Re: Variable expansion in recipes

[Brian Vandenberg]

There's two ways I'm parsing what you're asking:

a) use ${SOMEVAR} without recursive expansion
b) expand ${SOMEVAR} ahead of time, presumably so it doesn't expand it
multiple times

For (a) you'd use $(value SOMEVAR).

For (b) you can do it but may not be straightforward.  Which you choose
depends on why you want to do it:

1) Use $(eval) because expansion of ${SOMEVAR} is expensive; or because it
has side effects; or because you want to dynamically create recipes (meta
programming):

$(eval RECIPE = some stuff using ${SOMEVAR})


2) Pre-expand an operation & save into another variable either because it's
expensive or because the result could change depending on
environment/context:

old:
RECIPE = some stuff using $(shell pkg-config --cflags glib)
or
RECIPE = some stuff using `pkg-config --cflags glib`


new:
SOMEVAR := $(shell pkg-config --cflags glib)
RECIPE = some stuff using ${SOMEVAR}

-brian


On Tue, May 30, 2017 at 6:40 AM, Sébastien Hinderer <
address@hidden> wrote:

> Dear all,
>
> Is there a way to have make substitute a variable by its value in
> a recipe when the recipe is read, rather than when the recipe is used?
>
> Thanks,
>
> Sébastien.
>
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