From 45302415f33e0ab6b164f1557d84be45d5541b10 Mon Sep 17 00:00:00 2001 From: kballou Date: Mon, 18 Jan 2016 17:23:38 -0700 Subject: Add Learning Git in Reverse post --- content/blog/git-in-reverse.markdown | 704 +++++++++++++++++++++++++++++++++++ 1 file changed, 704 insertions(+) create mode 100644 content/blog/git-in-reverse.markdown (limited to 'content') diff --git a/content/blog/git-in-reverse.markdown b/content/blog/git-in-reverse.markdown new file mode 100644 index 0000000..7157203 --- /dev/null +++ b/content/blog/git-in-reverse.markdown @@ -0,0 +1,704 @@ +--- +title: "Learning Git in Reverse" +description: "A backwards introduction to the information manager from hell" +tags: + - "Git" + - "Learning" + - "Talks" + - "zData" +date: "2016-01-18" +pubdate: "2016-01-20" +categories: + - "Development" +slug: "git-in-reverse" +--- + +> The content of this post is drafted from contents of a [similarly titled +> presentation][23]. + +It is certainly counter-intuitive to learn to drive by first going backwards, +so why learn how to use Git in reverse? The short answer is: knowing the +internals of Git _should_ make the commands and workflows of Git more +accessible and understandable. + +We will start by touring the plumbing commands and walk all the way through +branching. + +## What is Git± ## + +![XKCD on Git](http://imgs.xkcd.com/comics/git.png "If that doesn't fix it, +git.txt contains the phone number of a friend of mine who understands git. Just +wait through a few minutes of 'It's really pretty simple, just think of +branches as...' and eventually you'll learn the commands that will fix +everything.") + +Git is a few things to many people, and creating a standard definition is our +first step to fully understanding the nebulous Git. + +Git, developed by Linus Torvalds, is a distributed version control system +(DVCS). This means, Git is a tool for managing, typically, source code and its +related versioning. It accomplishes this by creating a distributed acyclic +graph of the code and folder structure and tracking the changes in the graph. + +Git internally accomplishes this by using a key-value or content addressable +filesystem. Git only knows how to store "objects". There is really no other +_real_ thing that Git is storing. + +## Plumbing ## + +We will start by learning a few of the most basic plumbing commands of Git, +beginning with the [`git-hash-object(1)`][5] command: + +### Git Objects ### + +Git objects are a [zlib][3] compressed binary file stored under the +`.git/objects` folder of any Git repository. They are typically created with +the [`git-hash-object(1)`][5] command are very basic in content: several bytes +of header information used by Git, type and size, and the full contents of the +file Git is storing. + +For the majority of this post, we will be referencing objects created in a +temporary repository: + + $ cd /tmp + $ git init foo + $ cd foo + +> The [`git-init(1)`][4] command creates a new local Git repository in the +> current directory or creates a new directory with a newly initialized Git +> repository. + +After creating a new Git repository, let's examine its current contents: + + ± find .git + .git + .git/objects + .git/objects/info + .git/objects/pack + .git/config + .git/HEAD + .git/hooks + .git/hooks/post-checkout + .git/hooks/post-commit + .git/hooks/ctags + .git/hooks/post-merge + .git/hooks/post-rewrite + .git/refs + .git/refs/tags + .git/refs/heads + +We see that Git has created several folders and files for its internal usage. +We, as developers and users of Git, should generally never need to do anything +to these files, with a small exception for `.git/hooks`. + +As noted before, `.git/objects` will be where Git will store all the objects +(source code and related) we create. `.git/hooks` are used for add custom +operations (white-space, conversions, `ctags`, etc.) to Git's operation. +`.git/refs` is where Git stores information about tags and branches. +`.git/config` is a file for local Git configuration options. This file will +store information about our repository and where it will go for +synchronization. `.git/HEAD` stores a reference to the working copy commit +hash. + +With all this out of the way, we can now start creating objects. + +#### [`git-hash-object(1)`][5] #### + +We can start out by providing some content for [`git-hash-object(1)`][5]: + + ± echo 'foo' | git hash-object --stdin + 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +[`git-hash-object(1)`][5] typically expects filenames, so we provide `--stdin` +to tell it we are passing contents from the standard input stream. + +However, since we haven't told Git to store the contents, we have no objects +stored in the `.git/objects` folder. We will need to pass the `-w` flag to +[`git-hash-object(1)`][5] to tell Git to store the contents. + + ± echo 'foo' | git hash-object -w --stdin + 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +Now, if we examine the `.git/objects` folder, we will see a new folder and a +new file: + + ± find .git/objects -type f + .