TweetFollow Us on Twitter

Sharing with Git

Volume Number: 23
Issue Number: 03
Column Tag: Programming

Sharing with Git

Learn how to use Git to share your Xcode projects

by José R.C. Cruz

Introduction

CVS, Subversion, and Git let several users work the same project. Users can contribute their changes and avoid getting in each other's way. They can retrace their steps if they make a mistake. They can also review each other's changes with little effort.

But CVS and Subversion use a central repository, at risk to data loss without a good backup plan. Git, on the other hand, supports the use of distributed repositories. Each user keeps a separate repository for the same project. They then update each other's repositories at specific times in the project schedule.

This article shows how to use Git to setup a basic distributed repository. It shows how to move data between repositories. It also shows other ways to send data updates when those repositories are not available.

Planning Your Repository

Git lets you setup your project repository in many ways. The simplest way is to use a central repository (Figure 1). User A checks out a copy of the project on which he makes his changes. Then he commits his changes back into the repository, thus allowing user B to update her copy as well.


Figure 1. The centralized setup

But this setup, as stated earlier, has a set of problems. First, losing the repository means losing all project data. Second, users need constant access to the repository in order to commit their changes. Third, the repository can get large and unwieldy as time goes on.

A different way is to use a two-tier setup (Figure 2). Here, a public repository contains all the files needed by the project. Next, users A and B have their own private repositories, which are direct duplicates of the public one. User A makes his changes to the project and updates his repository. User B also does the same to hers. Then, at an agreed time, users A and B update the public repository with data from their private ones. They also work with the project head to resolve any conflicts that occur.


Figure 2. The two-tier setup

Since users A and B have their own repositories, they access the public one only when they need to. They are also free to try out new ideas, knowing that they will send only those changes that worked to the public repository. And if user A loses his repository, he can make a new one using the public repository.

A more radical way is to use a round-robin setup (Figure 3). First, user A creates a private repository for his project. Then he creates a public copy of that same repository. User B, who just joined in, gets a copy of user A's public repository. She then makes another copy to serve as her public repository. During the course of the project, user A sends updates from his private to his public repository. But he receives updates from user B's public one. The same steps also hold for user B.


Figure 3. The round-robin setup

The round-robin setup removes the need for a central repository. It does, however, need more storage resources. It can also be more difficult to maintain when a lot of users are involved.

Enter The Daemon

You normally store the public repository on the network volume. How you access it depends on what server daemon you used. That same daemon also dictates the setting for the global option –git-dir or for the environment variable GIT_DIR.

For example, assume you place the repository for project foobar on the network volume foobar.net. If the server daemon is Apache, add the following URL in your Git commands.

   git –git-dir=http://foobar.com/foobar/ ...

If it is rsync, add the following lines to your .bash_profile file.

   GIT_DIR=rsynch://foobar.com/foobar
   Export $GIT_DIR

Git also supports the use of https and ssh as valid daemons. But the one we will look into is the git daemon.

The git daemon

The git daemon provides basic TCP/IP services for the Git repository (Figure 4). It listens to port 9418 and handles any SCM requests that appear on that port. It is easy to setup and use than most network servers. It does not yet support authentication, but this support may appear in future revisions.

Below is the basic syntax of the git daemon command.

git daemon options –base-path=volume_path white_list

The options argument consists of one or more flags to control the daemon. The –base-path option sets the path to the network volume holding the repositories. The white_list argument is a list of paths to each repository serviced by the daemon.


