How can I tell if Docker Desktop is running in a Powershell script?

Question

I have a Powershell script in which I need to know if Docker Desktop is currently running.

I have read that one way to do it is to use docker ps and see if I get back a container list or an error message. But I'm struggling to make use of this in an actual script. I haven't worked out how to capture and act on the result correctly.

Here's what I have so far:

function IsDockerDesktopRunning()
{
    $dockerPsResult = docker ps | Out-String

    Write-Host "Result is:"
    Write-Host $dockerPsResult

    if (($dockerPsResult).StartsWith("error"))
    {
        return $false
    }
    return $true
}

$isRunning = IsDockerDesktopRunning
Write-Host $isRunning

When when it's not running, the result looks like this:

error during connect: This error may indicate that the docker daemon is not running.: Get "http://%2F%2F.%2Fpipe%2Fdocker_engine/v1.24/containers/json": open //./pipe/docker_engine: The system cannot find the file specified.
Result is:

True

As you can see, it looks the output from the docker ps command gets output as it's executed and the variable isn't populated.

Is there a way to correctly capture the output? Or, should I tackle the problem a different way?

Answer 1

To capture the error output as well, redirect stderr to stdout like this.

$docker = docker ps 2>&1

You can use this to determine if docker desktop is running.

if((docker ps 2>&1) -match '^(?!error)'){
   Write-Host "Docker is running"
}