when does ${XX} in variable names get expanded?

when does ${XX} in variable names get expanded?

[Lu, Lianhao]

Hi guys,

For the following variable definition in bitbake,

VVV = "llu"
A_${VVV} = "VVV"
A_llu = "llu"

B = "${@bb.data.getVar('A_llu', d, True)}"
C := "${@bb.data.getVar('A_llu', d, True)}"

Why B is "VVV" and C is "llu" in final? I'm wondering when is the ${VVV} in the variable name of A_${VVV} expanded.

Best Regards,
-Lianhao Lu

Re: when does ${XX} in variable names get expanded?

[Richard Purdie]

On Thu, 2011-08-04 at 17:19 +0800, Lu, Lianhao wrote:
> For the following variable definition in bitbake,
> 
> VVV = "llu"
> A_${VVV} = "VVV"
> A_llu = "llu"
> 
> B = "${@bb.data.getVar('A_llu', d, True)}"
> C := "${@bb.data.getVar('A_llu', d, True)}"
> 
> Why B is "VVV" and C is "llu" in final? I'm wondering when is the ${VVV} in the variable name of A_${VVV} expanded.

During finalise() there is a call to d.expandKeys(). That call will
cause A_${VVV} to overwrite A_llu. If you look at the variable before
that you will get one value, if you look at it after that you will see
the other.

In your example above := is the immediate assignment/expansion operator,
"immediate" being the key part so finalise() hasn't happened yet.

Cheers,

Richard

Re: when does ${XX} in variable names get expanded?

[Khem Raj]

On 08/04/2011 02:19 AM, Lu, Lianhao wrote:
> Hi guys,
>
> For the following variable definition in bitbake,
>
> VVV = "llu"
> A_${VVV} = "VVV"
> A_llu = "llu"
>
> B = "${@bb.data.getVar('A_llu', d, True)}"
> C := "${@bb.data.getVar('A_llu', d, True)}"
>
> Why B is "VVV" and C is "llu" in final? I'm wondering when is the ${VVV} in the variable name of A_${VVV} expanded.
>

:= demands immediate expansion so any variables thats in the expression 
will be evaluated right there

where as = will be evaluated on reference and the variables it uses will 
be read/evaluated at that time.

> Best Regards,
> -Lianhao Lu
>
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