Figure 4. The git daemon

Launch the daemon

Assume that your project repository foobar is in the network volume /Volumes/Server/Projects. Also, assume that the volume uses the domain name foobar.net. To start the daemon, enter the following statement at the Terminal prompt.

   git daemon –base-path=/Volumes/Server/Projects \
      /Volumes/Projects/foobar &

The '&' token tells the daemon to launch itself in the background. Otherwise, you will be unable to enter more command unless you stop the daemon with a Ctrl-C keystroke. To check if the daemon is running correctly, type the following statement at the prompt.

   git ls-remote git://foobar.net/foobar

Git should then display a list of nodes and SHA1 keys as shown below.

b491b9426501f78575632588d2a86dbbb242df1d        HEAD
b491b9426501f78575632588d2a86dbbb242df1d        refs/heads/master

Now assume you want to include the repository barfoo to the daemon's white list. To do so, first stop the daemon using the kill command to. Then launch the daemon again as follows.

   git daemon –base-path=/Volumes/Server/Projects \
      /Volumes/Projects/foobar /Volumes/Projects/barfoo &

When you enter the directory paths, make sure to type the paths in full. Avoid using shortcut tokens such as '~'. Also avoid adding a trailing '/' to each directory path. Either token will only prevent the daemon from finding the repository.

Starting the daemon from a Terminal session does have one problem. If you end the session, i.e. by closing the window, you stop the daemon as well. A better approach is to start the daemon using either inetd or launchd. For instructions on how to do so, see the references listed at the end of this article.

Configuring the daemon

You can change how the daemon behaves by using one or more options. For instance, the daemon sends its error messages to stderr, which is the Terminal window. To send those messages to the file system.log instead, add the –syslog option.

   git daemon –syslog ...

Also, the daemon listens to port 9418 for incoming requests. To use a different port, e.g. 9500, pass the new number using the –port option.

   git daemon –port=9500 ...

Make sure that the new port number is not used by other network services. To see if the number is available, check the /etc/services file as follows.

   more /etc/services | grep 9500

By default, the daemon uses only those repositories in its white list that have the zero-byte file gitdaemonexportok.

To remove this limitation, add the –export-all option.

   git daemon –export-all ...

The daemon now handles all the repositories in its white list, as long as they have the subdirectories .git/objects and .git/refs. If these two subdirectories are missing, the daemon will return an error message. You can also add the zero-byte file to the repository by entering the following statement.

   touch /Volumes/Projects/foobar/.git/config/git-daemon-export-ok

For a detailed list of other daemon options, read the following online document.

http://www.kernel.org/pub/software/scm/git/docs/git-daemon.html

Facing The Public

Before you let other users to access your repository, first make sure that its data is ready for public use. Check if the project compiles without any problems. See if the project has the minimum set of support documents such as a README and a version history file. Use the git fsck and git gc commands to remove unwanted data from the repository. Also, backup the repository before making it public.

These extra checks will help ensure a reliable and error-free repository.

Making clones

Use the git clone command to make a copy of the project repository. The command stores the copy in the location of your own choosing. It also updates the copy with data that links it back to the original.


Figure 5. The git clone command

The basic syntax of the command is as follows.

git clone options repository_url destination_path

The repository_url argument is the URL to the repository being copied. The destination_path argument is the location of the copy. The options argument consists of one ore more settings to control the copy process.

Assume, for example, you want a copy of the project repository foobar. To make the copy, enter the git clone command as follows.

   git clone git://foobar.net/foobar /Volumes/Projects/private

First, Git sends a copy request to the daemon. The daemon responds by sending back the repository data. Next, Git stores the copy in the directory /Volumes/Projects/private. It then marks the copy as the master, the original as the origin.

Choosing which repository to copy depends on the project's state and setup. In an ongoing project, make a copy of public repository. The copy then serves as your private repository. In a new project, however, make a copy of your private repository. In this case, the copy itself becomes the public one.

Exchanging data

Use the git pull command to move data from the public repository to your private one. This command uses the public data to update your repository (Figure 6). It also updates your working copy, if present. It then reports any conflicts found during the update.


Figure 6. The git pull command

Below is the basic syntax of the git pull command.

   git pull options repository_url references

The options argument consists of one or more settings to control the pull process. The repository_url argument is the location of the public repository. The references argument consists of the nodes or branches where the data is to be pulled. Leave this blank to retrieve only the latest updates.

