|
|
------------------------------------------------- |
|
$ git branch -r |
|
linux-nfs/master |
|
origin/master |
|
------------------------------------------------- |
|
|
|
If you run "git fetch <remote>" later, the tracking branches for the |
|
named <remote> will be updated. |
|
|
|
If you examine the file .git/config, you will see that git has added |
|
a new stanza: |
|
|
|
------------------------------------------------- |
|
$ cat .git/config |
|
... |
|
[remote "linux-nfs"] |
|
url = git://linux-nfs.org/pub/nfs-2.6.git |
|
fetch = +refs/heads/*:refs/remotes/linux-nfs/* |
|
... |
|
------------------------------------------------- |
|
|
|
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 |
|
gitlink:git-config[1] for details.) |
|
|
|
Exploring git history |
|
===================== |
|
|
|
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 |
|
"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 |
|
gitlink:git-bisect[1] command can help you do this: |
|
|
|
------------------------------------------------- |
|
$ git bisect start |
|
$ git bisect good v2.6.18 |
|
$ git bisect bad master |
|
Bisecting: 3537 revisions left to test after this |
|
[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] |
|
------------------------------------------------- |
|
|
|
If you run "git branch" at this point, you'll see that git has |
|
temporarily moved you to a new branch named "bisect". This branch |
|
points to a commit (with commit id 65934...) that is reachable from |
|
v2.6.19 but not from v2.6.18. Compile and test it, and see whether |
|
it crashes. Assume it does crash. Then: |
|
|
|
------------------------------------------------- |
|
$ git bisect bad |
|
Bisecting: 1769 revisions left to test after this |
|
[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings |
|
------------------------------------------------- |
|
|
|
checks out an older version. Continue like this, telling git at each |
|
stage whether the version it gives you is good or bad, and notice |
|
that the number of revisions left to test is cut approximately in |
|
half each time. |
|
|
|
After about 13 tests (in this case), it will output the commit id of |
|
the guilty commit. You can then examine the commit with |
|
gitlink:git-show[1], find out who wrote it, and mail them your bug |
|
report with the commit id. Finally, run |
|
|
|
------------------------------------------------- |
|
$ git bisect reset |
|
------------------------------------------------- |
|
|
|
to return you to the branch you were on before and delete the |
|
temporary "bisect" branch. |
|
|
|
Note that the version which git-bisect checks out for you at each |
|
point is just a suggestion, and you're free to try a different |
|
version if you think it would be a good idea. For example, |
|
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: |
|
|
|
- 40-hexdigit object name |
|
- branch name: refers to the commit at the head of the given |
|
branch |
|
- tag name: refers to the commit pointed to by the given tag |
|
(we've seen branches and tags are special cases of |
|
<<how-git-stores-references,references>>). |
|
- HEAD: refers to the head of the current branch |
|
|
|
There are many more; see the "SPECIFYING REVISIONS" section of the |
|
gitlink:git-rev-parse[1] man page for the complete list of ways to |
|
name revisions. Some examples: |
|
|
|
------------------------------------------------- |
|
$ git show fb47ddb2 # the first few characters of the object name |
|
# are usually enough to specify it uniquely |
|
$ git show HEAD^ # the parent of the HEAD commit |
|
$ git show HEAD^^ # the grandparent |
|
$ git show HEAD~4 # the great-great-grandparent |
|
------------------------------------------------- |
|
|
|
Recall that merge commits may have more than one parent; by default, |
|
^ and ~ follow the first parent listed in the commit, but you can |
|
also choose: |
|
|
|
------------------------------------------------- |
|
$ git show HEAD^1 # show the first parent of HEAD |
|
$ git show HEAD^2 # show the second parent of HEAD |
|
------------------------------------------------- |
|
|
|
In addition to HEAD, there are several other special names for |
|
commits: |
|
|
|
Merges (to be discussed later), as well as operations such as |
|
git-reset, which change the currently checked-out commit, generally |
|
set ORIG_HEAD to the value HEAD had before the current operation. |
|
|
|
The git-fetch operation always stores the head of the last fetched |
|
branch in FETCH_HEAD. For example, if you run git fetch without |
|
specifying a local branch as the target of the operation |
|
|
|
------------------------------------------------- |
|
$ git fetch git://example.com/proj.git theirbranch |
|
------------------------------------------------- |
|
|
|
the fetched commits will still be available from FETCH_HEAD. |
|
|
|
When we discuss merges we'll also see the special name MERGE_HEAD, |
|
which refers to the other branch that we're merging in to the current |
|
branch. |
|
|
|
The gitlink: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 |
|
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 gitlink:git-tag[1] man |
|
page for details. |
|
|
|
Browsing revisions |
|
------------------ |
|
|
|
The gitlink: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 |
|
$ git log master..test # ...reachable from test but not master |
|
$ git log master...test # ...reachable from either test or master, |
|
# but not both |
|
$ git log --since="2 weeks ago" # commits from the last 2 weeks |
|
$ git log Makefile # commits which modify Makefile |
|
$ git log fs/ # ... which modify any file under fs/ |
|
$ git log -S'foo()' # commits which add or remove any file data |
|
# matching the string 'foo()' |
|
------------------------------------------------- |
|
|
|
And of course you can combine all of these; the following finds |
|
commits since v2.5 which touch the Makefile or any file under fs: |
|
|
|
------------------------------------------------- |
|
$ git log v2.5.. Makefile fs/ |
|
------------------------------------------------- |
|
|
|
You can also ask git log to show patches: |
|
|
|
------------------------------------------------- |
|
$ git log -p |
|
------------------------------------------------- |
|
|
|
See the "--pretty" option in the gitlink:git-log[1] man page for more |
|
display options. |
|
|
|
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 |
|
gitlink: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 |
|
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 |
|
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 |
|
routes. You could compare the object names: |
|
|
|
------------------------------------------------- |
|
$ git rev-list origin |
|
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. |
|
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 |
|
releases. |
|
|
|
You could just visually inspect the commits since e05db0fd: |
|
|
|
------------------------------------------------- |
|
$ gitk e05db0fd.. |
|
------------------------------------------------- |
|
|
|
Or you can use gitlink:git-name-rev[1], which will give the commit a |
|
name based on any tag it finds pointing to one of the commit's |
|
descendants: |
|
|
|
------------------------------------------------- |
|
$ git name-rev e05db0fd |
|
e05db0fd tags/v1.5.0-rc1^0~23 |
|
------------------------------------------------- |
|
|
|
The gitlink:git-describe[1] command does the opposite, naming the |
|
revision using a tag on which the given commit is based: |
|
|
|
------------------------------------------------- |
|
$ git describe e05db0fd |
|
v1.5.0-rc0-ge05db0f |
|
------------------------------------------------- |
|
|
|
but that may sometimes help you guess which tags might come after the |
|
given commit. |
|
|
|
If you just want to verify whether a given tagged version contains a |
|
given commit, you could use gitlink:git-merge-base[1]: |
|
|
|
------------------------------------------------- |
|
$ git merge-base e05db0fd v1.5.0-rc1 |
|
e05db0fd4f31dde7005f075a84f96b360d05984b |
|
------------------------------------------------- |
|
|
|
The merge-base command finds a common ancestor of the given commits, |
|
and always returns one or the other in the case where one is a |
|
descendant of the other; so the above output shows that e05db0fd |
|
actually is an ancestor of v1.5.0-rc1. |
|
|
|
Alternatively, note that |
|
|
|
------------------------------------------------- |
|
$ git log v1.5.0-rc1..e05db0fd |
|
------------------------------------------------- |
|
|
|
will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
|
