what do $$PWD and . mean in .pro in qt
<p>I came across a lib missing problem in my app, it turns out that this might relate to my understanding of <code>$$PWD</code> and <code>.</code> in .pro file of qt project.</p>

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<li><p>So do <code>$$PWD</code> and <code>.</code> both mean <strong>the dir, which contains the .pro file</strong> OR <strong>the dir, which is generated by building process(like: ****-build-desktop-Qt_4_8_1_in_PATH__System__Debug)</strong>. Or, they mean different things.</p></li>
<li><p>in some variable declaration like <code>OBJECTS_DIR = obj/Obj</code>, it looks like that <code>.</code> means the <strong>generated dir</strong>.  Whereas, in <code>HEADERS  += remoteclient.h ./RealPlay/realplay.h \</code>, it looks like that <code>.</code> means <strong>the dir that contains .pro file</strong>.</p></li>
<li><p>How about their meanings in LIBS and DESTDIR, etc. ?</p></li>
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