Assume you want to update your private copy of the foobar repository. To start the update, enter the git pull command as follows.

   git pull git://foobar.net/foobar

The above command gets the latest updates from the public repository. Then it merges them with the HEAD node on the private copy. To get updates from a specific node, e.g. version_1, enter the command as follows.

   git pull git://foobar.net/foobar version_1

To display a diff report after data is retrieved, add a –summary option.

   git pull –summary git://foobar.net/foobar

To keep the data from merging with your private repository, add a –no-commit option.

   git pull –no-commit git://foobar.net/foobar

Use the git push command to move data from your private repository to the public one (Figure 7). If you are using the git daemon, make sure to tell the daemon to allow the push request. To do so, enter the following git config command on the server side.

   git config daemon.receivepack true


Figure 7. The git push command

The git push command has the same syntax as the pull command. But it has a much smaller set of options than the latter. Also, its use consists mostly of moving the latest updates to the public one. For instance, to update the public repository foobar, enter the command as follows.

   git push git://foobar.net/foobar master:master

Make sure to update your private repository first before updating the public one. You will find that it is much easier and safer to resolve any conflicts on the private copy than on the public one.

The Daemon Is Down

There can be times when you will be unable to connect to the public repository. The server daemon may have crashed or terminated. The network may be unreachable. The repository itself may be corrupted. Or the server that hosts the repository may be getting upgrades.

For these cases, Git gives you two ways to still share your project changes with other users. You can use Git to make patches from your private repository. You can also use it to archive specific revisions in your repository. Then, you can send these patches or archives to those users via other means such as e-mail or portable media.

Making patches

Use the git diff command to make a patch for specific revisions of your project files (Figure 8). You can make a patch for the working copy of a project file against the one in the repository. You can make another patch for two revisions of the project in the repository.


Figure 8. The git diff command

For example, to make a patch for the project file foobar.html, enter the command as follows.

   git diff foobar.html > foobar.diff

Git first compares foobar.html with its latest revision in the repository. Then it stores any changes it finds in the patch file foobar.diff. To make a patch against the second latest revision of foobar.html, enter the command as follows.

   git diff HEAD^ foobar.html > foobar.diff

To make a patch for the latest and second latest revision of project foobar, enter the command as follows.

   git diff HEAD HEAD^ > foobar.diff

To make a patch for a binary file such as foobar.jpg, add a –binary option to the command.

   git diff –binary foobar.jpg > foobar.diff

To make a patch for more than one file, enter their names as a space-delimited list.

   git diff –binary foobar.html foobar.jpg > foobar.diff

Notice that the above example uses the –binary option since at least one of the files is a binary file. You can exclude this option if all the files are text files. Also, patch files use either a .diff or .patch suffix. But you can use your own suffix as long as you inform this to your fellow users.

Use the git apply command to update your repository with a patch. But check first to see if the patch is for a group of text files or for a group of text and binary files. If the patch is for text files only, enter the command as follows.

   git apply foobar.diff

If it is for binary files only or for text and binary files, add a –binary option to the command.

   git apply –binary foobar.diff

Either way, Git will use the patch to update the right file. It will, however, leave the updated files uncommitted. You must verify and commit the updated files manually. Doing so will protect your repository from unwanted changes.

Making archives

Use the git archive command to archive revisions of a project in the repository (Figure 9). This command can make two types of archives: tarballs and zip files. Choose the one most suited to your needs.


Figure 9. The git archive command

The basic syntax of the git archive command is as follows.

git archive options –format=type revision > archive_path

The options argument consist of one or more flags to control the archival process. The –format option selects the archive format. The revision argument is the project revision to be archived. And the archive_path argument is the name and path of the archive.

Assume you want to archive the latest revision of the project repository foobar. To make a tarball archive, enter the command as follows.

   git archive –format=tar HEAD > foobar.tar

To make a zip archive, change the –format option as follows.

   git archive –format=zip HEAD > foobar.zip

Notice that both examples has the archive's suffix set explicitly. Make sure to do so as the command itself will not set the right suffix for you.

