These are first few lines I add to all my SharePoint on-premises scripts. It makes sure that the script is running with admin privileges and loads the Microsoft.SharePoint.PowerShell module. If there are any issue it aborts the script. It pulls some inspiration from the SharePoint Management Shell initialization script sharepoint.ps1.

SharePoint-Starter-Script.ps1

function Get-AdminStatus {
    $identity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
    $principal = New-Object System.Security.Principal.WindowsPrincipal $identity
    $principal.IsInRole
    $status = $principal.IsInRole("Administrators")
    $principal = $null
    $identity.Dispose()
    return $status
}

if (Get-AdminStatus -eq $false) {
  Write-Host "Aborting script - SharePoint requires running with administrator privileges"
  return
}

$Host.Runspace.ThreadOptions = "ReuseThread"
Add-PsSnapin Microsoft.SharePoint.PowerShell -ErrorAction 0

if ((Get-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction 0) -eq $null) {
  Write-Host "Aborting script - SharePoint PowerShell module does not appear to be loaded"
  return
}