Tips

1. Use git help <verb> to learn the Git commands.

2. How to delete unpushed commits?
   git reset --hard origin/master

3. How to delete orphan commits?
   git gc --prune=now --aggressive

4. How to undo pushed commits?

   git log
   git checkout <older commit hash tag>
   git checkout master
   git revert <older commit hash tag>
   git commit -m "Undo <older commit hash tag>"
   git revert ...
   git commit ...
   git revert ...
   git commit ...
   

   BTW, We can use git log --oneline to view a short list of log history.

5. How to remove big file in pushed GitHub history?
   https://help.github.com/en/github/authenticating-to-github/removing-sensitive-data-from-a-repository

• 5.1 Run in the repo

  git filter-branch --force --index-filter "git rm -r --cached --ignore-unmatch <unwanted_folder/[unwanted_file]>" --prune-empty -- --all
  Rewrite abcdefabcdedfefcfefafcfefd98738127382630 (24/29) (28 seconds passed, remaining 5 predicted)    rm 'XXXX/YYYY.ZZZ'
  Rewrite cfaecbacfdedfefc394893fefd987381273826ec (29/29) (34 seconds passed, remaining 0 predicted)
  Ref 'refs/heads/master' was rewritten
  WARNING: Ref 'refs/remotes/origin/Cathy' is unchanged
  Ref 'refs/remotes/origin/master' was rewritten
  WARNING: Ref 'refs/remotes/origin/master' is unchanged
  

  Possible error encountered:
  fatal: bad revision 'rm'
  Cause:
  Windows must use “ instead of ‘

• 5.2 Success

  C:\XXXX\YYYY>git push origin --force --all
  Enumerating objects: 1744, done.
  Counting objects: 100% (1744/1744), done.
  Delta compression using up to 12 threads
  Compressing objects: 100% (488/488), done.
  Writing objects: 100% (1744/1744), 39.24 MiB | 378.00 KiB/s, done.
  Total 1744 (delta 645), reused 1738 (delta 642)
  remote: Resolving deltas: 100% (645/645), done.
  To https://github.com/XXXX/YYYY.git
   +03f9ee8...9085268 master -> master (forced update)
  

  Possible error encountered:

  C:\XXXX\YYYY>git push origin master --force
  Enumerating objects: 1744, done.
  Counting objects: 100% (1744/1744), done.
  Delta compression using up to 12 threads
  Compressing objects: 100% (488/488), done.
  error: RPC failed; curl 56 OpenSSL SSL_read: SSL_ERROR_SYSCALL, errno 10054
  Writing objects: 100% (1744/1744), 39.24 MiB | 107.00 KiB/s, done.
  Total 1744 (delta 645), reused 1738 (delta 642)
  fatal: the remote end hung up unexpectedly
  Everything up-to-date
  

  Cause:
  Network slowness

• Note!!!
  The current branch still have big files, even if you run git gc --prune=now --aggressive.
  But the big file will be only removed in remote and new-cloned repositories.