qmake variables, difference of $$VAR and $${VAR}

qmake, qt-creator, qt4

Solution

According to the documentation the two notations are almost equivalent. The only difference is that `the second notation allows you to append the contents of the variable to another value without separating the two with a space`.

Problem

For Qt qmake variables I sometimes see different notations. Examples ``` $$PWD $${PWD} ``` For me it seems to work the same, what is the difference?

Original source