Get Azure Devops pipeline predefined variables in posix linux path

I'm trying to pass the $(Build.ArtifactStagingDirectory) variable to a dockerfile using docker task like this:

  - task: Docker@2
    displayName: "Create docker image"
    inputs:
      command: 'build'
      Dockerfile: '**/Dockerfile.publish'
      arguments: '--build-arg APP=$(Build.ArtifactStagingDirectory)/Api'

But this fails because the path is in Windows style (like C:\agent\bla\)

What would be the best solution here?

It appears you're using Windows self-hosted agent, and would like a linux POSIX path instead of windows path.

You can add a pre task, convert the path:

- bash: |
    # Convert the path to POSIX format
    posix_path=$(echo "$(Build.ArtifactStagingDirectory)" | sed -e 's/\\/\//g' -e 's/:\([^/]\)/\1/g')
    echo $posix_path
    echo "##vso[task.setvariable variable=linuxposix_path;]$posix_path"

- task: Docker@2
  displayName: "Create docker image"
  inputs:
    command: 'build'
    Dockerfile: '**/Dockerfile.publish'
    arguments: '--build-arg APP=$(linuxposix_path)/Api'