because it outputs only commits that are not reachable from v1.5.0-rc1. |
|
|
|
As yet another alternative, the gitlink:git-show-branch[1] command lists |
|
the commits reachable from its arguments with a display on the left-hand |
|
side that indicates which arguments that commit is reachable from. So, |
|
you can run something like |
|
|
|
------------------------------------------------- |
|
$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 |
|
! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if |
|
available |
|
! [v1.5.0-rc0] GIT v1.5.0 preview |
|
! [v1.5.0-rc1] GIT v1.5.0-rc1 |
|
! [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. |
|
|
|
|
|
Developing with git |
|
=================== |
|
|
|
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 gitlink:git-config[1] for |
|
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 |
|
$ git init |
|
$ git add . # include everything below ./ in the first commit: |
|
$ git commit |
|
------------------------------------------------- |
|
|
|
[[how-to-make-a-commit]] |
|
how to make a commit |
|
-------------------- |
|
|
|
Creating a new commit takes three steps: |
|
|
|
1. Making some changes to the working directory using your |
|
favorite editor. |
|
2. Telling git about your changes. |
|
3. Creating the commit using the content you told git about |
|
in step 2. |
|
|
|
In practice, you can interleave and repeat steps 1 and 2 as many |
|
times as you want: in order to keep track of what you want committed |
|
at step 3, git maintains a snapshot of the tree's contents in a |
|
special staging area called "the index." |
|
|
|
At the beginning, the content of the index will be identical to |
|
that of the HEAD. The command "git diff --cached", which shows |
|
the difference between the HEAD and the index, should therefore |
|
produce no output at that point. |
|
|
|
Modifying the index is easy: |
|
|
|
To update the index with the new contents of a modified file, use |
|
|
|
------------------------------------------------- |
|
$ git add path/to/file |
|
------------------------------------------------- |
|
|
|
To add the contents of a new file to the index, use |
|
|
|
------------------------------------------------- |
|
$ git add path/to/file |
|
------------------------------------------------- |
|
|
|
To remove a file from the index and from the working tree, |
|
|
|
------------------------------------------------- |
|
$ git rm path/to/file |
|
------------------------------------------------- |
|
|
|
After each step you can verify that |
|
|
|
------------------------------------------------- |
|
$ git diff --cached |
|
------------------------------------------------- |
|
|
|
always shows the difference between the HEAD and the index file--this |
|
is what you'd commit if you created the commit now--and that |
|
|
|
------------------------------------------------- |
|
$ git diff |
|
------------------------------------------------- |
|
|
|
shows the difference between the working tree and the index file. |
|
|
|
Note that "git add" always adds just the current contents of a file |
|
to the index; further changes to the same file will be ignored unless |
|
you run git-add on the file again. |
|
|
|
When you're ready, just run |
|
|
|
------------------------------------------------- |
|
$ git commit |
|
------------------------------------------------- |
|
|
|
and git will prompt you for a commit message and then create the new |
|
commit. Check to make sure it looks like what you expected with |
|
|
|
------------------------------------------------- |
|
$ git show |
|
------------------------------------------------- |
|
|
|
As a special shortcut, |
|
|
|
------------------------------------------------- |
|
$ git commit -a |
|
------------------------------------------------- |
|
|
|
will update the index with any files that you've modified or removed |
|
and create a commit, all in one step. |
|
|
|
A number of commands are useful for keeping track of what you're |
|
about to commit: |
|
|
|
------------------------------------------------- |
|
$ git diff --cached # difference between HEAD and the index; what |
|
# would be commited if you ran "commit" now. |
|
$ 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 |
|
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 |
|
gitlink: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 |
|
branch--then you are warned; the output may look something like this: |
|
|
|
------------------------------------------------- |
|
$ 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. |
|
------------------------------------------------- |
|
|
|
Conflict markers are left in the problematic files, and after |
|
you resolve the conflicts manually, you can update the index |
|
with the contents and run git commit, as you normally would when |
|
creating a new file. |
|
|
|
If you examine the resulting commit using gitk, you will see that it |
|
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]] |
|
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, gitlink:git-commit[1] will |
|
fail: |
|
|
|
------------------------------------------------- |
|
$ git commit |
|
file.txt: needs merge |
|
------------------------------------------------- |
|
|
|
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. It uses an unusual syntax: |
|
|
|
------------------------------------------------- |
|
$ git diff |
|
diff --cc file.txt |
|
index 802992c,2b60207..0000000 |
|
--- a/file.txt |
|
+++ b/file.txt |
|
@@@ -1,1 -1,1 +1,5 @@@ |
|
++<<<<<<< HEAD:file.txt |
|
+Hello world |
|
++======= |
|
+ Goodbye |
|
++>>>>>>> 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. |
|
|
|
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 |
|
diff --cc file.txt |
|
index 802992c,2b60207..0000000 |
|
--- a/file.txt |
|
+++ b/file.txt |
|
@@@ -1,1 -1,1 +1,1 @@@ |
|
- Hello world |
|
-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. |
|
|
|
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 |
|
------------------------------------------------- |
|
|
|
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]] |
|
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 |
|
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 |
|
contained within the other--so every commit present in the one is |
|
already contained in the other--then git just performs a |
|
<<fast-forwards,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 |
|
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: |
|
|
|
1. You can create a new commit that undoes whatever was done |
|
by the previous commit. This is the correct thing if your |
|
mistake has already been made public. |
|
|
|
2. You can go back and modify the old commit. You should |
|
never do this if you have already made the history public; |
|
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; |
|
just pass the gitlink: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, |
|
resolving a merge>>. |
|
|
|
[[fixing-a-mistake-by-editing-history]] |
|
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 |
|
<<undoing-a-merge,destroy it using git-reset>>. |
|
|
|
Alternatively, you |
|
can edit the working directory and update the index to fix your |
|
mistake, just as if you were going to <<how-to-make-a-commit,create a |
|
new commit>>, then run |
|
|
|
------------------------------------------------- |
|
$ 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. |
|
|
|
Again, you should never do this to a commit that may already have |
|
been merged into another branch; use gitlink: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 |
|
<<cleaning-up-history,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 |
|
gitlink: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 |
|
gitlink: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 gitlink: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 gitlink: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 |
|
dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
|
dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
|
dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb |
|
dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f |
|
dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e |
|
dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 |
|
dangling tree b24c2473f1fd3d91352a624795be026d64c8841f |
|
... |
|
------------------------------------------------- |
|
|
|
Dangling objects are objects that are harmless, but also unnecessary; |
|
you can remove them at any time with gitlink:git-prune[1] or the --prune |
|
option to gitlink: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 <<dangling-objects>>. |
