// Set global gitignore file
git config --global core.excludesfile <filename>

Key points

• .gitignore lets you configure Git so that it ignores specific files or files that match a certain pattern.
• .html in your .gitignore matches on all files with an .html extension, in any directory or subdirectory of your project.
• /*.html matches all files with an .html extension, but only in subdirectories of your project.
• ! negates a matching rule.
• You can have multiple .gitignore files inside various directories of your project to override higher-level matches in your project.
• You can find where your global .gitignore lives with the command git config --global core.excludesfile.
• Make a custom global .gitignore file and use it in all project by git config —global core.excludesfile <filename>
• GitHub hosts some excellent started .gitignore files at https://github.com/github/gitignore.