Ignoring Things

Last updated on 2025-11-11 | Edit this page

Overview

Questions

  • What is a .gitignore file?
  • Why should we use it?
  • How do we create and manage it?

Objectives

  • Explain the purpose of a .gitignore file in Git repositories
  • Create and edit a .gitignore file to exclude unnecessary files
  • Understand common patterns and pitfalls when using .gitignore

What is .gitignore?

When using Git, you often have files that you don’t want to track. These could be:

  • Temporary files created by your text editor or IDE
  • Output files from running your code
  • Large data files or binary files
  • Configuration files specific to your machine

Git provides a file named .gitignore where you can list patterns that match files or directories Git should ignore.

Why Use .gitignore?

If you don’t ignore unnecessary files:

  • Your repository becomes cluttered
  • You may accidentally share sensitive or large files
  • Your collaborators may run into issues syncing or running code

Common Examples

Here are some typical entries in an R project’s .gitignore file:

.Rhistory
.RData
.Rproj.user/
*.csv
*.xlsx
data/
  • .Rhistory, .RData: Temporary R session files
  • *.csv, *.xlsx: Data files you don’t want versioned
  • data/: An entire directory
A sample .gitignore file
A sample .gitignore file

How to Create and Use .gitignore

You can create the file manually:

BASH 

touch .gitignore

And then edit it:

BASH 

nano .gitignore

Or use RStudio’s Git pane: It often shows ignored files in grey.

Does It Remove Already-Tracked Files?

No. .gitignore only affects new files. If you’ve already added a file to Git, .gitignore won’t stop it from being tracked. To remove a file already tracked:

BASH 

git rm --cached filename

Then add it to .gitignore.

Challenge: Ignore and Track

Challenge

Challenge

  1. Create a file called secret.txt and add some text to it.
  2. Add it to your .gitignore.
  3. Try running git status — is it listed?
  4. Add and commit your .gitignore file.

BASH 

echo "my password" > secret.txt
echo "secret.txt" >> .gitignore
git status   # secret.txt should not appear under "Untracked files"
git add .gitignore
git commit -m "Add gitignore to exclude secret.txt"

Advanced Tip: Ignore Locally Only

If you want to ignore files only on your machine (not share with others), you can use:

BASH 

.git/info/exclude

This works like .gitignore, but it’s not committed to the repository.

Key Points
  • Use .gitignore to prevent tracking of unnecessary or sensitive files
  • Edit .gitignore early in your project to keep your history clean
  • Use .git/info/exclude for machine-specific ignores
  • Files already tracked by Git won’t be ignored retroactively