QMake - How to add and use a variable into the .pro file

Question

I have a qmake file generated by Qt creator. I am modifying it but I do not manage to understand how to create a variable.

For example, I want to declare the library

Answer 1

Other useful variable type: $$[...] This means "configuration option that were set when Qt was built"

Example:

message($$[QT_INSTALL_BINS])

This gives:

C:\Qt\Qt5.0.2\5.0.2\msvc2010_opengl\bin