How do you make an update installer with NSIS?

You might want to reconsider using NSIS. If you are into patching and distributing updates you will probably get the most benefit from using an installer technology that utilises the Windows Installer capabilities (msiexec).

NSIS is basically a program that runs and does what you want whereas a Windows Installer type installer forces you to split your application into features and components which can be managed by the windows installer msi service. MSI will track things like what versions of products you have installed, whether running the installer again will run in maintenance mode, whether you are allowed to install 2 products of different versions, whether a patch can be applied to a particular version of a product or any other question relating to updates and installs.

Basically most of the stuff you are requesting will be available out-of-the-box if you change to a Windows Installer technology. Whereas if you use NSIS (which doesn't use Windows Installer technology) then you will have to implement it all yourself.

Just as an example there is a pretty comprehensive installer builder called AdvancedInstaller ( http://www.advancedinstaller.com/ ) that sounds like what you want. Alternatively, if you want to spend the rest of your life trawling forums and newsgroups then there is an open source product called WiX that does something similar ;)

In spite of my previous comment I have written a 5000 line installer using NSIS with 13 custom pages. I have even looked at patching and it's a bit of a hack. The main bit of advice is to make sure you are patching the version you think you are patching then use one of the patching plugins available.

There are several patching technologies that compare files and produce patch change files and the NSIS code required to "install" them. I have found that NSIS Patch Gen did what I wanted pretty well with the least amount of hassle. The documentation is a bit thin but once you figure it out you think "Oh yeh".

You are probably going to have a little bit of trouble with an automatically generated Change Log. I would suggest that you create the Change Log yourself (or at least add the extra changes to it with each application change you make) and just include it as if it was a normal application file and let the patch generator update it.

http://sourceforge.net/projects/nsispatchgen/