Is this valid?
MSBuild /t=all /configuration=all
I want to build ALL configurations of all projects in a sln file, etc from the command lin
You can't by default build all configurations using MSBuild command line options. In order to do this you need to create a new target (VS Project).
The way I do it is:
msbuild /t:BuildAll /Configuration:"Debug;Release;ContinuousIntegration"
I make a standard Target, and call it BuildAll, and for every project I wanted to automate, I'd just create that Target and make it depend on all the targets you want to build automatically.