Windows task scheduler runs 'at system startup' tasks differently from other tasks - windows

Question

I have a powershell script that needs to run 24 * 7.
To make sure it does this, I have created two (almost) identical tasks listed in task scheduler. One starts the task every day at midnight, the other is set to run with the trigger 'At System startup'. The script is set to exit at a minute to midnight.
So far so good, everything works fine. All my bases are covered. The scheduled task takes care of the script 99% of the time, and the 'on startup' task covers the occasional power-failure
However, I've noticed a subtle difference when I look at the process details.
If I open a powershell session and check the pid for the task that started at midnight using this -
PS C:\Users\Elvis> get-wmiobject win32_process | where{$_.ProcessId -eq nnnn}
(where nnnn is the PID) I see lots of details listed, including this....
CommandLine : "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -NoExit -command "&c:\myDir\myScript.ps1"
This makes sense, it's exactly what I put into the task definition.
If do a similar thing with the task that starts on boot-up, then instead of seeing the full command line I just get
CommandLine :
This may not seem important, but I want to check that no other versions of the script are running when I start a new copy. I do this by including this line in the script. (basically it checks for other powershell process running the same script name but with a different PID)
get-wmiobject win32_process | where{$_.processname -eq 'powershell.exe' -and $_.ProcessId -ne $pid -and $_.commandline -match 'myScript'}
I need to be able to either persuade the task scheduler to include the script name in the process details, or find another way to check if there's another copy of the script already running

Answer 1

Use what I call a "PID lockfile". Write the PID to a known file path, if the file already exists, check for the PID. If it's already running, throw an error or otherwise exit. When the script exits have it delete that file.
$lockfilePath = "\path\to\script.pid"
try {
if( Test-Path -PathType Leaf $lockFilePath ) {
$oldPid = ( Get-Content -Raw $lockfilePath ).Trim()
if( Get-Process -Id $oldPid -EA SilentlyContinue ) {
throw "Only one instance of this script can run at a time"
}
}
$PID > $lockfilePath
# Rest of your script goes within this try block
} finally {
# Add a catch block if you like but this finally code
# guarantees a deletion attempt will be made on the
# PID file whether the try block succeeds or errors
if( Test-Path -PathType Leaf $lockfilePath ) {
Remove-Item $lockfilePath -Force -EA Continue
}
}