Directory.Build.targets

<Project>
  <PropertyGroup>
    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
  </PropertyGroup>
  <Target Name="UpdateAppSettings" AfterTargets="Build;Publish"
    Condition=" '$(UpdateAppSettings)' == 'true' and Exists('$(MSBuildProjectDirectory)\appsettings.json') ">
    <PropertyGroup>
      <AppSettingsInputFile>$(MSBuildProjectDirectory)\appsettings.json</AppSettingsInputFile>
      <AppSettingsOriginalString>"InstrumentationKey":  ""</AppSettingsOriginalString>
      <AppSettingsReplaceString>"InstrumentationKey":  "$(RoslynPadTelemetryKey)"</AppSettingsReplaceString>
    </PropertyGroup>
    <WriteLinesToFile
      File="$(OutDir)\appsettings.json"
      Lines="$([System.IO.File]::ReadAllText($(AppSettingsInputFile)).Replace($(AppSettingsOriginalString), $(AppSettingsReplaceString)))"
      Overwrite="true"
      Encoding="Unicode"/>
    <WriteLinesToFile
      Condition=" '$(PublishDir)' != '' "
      File="$(PublishDir)\appsettings.json"
      Lines="$([System.IO.File]::ReadAllText($(AppSettingsInputFile)).Replace($(AppSettingsOriginalString), $(AppSettingsReplaceString)))"
      Overwrite="true"
      Encoding="Unicode"/>
  </Target>
</Project>