From this post you can create a step that set its output with the value $(date +'%Y-%m-%d')

Then use this output using ${{ steps.date.outputs.date }}. The following show an example for environment variables and for inputs :

on: [push, pull_request]
name: build
jobs:
  build:
    name: Example
    runs-on: ubuntu-latest
    steps:
      - name: Get current date
        id: date
        run: echo "::set-output name=date::$(date +'%Y-%m-%d')"
      - name: Test with environment variables
        run: echo $TAG_NAME - $RELEASE_NAME
        env:
          TAG_NAME: nightly-tag-${{ steps.date.outputs.date }}
          RELEASE_NAME: nightly-release-${{ steps.date.outputs.date }}
      - name: Test with input
        uses: actions/hello-world-docker-action@master
        with:
          who-to-greet: Mona-the-Octocat-${{ steps.date.outputs.date }}

Outputs :

* Test with environment variables
nightly-tag-2020-03-31 - nightly-release-2020-03-31

* Test with input
Hello Mona-the-Octocat-2020-03-31

@mwalter,

The expression syntax ${{ env.NOW }} is an correct way to access the custom env, just like @airtower-luna has suggested.

steps:
  - name: set env
    run: echo "::set-env name=NOW::$(date +'%Y-%m-%dT%H:%M:%S')"

name: create release

uses: ncipollo/release-action@v1

with:

artifacts: my-artifact

tag: ${{ env.NOW }}

token: ${{ secrets.GITHUB_TOKEN }}

This expression can correctly pass the value of env.NOW into the action “ncipollo/release-action@v1”.

The root cause of you still get the invalid tag_name error is that the format (DateTime) of the tag_name you set is not supported on GitHub.

Errors:
- tag_name is not a valid tag
- tag_name is not well-formed
- Published releases must have a valid tag

I tried to manually create a release, and I used the same date-time format to set the tag (e.g. 2020-06-22T02:11:39), then I got the “Invalid tag name” error.