Git corrupted repo: how to pick a git object from a clean repository

Question

This is one of the numerous questions regarding a Git repo that is corrupted, precisely a loose object that went wrong:

$ git gc
Counting objects: 3299, done         


        

Answer 1

If the file exists elsewhere

The object of the clean repository has been repacked, that's why it doesn't exist anymore as a file.

To restore it, first save it as a file, from the clean repository, with

git show 831a5d31af4a0af2f5a367689bee27a44efc22c9 > 831a5-file

Move 831a5-file in the corrupted repo, and run

git hash-object -w 831a5-file

Make sure that the SHA1 given in the output is 831a5d31af4a0af2f5a367689bee27a44efc22c9

This will store the object, and the repository is fixed!

If the file does not exist elsewhere

If the file doesn't exist elsewhere, i.e. the corruption occurred after commit but before you were able to push, there is a way to restore your repo and and re-commit the changes. See this answer to a related question.