Create comma-separated lists in GNU Make

Question

I have a Makefile with a set of booleans which must be used to control the flags for an external application. The problem is that the flag must be passed as a comma-separated s

Answer 1

First you create the two white-space separated lists, either using your method, or thiton's. Then you use the little trick from the end of section 6.2 of the GNU make manual to create a variable holding a single space, and one holding a comma. You can then use these in $(subst ...) to change the two lists to comma-separated.

PARTS  := A B C

BOOL_A := y
BOOL_B := n
BOOL_C := y

WITH_LIST    := $(foreach part, $(PARTS), $(if $(filter y, $(BOOL_$(part))), $(part)))
WITHOUT_LIST := $(filter-out $(WITH_LIST), $(PARTS))

null  :=
space := $(null) #
comma := ,

WITH_LIST    := $(subst $(space),$(comma),$(strip $(WITH_LIST)))
WITHOUT_LIST := $(subst $(space),$(comma),$(strip $(WITHOUT_LIST)))

all:
    ./app --with=$(WITH_LIST) --with-out=$(WITHOUT_LIST)