How to Use a .gitignore file

Introduction

When you make commits in a git repository,
you choose which files to stage to commit.
But what if there are some files that you never want to commit?

How .gitignore Works

A .gitignore file is a plain text file
where each line contains a pattern/directories to ignore.
You can have mutiple .gitignore files.
The patterns in the files are relative to the location of that .gitignore file.

Patterns

# Literal file names
test.py

#        Directories 
##  You can ignore entire directories,
##  just by including their paths and putting a slash(/) on the end.
logs/
#   If you leave the slash off the end,
#   it will match both files and directories.

#        Wildcard
##  The * matches zero or more characters(except the slash /).
*.log 
##  You can also use the ?,which matches any one character except for the slash.

#        Negation
##  You can use a prefix of `!` to negate a file that would be ignored.
!example.log

#       Double Asterisk 
##  ** can be used to match any number of directories.
**/.idea/

Local Repository .gitignore Rules

If there are some files you want to ignore for just this repository,
you can put them in .git/info/exclude

Global .gitignore Rules

If there are some files you want to ignore in all repositories on your computer,
you can put them in a global .gitignore file ~/.gitignore.

git config --global core.excludesFile ~/.gitignore

Notes

Git will not ignore the file if you have already committed if.
You have to untrack the file first.

git rm --cached FILENAME 
git rm -r --cached DIRECTORIES 

Debugging

If you’re having trouble,
you can use git check-ignore -v filename/directories