Execute a script file when comment on a PR that introduces the file to be executed

[damianomuzzolon2]

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Question

What GitHub Actions topic or product is this about?

Workflow Configuration

Discussion Details

Hello,
here is my goal: create a workflow to run a file "script.py" when the comment "execute" is added to a PR.
The current issue is that the PR is adding script.py and the workflow fails because it's not able to find the script.py (error "no such file or directory").
Here is the workflow file i am using, could anyone help me understanding how to solve the issue?
I am still practicing with Github Actions so my workflow might not be the best implementation.

name: run-file-on-comment
on:
  issue_comment:
    types: [created, edited]
jobs:
  run-script:
    if: ${{ github.event.issue.pull_request && github.event.comment.body == 'execute' }}
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
    - uses: actions/checkout@v4
    - name: set-up-python
      uses: actions/setup-python@v3
      with:
        python-version: "3.10"
    - name: install-dependencies
      run: |
        python -m pip install --upgrade pip
        pip install flake8
        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
    - name: run-lint
      run: |
        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
    - name: run-script
      run: |
        python3 script.py

[Argh94]

Hey there! Thanks for sharing your question and workflow file—I’m happy to help you figure out why your GitHub Actions workflow is failing with the "no such file or directory" error when trying to run script.py on a pull request (PR) comment saying "execute." Since you’re still practicing with GitHub Actions (same here, it’s a learning curve!), I’ll break down what’s likely causing the issue, suggest fixes, and explain how to improve your workflow based on my own experience and the GitHub Actions docs.What’s Causing the Issue?From your description and workflow file, the error "no such file or directory" when running python3 script.py suggests that the script.py file, which is being added or modified in the PR, isn’t available in the workflow’s file system when the workflow runs. This is a common issue with GitHub Actions when dealing with PRs, because the default actions/checkout@v4 step checks out the base branch of the PR (e.g., main), not the changes in the PR’s branch (where script.py exists). Let’s dive into fixing this and making sure your workflow runs as intended.Why the Workflow FailsYour workflow is triggered when a comment like "execute" is added to a PR, and it uses actions/checkout@v4 to fetch the repository. By default, this action checks out the commit at the head of the base branch (e.g., main), not the PR’s branch where script.py is added. So, when the run-script step tries to execute python3 script.py, the file isn’t found because it only exists in the PR’s branch, not in the base branch.How to Fix the WorkflowTo make sure script.py is available, you need to check out the PR’s branch (the head ref) instead of the base branch. Here’s how you can modify your workflow, along with some improvements to make it more robust:yaml

name: run-file-on-comment
on:
issue_comment:
types: [created, edited]
jobs:
run-script:
if: ${{ github.event.issue.pull_request && github.event.comment.body == 'execute' }}
runs-on: ubuntu-latest
permissions:
pull-requests: write
contents: read
steps:
# Check out the PR's branch (head ref) instead of the base branch
- name: Checkout PR branch
uses: actions/checkout@v4
with:
ref: ${{ github.event.pull_request.head.sha }}
# Set up Python environment
- name: Set up Python
uses: actions/setup-python@v5
with:
python-version: "3.10"
# Install dependencies
- name: Install dependencies
run: |
python -m pip install --upgrade pip
pip install flake8
if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
# Run linting
- name: Run lint
run: |
flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
# Run the script
- name: Run script
run: |
python3 script.py

Key Changes and ExplanationsCheckout the PR’s Branch:Added ref: ${{ github.event.pull_request.head.sha }} to the actions/checkout@v4 step. This tells the action to check out the specific commit from the PR’s branch (the head SHA), ensuring script.py is available in the workflow’s file system.
Why This Fixes It: The github.event.pull_request.head.sha points to the latest commit in the PR’s branch, which includes script.py. Without this, you’re only getting the base branch’s files, where script.py doesn’t exist yet.

Updated actions/setup-python to @v5:I upgraded to the latest version (@v5) for better compatibility and support. This ensures your Python setup is using the most recent features and bug fixes.

Added contents: read Permission:Your workflow already includes pull-requests: write, but I added contents: read to ensure the workflow can read the repository’s files (like script.py). This follows GitHub’s best practices for least privilege.

Kept Your Logic Intact:The if condition (github.event.issue.pull_request && github.event.comment.body == 'execute') is solid for triggering the workflow only on PR comments saying "execute." I didn’t change this since it’s working as intended.
The linting and dependency steps are fine, assuming script.py doesn’t rely on specific files or paths that might also be missing.