To display a list of files added to the archive, add a –verbose option.

   git archive –format=tar HEAD –verbose > foobar.tar

To add a prefix, e.g. foo_, to each archived file, use the –prefix option.

   git archive –format=tar –prefix=foo_ HEAD > foobar.tar

Finally, if you get an archive from another user, use either the tar or unzip tool to open the archive. But make sure to do so in a directory separate from your working copy. That way you will avoid overwriting your project files by accident.

Concluding Remarks

Git makes it easy for several users to share their project data with each other. It supports most server protocols, as well as provides its own server daemon. It can move data from one repository to another, or copy a specific repository. It can make patches or archives for specific project revisions.

These sharing features makes Git well suited for handling distributed setups. But Git can also handle a centralized setup, which may suit certain projects. This flexibility is one of the reasons why Git is getting a lot of notice from the developer world.

Bibliography and References

Marczak, Edward. "launchd: Judge, Jury, Executioner". MacTech Magazine, XXI:6. Xplain Corporation. Online:

http://www.mactech.com/articles/mactech/Vol.21/21.06/launchd/index.html.

Fields, J. Bruce. "Sharing development with others". Git Users Manual. 2007 Aug 11. From the Linux Kernel Archives. Online:

http://www.kernel.org/pub/software/scm/git/docs/user-manual.html#sharing-development

Hamano, Junio C. "Repository Administration". Everyday Git with 20 Commands or So. 2007 Nov 03. From the Linux Kernel Archives. Online:

http://www.kernel.org/pub/software/scm/git/docs/everyday.html


JC is a freelance engineering writer who lives happily in North Vancouver, British Columbia. He is a regular contributor to MacTech and REALbasic Developer. He also spends quality time with his nephew. He can be reached at anarakisware@gmail.com.

 
AAPL
$99.18
Apple Inc.
-1.57
MSFT
$45.90
Microsoft Corpora
-0.46
GOOG
$568.27
Google Inc.
-9.09

MacTech Search:
Community Search:

Software Updates via MacUpdate

Cocktail Family License (5 Macs) 7.6.1 -...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cocktail 8.0 Beta 2 - General maintenanc...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
QuickBooks 2015 16.0.0.1352 R1 - Financi...
QuickBooks 2015 helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save.... Read more
Mac DVDRipper Pro 5.0.1 - Copy, backup,...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
Apple OS X bash Update 1.0 - Fix for sec...
The OS X bash Update fixes a security flaw in the bash UNIX shell on OS X 10.9.5 (also on OS X 10.8 and 10.7 [see Related Links below]). OS X 10.9.5 or later Downloads for OS X 10.8 and OS X 10.7 in... Read more
SyncTwoFolders 2.0.5 - Syncs two user-sp...
SyncTwoFolders simply synchronizes two folders. It supports synchronization across mounted network drives and it is a possibility to run a simulation showing in a log what will be done. Please visit... Read more
FinderPop 2.5.7 - Classic Mac utility, n...
FinderPop is a Universal preference pane that extends OS X's contextual menus using a FinderPop Items folder much as the Apple Menu Items folder used to do for the Apple menu. It has other features... Read more
VueScan 9.4.45 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
LibreOffice 4.3.2.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
calibre 2.4 - Complete e-library managem...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more

