Git Basics: Ignoring Generated Files

A build directory or local log usually does not belong in a commit. A project’s .gitignore records patterns for files Git should leave untracked.

Run these commands in Bash with Git 2.28 or newer installed. Start a fresh temporary repository for this article:

git_practice=$(mktemp -d) || exit
cd "$git_practice" || exit
git init -q -b main
git config user.name 'Practice User'
git config user.email 'practice@example.invalid'
git config commit.gpgsign false

The identity and signing settings apply only to this repository. Use your own identity in real projects. The temporary files remain afterward. Examples assume default Git settings; if a pager opens, press q to leave it.

Add two rules

printf '/build/\n*.log\n' > .gitignore
mkdir build
printf 'generated output\n' > build/result.txt
printf 'started\n' > app.log
printf 'Practice project\n' > README.md
git status --short

?? .gitignore
?? README.md

/build/ matches the directory at this repository’s root. *.log matches names ending in .log at any level below this .gitignore. Neither rule deletes a file.

Check what was ignored

git status --short --ignored

?? .gitignore
?? README.md
!! app.log
!! build/

!! marks ignored paths. To find the exact rule responsible for one file:

git check-ignore -v app.log

.gitignore:2:*.log	app.log

The fields identify the ignore file, line number, pattern, and path. Git separates the pattern from the path with a tab. This is useful when a file seems to be missing from status output.

Save the shared rules

git add .gitignore README.md
git commit -q -m 'Ignore generated files'
git ls-files

.gitignore
README.md

The committed rules will travel with the project. For a rule that should stay local to this repository, use .git/info/exclude instead.

Ignore rules do not stop tracking a file that is already committed. They also do not erase old commits or protect secrets. If a credential was committed, revoke or rotate it rather than relying on a new ignore rule.

References

Git ignore manual and Git check-ignore manual

Acknowledgements

This post was created with assistance from AI.