How can I get the installer filename?
From NSIS Wiki
As of NSIS 2.26, $EXEPATH contains the full path to the installer.
For earlier versions, you can get the filename of your installer using the System plug-in:
System::Call 'kernel32::GetModuleFileNameA(i 0, t .R0, i 1024) i r1' ;$R0 will contain the installer filename
More information can be found at Get installer filename