|
|
|
|
|
Recovering lost changes |
|
~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
Reflogs |
|
^^^^^^^ |
|
|
|
Say you modify a branch with gitlink: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 |
|
old history using, for example, |
|
|
|
------------------------------------------------- |
|
$ git log master@{1} |
|
------------------------------------------------- |
|
|
|
This lists the commits reachable from the previous version of the head. |
|
This syntax can be used to with any git command that accepts a commit, |
|
not just with git log. Some other examples: |
|
|
|
------------------------------------------------- |
|
$ git show master@{2} # See where the branch pointed 2, |
|
$ git show master@{3} # 3, ... changes ago. |
|
$ gitk master@{yesterday} # See where it pointed yesterday, |
|
$ gitk master@{"1 week ago"} # ... or last week |
|
------------------------------------------------- |
|
|
|
The reflogs are kept by default for 30 days, after which they may be |
|
pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn |
|
how to control this pruning, and see the "SPECIFYING REVISIONS" |
|
section of gitlink: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 |
|
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 |
|
the lost commits; run git-fsck and watch for output that mentions |
|
"dangling commits": |
|
|
|
------------------------------------------------- |
|
$ git fsck |
|
dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
|
dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 |
|
dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 |
|
... |
|
------------------------------------------------- |
|
|
|
You can examine |
|
one of those dangling commits with, for example, |
|
|
|
------------------------------------------------ |
|
$ gitk 7281251ddd --not --all |
|
------------------------------------------------ |
|
|
|
which does what it sounds like: it says that you want to see the commit |
|
history that is described by the dangling commit(s), but not the |
|
history that is described by all your existing branches and tags. Thus |
|
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 |
|
------------------------------------------------ |
|
|
|
|
|
Sharing development with others |
|
=============================== |
|
|
|
[[getting-updates-with-git-pull]] |
|
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 <<Updating-a-repository-with-git-fetch,how to |
|
keep remote tracking branches up to date>> with gitlink:git-fetch[1], |
|
and how to merge two branches. So you can merge in changes from the |
|
original repository's master branch with: |
|
|
|
------------------------------------------------- |
|
$ git fetch |
|
$ git merge origin/master |
|
------------------------------------------------- |
|
|
|
However, the gitlink:git-pull[1] command provides a way to do this in |
|
one step: |
|
|
|
------------------------------------------------- |
|
$ git pull origin master |
|
------------------------------------------------- |
|
|
|
In fact, "origin" is normally the default repository to pull from, |
|
and the default branch is normally the HEAD of the remote repository, |
|
so often you can accomplish the above with just |
|
|
|
------------------------------------------------- |
|
$ git pull |
|
------------------------------------------------- |
|
|
|
See the descriptions of the branch.<name>.remote and |
|
branch.<name>.merge options in gitlink:git-config[1] to learn |
|
how to control these defaults depending on the current branch. |
|
|
|
In addition to saving you keystrokes, "git pull" also helps you by |
|
producing a default commit message documenting the branch and |
|
repository that you pulled from. |
|
|
|
(But note that no such commit will be created in the case of a |
|
<<fast-forwards,fast forward>>; instead, your branch will just be |
|
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 |
|
just be to send them as patches in email: |
|
|
|
First, use gitlink: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 gitlink: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 gitlink: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 |
|
will stop, and you can fix the conflicts as described in |
|
"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells |
|
git to perform a merge; if you would prefer it just to abort and |
|
leave your tree and index untouched, you may omit that option.) |
|
|
|
Once the index is updated with the results of the conflict |
|
resolution, instead of creating a new commit, just run |
|
|
|
------------------------------------------------- |
|
$ git am --resolved |
|
------------------------------------------------- |
|
|
|
and git will create the commit for you and continue applying the |
|
remaining patches from the mailbox. |
|
|
|
The final result will be a series of commits, one for each patch in |
|
the original mailbox, with authorship and commit log message each |
|
taken from the message containing each patch. |
|
|
|
[[setting-up-a-public-repository]] |
|
Setting up a public repository |
|
------------------------------ |
|
|
|
Another way to submit changes to a project is to simply tell the |
|
maintainer of that project to pull from your repository, exactly as |
|
you did in the section "<<getting-updates-with-git-pull, Getting |
|
updates with git pull>>". |
|
|
|
If you and maintainer both have accounts on the same machine, then |
|
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 |
|
use |
|
|
|
------------------------------------------------- |
|
$ git clone /path/to/repository |
|
$ git pull /path/to/other/repository |
|
------------------------------------------------- |
|
|
|
If this sort of setup is inconvenient or impossible, another (more |
|
common) option is to set up a public repository on a public server. |
|
This also allows you to cleanly separate private work in progress |
|
from publicly visible work. |
|
|
|
You will continue to do your day-to-day work in your personal |
|
repository, but periodically "push" changes from your personal |
|
repository into your public repository, allowing other developers to |
|
pull from that repository. So the flow of changes, in a situation |
|
where there is one other developer with a public repository, looks |
|
like this: |
|
|
|
you push |
|
your personal repo ------------------> your public repo |
|
^ | |
|
| | |
|
| you pull | they pull |
|
| | |
|
| | |
|
| they push V |
|
their public repo <------------------- their repo |
|
|
|
Now, assume your personal repository is in the directory ~/proj. We |
|
first create a new clone of the repository: |
|
|
|
------------------------------------------------- |
|
$ git clone --bare proj-clone.git |
|
------------------------------------------------- |
|
|
|
The resulting directory proj-clone.git will contains a "bare" git |
|
repository--it is just the contents of the ".git" directory, without |
|
a checked-out copy of a working directory. |
|
|
|
Next, copy proj-clone.git to the server where you plan to host the |
|
public repository. You can use scp, rsync, or whatever is most |
|
convenient. |
|
|
|
If somebody else maintains the public server, they may already have |
|
set up a git service for you, and you may skip to the section |
|
"<<pushing-changes-to-a-public-repository,Pushing changes to a public |
|
repository>>", below. |
|
|
|
Otherwise, the following sections explain how to export your newly |
|
created public repository: |
|
|
|
[[exporting-via-http]] |
|
Exporting a git repository via http |
|
----------------------------------- |
|
|
|
The git protocol gives better performance and reliability, but on a |
|
host with a web server set up, http exports may be simpler to set up. |
|
|
|
All you need to do is place the newly created bare git repository in |
|
a directory that is exported by the web server, and make some |
|
adjustments to give web clients some extra information they need: |
|
|
|
------------------------------------------------- |
|
$ mv proj.git /home/you/public_html/proj.git |
|
$ cd proj.git |
|
$ git update-server-info |
|
$ chmod a+x hooks/post-update |
|
------------------------------------------------- |
|
|
|
(For an explanation of the last two lines, see |
|
gitlink:git-update-server-info[1], and the documentation |
|
link:hooks.txt[Hooks used by git].) |
|
|
|
Advertise the url of proj.git. Anybody else should then be able to |
|
clone or pull from that url, for example with a commandline like: |
|
|
|
------------------------------------------------- |
|
$ git clone http://yourserver.com/~you/proj.git |
|