Latest Forum Discussions

See All

iKeywi - Customizable 5-Row Keyboard (U...
iKeywi - Customizable 5-Row Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $.99, Version: 1.0 (iTunes) Description: Want to add an extra row to your iPhone/iPad? One of the most popular keyboard extension in iOS... | Read more »
Manage Your Cloud – Wunderlist Now Suppo...
Manage Your Cloud – Wunderlist Now Supports Dropbox Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Nexticy Review
Nexticy Review By Jennifer Allen on October 1st, 2014 Our Rating: :: IDEAL FORM CREATIONiPad Only App - Designed for the iPad Nexticy allows you to make your own forms for research purposes or to organize your business better. It’s... | Read more »
Tiny Troopers: Alliance Marches onto the...
Tiny Troopers: Alliance Marches onto the App Store Tomorrow Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Tiny Troopers: Alliance, by Kukouri, is a | Read more »
HeroCraft Introduces Unlimited Sequel to...
HeroCraft Introduces Unlimited Sequel to WW2: Sandbox. Strategy & Tactics Posted by Jessica Fisher on October 1st, 2014 [ permalink ] | Read more »
RGB Express Review
RGB Express Review By Jennifer Allen on October 1st, 2014 Our Rating: :: DELIGHTFUL PUZZLINGUniversal App - Designed for iPhone and iPad Guide trucks along their delivery routes in RGB Express, a testing but charming puzzle game... | Read more »
The Sagas of Fire*Wolf (Games)
The Sagas of Fire*Wolf 1.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0 (iTunes) Description: | Read more »
BuggyFun Review
BuggyFun Review By Amy Solomon on October 1st, 2014 Our Rating: iPad Only App - Designed for the iPad BuggyFun allows children to create their own tracks for bugs to interact with for a unique open-ended experience.   | Read more »
Fold the Adventure Review
Fold the Adventure Review By Jennifer Allen on October 1st, 2014 Our Rating: :: AWKWARD FOLDSUniversal App - Designed for iPhone and iPad Fold pieces of paper to create platforms for a princely rabbit in this puzzle game; something... | Read more »
WW2: Sandbox. Strategy & Tactics (G...
WW2: Sandbox. Strategy & Tactics 1.0.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.0 (iTunes) Description: ***NOTE: Compatible with iPhone 4s and up, iPad 2 and up - may not work properly on earlier devices... | Read more »

Price Scanner via MacPrices.net

Amazon offers 13-inch MacBook Air for $899, $...
Amazon.com has the 13″ 1.4GHz 128GB MacBook Air on sale for $100 off MSRP including free shipping: - 13″ 1.4GHz 128GB MacBook Air: $899.99 Read more
Apple resting On Its iPhone Laurels? – The ‘B...
Apple calls its new iPhone 6 and 6 Plus “The Biggest Advancements in iPhone History,” but does reality live up to the hype? “Seldom have so many waited so breathlessly for so little,” tweeted veteran... Read more
Roundup of Apple Mac and iPad Education disco...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Apple Boycotts German Magazine Computer Bild...
Apple has revoked its PR accreditation of Germany’s Computer Bild, Europe’s best-selling PC magazine, in reaction to Bild’s posting of a “#Bentgate” YouTube video. Axel Telzerow, editor in chief of... Read more
iPhone 6 & iPhone 6 Plus Available in Chi...
Apple has announced that iPhone 6 and iPhone 6 Plus will be available in China beginning Friday, October 17 from the Apple Online Store (http://www.apple.com), Apple’s retail stores, and an expansive... Read more
MacBook Airs on sale for $100 off MSRP, start...
Best Buy has the new 2014 MacBook Airs on sale for $100 off MSRP on their online store. Choose free home shipping or free local store pickup (if available). Prices valid for online orders only, in-... Read more
Apple Releases OS X Mavericks bash Update 1.0...
Apple has released a patch update for OS X Mavericks users to address the recently-detected “Shellshock” security bug in BSD UNIX’s bash shell. Apple says only a few Mac users who had manually... Read more
Pivotal Payments Ready for Apple Pay – FlexPo...
Pivotal Payments, a provider of merchant services and global payment processing solutions, has announced its proprietary FlexPoint platform will support credit and debit transactions through Apple’s... Read more
iStabilizer Announces Tabarm — First Friction...
iStabilizer, a specialist in universal lightweight compact tripods, steady cams, dollies, mounts, and remotes for smartphones, tablets, and cameras, announced today the iStabilizer tabArm, the first... Read more
IStabilizer Flex Smartphone Tripod Wins Usa T...
iStabilizer, a specialist in universal lightweight compact tripods, steady cams, and other products for smartphones, tablets, and cameras, has announced today that its iStabilizer Flex smartphone... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.