Session 6 · Ways to exclude files#

The big idea#

Some files should never go into a repository: passwords, logs, build output, editor settings, the node_modules folder. A .gitignore file lists patterns for files Git should pretend not to see. Ignored files do not show in git status and git add . skips them.

Everyday example: the “do not photocopy” tray at an office. Confidential papers, rough drafts and the tea-stained scribbles go in it. When someone says “copy everything on my desk”, the clerk skips that tray.

How Git decides what to skip Git checks .gitignore, then .git/info/exclude and the global ignore file. A file already tracked is never ignored. new file untracked matches an ignore rule? .gitignore · exclude yes: skipped by git add no: shows up in status Already committed? Ignore rules do nothing. git rm --cached FILE stops tracking it and keeps the file on disk
Git checks .gitignore, then .git/info/exclude and the global ignore file. A file already tracked is never ignored.

Ignore rules at work#

git config --global user.name "Dev User"
git config --global user.email "dev@example.com"
git config --global init.defaultBranch main
git init -q shop
cd shop
touch app.py secrets.env debug.log error.log notes.txt important.txt
mkdir build && touch build/out.bin

echo '--- before .gitignore: everything is untracked'
git status -s

printf '%s\n' '# secrets' 'secrets.env' '' '# logs' '*.log' '' '# build output' 'build/' '' '# all text files, except one' '*.txt' '!important.txt' > .gitignore
echo '--- after .gitignore'
git status -s

echo '--- why is a file ignored? (-v shows the rule)'
git check-ignore -v debug.log build/out.bin notes.txt
echo '--- is important.txt ignored? (exit code 1 = no)'
git check-ignore important.txt; echo "exit code $?"

echo '--- files you can see in the folder but Git skips'
git status --ignored -s | grep '^!!'

echo '--- an ignore rule only affects UNTRACKED files'
git add -f secrets.env
git commit -q -m "Oops, committed secrets"
echo "password=123" >> secrets.env
git status -s
echo '--- fix: stop tracking it, keep the file on disk'
git rm -q --cached secrets.env
git commit -q -m "Stop tracking secrets.env"
git status -s

echo '--- a private rule for this clone only (never committed)'
echo "scratch/" >> .git/info/exclude
mkdir scratch && touch scratch/ideas.txt
git status -s

--- before .gitignore: everything is untracked
?? app.py
?? build/
?? debug.log
?? error.log
?? important.txt
?? notes.txt
?? secrets.env
--- after .gitignore
?? .gitignore
?? app.py
?? important.txt
--- why is a file ignored? (-v shows the rule)
.gitignore:5:*.log	debug.log
.gitignore:8:build/	build/out.bin
.gitignore:11:*.txt	notes.txt
--- is important.txt ignored? (exit code 1 = no)
exit code 1
--- files you can see in the folder but Git skips
!! build/
!! debug.log
!! error.log
!! notes.txt
!! secrets.env
--- an ignore rule only affects UNTRACKED files
 M secrets.env
?? .gitignore
?? app.py
?? important.txt
--- fix: stop tracking it, keep the file on disk
?? .gitignore
?? app.py
?? important.txt
--- a private rule for this clone only (never committed)
?? .gitignore
?? app.py
?? important.txt

Reading the output:

  • Before .gitignore seven things appear as untracked, including secrets.env and the build/ folder.

  • After, only .gitignore, app.py and important.txt remain. important.txt survived thanks to the negation rule !important.txt, which re-includes a file that *.txt would have ignored.

  • git check-ignore -v tells you which rule in which line ignores a file, the quickest way to debug a pattern. For important.txt it printed nothing and exit code 1, meaning “not ignored”.

  • git status --ignored lists the ignored files (marked !!) in case you want to see them.

  • The secrets.env trap. We force-added it and committed, and then ignore rules stopped working for it: editing it showed M secrets.env. An ignore rule only affects untracked files.

  • git rm --cached removed it from Git’s tracking but kept the file on disk; after that it is ignored again. (If a secret was already pushed, assume it is public: change the password. Removing it from history is a separate, harder job.)

  • .git/info/exclude works like .gitignore but is private to your clone and is never committed. The scratch/ folder is hidden from git status without touching the shared file.

Pattern cheat sheet#

Pattern

Matches

*.log

Any file ending in .log, in any folder

build/

The folder build and everything inside

/todo.txt

Only todo.txt in the top folder

!important.txt

Re-include a file an earlier rule ignored

docs/**/*.pdf

PDFs anywhere under docs

# comment

A comment line

Three places for rules: the project’s .gitignore (shared with the team, committed), .git/info/exclude (just you, this clone) and a global file (git config --global core.excludesFile ~/.gitignore_global) for things like .DS_Store that you never want in any repository.

Other ways to leave files out of one commit#

  • git add -- ':!README.md' skips a file for this add only (Session 5).

  • git restore --staged FILE takes it back out of the staging area.

  • git update-index --skip-worktree FILE asks Git to stop noticing local edits to a tracked file, handy for a personal copy of a config file. Undo with --no-skip-worktree.

Common mistakes#

  • Adding the pattern after the file is committed. It has no effect; use git rm --cached as shown.

  • Ignoring .gitignore itself. You want it committed so teammates get the same rules.

  • Expecting *.txt to be re-included by a later !file inside an ignored folder. If a folder is ignored, Git never looks inside it, so a negation for a file inside will not work.

  • Committing secrets “just once”. Once pushed, treat the secret as leaked.

  • Writing build when you mean build/. Without the slash it also matches a file called build.

Hands-on exercises#

Exercise 1. Ignore all .log files and the dist/ folder. Prove it with git check-ignore -v.

Solution 
printf '*.log\ndist/\n' > .gitignore
touch app.log && mkdir dist && touch dist/bundle.js
git check-ignore -v app.log dist/bundle.js

It prints the rule and line for each: .gitignore:1:*.log app.log and .gitignore:2:dist/ dist/bundle.js.

Exercise 2. Ignore every .txt file except keep.txt.

Solution 
printf '*.txt\n!keep.txt\n' > .gitignore
touch a.txt keep.txt
git status -s

a.txt is hidden; keep.txt (and .gitignore) show as ??.

Exercise 3. You committed .env by mistake. Stop tracking it but keep it on your disk.

Solution 
echo ".env" >> .gitignore
git rm --cached .env
git add .gitignore
git commit -m "Stop tracking .env"

The file remains in the folder, is ignored from now on, and the commit removes it from the project going forward. If it contained a real password, change that password, because it is still in the earlier history.

Practice#

Take the Session 6 quiz. The original Ways to Exclude Files in Git page is in the reference section.