------------------------------------------------- |
|
|
|
(See also |
|
link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] |
|
for a slightly more sophisticated setup using WebDAV which also |
|
allows pushing over http.) |
|
|
|
[[exporting-via-git]] |
|
Exporting a git repository via the git protocol |
|
----------------------------------------------- |
|
|
|
This is the preferred method. |
|
|
|
For now, we refer you to the gitlink:git-daemon[1] man page for |
|
instructions. (See especially the examples section.) |
|
|
|
[[pushing-changes-to-a-public-repository]] |
|
Pushing changes to a public repository |
|
-------------------------------------- |
|
|
|
Note that the two techniques outline above (exporting via |
|
<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other |
|
maintainers to fetch your latest changes, but they do not allow write |
|
access, which you will need to update the public repository with the |
|
latest changes created in your private repository. |
|
|
|
The simplest way to do this is using gitlink:git-push[1] and ssh; to |
|
update the remote branch named "master" with the latest state of your |
|
branch named "master", run |
|
|
|
------------------------------------------------- |
|
$ git push ssh://yourserver.com/~you/proj.git master:master |
|
------------------------------------------------- |
|
|
|
or just |
|
|
|
------------------------------------------------- |
|
$ git push ssh://yourserver.com/~you/proj.git master |
|
------------------------------------------------- |
|
|
|
As with git-fetch, git-push will complain if this does not result in |
|
a <<fast-forwards,fast forward>>. Normally this is a sign of |
|
something wrong. However, if you are sure you know what you're |
|
doing, you may force git-push to perform the update anyway by |
|
proceeding the branch name by a plus sign: |
|
|
|
------------------------------------------------- |
|
$ git push ssh://yourserver.com/~you/proj.git +master |
|
------------------------------------------------- |
|
|
|
As with git-fetch, you may also set up configuration options to |
|
save typing; so, for example, after |
|
|
|
------------------------------------------------- |
|
$ cat >.git/config <<EOF |
|
[remote "public-repo"] |
|
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 gitlink:git-config[1] for |
|
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 |
|
link:cvs-migration.txt[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 |
|
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, ? |
|
|
|
|
|
[[cleaning-up-history]] |
|
Rewriting history and maintaining patch series |
|
============================================== |
|
|
|
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 |
|
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 |
|
may find that it is too much to digest all at once. |
|
|
|
If you present them with the entire history of your work, complete with |
|
mistakes, corrections, and dead ends, they may be overwhelmed. |
|
|
|
So the ideal is usually to produce a series of patches such that: |
|
|
|
1. Each patch can be applied in order. |
|
|
|
2. Each patch includes a single logical change, together with a |
|
message explaining the change. |
|
|
|
3. No patch introduces a regression: after applying any initial |
|
part of the series, the resulting project still compiles and |
|
works, and has no bugs that it didn't have before. |
|
|
|
4. 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 |
|
"origin", and create some commits on top of it: |
|
|
|
------------------------------------------------- |
|
$ git checkout -b mywork origin |
|
$ vi file.txt |
|
$ git commit |
|
$ vi otherfile.txt |
|
$ git commit |
|
... |
|
------------------------------------------------- |
|
|
|
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 |
|
gitlink:git-rebase[1]: |
|
|
|
------------------------------------------------- |
|
$ git checkout mywork |
|
$ git rebase origin |
|
------------------------------------------------- |
|
|
|
This will remove each of your commits from mywork, temporarily saving |
|
them as patches (in a directory named ".dotest"), update mywork to |
|
point at the latest version of origin, then apply each of the saved |
|
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 |
|
add" to update the index with those contents, and then, instead of |
|
running git-commit, just run |
|
|
|
------------------------------------------------- |
|
$ 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 |
|
------------------------------------------------- |
|
|
|
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 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 gitlink: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 |
|
$ gitk origin..mywork & |
|
------------------------------------------------- |
|
|
|
And browse through the list of patches in the mywork branch using gitk, |
|
applying them (possibly in a different order) to mywork-new using |
|
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 gitlink: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 |
|
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 |
|
two developers had independently done the work on the old and new heads |
|
in parallel. At this point, if someone attempts to merge the new head |
|
in to their branch, git will attempt to merge together the two (old and |
|
new) lines of development, instead of trying to replace the old by the |
|
new. The results are likely to be unexpected. |
|
|
|
You may still choose to publish branches whose history is rewritten, |
|
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. |
|
|
|
Advanced branch management |
|
========================== |
|
|
|
Fetching individual branches |
|
---------------------------- |
|
|
|
Instead of using gitlink: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 |
|
to fetch the branch named "todo" from the remote repository, and to |
|
store it locally under the name refs/heads/my-todo-work. |
|
|
|
You can also fetch branches from other repositories; so |
|
|
|
------------------------------------------------- |
|
$ git fetch git://example.com/proj.git master:example-master |
|
------------------------------------------------- |
|
|
|
will create a new branch named "example-master" and store in it the |
|
branch named "master" from the repository at the given URL. If you |
|
already have a branch named example-master, it will attempt to |
|
"fast-forward" to the commit given by example.com's master branch. So |
|
next we explain what a fast-forward is: |
|
|
|
[[fast-forwards]] |
|
Understanding git history: fast-forwards |
|
---------------------------------------- |
|
|
|
In the previous example, when updating an existing branch, "git |
|
fetch" checks to make sure that the most recent commit on the remote |
|
branch is a descendant of the most recent commit on your copy of the |
|
branch before updating your copy of the branch to point at the new |
|
commit. Git calls this process a "fast forward". |
|
|
|
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 |
|
a descendant of the old head. For example, the developer may have |
|
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. |
|
|
|
In that case, you can still force git to update to the new head, as |
|
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 |
|
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 |
|
repository that you originally cloned from. This information is |
|
stored in git configuration variables, which you can see using |
|
gitlink:git-config[1]: |
|
|
|
------------------------------------------------- |
|
$ git config -l |
|
core.repositoryformatversion=0 |
|
core.filemode=true |
|
core.logallrefupdates=true |
|
remote.origin.url=git://git.kernel.org/pub/scm/git/git.git |
|
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* |
|
branch.master.remote=origin |
|
branch.master.merge=refs/heads/master |
|
------------------------------------------------- |
|
|
|
If there are other repositories that you also use frequently, you can |
|
create similar configuration options to save typing; for example, |
|
after |
|
|
|
------------------------------------------------- |
|
$ git config remote.example.url git://example.com/proj.git |
|
------------------------------------------------- |
|
|
|
then the following two commands will do the same thing: |
|
|
|
------------------------------------------------- |
|
$ git fetch git://example.com/proj.git master:refs/remotes/example/master |
|
$ git fetch example master:refs/remotes/example/master |
|
------------------------------------------------- |
|
|
|
