Explain .gitignore code

What this .gitignore sample shows

patterns

Each line is a pattern, and # starts a comment. * matches any run of characters except /, so *.log left out both debug.log at the top and logs/today.log one folder down: a pattern with no slash in it matches in every folder. .env.* caught .env.local.

slashes and folders

A slash at the end, as in dist/, matches only folders and everything inside them: a plain file called dist was still listed by git status. A slash at the start ties the pattern to the folder the .gitignore is in, so /build/ left out build/out.js but kept src/build/helper.js.

negation

A line starting with ! brings back a file an earlier line left out, and the last line that matches wins. That kept .env.example, .vscode/extensions.json and uploads/.gitkeep while the rest of .env.*, .vscode/ and uploads/ stayed out.

tracked files

A .gitignore only affects files git isn't tracking yet. With .env already committed, adding it here changed nothing: git status still showed M .env after an edit. git rm --cached .env stopped tracking it and left the file on disk, and from then on git ignored it.

Good to know

• Run with git 2.55.0 on a test project with 15 files besides the .gitignore, git status listed only .gitignore, .env.example, .vscode/extensions.json, src/app.js, src/build/helper.js and uploads/.gitkeep; everything else was left out.
• git check-ignore -v <file> prints the line that decides a file, with its line number. For a file a ! line keeps, it prints that ! line, so check that the pattern it names doesn't start with ! before reading the file as ignored.
• Commit the .gitignore itself, so everyone working on the project gets the same rules. Rules that are only yours go in .git/info/exclude, which works the same way and is never shared: notes-to-self.md listed there was left out of git status in this repo only.

Watch out: ! can't bring back a file whose folder is left out, because git never looks inside that folder. With logs/ and then !logs/keep.txt, git status still didn't list logs/keep.txt. Writing logs/* leaves out the folder's contents instead of the folder, and then !logs/keep.txt worked.