add post on how to run pre-commit retrospectively

content/posts/run-precommit-retrospectively.md

@@ -0,0 +1,25 @@
+---
+title: "Run pre-commit retrospectively on all changed files in a PR"
+date: 2020-10-02T16:10:57+02:00
+lastmod: 2023-12-25T16:10:57+02:00
+draft: false
+---
+
+When I was developing [sktime], we sometimes had new contributors who opened a PR but forgot to set up [pre-commit]. 
+
+This is how you can run pre-commit retrospectively on all changed files in the PR from a `<feature-branch>` into `main`. 
+First make sure that `main` is up-to-date, so that your local git state reflects the PR on the remote repository.
+If you are working with a fork, take a look at GitHub's guide on [how to sync a fork].
+
+Then run the following:
+
+```bash
+git checkout <feature-branch>
+pre-commit run --files $(git diff --name-only HEAD main)
+```
+
+[sktime]: https://github.com/sktime/sktime
+[pre-commit]: https://pre-commit.com/
+[how to sync a fork]: https://docs.github.com/en/free-pro-team@latest/github/collaborating-with-issues-and-pull-requests/syncing-a-fork
+[Gist]: https://gist.github.com/mloning/6f4b8d412743968af6b2da8b4eaaf2bf
+