What is `.gitignore` and what is it for?

.gitignore is a file where you list the patterns of files and folders you want Git to ignore, meaning it won't track them or include them in commits. It's used to leave out things that shouldn't be versioned: dependencies (node_modules/), local configuration files, secrets (.env), builds, and operating system files.

Not everything in your folder should go into the repository. For example, node_modules/ is huge and can be regenerated; a .env file can contain passwords. .gitignore tells Git: "don't even look at these files."

Pattern rules:

• One line per pattern.
• carpeta/ ignores an entire folder.
• *.log ignores all files with that extension.
• # marks a comment.
• !archivo makes an exception (don't ignore something that an earlier pattern was ignoring).

Important: .gitignore only affects untracked files. If a file is already being tracked by Git, adding it to .gitignore won't stop it from being tracked; you first have to untrack it.

# Example of the content of a .gitignore file:

# Dependencies
node_modules/

# Environment variables with secrets
.env

# Logs
*.log

# System files
.DS_Store

# Ignore the build folder, but NOT a specific file inside it
build/
!build/importante.txt

# If a file was ALREADY tracked, .gitignore isn't enough:
# you have to stop tracking it (without deleting it from disk)
git rm --cached .env
git commit -m "Deja de rastrear .env"
# From here on, .gitignore does ignore it

Adding a file to .gitignore expecting it to disappear from the repo, when that file was already committed. .gitignore only ignores files that Git isn't tracking yet. To stop tracking one that's already tracked, you have to use git rm --cached. Another classic mistake: pushing node_modules/ or .env because you didn't have a .gitignore from the start.

".gitignore is a file where I put patterns of files and folders I want Git to ignore, so I don't version things like node_modules, .env files with secrets, builds, or system files. I use patterns like carpeta/ or *.log. Something key: .gitignore only applies to files that Git isn't tracking yet; if something was already committed, I first have to untrack it with git rm --cached."