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

QMake uses its own syntax for variable references.

• VAR = foobar => Assign value to variable when qmake is run
• $$VAR => QMake variable's value at the time qmake is run
• $${VAR} => QMake variable's value at the time qmake is run (identical but enclosed to separate from surrounding text)
• $(VAR) => Contents of an Environment variable at the time Makefile (not qmake) is run
• $$(VAR) =>Contents of an Environment variable at the time qmake (not Makefile) is run

Try it like this

MYPATH = /lib/aaa/bbb
unix:!macx:!symbian: LIBS += -L$${MYPATH}

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