Version Control With Git

Git is a version control system (like SVN and CSV). Among Git's many powerful features, these were most attractive to me:

• Git makes it easy to create branches. The idea is that you have a master branch that's always in a “releasable” state, while you add new features on a separate branch. Once your new feature is finished, you merge the “new feature branch” into the master branch.
• It's very easy to specify which files and directories git should ignore.
• Git has a “bisect” feature which assists you in finding the specific revision where you unknowingly introduced a bug.

Please check this excellent tutorial for a high level introduction to the concepts behind Git: Understanding Git Conceptually.

Please Note: if you're using github.com as the remote repository server, just create a new repository on their website and follow their instructions.

The following procedure is taken from ”Setting up a new remote git repository”.

Set up the new bare repo on the remote server:

$ ssh myserver.com
Welcome to myserver.com!
$ mkdir /var/git/myapp.git && cd /var/git/myapp.git
$ git --bare init
Initialized empty Git repository in /var/git/myapp.git
$ exit

Please note: this assumes that you have a git user on your remote system who is authorized to log in through ssh. Also: use chmod and chown for the new directory!

On your local system, add the remote repository and push (omit git init if you already have a local git repository):

$ cd ~/Sites/myapp
$ git init
$ git remote add origin ssh://git@myserver.com/var/git/myapp.git
$ git push origin master

The original tutorial goes on to explain that you can specify the default remote repository by updating the git config file. However, when I checked my config file, it already contained the necessary settings for pushing and pulling to the default remote repository:

[branch "master"]
  remote = origin
  merge = refs/heads/master

Now you can simply git push and git pull.

To start using the GIT client for Windows you can use the following tutorial: http://nathanj.github.com/gitguide/tour.

When you get to the step Pushing to a Remote Server follow the following instructions:

• Generate a private and public key
• Specify your passphrase
• Export the key using Conversions → Export OpenSSH key
• Save the file with the name id_rsa at the source location of your ssh. This is usually C:\Users\[username]\.ssh
• Save the private key
• Copy the public key to the clipboard. Do not save the public key as it saves in a different format than recognized at github.com
• Add the public key to your account at github.com

Now follow the rest of the instructions as specified in the tutorial.

You can use the command git submodule to populate a directory of your own project with a foreign repository.

Use cases:

• Adding a 3rd party Rails plugin to vendor/plugins.
• Importing the Moodle Soda module into your mod directory.

Here's a tutorial: Using git submodules to track plugins, which explains everything in great detail. This tutorial is more concise: Git Submodules: Adding, Using, Removing, Updating.

The short version:

git submodule add git@github.com:solin-repo/soda public_html/local/soda

By default, git will checkout the master branch. If you need a different branch, just move into the submodule's directory and perform a 'normal' checkout:

git checkout moodle19

Go ahead, make the changes. Move into the submodule's directory and perform the exact same git commands that you would normally use to commit and push.

To update your local repository with a remote submodule, do the following in the root of your git repository:

onno@mac-mini:~/php/kompas$ git submodule init
onno@mac-mini:~/php/kompas$ git submodule update

The result:

Initialized empty Git repository in /home/onno/php/kompas/public_html/mod/soda/.git/
remote: Counting objects: 337, done.
remote: Compressing objects: 100% (133/133), done.
remote: Total 337 (delta 238), reused 295 (delta 196)
Receiving objects: 100% (337/337), 259.68 KiB | 58 KiB/s, done.
Resolving deltas: 100% (238/238), done.
Submodule path 'public_html/mod/soda': checked out 'bf7200df78ff0d9a80494e30170ba04d12233e4d'

From Stack Overflow:

git config core.filemode false

From git-config(1):

       core.fileMode
           If false, the executable bit differences between the index and the
           working copy are ignored; useful on broken filesystems like FAT.
           See git-update-index(1). True by default.

The .gitignore file is committed to the repository - everybody using the repo is affected by it. If you want to ignore things (files, directories) locally, use: .git/info/exclude. The exclude file uses the same directives / instructions as the .gitignore file.

Adding a tag to a commit allows you to easily find the commit, even after a while. The tag will serve as a name that can be used besides the commit id.

To add a tag to a certain commit, you'll have to find the commit id. You can look them up with the following command:

git log

With the commit id you can create a new (local) tag:

git tag tag_name commit_id

To push the tag to the remote server you can use:

git push --tags

Here's how to push a local branch to remote:

git push --set-upstream origin new-branch

Use git grep to search a local repository. Example:

git grep 'function get_users'

To limit the search to a subtree, specify the directory outside the commandline options, using a 'pathspec':

git grep 'function get_users' -- 'mod/usermanager'

The '–' signals the end of the commandline arguments. Please note the space between – and the pathspec.

ATTENTION: if you have a git submodule in your repo, git grep will not search this submodule. You have to descend into the submodule first.

To stop tracking a file that is currently tracked, use:

git rm --cached $THE_FILE_NAME

(and add the file name in .gitignore or .git/info/exclude).

This will not delete the actual file.