TopolearnA clean repo has only source files; ignoring generated files avoids noise, conflicts and leaked secrets.
A `.gitignore` file lists patterns for files Git should treat as invisible: they won't show as untracked and git add . will skip them. Commit the .gitignore itself so the whole team shares it.
Pattern rules:
*.logmatches any.logfile in any directory.build/(trailing slash) matches only directories namedbuild./config.local(leading slash) matches only at the level of this.gitignore.**/tmpmatchestmpat any depth;docs/**/*.pdfany PDF underdocs.!keep.logre-includes something an earlier pattern excluded. You cannot re-include a file if its parent directory is ignored.- Lines starting with
#are comments.
.gitignore files can live in subdirectories and apply from there downward. For personal patterns that don't belong in the project (your editor's swap files, .DS_Store), use a global ignore file set by core.excludesFile, or .git/info/exclude for one repository.
The big gotcha: ignore rules only affect untracked files. If a file is already committed, adding it to .gitignore does nothing. Stop tracking it with git rm --cached <file> (which keeps it on disk) and commit that.
When a file is mysteriously ignored, git check-ignore -v <path> prints the exact file and line responsible. Templates for most languages live at github.com/github/gitignore.
Example
cat > .gitignore <<'END'
# dependencies and build output
node_modules/
dist/
*.log
# local secrets, but keep the example
.env*
!.env.example
END
git check-ignore -v dist/app.js
# .gitignore:3:dist/ dist/app.js
# Already committed .env by mistake? Stop tracking, keep the file
git rm --cached .env
git commit -m "Stop tracking .env"Remember
- Commit .gitignore so everyone ignores the same files
- Ignore rules don't apply to files already tracked: use git rm --cached
- git check-ignore -v explains why a path is ignored
Watch out for
- Adding a committed secret to .gitignore and assuming it's gone — it's still in history and must be rotated.