[OE-core] what is the value of 'BBPATH ?= ""' in layer.conf?

[Robert P. J. Day]

  perusing some wind river layers, and in the layer.conf file here:

https://github.com/WindRiver-OpenSourceLabs/wr-kernel/blob/LB21_7.0_RCPL0002/conf/layer.conf

i see the opening snippet:

  BBPATH ?= ""
  # We have a conf and classes directory, add to BBPATH
  BBPATH := "${LAYERDIR}:${BBPATH}"

what is the purpose of that initial assignment

  BBPATH ?= ""

if that variable has no value, won't it just expand to the empty
string so that the eventual effect is the same? or is there something
more subtle happening here?

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

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