How to use .gitignore Files

As a programming instructor, the number one mistake I see my students and graduates make when starting their side projects is that they forget to add a .gitignore file. In this article we’ll discuss what a .gitignore file is, how you set up a .gitignore file, and why that’s important.

What is a .gitignore File?

Put simply, a .gitignore file is a text file that tells git to not track specific files, directories, or types of files.

For example, the following .gitignore file tells git to ignore .suo files, .dlls , and everything in the node_modules directory:

*.suo
*.dll
node_modules

Full .gitignore files are much larger than this, but this gives you a good idea of what’s in a typical .gitignore file.

If you have a .gitignore file in your repository, git will ignore all matching files and folders when you attempt to add them.

Not every file in your programming projects is critically important and needs to be tracked by git. Many files are the specific results of compiling your code on one specific machine or operating system and should not be tracked by version control. For example, two people on two different operating systems may generate two different executable files from the same code. While the executable may work on one machine, it may cause serious problems for the other.

Additionally, many temporary files take up a significant amount of disk space and would make your git repository needlessly large.

Because of these reasons, we use a .gitignore file to filter out unnecessary files as we check in our code. We then rely on the person who pulls our code to rebuild the code on their machine. Once they are done with their work, they commit their code changes and you’ll have those changes as well once you pull.

Because we do check in the .gitignore file, all users will share the same rules for what files get checked in and what files get ignored.

How do you Create a .gitignore File?

Now that we’ve discussed what a .gitignore file is and why you would want one, let’s talk about how you get one.

Typically you get a .gitignore file in one of two ways:

• You create the .gitignore file yourself and manually add in rules to the file
• You start with a pre-created .gitignore file that matches the languages and technologies that you work with.

Creating a .gitignore file is as easy as right clicking in File Explorer and choosing to create a new file, then naming it .gitignore. You can also run the touch bash command to create the empty file with touch .gitignore.

Important Note: .gitignore files can go in any directory of your application and affect all nested directories. However, I recommend putting your .gitignore file in your repository root directory for the most consistent results.

However, I almost never manually create a .gitignore file. Instead, I start from a pre-existing template.

Using an existing .gitignore Template

Most of the time I start my projects by using a pre-existing .gitignore template.

One of the options that GitHub and other git providers give you when you create a new repository is to select a .gitignore template from a list of supported ones as pictured below:

This will select a pre-built .gitignore file for you to work with in your program. See GitHub’s documentation for more details about this feature and the languages supported in it.

Important Note: The correct .gitignore template may not match the name of your language. For example, when writing C# code you might think your template name would be csharp or even dotnet when all dotnet languages share a single VisualStudio template instead. Similarly, JavaScript is categorized under Node instead of JavaScript.

This feature significantly helps when creating new repositories, but what if you’ve already created your repository?

Thankfully, GitHub publishes a GitIgnore repository that contains a variety of .gitignore files for various languages. This is my default resource when I need to find a new .gitignore file and don’t have a template to borrow from an existing project.

Adding to your .gitignore File

Once you have a .gitignore file you like, you may find instances where you want to customize the .gitignore file for your specific project.

If you find particular files or folders that you want to add to .gitignore files, just add the files by their name or path to the bottom of the .gitignore file.

For example, to ignore a workspace.json file in the .obsidian directory and the contents of the _gen subdirectory in the resources directory, you’d add the following entries:

.obsidian/workspace.json
/resources/_gen/

See the git documentation for more information on the patterns and formatting supported in .gitignore files.

Additionally, many graphical git tools like GitKraken will allow you to right click on files and add them to your .gitignore file during commit.

Closing Thoughts

All told, .gitignore files are a flexible and easy way to control what goes into your git repositories.

As a senior member of the technical community, I know a number of hiring managers who look for .gitignore files in the side projects new developers have made. While the absence of a .gitignore file is not a deal-breaker for them, the presence of one often shows the manager the potential hire is ready to write code professionally.

The moral of the story: if you’re working with git, have a .gitignore file and your code will be more portable, contain less “junk” files, take up less space, and will feel more like professional code.