Even better, if you add one more option: |
|
|
|
------------------------------------------------- |
|
$ git config remote.example.fetch master:refs/remotes/example/master |
|
------------------------------------------------- |
|
|
|
then the following commands will all do the same thing: |
|
|
|
------------------------------------------------- |
|
$ git fetch git://example.com/proj.git master:ref/remotes/example/master |
|
$ git fetch example master:ref/remotes/example/master |
|
$ git fetch example example/master |
|
$ git fetch example |
|
------------------------------------------------- |
|
|
|
You can also add a "+" to force the update each time: |
|
|
|
------------------------------------------------- |
|
$ git config remote.example.fetch +master:ref/remotes/example/master |
|
------------------------------------------------- |
|
|
|
Don't do this unless you're sure you won't mind "git fetch" possibly |
|
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 |
|
gitlink:git-config[1]. |
|
|
|
See gitlink:git-config[1] for more details on the configuration |
|
options mentioned above. |
|
|
|
|
|
[[git-internals]] |
|
Git internals |
|
============= |
|
|
|
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 |
|
of objects. All objects are named by their content, which is |
|
approximated by the SHA1 hash of the object itself. Objects may refer |
|
to other objects (by referencing their SHA1 hash), and so you can |
|
build up a hierarchy of objects. |
|
|
|
All objects have a statically determined "type" aka "tag", which is |
|
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". |
|
|
|
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 "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. |
|
|
|
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 |
|
must have at least one root, and while you can tie several different |
|
root objects together into one project by creating a commit object which |
|
has two or more separate roots as its ultimate parents, that's probably |
|
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. |
|
|
|
Regardless of object type, all objects share the following |
|
characteristics: they are all deflated with zlib, and have a header |
|
that not only specifies their type, but also provides size information |
|
about the data in the object. It's worth noting that the SHA1 hash |
|
that is used to name the object is the hash of the original data |
|
plus this header, so `sha1sum` 'file' does not match the object name |
|
for 'file'. |
|
(Historical note: in the dawn of the age of git the hash |
|
was the sha1 of the 'compressed' object.) |
|
|
|
As a result, the general consistency of an object can always be tested |
|
independently of the contents or the type of the object: all objects can |
|
be validated by verifying that (a) their hashes match the content of the |
|
file and (b) the object successfully inflates to a stream of bytes that |
|
forms a sequence of <ascii type without space> + <space> + <ascii decimal |
|
size> + <byte\0> + <binary object data>. |
|
|
|
The structured objects can further have their structure and |
|
connectivity to other objects verified. This is generally done with |
|
the `git-fsck` program, which generates a full dependency graph |
|
of all objects, and verifies their internal consistency (in addition |
|
to just verifying their superficial consistency through the hash). |
|
|
|
The object types in some more detail: |
|
|
|
Blob Object |
|
----------- |
|
|
|
A "blob" object is nothing but a binary blob of data, and doesn't |
|
refer to anything else. There is no signature or any other |
|
verification of the data, so while the object is consistent (it 'is' |
|
indexed by its sha1 hash, so the data itself is certainly correct), it |
|
has absolutely no other attributes. No name associations, no |
|
permissions. It is purely a blob of data (i.e. normally "file |
|
contents"). |
|
|
|
In particular, since the blob is entirely defined by its data, if two |
|
files in a directory tree (or in multiple different versions of the |
|
repository) have the same contents, they will share the same blob |
|
object. The object is totally independent of its location in the |
|
directory tree, and renaming a file does not change the object that |
|
file is associated with in any way. |
|
|
|
A blob is typically created when gitlink:git-update-index[1] |
|
is run, and its data can be accessed by gitlink:git-cat-file[1]. |
|
|
|
Tree Object |
|
----------- |
|
|
|
The next hierarchical object type is the "tree" object. A tree object |
|
is a list of mode/name/blob data, sorted by name. Alternatively, the |
|
mode data may specify a directory mode, in which case instead of |
|
naming a blob, that name is associated with another TREE object. |
|
|
|
Like the "blob" object, a tree object is uniquely determined by the |
|
set contents, and so two separate but identical trees will always |
|
share the exact same object. This is true at all levels, i.e. it's |
|
true for a "leaf" tree (which does not refer to any other trees, only |
|
blobs) as well as for a whole subdirectory. |
|
|
|
For that reason a "tree" object is just a pure data abstraction: it |
|
has no history, no signatures, no verification of validity, except |
|
that since the contents are again protected by the hash itself, we can |
|
trust that the tree is immutable and its contents never change. |
|
|
|
So you can trust the contents of a tree to be valid, the same way you |
|
can trust the contents of a blob, but you don't know where those |
|
contents 'came' from. |
|
|
|
Side note on trees: since a "tree" object is a sorted list of |
|
"filename+content", you can create a diff between two trees without |
|
actually having to unpack two trees. Just ignore all common parts, |
|
and your diff will look right. In other words, you can effectively |
|
(and efficiently) tell the difference between any two random trees by |
|
O(n) where "n" is the size of the difference, rather than the size of |
|
the tree. |
|
|
|
Side note 2 on trees: since the name of a "blob" depends entirely and |
|
exclusively on its contents (i.e. there are no names or permissions |
|
involved), you can see trivial renames or permission changes by |
|
noticing that the blob stayed the same. However, renames with data |
|
changes need a smarter "diff" implementation. |
|
|
|
A tree is created with gitlink:git-write-tree[1] and |
|
its data can be accessed by gitlink:git-ls-tree[1]. |
|
Two trees can be compared with gitlink:git-diff-tree[1]. |
|
|
|
Commit Object |
|
------------- |
|
|
|
The "commit" object is an object that introduces the notion of |
|
history into the picture. In contrast to the other objects, it |
|
doesn't just describe the physical state of a tree, it describes how |
|
we got there, and why. |
|
|
|
A "commit" is defined by the tree-object that it results in, the |
|
parent commits (zero, one or more) that led up to that point, and a |
|
comment on what happened. Again, a commit is not trusted per se: |
|
the contents are well-defined and "safe" due to the cryptographically |
|
strong signatures at all levels, but there is no reason to believe |
|
that the tree is "good" or that the merge information makes sense. |
|
The parents do not have to actually have any relationship with the |
|
result, for example. |
|
|
|
Note on commits: unlike real SCM's, commits do not contain |
|
rename information or file mode change information. All of that is |
|
implicit in the trees involved (the result tree, and the result trees |
|
of the parents), and describing that makes no sense in this idiotic |
|
file manager. |
|
|
|
A commit is created with gitlink:git-commit-tree[1] and |
|
its data can be accessed by gitlink:git-cat-file[1]. |
|
|
|
Trust |
|
----- |
|
|
|
An aside on the notion of "trust". Trust is really outside the scope |
|
of "git", but it's worth noting a few things. First off, since |
|
everything is hashed with SHA1, you 'can' trust that an object is |
|
intact and has not been messed with by external sources. So the name |
|
of an object uniquely identifies a known state - just not a state that |
|
you may want to trust. |
|
|
|
Furthermore, since the SHA1 signature of a commit refers to the |
|
SHA1 signatures of the tree it is associated with and the signatures |
|
of the parent, a single named commit specifies uniquely a whole set |
|
of history, with full contents. You can't later fake any step of the |
|
way once you have the name of a commit. |
|
|
|
So to introduce some real trust in the system, the only thing you need |
|
to do is to digitally sign just 'one' special note, which includes the |
