[yocto] which yocto doc explains bitbake assignment variations?

[Mark Hatle]

On 3/29/12 4:47 PM, Robert P. J. Day wrote:
>
>    somewhere, i'm assuming there's a decent explanation of the
> different bitbake assignment variations (=, ?=, ??=), but i don't
> immediately see it, and i think it's pretty important that that's
> explained properly.  pointer?
>
> rday
>

The bitbake manual has this information in it.  I don't know of a current 
version that is posted online, but you should be able to generate it from within 
bitbake itself.

(and older version: http://docs.openembedded.org/bitbake/html/)

But for the record the variations:

Immediate, overwrite existing values:
   variable = "value"

Conditional, only if not previously set:
   variable ?= "value"

Conditional, late evaluation -- i.e. at the end, only if set:
   variable ??= "value"

Immediate, expand variables immediately:
   variable := "${value}"

Append with spaces:
   variable += "value"

Prepend with spaces:
   variable =+ "value"

Append without spaces:
   variable .= "value"

Prepend without spaces:
   variable =. "value"

Append "late" evaluation:
   variable_append = "value"

--Mark