Why does a powershell script not run in sccm?

If I run from an elevated command prompt
{query user | Select-String '^>(\w+)' | ForEach-Object { $_.Matches[0].Groups[1].Value }}
it returns the interactive logged on user (and not the elevated user account name).
But it fails in a powershell task sequence.
To test this I created a package (run as admin, allow user interaction) with a .bat script which runs these commands:
c:\Windows\ccmcache\3x>powershell -encodedcommand cQB1AGUAcgB5ACAAdQBzAGUAcgAgAHwAIABTAGUAbABlAGMAdAAtAFMAdAByAGkAbgBnACAAJwBeAD4AKABcAHcAKwApACcAIAB8ACAARgBvAHIARQBhAGMAaAAtAE8AYgBqAGUAYwB0ACAAewAgACQAXwAuAE0AYQB0AGMAaABlAHMAWwAwAF0ALgBHAHIAbwB1AHAAcwBbADEAXQAuAFYAYQBsAHUAZQAgAH0A
pause

but it fails with
query : The term 'query' is not recognized as the name of a cmdlet, function, script file, or operable program. Check
the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1

• query user | Select-String '^>(\w+)' | ForEach-Object { $_.Matches[0] ...
• ~~~~~
• CategoryInfo : ObjectNotFound: (query:String) [], CommandNotFoundException
• FullyQualifiedErrorId : CommandNotFoundException

I have also tried the same script (from ccmcache folder) as a system cmd session via PsExec64.exe -i -s cmd.exe and it works as expected
NB I want to use this in a task sequence to determine the interactive user account to create a scheduled task to runas the logged on user

Thanks
David