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From: Paul Eggleton <paul.eggleton@linux.intel.com>
To: Kang Kai <Kai.Kang@windriver.com>
Date: Mon, 22 Aug 2011 19:46:25 +0100
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Cc: Patches and discussions about the oe-core layer
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Subject: Re: question about meta/class/qmake-base.bbclass
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On Monday 22 August 2011 10:42:42 Kang Kai wrote:
> When I read the file  meta/class/qmake-base.bbclass, I find that that
> are 2 lines:
>      unset QMAKESPEC || true
>      ${OE_QMAKE_QMAKE} -makefile -spec ${QMAKESPEC} -o Makefile
> $QMAKE_VARSUBST_PRE $AFTER $PROFILES $QMAKE_VARSUBST_POST || die "Error
> calling ${OE_QMAKE_QMAKE} on $PROFILES"
> 
> I am confused that why unset QMAKESPEC first and then use it a argument
> for qmake?

It's not obvious, but think that the difference here is between $QMAKESPEC and 
${QMAKESPEC} - the first one is a reference to an environment variable, the 
second is a reference to an OE/BitBake variable. So "unset QMAKESPEC" is just 
clearing out the environment variable; ${QMAKESPEC} would still have a value.

Cheers,
Paul

-- 

Paul Eggleton
Intel Open Source Technology Centre