How to trigger workflow when all files in PR are .csv - github

Question

I'd like to create a workflow in GitHub that triggers when all the changed files are .csv. I've been looking at GitHub's workflow syntax and I can only find instances where workflows are triggered when at least 1 certain file/directory is excluded or included.
My initial approach was
on:
push:
paths:
- '**.csv'
But this workflow will trigger as long as 1 file ends in .csv

Answer 1

What I ended up doing was running a workflow that tirggers when .csv files are added in the PR. Then a job starts that collects all the names of the files changed. Last it loops through the files changed and returns 'false' if any file doesn't end in .csv.
You can then add another job that uses the value of needs.compare.outputs.compare
name: csv-check
on:
pull_request:
branches:
- '**'
paths:
- '**.csv'
jobs:
changed_files:
runs-on: ubuntu-latest
outputs:
all: ${{ steps.changes.outputs.all }}
steps:
- name: Checkout repository
uses: actions/checkout#v2
with:
fetch-depth: 2
- name: Get changed files
id: changes
run: |
echo "::set-output name=all::$(git diff --name-only --diff-filter=ACMRT ${{ github.event.pull_request.base.sha }} ${{ github.sha }} | xargs)"
compare:
runs-on: ubuntu-latest
needs: changed_files
outputs:
compare: ${{ steps.all_csv.outputs.compare }}
if: ${{ needs.changed_files.outputs.all }}
steps:
- name: echo changed files
id: all_csv
run: |
echo "::set-output name=compare::true"
for file in ${{ needs.changed_files.outputs.all }}; do
if [[ $file != *.csv ]]; then
echo "::set-output name=compare::false"
fi
done

Answer 2

I suggest to review https://github.com/dorny/paths-filter - "GitHub Action that enables conditional execution of workflow steps and jobs, based on the files modified by pull request, on a feature branch, or by the recently pushed commits".