|
name of a top-level commit. Your digital signature shows others |
|
that you trust that commit, and the immutability of the history of |
|
commits tells others that they can trust the whole history. |
|
|
|
In other words, you can easily validate a whole archive by just |
|
sending out a single email that tells the people the name (SHA1 hash) |
|
of the top commit, and digitally sign that email using something |
|
like GPG/PGP. |
|
|
|
To assist in this, git also provides the tag object... |
|
|
|
Tag Object |
|
---------- |
|
|
|
Git provides the "tag" object to simplify creating, managing and |
|
exchanging symbolic and signed tokens. The "tag" object at its |
|
simplest simply symbolically identifies another object by containing |
|
the sha1, type and symbolic name. |
|
|
|
However it can optionally contain additional signature information |
|
(which git doesn't care about as long as there's less than 8k of |
|
it). This can then be verified externally to git. |
|
|
|
Note that despite the tag features, "git" itself only handles content |
|
integrity; the trust framework (and signature provision and |
|
verification) has to come from outside. |
|
|
|
A tag is created with gitlink:git-mktag[1], |
|
its data can be accessed by gitlink:git-cat-file[1], |
|
and the signature can be verified by |
|
gitlink:git-verify-tag[1]. |
|
|
|
|
|
The "index" aka "Current Directory Cache" |
|
----------------------------------------- |
|
|
|
The index is a simple binary file, which contains an efficient |
|
representation of a virtual directory content at some random time. It |
|
does so by a simple array that associates a set of names, dates, |
|
permissions and content (aka "blob") objects together. The cache is |
|
always kept ordered by name, and names are unique (with a few very |
|
specific rules) at any point in time, but the cache has no long-term |
|
meaning, and can be partially updated at any time. |
|
|
|
In particular, the index certainly does not need to be consistent with |
|
the current directory contents (in fact, most operations will depend on |
|
different ways to make the index 'not' be consistent with the directory |
|
hierarchy), but it has three very important attributes: |
|
|
|
'(a) it can re-generate the full state it caches (not just the |
|
directory structure: it contains pointers to the "blob" objects so |
|
that it can regenerate the data too)' |
|
|
|
As a special case, there is a clear and unambiguous one-way mapping |
|
from a current directory cache to a "tree object", which can be |
|
efficiently created from just the current directory cache without |
|
actually looking at any other data. So a directory cache at any one |
|
time uniquely specifies one and only one "tree" object (but has |
|
additional data to make it easy to match up that tree object with what |
|
has happened in the directory) |
|
|
|
'(b) it has efficient methods for finding inconsistencies between that |
|
cached state ("tree object waiting to be instantiated") and the |
|
current state.' |
|
|
|
'(c) it can additionally efficiently represent information about merge |
|
conflicts between different tree objects, allowing each pathname to be |
|
associated with sufficient information about the trees involved that |
|
you can create a three-way merge between them.' |
|
|
|
Those are the ONLY three things that the directory cache does. It's a |
|
cache, and the normal operation is to re-generate it completely from a |
|
known tree object, or update/compare it with a live tree that is being |
|
developed. If you blow the directory cache away entirely, you generally |
|
haven't lost any information as long as you have the name of the tree |
|
that it described. |
|
|
|
At the same time, the index is at the same time also the |
|
staging area for creating new trees, and creating a new tree always |
|
involves a controlled modification of the index file. In particular, |
|
the index file can have the representation of an intermediate tree that |
|
has not yet been instantiated. So the index can be thought of as a |
|
write-back cache, which can contain dirty information that has not yet |
|
been written back to the backing store. |
|
|
|
|
|
|
|
The Workflow |
|
------------ |
|
|
|
Generally, all "git" operations work on the index file. Some operations |
|
work *purely* on the index file (showing the current state of the |
|
index), but most operations move data to and from the index file. Either |
|
from the database or from the working directory. Thus there are four |
|
main combinations: |
|
|
|
working directory -> index |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
You update the index with information from the working directory with |
|
the gitlink:git-update-index[1] command. You |
|
generally update the index information by just specifying the filename |
|
you want to update, like so: |
|
|
|
------------------------------------------------- |
|
$ git-update-index filename |
|
------------------------------------------------- |
|
|
|
but to avoid common mistakes with filename globbing etc, the command |
|
will not normally add totally new entries or remove old entries, |
|
i.e. it will normally just update existing cache entries. |
|
|
|
To tell git that yes, you really do realize that certain files no |
|
longer exist, or that new files should be added, you |
|
should use the `--remove` and `--add` flags respectively. |
|
|
|
NOTE! A `--remove` flag does 'not' mean that subsequent filenames will |
|
necessarily be removed: if the files still exist in your directory |
|
structure, the index will be updated with their new status, not |
|
removed. The only thing `--remove` means is that update-cache will be |
|
considering a removed file to be a valid thing, and if the file really |
|
does not exist any more, it will update the index accordingly. |
|
|
|
As a special case, you can also do `git-update-index --refresh`, which |
|
will refresh the "stat" information of each index to match the current |
|
stat information. It will 'not' update the object status itself, and |
|
it will only update the fields that are used to quickly test whether |
|
an object still matches its old backing store object. |
|
|
|
index -> object database |
|
~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
You write your current index file to a "tree" object with the program |
|
|
|
------------------------------------------------- |
|
$ git-write-tree |
|
------------------------------------------------- |
|
|
|
that doesn't come with any options - it will just write out the |
|
current index into the set of tree objects that describe that state, |
|
and it will return the name of the resulting top-level tree. You can |
|
use that tree to re-generate the index at any time by going in the |
|
other direction: |
|
|
|
object database -> index |
|
~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
You read a "tree" file from the object database, and use that to |
|
populate (and overwrite - don't do this if your index contains any |
|
unsaved state that you might want to restore later!) your current |
|
index. Normal operation is just |
|
|
|
------------------------------------------------- |
|
$ git-read-tree <sha1 of tree> |
|
------------------------------------------------- |
|
|
|
and your index file will now be equivalent to the tree that you saved |
|
earlier. However, that is only your 'index' file: your working |
|
directory contents have not been modified. |
|
|
|
index -> working directory |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
You update your working directory from the index by "checking out" |
|
files. This is not a very common operation, since normally you'd just |
|
keep your files updated, and rather than write to your working |
|
directory, you'd tell the index files about the changes in your |
|
working directory (i.e. `git-update-index`). |
|
|
|
However, if you decide to jump to a new version, or check out somebody |
|
else's version, or just restore a previous tree, you'd populate your |
|
index file with read-tree, and then you need to check out the result |
|
with |
|
|
|
------------------------------------------------- |
|
$ git-checkout-index filename |
|
------------------------------------------------- |
|
|
|
or, if you want to check out all of the index, use `-a`. |
|
|
|
NOTE! git-checkout-index normally refuses to overwrite old files, so |
|
if you have an old version of the tree already checked out, you will |
|
need to use the "-f" flag ('before' the "-a" flag or the filename) to |
|
'force' the checkout. |
|
|
|
|
|
