qmake syntax: += vs. *= (plus vs. asterisk)

Question

What is the difference between the following statements, using a plus vs. an asterisk in .pro files?:

LIBS *= -lz

vs.

LIBS += -lz

Answer 1

The *= operator adds a value to the list of values in a variable, but only if it is not already present. This prevents values from being included many times in a variable.