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +When Git stores objects, it splits the 40 character hash into two parts: the +first two characters and the last 38. The first two characters, in this case +25, as the folder, and the last 38, `7cc5642cb1a054f08cc83f2d943e56fd3ebe99`, +as the file. The purpose of splitting the hash is to make indexing quicker. +Some of the original motivations for developing Git was a requirement of speed +and performance, can't manage decades of kernel history with a slow tool. + +We can use another Git plumbing command to extract the contents of the object: +`git-cat-file`: + + ± git cat-file -p 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 + foo + +Passing `-p` to `git-cat-file` tells Git to infer the type of the object. +Otherwise, we need to tell Git what the object is. + +Moreover, because we know the objects are zlib compressed, we can use a tool +like `zlib-flate` or similar to peer inside the contents of the files +ourselves: + + ± cat .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 \ + > | zlib-flate -uncompress + blob 4foo + +Here we see the metadata that Git uses itself, but is otherwise the contents we +expect. + +Perfect. We can store content in Git's object store and we can retrieve the +contents. However, attempting to manage files in this way will be more taxing +than any form of development. Furthermore, we don't have a way to store +filenames yet. Thus, we will need a new type of object, trees. + +### Git Trees ### + +Trees are objects. + +Trees are similarly zlib compressed binaries of the internal data structure of +tracked folder structure of the repository. We create Git trees using the +[`git-update-index(1)`][6] and [`git-write-tree(1)`][7] plumbing commands. + +Since we have an object already added to the Git object store, we can go ahead +and create a basic tree: + + ± git update-index --add --cacheinfo 100644 \ + 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 foo.txt + ± git write-tree + fcf0be4d7e45f0ef9592682ad68e42270b0366b4 + +Thus far, we have created two objects, one to store the contents of `foo.txt` +and another as the tree, which stores binding between the contents and the +filename for `foo.txt`. + +Visually, this may look like something similar to the following image: + +![Git Tree 1][git-tree-1] + +If we inspect the `.git/objects` directory, we should see a new object: + + ± find .git/objects -type f + .git/objects/fc/f0be4d7e45f0ef9592682ad68e42270b0366b4 + .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +As we expected, there is a new folder and new file, `fc` and +`f0be4d7e45f0ef9592682ad68e42270b0366b4`, respectively. + +Since Git trees are actually objects, we can use the `git-cat-file` command +again to print out the contents of the tree: + + ± git cat-file -p fcf0be4d7e45f0ef9592682ad68e42270b0366b4 + 100644 blob 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 foo.txt + +That is, trees are objects where the contents of the object describes a folder +structure "tree". It uses 4 columns for each element of the tree where the +first number uses something similar to the Unix permissions octals; the second +defines the type of object, this can be either `blob` or `tree`; the third is +the hash of the object the entry points to; finally, the last element is the +filename of the object or folder name if the element is a tree. + +A more complicated example of a Git tree may look like the following image: + +![Git Tree 2][git-tree-2] + +Now we have file names and the ability to track folders, however, we are still +managing and holding onto the checksums ourselves. Furthermore, we have no +reference to who, when, why, or from where changes are being made. We need +another object to store this information. + +### Git Commits ### + +This will sound familiar: Git commits are ... objects. + +Git stores commits the same way it stores files and trees, as a zlib compressed +binary in the `.git/objects` folders. Similar to trees, the contents of the +object is specifically formatted, but they are stored the same nonetheless. We +can create commits using the [`git-commit-tree(1)`][8] plumbing command. + +The [`git-commit-tree(1)`][8] command takes a message, a tree, and optionally a +parent commit, and creates a commit object. If the parent is not specified, it +creates a root commit. + +We have just created a tree, let's see what committing that tree looks like: + + ± echo 'our first commit' \ + > | git commit-tree fcf0be4d7e45f0ef9592682ad68e42270b0366b4 + d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + +> Notice, the hash returned here _will_ be different. This hash is dependent on +> time and the author. + +Inspecting our `.git/objects` store, we will see our new object: + + ± find .git/objects -type f + .git/objects/d7/ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + .git/objects/fc/f0be4d7e45f0ef9592682ad68e42270b0366b4 + .