Finally, there are a few odds and ends which are not purely moving |
|
from one representation to the other: |
|
|
|
Tying it all together |
|
~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
To commit a tree you have instantiated with "git-write-tree", you'd |
|
create a "commit" object that refers to that tree and the history |
|
behind it - most notably the "parent" commits that preceded it in |
|
history. |
|
|
|
Normally a "commit" has one parent: the previous state of the tree |
|
before a certain change was made. However, sometimes it can have two |
|
or more parent commits, in which case we call it a "merge", due to the |
|
fact that such a commit brings together ("merges") two or more |
|
previous states represented by other commits. |
|
|
|
In other words, while a "tree" represents a particular directory state |
|
of a working directory, a "commit" represents that state in "time", |
|
and explains how we got there. |
|
|
|
You create a commit object by giving it the tree that describes the |
|
state at the time of the commit, and a list of parents: |
|
|
|
------------------------------------------------- |
|
$ git-commit-tree <tree> -p <parent> [-p <parent2> ..] |
|
------------------------------------------------- |
|
|
|
and then giving the reason for the commit on stdin (either through |
|
redirection from a pipe or file, or by just typing it at the tty). |
|
|
|
git-commit-tree will return the name of the object that represents |
|
that commit, and you should save it away for later use. Normally, |
|
you'd commit a new `HEAD` state, and while git doesn't care where you |
|
save the note about that state, in practice we tend to just write the |
|
result to the file pointed at by `.git/HEAD`, so that we can always see |
|
what the last committed state was. |
|
|
|
Here is an ASCII art by Jon Loeliger that illustrates how |
|
various pieces fit together. |
|
|
|
------------ |
|
|
|
commit-tree |
|
commit obj |
|
+----+ |
|
| | |
|
| | |
|
V V |
|
+-----------+ |
|
| Object DB | |
|
| Backing | |
|
| Store | |
|
+-----------+ |
|
^ |
|
write-tree | | |
|
tree obj | | |
|
| | read-tree |
|
| | tree obj |
|
V |
|
+-----------+ |
|
| Index | |
|
| "cache" | |
|
+-----------+ |
|
update-index ^ |
|
blob obj | | |
|
| | |
|
checkout-index -u | | checkout-index |
|
stat | | blob obj |
|
V |
|
+-----------+ |
|
| Working | |
|
| Directory | |
|
+-----------+ |
|
|
|
------------ |
|
|
|
|
|
Examining the data |
|
------------------ |
|
|
|
You can examine the data represented in the object database and the |
|
index with various helper tools. For every object, you can use |
|
gitlink:git-cat-file[1] to examine details about the |
|
object: |
|
|
|
------------------------------------------------- |
|
$ git-cat-file -t <objectname> |
|
------------------------------------------------- |
|
|
|
shows the type of the object, and once you have the type (which is |
|
usually implicit in where you find the object), you can use |
|
|
|
------------------------------------------------- |
|
$ git-cat-file blob|tree|commit|tag <objectname> |
|
------------------------------------------------- |
|
|
|
to show its contents. NOTE! Trees have binary content, and as a result |
|
there is a special helper for showing that content, called |
|
`git-ls-tree`, which turns the binary content into a more easily |
|
readable form. |
|
|
|
It's especially instructive to look at "commit" objects, since those |
|
tend to be small and fairly self-explanatory. In particular, if you |
|
follow the convention of having the top commit name in `.git/HEAD`, |
|
you can do |
|
|
|
------------------------------------------------- |
|
$ git-cat-file commit HEAD |
|
------------------------------------------------- |
|
|
|
to see what the top commit was. |
|
|
|
Merging multiple trees |
|
---------------------- |
|
|
|
Git helps you do a three-way merge, which you can expand to n-way by |
|
repeating the merge procedure arbitrary times until you finally |
|
"commit" the state. The normal situation is that you'd only do one |
|
three-way merge (two parents), and commit it, but if you like to, you |
|
can do multiple parents in one go. |
|
|
|
To do a three-way merge, you need the two sets of "commit" objects |
|
that you want to merge, use those to find the closest common parent (a |
|
third "commit" object), and then use those commit objects to find the |
|
state of the directory ("tree" object) at these points. |
|
|
|
To get the "base" for the merge, you first look up the common parent |
|
of two commits with |
|
|
|
------------------------------------------------- |
|
$ git-merge-base <commit1> <commit2> |
|
------------------------------------------------- |
|
|
|
which will return you the commit they are both based on. You should |
|
now look up the "tree" objects of those commits, which you can easily |
|
do with (for example) |
|
|
|
------------------------------------------------- |
|
$ git-cat-file commit <commitname> | head -1 |
|
------------------------------------------------- |
|
|
|
since the tree object information is always the first line in a commit |
|
object. |
|
|
|
Once you know the three trees you are going to merge (the one "original" |
|
tree, aka the common case, and the two "result" trees, aka the branches |
|
you want to merge), you do a "merge" read into the index. This will |
|
complain if it has to throw away your old index contents, so you should |
|
make sure that you've committed those - in fact you would normally |
|
always do a merge against your last commit (which should thus match what |
|
you have in your current index anyway). |
|
|
|
To do the merge, do |
|
|
|
------------------------------------------------- |
|
$ git-read-tree -m -u <origtree> <yourtree> <targettree> |
|
------------------------------------------------- |
|
|
|
which will do all trivial merge operations for you directly in the |
|
index file, and you can just write the result out with |
|
`git-write-tree`. |
|
|
|
|
|
Merging multiple trees, continued |
|
--------------------------------- |
|
|
|
Sadly, many merges aren't trivial. If there are files that have |
|
been added.moved or removed, or if both branches have modified the |
|
same file, you will be left with an index tree that contains "merge |
|
entries" in it. Such an index tree can 'NOT' be written out to a tree |
|
object, and you will have to resolve any such merge clashes using |
|
other tools before you can write out the result. |
|
|
|
You can examine such index state with `git-ls-files --unmerged` |
|
command. An example: |
|
|
|
------------------------------------------------ |
|
$ git-read-tree -m $orig HEAD $target |
|
$ git-ls-files --unmerged |
|
100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c |
|
100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c |
|
100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c |
|
------------------------------------------------ |
|
|
|
Each line of the `git-ls-files --unmerged` output begins with |
|
the blob mode bits, blob SHA1, 'stage number', and the |
|
filename. The 'stage number' is git's way to say which tree it |
|
came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD` |
|
tree, and stage3 `$target` tree. |
|
|
|
Earlier we said that trivial merges are done inside |
|
`git-read-tree -m`. For example, if the file did not change |
|
from `$orig` to `HEAD` nor `$target`, or if the file changed |
|
from `$orig` to `HEAD` and `$orig` to `$target` the same way, |
|
obviously the final outcome is what is in `HEAD`. What the |
|
above example shows is that file `hello.c` was changed from |
|
`$orig` to `HEAD` and `$orig` to `$target` in a different way. |
|
You could resolve this by running your favorite 3-way merge |
|
program, e.g. `diff3` or `merge`, on the blob objects from |
|
these three stages yourself, like this: |
|
|
|
------------------------------------------------ |
|
$ git-cat-file blob 263414f... >hello.c~1 |
|
$ git-cat-file blob 06fa6a2... >hello.c~2 |
|
$ git-cat-file blob cc44c73... >hello.c~3 |
|
$ merge hello.c~2 hello.c~1 hello.c~3 |
|
------------------------------------------------ |
|
|
|
This would leave the merge result in `hello.c~2` file, along |
|
with conflict markers if there are conflicts. After verifying |
|
the merge result makes sense, you can tell git what the final |
|
merge result for this file is by: |
|
|
|
------------------------------------------------- |
|
$ mv -f hello.c~2 hello.c |
|
$ git-update-index hello.c |
|
------------------------------------------------- |
|
|
|
When a path is in unmerged state, running `git-update-index` for |
|
that path tells git to mark the path resolved. |
