This is the script I created to detect if v3.5 is on the machine and if not to install it silently:

Script Name: Install .NET Framework 3.5
Script Description: Silently installs .NET Framework 3.5. If the machine is missing v1/2 it will automatically update to the new version.

IF Test Registry Key
Parameter 1 : HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.5
Absent :
THEN
Get Variable
Parameter 1 : 10
Parameter 2 :
Parameter 3 : temp
OS Type : 0
Write File
Parameter 1 : #temp#\doNetFx35setup.exe
Parameter 2 : VSASharedFiles\dotNetFx35setup.exe
OS Type : 0
Execute File
Parameter 1 : #temp#\doNetFx35setup.exe
Parameter 2 : /q /norestart
Parameter 3 : 1
OS Type : 0
Write Script Log Entry
Parameter 1 : Application deployed successfully - .NET Framework 3.5
OS Type : 0
ELSE
Write Script Log Entry
Parameter 1 : .NET Framework 3.5 already installed
OS Type : 0




Legacy Forum Name: .NET Framework 3.5 Silent Install,
Legacy Posted By Username: japaquette