powershell to get sql server memory counters and show value

Aaron Bertrand wrote a good post on it that is pretty detailed...How I use PowerShell to collect Performance Counter data.

Then Laerte Junior has an excelent walk through on how he finds the counters he wants in a Simple-Talk article: Gathering Perfmon Data with Powershell. This might be where you want to start. It has some cmdlets that he uses to capture the counters for a particular instance I believe.

See if this is what you need:

$listofmetrics = (Get-Counter -ListSet "*Databases" -ComputerName $hostname).Counter | Where {$_ -like "*\Transactions/sec"}
$listofmetrics | Get-Counter