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# $NetBSD: varname-empty.mk,v 1.5 2020/08/22 21:22:24 rillig Exp $
#
# Tests for the special variable with the empty name.
#
# The variable "" is not supposed to be assigned any value.
# This is because it is heavily used in the .for loop expansion,
# as well as to generate arbitrary strings, as in ${:Ufallback}.
# Until 2020-08-22 it was possible to assign a value to the variable with
# the empty name, leading to all kinds of unexpected effects.
?= default
= assigned # undefined behavior until 2020-08-22
+= appended
:= subst
!= echo 'shell-output'
# The .for loop expands the expression ${i} to ${:U1}, ${:U2} and so on.
# This only works if the variable with the empty name is guaranteed to
# be undefined.
.for i in 1 2 3
NUMBERS+= ${i}
.endfor
all:
@echo out: ${:Ufallback}
@echo out: ${NUMBERS}
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