gnu make - How can default env variable in gnu makefile target -


i want this

test.install:         export build_number=${build_number:-$${another_var}}

but not working. come blank

edit:

this works fine. provided export build_number in shell before invoking make command

test.install:         export build_number=${build_number}

these not working . both give blank build_number

test.install:         export build_number=${build_number:-$${another_var}}

and

test.install:         export build_number=${build_number:-55}}

if want expand variables in bash rather in makefile, you'll need escape expansion otherwise make going variable literally called build_number:-${another_var} or build_number:-55

test.install:         export build_number=$${build_number:-$${another_var}}  test.install:         export build_number=$${build_number:-55}}

-

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