AzureDevOps Pipeline variable assignment of Powershell script task output

Question

I have a YAML pipeline which defines a variable called vmPrivateIp:

pr: none
  trigger: none

variables:
  vmName: 'MyVmName'
  vmPrivateIp: '10.0.0.1'

I want to assign this variable with the result of a script task which obtains the private IP of MyVmName:

- task: PowerShell@2
  inputs:
  targetType: 'inline'
  script: |
    $IP = (Get-AzNetworkInterface -Name $(vmName)-nic -ResourceGroupName MyResourceGroup).IpConfigurations.PrivateIpAddress
    Write-Host "##vso[task.setvariable variable=vmPrivateIp,isOutput=true]$IP"
    Write-Host $(vmPrivateIp)

The task runs fine but the variable still contains the initial value

What do I need to do in order to successfully assign the result of the script task to vmPrivateIp?

What's happening here is that your variables are locally scoped to the script. The YAML tells Azure to create a PowerShell instance, run the script, and then close it. There is no persistence by default by variable names. This is for good reason otherwise every program you ever run would be crippled by naming conflicts. Check out this for more information: learn.microsoft.com/en-us/azure/devops/pipelines/scripts/…. — Efie
– Efie, Commented Mar 8, 2021 at 17:52

Bright Ran · Accepted Answer · 2021-03-10 08:51:12Z

In a job, if you use the 'SetVariable' command in a step to set up an output variable with a new value, it is functionally equivalent to creating a new output variable that has the same name but different value with the pipeline variable. The pipeline variable and its initial value still are available.

This output variable is only available to the subsequent steps in the same job and the subsequent jobs that depend on current job. For the step which runs the 'SetVariable' command to set up this output variable, this output variable is not available.

For the subsequent steps in the same job, you should use the expression "$(stepId.varName)" to access the value of the output variable. The expression "$(varName)" will return the value of the pipeline variable that is the initial value.
For each subsequent job that depends on current job, you should use the expression "$[dependencies.jobId.outputs['stepId.varName']]" to assign the value of the output variable to a job variable, then in the steps of the job you can access the value through this job variable.

To view more details, you can see "SetVariable: Initialize or modify the value of a variable" and "Set a multi-job output variable".

An example as reference:

azure-pipelines.yml

variables:
  vmPrivateIp: '10.0.0.1'

jobs:
- job: 'JobA'
  displayName: 'Job A'
  steps:
  - task: PowerShell@2
    inputs:
      targetType: 'inline'
      script: Write-Host "vmPrivateIp = $(vmPrivateIp)"
    displayName: 'View IP before update'

  - task: PowerShell@2
    name: 'UpdateIp'
    inputs:
      targetType: 'inline'
      script: Write-Host "##vso[task.setvariable variable=vmPrivateIp;isoutput=true]10.0.0.2"
    displayName: 'Update IP and set output'

  - task: PowerShell@2
    inputs:
      targetType: 'inline'
      script: |
        Write-Host "vmPrivateIp = $(vmPrivateIp)"
        Write-Host "UpdateIp.vmPrivateIp = $(UpdateIp.vmPrivateIp)"
    displayName: 'View IP after update'

- job: 'JobB'
  displayName: 'Job B'
  dependsOn: 'JobA'
  variables:
    IP_from_JobA: $[dependencies.JobA.outputs['UpdateIp.vmPrivateIp']]
  steps:
  - task: PowerShell@2
    inputs:
      targetType: 'inline'
      script: Write-Host "IP_from_JobA = $(IP_from_JobA)"
    displayName: 'View IP from JobA'

Result

Since this answer comes from someone at Microsoft, I'd like to take the opportunity to suggest that the documentation be enhanced on this topic. It says that this is intended to communicate values to other tasks/jobs/stages, but 1) doesn't say that it can't make them available to the current step because it's scraping console output, and 2) to clarify the role of isOutput - because it seems necessary everywhere?

WaitingForGuacamole · Accepted Answer · 2021-03-11 13:59:46Z

3

The purpose of task.setVariable is to communicate variable values to other tasks, jobs, and stages of your pipeline. You can't expect it to reflect a value into a variable within the task because it operates effectively after the task has completed - the pipeline runs Powershell, then scans the output for task.setVariable, and sets variables accordingly. So, within a task, you use the Powershell variable itself.

- task: PowerShell@2
  name: GetPrivateIp
  inputs:
  targetType: 'inline'
  script: |
    # Lives local to this script
    $IP = (Get-AzNetworkInterface -Name $(vmName)-nic -ResourceGroupName MyResourceGroup).IpConfigurations.PrivateIpAddress
    # Sets release variable after execution
    Write-Host "##vso[task.setvariable variable=privateIp;isOutput=true]$IP"
    # Writes your initial value as declared
    Write-Host $(vmPrivateIp)
- task: PowerShell@2
  name: UsePrivateIp
  inputs:
  targetType: 'inline'
  script: |
    Write-Host "$(GetPrivateIp.privateIp)"

Note that this syntax is for communication within a job - a different syntax is needed to communicate the variable to another job or stage of your pipeline.

edited Mar 11, 2021 at 13:59

answered Mar 8, 2021 at 20:02

WaitingForGuacamole

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5 Comments

Mike Over a year ago

this looks to be exactly what I need, but when I run it, I get an error: + Write-Host "$(GetPrivateIp.privateIp)" + ~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : ObjectNotFound: (GetPrivateIp.privateIp:String) [], ParentContainsErrorRecordException + FullyQualifiedErrorId : CommandNotFoundException

Bright Ran Over a year ago

Hi @Mike., Whether the 'UsePrivateIp' step to access the output is the subsequent step of the "GetPrivateIp" step in the same job? If the 'UsePrivateIp' step is in another job, you can't use the expression "$(GetPrivateIp.privateIp)" to access the output. This error should be caused by this. To access the output in another job, you need to use another expression. For more details, please see my answer.

Mike Over a year ago

Thank you @BrightRan-MSFT for this response. And your answer too was extremely helpful, I have not yet tried it but will very soon. Regarding the error I'm getting, it is confusing because it is in the same job. I copied the content above exactly as is and put it in a job step, ran and got the error above. Will keep digging to see if I missed something.

Bright Ran Over a year ago

Hi @Mike., For us to investigate this issue further, could you please share the complete YAML of the job? In addition, as I mentioned in my answer, the command lines Write-Host "$(GetPrivateIp.privateIp)" and Write-Host "##vso[task.setvariable variable=privateIp,isOutput=true]$IP" should be in the same job, but different steps. The step to run command line Write-Host "$(GetPrivateIp.privateIp)" should be after the step to run the command line Write-Host "##vso[task.setvariable variable=privateIp,isOutput=true]$IP".

WaitingForGuacamole Over a year ago

Whoops, typo that's been corrected - needs to be a semi-colon before isOutput=true.

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