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +Similar to trees and files, we can use the `git-cat-file` command to inspect +the newly created commit object: + + ± git cat-file -f d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + tree fcf0be4d7e45f0ef9592682ad68e42270b0366b4 + author kballou 1453219069 -0700 + committer kballou 1453219069 -0700 + + our first commit + +Breaking down this structure, we have 4 lines, the first line tells which tree +this commit is saving. Since a tree already contains the information of all the +objects that are currently being tracked, the commit only needs to save the +root tree to be able to save _all_ the information for a commit. The second and +third line tell us the author and committer, often these will be the same. They +will be different for GitHub pull requests, or in other situations where the +author of the patch or change is different from the maintainer of the project. +Finally, after a blank line, the rest of the file is reserved for the commit +message; since "our first commit" message is short, it only takes a single +line. + +![git commit 1][git-commit-1] + +To inform Git that we have created a commit, we need to add some information to +a few files. First, we need create the `master` reference. We do this by +putting the full commit hash into a file called `.git/refs/heads/master`: + + ± echo d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 > .git/refs/heads/master + +The next thing we should do is update the `.git/HEAD` file to point to our new +reference: + + ± echo 'ref: refs/heads/master' > .git/HEAD + +This brings Git up to speed on everything we have done manually, similarly, +this is what Git does for us when we use the porcelain commands for managing +code. However, it's not really recommended to be manually touching these files, +and in fact, there is another plumbing command for updating these files: +[`git-update-ref(1)`][9]. Instead of the two commands above, we can use a +single invocation of [`git-update-ref(1)`][9] to perform the above: + + ± git update-ref refs/heads/master d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + +Notice, [`git-update-ref(1)`][9] is an idempotent operation, that is, if the +reference has already been changed to the current hash, running this command +again will yield no change. + +Before we get into the porcelain commands, let's walk through the motions +again: + + ± echo 'bar' > bar.txt + ± git hash-object -w bar.txt + 5716ca5987cbf97d6bb54920bea6adde242d87e6 + ± git update-index --add --cacheinfo 100644 \ + > 5716ca5987cbf97d6bb54920bea6adde242d87e6 bar.txt + ± git write-tree + b98c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + +So far, we have added a new file, `bar.txt` with the contents of `bar`. We have +added the file to a new tree and we have written the tree to the object store. +Before we commit the new tree, let's perform a quick inspection of the tree: + + ± git cat-file -p b98c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + 100644 blob 5716ca5987cbf97d6bb54920bea6adde242d87e6 bar.txt + 100644 blob 257cc5642cb1a054f08cc83f2d943e56fd3ebe99 foo.txt + +An entry for `foo.txt` is present in this new tree. Git is implicitly tracking +previous objects, and carrying them forward, we didn't have to do anything for +Git to do this. Furthermore, the only new objects in the object store so far is +the new object for the contents of `bar.txt` and the object for the new tree: + + ± find .git/objects -type f + .git/objects/b9/8c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + .git/objects/57/16ca5987cbf97d6bb54920bea6adde242d87e6 + .git/objects/d7/ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + .git/objects/fc/f0be4d7e45f0ef9592682ad68e42270b0366b4 + .