Thursday, May 15, 2014

5 Things You Might Not Know About Git

Git is a version control system that has gained a lot of popularity over the past few years. It started out as a custom-designed VCS (version control system) for the Linux kernel and has since ballooned in popularity, arguably thanks to Github, a free source code hosting site that is powered by Git. Below are five facts about Git that you might not know:

1. Stashing

This command saves all the uncommitted modifications you've made to your working copy, and then reverts your working copy back to its original state. This is useful if you want to switch branches, but your changes are in an incomplete state and you don't want to commit anything yet (git will not allow you to switch branches if you have uncommitted changes).

The command to run a stash operation is git stash. When you're ready to re-apply your stashed changes, run git stash apply.

You can also create multiple stashes. To see a list of all stashes, run git stash list. By default, when you run git stash apply, it will apply the stash at the top of the list. To apply a different stash, run git stash apply stash@{2} where stash@{2} is the name of the stash as shown in the stash list.

Also note that when you apply a stash, it will remain in the stash list. To delete a stash, run git stash drop. Or, you can run git stash pop to apply a stash and then delete it.

Stashes are only stored in your local repository. They cannot be pushed to remote repositories.

For more information, see:

2. Amending commits

With most other version control systems, if you forgot to include a file in a commit, you have to make a second commit. This is annoying because it makes the commit history longer than it should be. With Git, instead of making a second commit, you can "amend" the previous commit. This will merge your commit in with the previous one.

> git commit --amend

For more information, see:

3. Git is a file system

At its core, Git is actually a key/value data store. The commands that you use on a daily basis, like push and commit, are tools that are built on top of the data store. To demonstrate, I'll show you how to add and retrieve files from a Git repository, without using any of the typical Git commands.

First, initialize an empty repository:

> git init
Initialized empty Git repository in /home/michael/git-blog/.git/

Next, add a file to the repository. This command will return a SHA-1 hash, which we will need to retrieve the file again.

> echo 'file data' | git hash-object -w --stdin 

Then, retrieve the file like so:

> git cat-file -p 987721052266a93a2509c3a8ac9e8c86341d0835
file data

For more information, see:

4. Commit message templates

If you work in a corporate environment, your team might have a policy on how commit messages have to be formatted. Git allows you to define a file that contains the default commit message to use for all commits.

> git config --global commit.template path/to/commit-message.txt

For more information, see:

5. Ignoring files during export

Git includes a command that lets you easily generate an archive file (.zip, .tar, etc) of your project. By default, all files in your project are included, but there may be some files which you want to exclude. To do this, use the export-ignore attribute:

> echo "test/ export-ignore" > .gitattributes
> git add .gitattributes
> git commit -m "Added .gitattributes file."
> git archive -o HEAD

For more information, see:

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