How to set environment variables in Visual Studio 2012?

Question

How to set environment variables in Visual Studio 2012?

For example, I need to install this:

$(MyDir) = "c:\my_dir" 

Answer 1

Open the project in a text editor and add to the top existing tag

 <PropertyGroup> <MyDir>c:\my_dir</MyDir> ...(leave existing ones here)... </PropertyGroup> 

There is probably some way to do this in the user interface, but I am only now editing the files manually. And its different user interface for each language (!)