Additional Tips to Avoid IssuesVerify script.py Path: If script.py is in a subdirectory (e.g., src/script.py), update the run-script step to include the correct path:yaml

run: python3 src/script.py

Double-check the file’s location in the PR’s branch to avoid path-related errors.
Handle Missing Dependencies: If script.py requires specific Python packages, ensure they’re listed in requirements.txt or install them explicitly in the install-dependencies step. For example:yaml

pip install -r requirements.txt || echo "No requirements.txt found"

Test the Workflow: After updating the workflow, add a comment saying "execute" to your PR to trigger it. Check the Actions tab in your repo to see if it runs successfully. If it fails, the logs will show details (e.g., if another file is missing).
Debugging Tip: Add a step to list files in the workspace to confirm script.py is checked out:yaml

• name: List files
  run: ls -R

Place this before the run-script step to verify the file exists.

My Thoughts as Someone Learning GitHub ActionsSince you mentioned you’re still practicing with GitHub Actions, I totally get how tricky it can be to figure out why something like this fails! I ran into a similar issue when I was trying to run a script in a PR, and it was confusing until I learned that actions/checkout doesn’t automatically grab the PR’s changes. Adding the ref field was a game-changer for me. Also, GitHub’s Actions documentation and community forums were super helpful for troubleshooting.If It Still Doesn’t WorkIf you apply these changes and still get errors, here are a couple of things to check:PR Context: Ensure the PR is open and the comment is exactly "execute" (case-sensitive). You can make it case-insensitive by tweaking the if condition:yaml

if: ${{ github.event.issue.pull_request && contains(github.event.comment.body, 'execute') }}

File Existence: If script.py is dynamically generated or in a weird path, the workflow might still fail. Share the full error log from the Actions tab, and I can help pinpoint the issue.
Permissions: If the workflow can’t access the PR’s branch, double-check that the GitHub Actions token (GITHUB_TOKEN) has the necessary permissions (contents: read should be enough).

I hope this helps get your workflow running smoothly! If you run into more errors or want me to review the updated workflow, just share the details, and I’ll dive in with you. Keep practicing—GitHub Actions gets easier with time!

[jihanurrahman33]

Hi @damianomuzzolon2,

Your workflow is checking out the default branch, but your script.py only exists on the PR branch. For issue_comment-triggered jobs, you need to explicitly check out the PR’s ref.

Try this version:

name: run-file-on-comment
on:
  issue_comment:
    types: [created]

jobs:
  run-script:
    # 1) Only run on PR comments
    # 2) Only when the comment body is exactly "execute" (case-insensitive, trimmed)
    # 3) Only when the commenter is a repo member/collaborator (security)
    if: >
      github.event.issue.pull_request &&
      startsWith(trim(github.event.comment.body), 'execute') &&
      (github.event.comment.author_association == 'MEMBER' ||
       github.event.comment.author_association == 'OWNER'  ||
       github.event.comment.author_association == 'COLLABORATOR')

    runs-on: ubuntu-latest

    permissions:
      contents: read
      pull-requests: write

    steps:
      # ✅ Check out the PR branch (so new files like script.py exist)
      - name: Checkout PR HEAD
        uses: actions/checkout@v4
        with:
          # Use the PR number from the issue_comment payload
          ref: refs/pull/${{ github.event.issue.number }}/head
          fetch-depth: 1

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: '3.10'

      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi

      - name: Lint (optional)
        run: |
          pip install flake8
          flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
          flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics

      - name: Run script
        run: |
          python3 script.py

Why this works

• refs/pull/${{ github.event.issue.number }}/head checks out the PR head commit, where script.py exists.
• On issue_comment, GitHub does not automatically give you the PR’s code; without the explicit ref, actions/checkout grabs the default branch, which is why you saw “no such file or directory.”

Notes

• If you prefer to run against the merge result (safer for integration checks), switch the ref to:

  ref: refs/pull/${{ github.event.issue.number }}/merge
  

  (This ref exists for most PRs targeting the same repo; if the PR is in a fork and the repo is private, you may need different handling.)
• Running code on a comment is powerful but can be risky. The author_association guard above limits who can trigger it.

Hope this helps!

[damianomuzzolon2]

@Argh94 and @jihanurrahman33 thank you for the hints and the explanation!
I tried both solutions and the one provided by @jihanurrahman33 worked as expected with my code!
Thank you

[jihanurrahman33]

Glad my solution worked out for you! Keep it up 👍