Determining if you are in the main script or being run/imported from another script

a.ps1

Import-Module ./common.psm1

Write-Host "This is a.ps1!"

./b.ps1

If(IsMain()){
  Write-Host "This is a protected part of a.ps1"
}

b.ps1

Import-Module ./common.psm1

Write-Host "This is b.ps1!"

If(IsMain()){
  Write-Host "This is a protected part of b.ps1"
}

common.psm1

function IsMain() {
 # (Get-Variable MyInvocation -Scope 0).Value.PSCommandPath -Eq (Get-Variable MyInvocation -Scope 2).Value.InvocationName
  (Get-Variable MyInvocation -Scope Local).Value.PSCommandPath -Eq (Get-Variable MyInvocation -Scope Global).Value.InvocationName
}

Export-ModuleMember -Function 'IsMain'

output.txt

> ./a.ps1

This is a.ps1!
This is b.ps1!
This is a protected part of a.ps1

> ./b.ps1

This is b.ps1!
This is a protected part of b.ps1