azure-pipelines-tasks: FileTransform task not working as expected for appsettings.json file variable substitution

I know how variable substitution works in release pipeline, just check “XML variable substitution” for XML files or write json filename in “JSON variable substitution” textbox. This works well if I’m deploying to “Web App on Windows” app service type. But as soon as I select “Web App on Linux” app service type “File Transforms & Variable Substitution Options” group disappears.

Then I decided to move variable substitution in build pipeline in YAML file (azure-pipelines.yml), that’s where problem started for me.

So, i’m trying to achieve appsettings.json file variable substitution in build pipeline. I already listed variables in library:

Here’s the json file:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*",
  "name": "value"
}

Here’s the code i have in azure-pipelines.yml:-

trigger:
 - master

pool:
  vmImage: 'ubuntu-latest'

variables:
  buildConfiguration: 'Release'

steps:
- task: DotNetCoreCLI@2
  displayName: 'Restore project'
  inputs:
    command: 'restore'
    projects: |
      **/WebApplication_Li_CI_CD.csproj
      **/WebApplication_Li_CI_CD_1.csproj
    feedsToUse: 'select'

- task: DotNetCoreCLI@2
  displayName: 'Build project'
  inputs:
    command: 'build'
    projects: |
      **/WebApplication_Li_CI_CD.csproj
      **/WebApplication_Li_CI_CD_1.csproj

- task: DotNetCoreCLI@2
  displayName: 'Publish project'
  inputs:
    command: publish
    projects: |
      **/WebApplication_Li_CI_CD.csproj
      **/WebApplication_Li_CI_CD_1.csproj
    publishWebProjects: True
    arguments: '--configuration $(BuildConfiguration) --output $(Build.ArtifactStagingDirectory)'
    zipAfterPublish: True

- task: CopyFiles@2
  displayName: 'Copy zip files'
  inputs:
    SourceFolder: '$(Build.SourcesDirectory)'
    Contents: '**\*.zip'
    TargetFolder: '$(Build.ArtifactStagingDirectory)'

- task: PublishBuildArtifacts@1
  displayName: 'Publish artifacts'


- task: FileTransform@1
  displayName: 'Update appsettings.json file'
  inputs:
    folderPath: '$(Build.ArtifactStagingDirectory)'
    fileType: 'json'
    targetFiles: '**/appsettings.json'

I tried to adjust folderPath in FileTransformation task, and received errors:

#folderPath: '$(System.DefaultWorkingDirectory)/**/*.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/s/**/*.zip

#folderPath: '$(System.DefaultWorkingDirectory)/_WebApplication_Linux_CI_CD/drop/WebApplication_Li_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/s/_WebApplication_Linux_CI_CD/drop/WebApplication_Li_CI_CD.zip

#folderPath: '$(Build.ArtifactStagingDirectory)/**/*.zip'
Error: More than one package matched with specified pattern: /home/vsts/work/1/a/**/*.zip. Please restrain the search pattern.

#folderPath: '$(Build.ArtifactStagingDirectory)/**/WebApplication_Linux_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/a/**/WebApplication_Linux_CI_CD.zip

#folderPath: '$(Build.ArtifactStagingDirectory)/_WebApplication_Linux_CI_CD/drop/WebApplication_Li_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/a/_WebApplication_Linux_CI_CD/drop/WebApplication_Li_CI_CD.zip

#folderPath: '$(Build.ArtifactStagingDirectory)/WebApplication_Linux_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/a/WebApplication_Linux_CI_CD.zip

#folderPath: '$(Build.ArtifactStagingDirectory)/drop/WebApplication_Linux_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/a/drop/WebApplication_Linux_CI_CD.zip

#folderPath: '$(Build.ArtifactStagingDirectory)/drop/**/WebApplication_Linux_CI_CD.zip'
Error: Nopackagefoundwithspecifiedpattern /home/vsts/work/1/a/drop/**/WebApplication_Linux_CI_CD.zip

And none of the combination works for me.