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +Now, we can commit this new tree using the [`git-commit-tree(1)`][8] command: + + ± echo 'our second commit' | git commit-tree \ + > -p d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 \ + > b98c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + b7fd7d75c1375858d8f355735a56228b3eb5e813 + +Let's inspect this newly minted commit: + + ± git cat-file -p b7fd7d75c1375858d8f355735a56228b3eb5e813 + tree b98c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + parent d7ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + author kballou 1453229013 -0700 + committer kballou 1453229013 -0700 + + our second commit + +This commit should look very similar to the previous commit we created. +However, here we have a line dedicated to the "parent" commit, which should +line up with the commit passed to the `-p` flag of [`git-commit-tree(1)`][8]. + +We can update the `master` reference, too, with the new hash: + + ± git update-ref refs/heads/master b7fd7d75c1375858d8f355735a56228b3eb5e813 + +Let's modify `foo.txt` and create another commit: + + ± echo 'foo 2' > foo.txt + ± git hash-object -w foo.txt + a3f555b643cbba18c0e69c82d8820c7487cebe15 + ± git update-index -add --cacheinfo 100644 \ + a3f555b643cbba18c0e69c82d8820c7487cebe15 foo.txt + ± git write-tree + 68b757546e08c1d9033c8802e4de1c0d591d90c8 + ± echo 'our third commit' | git commit-tree \ + > -p b7fd7d75c1375858d8f355735a56228b3eb5e813 \ + > 68b757546e08c1d9033c8802e4de1c0d591d90c8 + 354c7435a9959e662cea02495957daa93d875899 + ± echo 354c7435a9959e662cea02495957daa93d875899 > .git/refs/heads/master + +This final example, we have gone from creating a file, adding the file to a +tree, writing the tree, committing the tree, and finally, pushing forward the +`master` reference. + +There are a few more points to make before we go onto a brief tour of the +porcelain commands. + +Let's go ahead and inspect the current state of the object store: + + ± find .git/objects -type f + .git/objects/35/4c7435a9959e662cea02495957daa93d875899 + .git/objects/68/b757546e08c1d9033c8802e4de1c0d591d90c8 + .git/objects/a3/f555b643cbba18c0e69c82d8820c7487cebe15 + .git/objects/b7/fd7d75c1375858d8f355735a56228b3eb5e813 + .git/objects/57/16ca5987cbf97d6bb54920bea6adde242d87e6 + .git/objects/b9/8c9a9f9501ddcfcbe02a9de52964ed7dd76d5a + .git/objects/d7/ee3cdd8bfcc1b8c3f935302f2d2e78e69e4197 + .git/objects/fc/f0be4d7e45f0ef9592682ad68e42270b0366b4 + .git/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 + +There's a few things to notice here, every object we have created so far is +_still_ in the object store, the first version of `foo.txt` is still there +(`257cc5642...`). All the trees are still there, and of course the commits are +still around. This is because Git stores objects. It does not store computed +differences or anything of the sort, it simply stores the objects. Other +version control systems may store the patches, individually version files, +or even track file renames. Git does none of this. Git simply stores only the +objects you ask, it doesn't store the differences between any files, it doesn't +track that a file was renamed. Every commit points to the exact version of +_every_ file at that point in time. If a difference between the working file +and the stored version is asked for, it's computed, if a difference between +yesterday's version of a file and today's, it's computed. If a file was +renamed, it can be inferred by a similarity index and computing the difference +between Git trees. This achieves tremendous performance gains because computing +text differences is relatively cheap compared to attempting to manage code +patches as a means of versioning. + +## Porcelain ## + +Now that we have gone through our tour of the plumbing commands and Git +internals, we can start _actually_ use Git. It will be very rare that the +typical user of Git will ever be using any of the plumbing commands above or +touching files under the `.git` folder in their day-to-day work. For the +day-to-day usage of Git, we will be using the "porcelain" commands, the +commands that take the arduous steps above, and turn them into a pleasant walk +in the park. Essentially, everything we have done above can be accomplished +with two (2) commands in Git: [`git-add(1)`][10] and [`git-commit(1)`][11]. + +Let's initialize a new temporary repository for demonstration: + + $ cd /tmp + $ git init bar + $ cd bar + +After initializing the repository, we can add a file, say, `foo.txt`: + + ± echo 'foo' > foo.txt + +Next, we can use the [`git-add(1)`][10] command to stage the file to be +tracked: + + ± git add foo.txt + +Next, we can use the [`git-commit(1)`][11] command to commit the newly created +`foo.txt` file: + + ± git commit -m 'initial commit' + +Everything we have done so far is now achieved with these two commands. We have +stored the contents of the file, created a tree, and committed the tree. + +There are a few more commands that are very useful to using Git on a regular +basis: [`git-clone(1)`][12], [`git-status(1)`][13], [`git-log(1)`][14], +[`git-pull(1)`][15], [`git-push(1)`][16], and [`git-remote(1)`][17]. + +### [`git-clone(1)`][12] ### + +Before you can contribute to a project, you need your own copy of the +repository, this is where we would use [`git-clone(1)`][12]. As we have seen +before, we can create _new_ repositories with [`git-init(1)`][4], but we still +need a means of getting existing work from another source. + +Here's an example of using `git-clone`: + + $ git clone git://github.com/git/git.git + ... + +There are several protocols that can be used for the when cloning, listed here +in order of preference: + +* `SSH` + + - Bi-directional data transfer + + - Encrypted + + - Typically authenticated, especially without passwords + +* `Git` + + - Pull only + + - Intelligent transfer mechanism + +* `HTTP/S` + + - Bi-directional data transfer + + - Authenticated + + - Unintelligent transfer mechanism + +* `File` + +### [`git-status(1)`][13] ### + +Often, you will need to know the state of the current repository, and the go-to +command to view the current state of the repository is the +[`git-status(1)`][13] command. It will give you information about the currently +modified files, the currently untracked files, the branch you're one, if the +branch is tracked upstream, it will let you know if you have something to push, +etc. + +### [`git-log(1)`][14] ### + +[`git-log(1)`][14] is used to check the history of the repository. Using +[`git-log(1)`][14] with a few arguments, you can get a pretty concise image of +how your projects are changing. + +Some commonly used options you might use might be: + +* `--stat`: Show the files and number of changes for each commit + +* `--oneline`: Show each commit on a single line + +* `--summary`: Show condensed summary of header information + +### [`git-pull(1)`][15] and [`git-fetch(1)`][18] ### + +[`git-pull(1)`][15] is used to pull remote changes into your current working +copy. I prefer not use [`git-pull(1)`][15] because I find it to be slightly +[harmful][19]. Instead, I use either [`git-fetch(1)`][18] or a form of +[`git-remote(1)`][17]. + +[`git-fetch(1)`][18] is a similar command used for "fetching" remote changes, +but does not attempt to automatically merge them into the local branch. + +### [`git-push(1)`][16] ### + +[`git-push(1)`][16] will send your changes to the remote location. By default, +this command will not attempt to overwrite the remote if the changes cannot be +applied with a "fast-forward" merge operation. + +### [`git-remote(1)`][17] ### + +[`git-remote(1)`][17] is an overall "remote" management command. It allows you +to add remotes, rename remotes, and even fetch information about remotes. +"Remotes" are non-local/upstream sources of changes. The remote "origin" is the +default name for the remote of a clone. This could be a co-worker's repository +or it could be the central repository of the project. + +With the [`git-remote(1)`][17] command, we can add a new remote: + + ± git remote add upstream proto://remote + +We can rename a remote: + + ± git remote rename origin upstream + +And my favorite, we can fetch changes from the remote: + + ± git remote update -p origin + +I use this last command so much, in fact, I have created an alias in my +`~/.gitconfig` file: + + [alias] + up = !git remote update -p + +This way, I can decide when and _how_ I want to merge the upstream work into my +local copy. + +The above commands along with `git-add` and `git-commit` will cover the +majority of Git related tasks, as far as simple, non-branching workflows are +concerned. + +For more advanced usage of Git, we can continue to learn about code branching, +git branches, and merging techniques. + +## Branches ## + +Git branches are actually a very simplistic concept in both implementation and +intuition. Code and applications versioned by any version control tool have +their implicit branching points: when one user commits code that another user +isn't yet made aware, the code has diverged from a single path of existence to +multiple paths. This is a form of implicit branching and explicit branching +isn't much different. + +![Code Branching][code-branching] + +The structure of Git makes branching trivial, in fact, all that's required is +to create a file that marks the branch point of the code. That is, to create a +file under `.git/refs/heads` that contains the branch's base commit hash. From +there, the code can safely move forward without changing anything of the other +branches. + +![Git Branching][git-branching-1] + +Branching in Git is accomplished with [`git-branch(1)`][20] and +[`git-checkout(1)`][21]. + +The basic form of [`git-branch(1)`][20] is the following: + + ± git branch {branch_name} [optional branch point] + +If the branch point is not specified, [`git-branch(1)`][20] defaults