SIM is a click-once application
You can launch it from command line, but it's not so obvious how. There are a couple of ways to launch it. One would be to invoke something like iexplore.exe, pointing it to the URL of the SIM installation.
My preferred method is launching it via the local
.appref-ms file. You find it like this:
Open up "Start", find SIM.
Right click and Open File Location.
In this folder, you will find your
.appref-ms file. This is what you need to launch from your command line.
Automated installation from the command line
Is planned for SIM 2.0. Reference: https://github.com/Sitecore/Sitecore-Instance-Manager/issues/18
But there is another way.
Using the Hedgehog.Tds.Build.Sim.Console, which is a tool meant specifically to handle this current shortcoming.
Also blogged about by Jeremy Davis here: HOW DID I MISS THIS BIT OF SIM AUTOMATION?
"RepoFile:Sitecore 7.1 rev. 130926.zip"
"ConnectionString:Data Source=.;User ID=sitecore;Password=sitecore123"