How to replace string in expression with GitHub actions

Question

This is my action that returns $TOXENV that looks like this py3.6-django2.2 I'd like to $TOXENV to look like this instead py36-django22 is there any substitute/replace function that I could use to replace . char?

name: CI
on:
  workflow_dispatch:
    branches: [ master, actions ]
jobs:
  demo:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python: [3.6, 3.7, 3.8, 3.9]
        django: ['2.2', '3.0']
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-python@v1
        name: Set up Python ${{ matrix.python }} ${{ matrix.django }}
        with:
          python-version: ${{ matrix.python }}
      - name: python version
        env:
            TOXENV: "py${{ matrix.python }}-django${{ matrix.django }}"
        run:
          echo $TOXENV

You could use what is suggested here: stackoverflow.com/questions/2871181/… on your run last step to substitute the . for something else. — GuiFalourd
– GuiFalourd, Commented Apr 23, 2021 at 14:24
Thanks. That is a general substitution with sed but is there any build in function for GitHub Actions ? — Lukasz Dynowski
– Lukasz Dynowski, Commented Apr 23, 2021 at 15:53

Seff · Accepted Answer · 2022-06-23 07:36:58Z

17

Another way by using BASH native variable substitution:

  - name: python version
    env:
        TOXENV: "py${{ matrix.python }}-django${{ matrix.django }}"
    run: |
      TOXENV=${{ env.TOXENV }}
      TOXENV=${TOXENV//.} # replace all dots
      echo TOXENV=${TOXENV} >> $GITHUB_ENV # update GitHub ENV vars
  - name: print env
    run: echo ${{ env.TOXENV }}

The idea is to read the GitHub actions expression variable into a BASH variable and do the string manipulation then export or set-output to update in GitHub actions runtime.

answered Jun 23, 2022 at 7:36

Seff

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1 Comment

Marcel Melzig Over a year ago

Work perfectly. Even as a one liner: run: echo "TOXENV=${BRANCH/\//-}" >> $GITHUB_ENV. Changes slashes into dashes.

stephenwade · Accepted Answer · 2025-05-22 16:58:50Z

11

I don't think there's an easy way to do this in the env directive of your step when defining the value of TOXENV. The env directive accepts expressions, but the functions that can be used in expressions are limited, with nothing that can replace arbitrary characters. The closest I could find is format(), but that unfortunately requires numbered braces in the target string, which won't work for your situation.

Instead, perhaps you could set the value of TOXENV in the run directive using sed, then add it to the environment:

      - name: python version
        run:
          RAW_TOXENV="py${{ matrix.python }}-django${{ matrix.django }}"
          TOXENV=$(echo $RAW_TOXENV | sed 's/\.//')
          echo "TOXENV=$TOXENV" >> $GITHUB_ENV

edited May 22 at 16:58

stephenwade

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answered Apr 24, 2021 at 23:17

jidicula

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3 Comments

Lukasz Dynowski Over a year ago

I up vote the answer. It's a pity that for the moment (25 April 2021) functions doesn't include replace directive/function. Moving replace logic to run is at the moment only one solution.

hui chen Over a year ago

It's March 2022 and we still don't have a native string replace function available.

Brandon Aug 28 at 22:22

Nearly Sept 2025 and I still can't take the repo name and put it into a file system path / filename without clunky multistep fiddling. Cmon.

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