|
|
|
The above is the description of a git merge at the lowest level, |
|
to help you understand what conceptually happens under the hood. |
|
In practice, nobody, not even git itself, uses three `git-cat-file` |
|
for this. There is `git-merge-index` program that extracts the |
|
stages to temporary files and calls a "merge" script on it: |
|
|
|
------------------------------------------------- |
|
$ git-merge-index git-merge-one-file hello.c |
|
------------------------------------------------- |
|
|
|
and that is what higher level `git merge -s resolve` is implemented with. |
|
|
|
How git stores objects efficiently: pack files |
|
---------------------------------------------- |
|
|
|
We've seen how git stores each object in a file named after the |
|
object's SHA1 hash. |
|
|
|
Unfortunately this system becomes inefficient once a project has a |
|
lot of objects. Try this on an old project: |
|
|
|
------------------------------------------------ |
|
$ git count-objects |
|
6930 objects, 47620 kilobytes |
|
------------------------------------------------ |
|
|
|
The first number is the number of objects which are kept in |
|
individual files. The second is the amount of space taken up by |
|
those "loose" objects. |
|
|
|
You can save space and make git faster by moving these loose objects in |
|
to a "pack file", which stores a group of objects in an efficient |
|
compressed format; the details of how pack files are formatted can be |
|
found in link:technical/pack-format.txt[technical/pack-format.txt]. |
|
|
|
To put the loose objects into a pack, just run git repack: |
|
|
|
------------------------------------------------ |
|
$ git repack |
|
Generating pack... |
|
Done counting 6020 objects. |
|
Deltifying 6020 objects. |
|
100% (6020/6020) done |
|
Writing 6020 objects. |
|
100% (6020/6020) done |
|
Total 6020, written 6020 (delta 4070), reused 0 (delta 0) |
|
Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. |
|
------------------------------------------------ |
|
|
|
You can then run |
|
|
|
------------------------------------------------ |
|
$ git prune |
|
------------------------------------------------ |
|
|
|
to remove any of the "loose" objects that are now contained in the |
|
pack. This will also remove any unreferenced objects (which may be |
|
created when, for example, you use "git reset" to remove a commit). |
|
You can verify that the loose objects are gone by looking at the |
|
.git/objects directory or by running |
|
|
|
------------------------------------------------ |
|
$ git count-objects |
|
0 objects, 0 kilobytes |
|
------------------------------------------------ |
|
|
|
Although the object files are gone, any commands that refer to those |
|
objects will work exactly as they did before. |
|
|
|
The gitlink:git-gc[1] command performs packing, pruning, and more for |
|
you, so is normally the only high-level command you need. |
|
|
|
[[dangling-objects]] |
|
Dangling objects |
|
---------------- |
|
|
|
The gitlink:git-fsck[1] command will sometimes complain about dangling |
|
objects. They are not a problem. |
|
|
|
The most common cause of dangling objects is that you've rebased a |
|
branch, or you have pulled from somebody else who rebased a branch--see |
|
<<cleaning-up-history>>. In that case, the old head of the original |
|
branch still exists, as does obviously everything it pointed to. The |
|
branch pointer itself just doesn't, since you replaced it with another |
|
one. |
|
|
|
There are also other situations too that cause dangling objects. For |
|
example, a "dangling blob" may arise because you did a "git add" of a |
|
file, but then, before you actually committed it and made it part of the |
|
bigger picture, you changed something else in that file and committed |
|
that *updated* thing - the old state that you added originally ends up |
|
not being pointed to by any commit or tree, so it's now a dangling blob |
|
object. |
|
|
|
Similarly, when the "recursive" merge strategy runs, and finds that |
|
there are criss-cross merges and thus more than one merge base (which is |
|
fairly unusual, but it does happen), it will generate one temporary |
|
midway tree (or possibly even more, if you had lots of criss-crossing |
|
merges and more than two merge bases) as a temporary internal merge |
|
base, and again, those are real objects, but the end result will not end |
|
up pointing to them, so they end up "dangling" in your repository. |
|
|
|
Generally, dangling objects aren't anything to worry about. They can |
|
even be very useful: if you screw something up, the dangling objects can |
|
be how you recover your old tree (say, you did a rebase, and realized |
|
that you really didn't want to - you can look at what dangling objects |
|
you have, and decide to reset your head to some old dangling state). |
|
|
|
For commits, the most useful thing to do with dangling objects tends to |
|
be to do a simple |
|
|
|
------------------------------------------------ |
|
$ gitk <dangling-commit-sha-goes-here> --not --all |
|
------------------------------------------------ |
|
|
|
For blobs and trees, you can't do the same, but you can examine them. |
|
You can just do |
|
|
|
------------------------------------------------ |
|
$ git show <dangling-blob/tree-sha-goes-here> |
|
------------------------------------------------ |
|
|
|
to show what the contents of the blob were (or, for a tree, basically |
|
what the "ls" for that directory was), and that may give you some idea |
|
of what the operation was that left that dangling object. |
|
|
|
Usually, dangling blobs and trees aren't very interesting. They're |
|
almost always the result of either being a half-way mergebase (the blob |
|
will often even have the conflict markers from a merge in it, if you |
|
have had conflicting merges that you fixed up by hand), or simply |
|
because you interrupted a "git fetch" with ^C or something like that, |
|
leaving _some_ of the new objects in the object database, but just |
|
dangling and useless. |
|
|
|
Anyway, once you are sure that you're not interested in any dangling |
|
state, you can just prune all unreachable objects: |
|
|
|
------------------------------------------------ |
|
$ git prune |
|
------------------------------------------------ |
|
|
|
and they'll be gone. But you should only run "git prune" on a quiescent |
|
repository - it's kind of like doing a filesystem fsck recovery: you |
|
don't want to do that while the filesystem is mounted. |
|
|
|
(The same is true of "git-fsck" itself, btw - but since |
|
git-fsck never actually *changes* the repository, it just reports |
|
on what it found, git-fsck itself is never "dangerous" to run. |
|
Running it while somebody is actually changing the repository can cause |
|
confusing and scary messages, but it won't actually do anything bad. In |
|
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 |
|
=================================== |
|
|
|
This is a work in progress. |
|
|
|
The basic requirements: |
|
- It must be readable in order, from beginning to end, by |
|
someone intelligent with a basic grasp of the unix |
|
commandline, but without any special knowledge of git. If |
|
necessary, any other prerequisites should be specifically |
|
mentioned as they arise. |
|
- Whenever possible, section headings should clearly describe |
|
the task they explain how to do, in language that requires |
|
no more knowledge than necessary: for example, "importing |
|
patches into a project" rather than "the git-am command" |
|
|
|
Think about how to create a clear chapter dependency graph that will |
|
allow people to get to important topics without necessarily reading |
|
everything in between. |
|
|
|
Say something about .gitignore. |
|
|
|
Scan Documentation/ for other stuff left out; in particular: |
|
howto's |
|
some of technical/? |
|
hooks |
|
list of commands in gitlink:git[1] |
|
|
|
Scan email archives for other stuff left out |
|
|
|
Scan man pages to see if any assume more background than this manual |
|
provides. |
|
|
|
Simplify beginning by suggesting disconnected head instead of |
|
temporary branch creation? |
|
|
|
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? |
|
|
|
Include cross-references to the glossary, where appropriate. |
|
|
|
Document shallow clones? See draft 1.5.0 release notes for some |
|
documentation. |
|
|
|
Add a section on working with other version control systems, including |
|
CVS, Subversion, and just imports of series of release tarballs. |
|
|
|
More details on gitweb? |
|
|
|
Write a chapter on using plumbing and writing scripts.
|
|
|