to the +`HEAD` reference. + +Once the branch is created, you can switch to it using the +[`git-checkout(1)`][21] command: + + ± git checkout {branch_name} + +Moreover, if you're going to be creating a branch and immediately switching to +it, you can use the `-b` flag of [`git-checkout(1)`][21] to do these two steps +in one: + + ± git checkout -b {branch_name} [optional branch point] + +## Merging ## + +Once you're ready to merge your changes from one branch into another branch, +you can use the [`git-merge(1)`][22] command to accomplish that. + +There are a few different ways Git can merge your work between two branches. +The first Git will try is called "fast-forward" merging, where Git will attempt +to play the source branch's commits against the target branch, from the common +history point forward. + +![Git Fast Forward Merge Initial][git-ff-merge-1] + +![Git Fast Forward Merge Replay][git-ff-merge-2] + +However, this can only be accomplished if the target branch doesn't have any +changes of its own. + +If the target branch _does_ have changes that are not in the source branch, +Git will attempt to merge the trees and will create a merge commit (assuming +all went well). If a merge conflict arises, the user will need to correct it, +and attempt to re-apply the merge, the resolution of the merge will be in the +merge commit. For more information on merging, see the [`git-merge(1)`][22] +documentation. + +![Git Resolve Merge][git-resolve-merge] + +## Summary ## + +Git is not the most complicated version control system out there, and I hope +peering into the internals of Git demonstrates that fact. If anything, it may +seem that Git is very simplistic and unintelligent. But this is actually what +gives Git its power. It's simplistic (recursive) object storage is what gives +Git super powers. Git can infer file renames, branching is trivial, merging is +similarly easier, the storage and tree model are well understood concepts and +the tree and graph algorithms are well studied. + +However, this simplistic approach to storage also has a few problems. Tracking +binary files tends to be expensive because Git isn't storing the difference, +but each version of the file in its entirety. The zlib compression library also +isn't always amazing at compressing binary files either. + +Beyond these problems, Git is a very powerful and capable source control tool. + +### References ### + +[1]: http://git-scm.com/ + +* [Git SCM Site][1] + +[2]: http://git-scm.com/book/en/v2 + +* [Apress: Pro Git][2] + +[3]: https://en.wikipedia.org/wiki/Zlib + +* [zlib compression][3] + +[4]: https://www.kernel.org/pub/software/scm/git/docs/git-init.html + +[5]: https://www.kernel.org/pub/software/scm/git/docs/git-hash-object.html + +[6]: https://www.kernel.org/pub/software/scm/git/docs/git-update-index.html + +[7]: https://www.kernel.org/pub/software/scm/git/docs/git-write-tree.html + +[8]: https://www.kernel.org/pub/software/scm/git/docs/git-commit-tree.html + +[9]: https://www.kernel.org/pub/software/scm/git/docs/git-update-ref.html + +[10]: https://www.kernel.org/pub/software/scm/git/docs/git-add.html + +[11]: https://www.kernel.org/pub/software/scm/git/docs/git-commit.html + +[12]: https://www.kernel.org/pub/software/scm/git/docs/git-clone.html + +[13]: https://www.kernel.org/pub/software/scm/git/docs/git-status.html + +[14]: https://www.kernel.org/pub/software/scm/git/docs/git-log.html + +[15]: https://www.kernel.org/pub/software/scm/git/docs/git-pull.html + +[16]: https://www.kernel.org/pub/software/scm/git/docs/git-push.html + +[17]: https://www.kernel.org/pub/software/scm/git/docs/git-remote.html + +[18]: https://www.kernel.org/pub/software/scm/git/docs/git-fetch.html + +[19]: http://stackoverflow.com/questions/15316601/in-what-cases-could-git-pull-be-harmful#15316602 + +* [SO: Cases `git-pull` could be considered harmful][19] + +[20]: https://www.kernel.org/pub/software/scm/git/docs/git-branch.html + +[21]: https://www.kernel.org/pub/software/scm/git/docs/git-checkout.html + +[22]: https://www.kernel.org/pub/software/scm/git/docs/git-merge.html + +[23]: https://kennyballou.com/git-in-reverse.pdf + +[code-branching]: https://kennyballou.com/media/code-branching.png + +[git-branching-1]: https://kennyballou.com/media/git-branching-1.png + +[git-commit-1]: https://kennyballou.com/media/git-commit-1.png + +[git-ff-merge-1]: https://kennyballou.com/media/git-ff-merge-1.png + +[git-ff-merge-2]: https://kennyballou.com/media/git-ff-merge-2.png + +[git-resolve-merge]: https://kennyballou.com/media/git-resolve-merge.png + +[git-tree-1]: https://kennyballou.com/media/git-tree-1.png + +[git-tree-2]: https://kennyballou.com/media/git-tree-2.png -- cgit v1.2.1