Unless a repo consisted of several independent projects, it seems it would be simplest to just have one .gitignore file at the root of the repo than various ones throughout. Is there a standard best practice on this or some analysis online of when one approach is better than the other?
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git
Pro single
Easy to find.
Hunting down exclusion rules can be quite difficult if I have multiple gitignore, at several levels in the repo.
With multiple files, you also typically wind up with a fair bit of duplication.
Pro multiple
Scopes "knowledge" to the part of the file tree where it is needed.
Since Git only tracks files, an empty .gitignore is the only way to commit an "empty" directory.
(And before Git 1.8, the only way to exclude a pattern like my/**.example was to create my/.gitignore in with the pattern **.foo. This reason doesn't apply now, as you can do /my/**/*.example.)
I much prefer a single file, where I can find all the exclusions. I've never missed per-directory .svn, and I won't miss per-directory .gitignore either.
That said, multiple gitignores are quite common. If you do use them, at least be consistent in their use to make them reasonable to work with. For example, you may put them in directories only one level from the root.
As a tangential note, one case where the ability to have multiple .gitignore files is very useful is if you want an extra directory in your working copy that you never intend to commit. Just put a 1-byte .gitignore (containing just a single asterisk) in that directory and it will never show up in git status etc.
There are many scenarios where you want to commit a directory to your Git repo but without the files in it, for example the logs, cache, uploads directories etc.
So what I always do is to add a .gitignore file in those directories with the following content:
*
!.gitignore
With this .gitignore file, Git will not track any files in those directories yet still allow me to add the .gitignore file and hence the directory itself to the repo.
You can have multiple .gitignore, each one of course in its own directory.
To check which gitignore rule is responsible for ignoring a file, use git check-ignore: git check-ignore -v -- afile.
And you can have different version of a .gitignore file per branch: I have already seen that kind of configuration for ensuring one branch ignores a file while the other branch does not: see this question for instance.
If your repo includes several independent projects, it would be best to reference them as submodules though.
That would be the actual best practices, allowing each of those projects to be cloned independently (with their respective .gitignore files), while being referenced by a specific revision in a global parent project.
See true nature of submodules for more.
Note that, since git 1.8.2 (March 2013) you can do a git check-ignore -v -- yourfile in order to see which gitignore run (from which .gitignore file) is applied to 'yourfile', and better understand why said file is ignored.
See "which gitignore rule is ignoring my file?"
Source: Stackoverflow.com