Github Actions to see changed files - github

Question

I am trying to use actions to post a comment on a PR if a file has changed but my action is unable to see the changes.
jobs:
check:
runs-on: self-hosted
permissions:
pull-requests: write
steps:
- uses: actions/checkout#v2
with:
fetch-depth: 2
- name: Get all changed files and echo alert
env:
GITHUB_TOKEN: *******************
run: |
git diff --name-status
or if I change it to git status it outputs a message saying no changes working tree is clean, but I know one file has changed.
I tried using v1 instead of v2 but that doesn't work either.
Does anyone have any ideas on what i am doing wrong or how I can get this working?

Answer 1

Checkout is just "checking out" clean repository state for a given commit or PR.
If you expect to get changes files from PR, you can do it by using external actions, for examples:
- name: Get changed files using defaults
id: changed-files
uses: tj-actions/changed-files#v32
- name: List all added files
run: |
for file in ${{ steps.changed-files.outputs. modified_files }}; do
echo "$file was modified."
done

Answer 2

Use Github contexts: Learn GitHub Actions Contexts
Here is the command you probably need:
git diff --name-only ${{ github.event.after }} ${{ github.event.before }}
Also, you could affect the whole action by setting paths at the beginning of an action:
name: Action #1
on:
push:
branches:
- main
paths:
- <folder>/** // action will be triggered by push to the main branch AND when there are changed files in <folder>
pull_request:
branches:
- main
paths:
- <folder>/*.js // action will be triggered only on pull-requests AND when any .js files in <folder> have been changed