How can I split a single file from a git repo into a new repo?

Question

I have a git repo with several directories, and a single file, MyFile.ext.

/
  LargeDir1/
  LargeDir2/
  LargeDir3/
      .
      .
      .
  MyFile.ext

I'd like to start a new repo with just MyFile.ext in it, and keep all the history pertaining to it, but ignore everything else (all the LargeDirs). How can I do this?

For directories, I've successfully used this answer, but I tried that on a single file, and it doesn't work.

I've also tried this answer, which does delete everything except my file, but it also seems to leave all the history around.

Answer 1

Use git fast-export.

First you export the history of the file to a fast-import stream. Make sure you do this on the master branch.

cd oldrepo
git fast-export HEAD -- MyFile.ext >../myfile.fi

Then you create a new repo and import.

cd ..
mkdir newrepo
cd newrepo
git init
git fast-import <../myfile.fi
git checkout