Ignoring Files with .gitignore

.gitignore only affects files Git hasn’t started tracking yet. This lesson shows both halves of that rule: files it successfully hides, and one it doesn’t.

1) Ignored files vanish from status — before they’re tracked

$ printf 'node_modules/\n*.log\n.env\n' > .gitignore
$ mkdir node_modules && echo '{}' > node_modules/pkg.json
$ echo "run 1" > app.log
$ printf 'DEBUG=1\nSECRET=xyz\n' > .env
$ git status -s

?? .gitignore

Three new files exist — node_modules/pkg.json, app.log, .env — but only .gitignore itself shows up as untracked. The other three match a pattern and are invisible to status, add -A, and diff alike.

2) A pattern added after tracking starts does nothing

$ echo "CACHE=on" >> config.py
$ echo "config.py" >> .gitignore
$ git status -s

 M config.py
?? .gitignore

config.py was already tracked from an earlier lesson. Adding it to .gitignore now doesn’t retroactively hide it — Git still reports the modification, because ignore rules only decide whether to start tracking a file, not whether to keep watching one it already tracks.

3) Debug which rule matched, with check-ignore

$ git check-ignore -v .env app.log node_modules/pkg.json

.gitignore:3:.env	.env
.gitignore:2:*.log	app.log
.gitignore:1:node_modules/	node_modules/pkg.json

Each line shows <file>:<line-number>:<pattern> followed by the path it matched — exactly which rule is responsible, useful when a file is unexpectedly missing (or unexpectedly present) and the .gitignore has grown past a few lines.

4) Commit the .gitignore itself

$ git checkout -- config.py
$ git add .gitignore
$ git commit -m "Add .gitignore"
$ git log --oneline -1

39e53d1 Add .gitignore

config.py’s stray edit from step 2 is discarded (it was only there to demonstrate the “already tracked” case) — only .gitignore itself, now four lines, is committed. .env, app.log, and node_modules/ stay untracked exactly as designed.

Practice

1. Run git status -s --ignored to list ignored files explicitly, instead of the default behavior of hiding them completely.

   Solution

   !! .env
   !! app.log
   !! node_modules/

   !! marks an ignored path — a different marker from ?? (untracked) or M (modified).

2. Untrack config.py properly with git rm --cached config.py, commit that, then confirm git status goes quiet on further edits to it.

3. Add a negation pattern (!important.log) after a broader *.log rule in .gitignore, create important.log, and confirm git status shows it despite the earlier blanket rule.

4. Create a nested node_modules/ inside a subdirectory and confirm the same top-level node_modules/ pattern still matches it — .gitignore patterns apply recursively from the directory they’re in unless anchored with a leading /.

5. Add a leading slash (/config.py) to anchor a pattern to the repo root, then create a same-named file in a subdirectory and confirm the anchored pattern does not match it there.