Why -Command behaves differently for the same command ?

Question

I have a script called a.ps1 containing
exit 38
We can run this script in the following three ways and we will get three
different results. Can somebody explain what is going on? Why this behaviour?
References to good sources of information would be greatly apreciated.
PS> powershell -File .\a.ps1; $LastExitCode
38
PS> powershell -command { .\a.ps1 }; $LastExitCode
1
PS> powershell -command "& { .\a.ps1 }"; $LastExitCode
0
quilx

Answer 1

Hi Quilx,
I'm so sorry for missing your points, However, these information may be helpful for you:
The folowing is an example:
param($code=99)
exit $code
Save this in a.ps1 script file. Launch a cmd.exe and run your script
Powershell.exe –noprofile –file “pathtoscript.ps1” 1234
Echo %ERRORLEVEL%
This returns 1234 (or whatever code you submitted to your script when you called it). The reason why so many people have trouble with returning exit codes is that they miss the –file parameter:
Without –file, powershell.exe returns either 0 or 1. That’s because now your code is interpreted as a command, and when the command returns an exit code other than 0, PowerShell assumes it failed. It then returns its own exit code, which is always 0 (command
ran fine) or 1 (command failed).
Reference from:
Returning Exit Codes from PowerShell
Returning Exit Code from Script
Best Regards,
Anna