1# $NetBSD: varname-empty.mk,v 1.5 2020/08/22 21:22:24 rillig Exp $ 2# 3# Tests for the special variable with the empty name. 4# 5# The variable "" is not supposed to be assigned any value. 6# This is because it is heavily used in the .for loop expansion, 7# as well as to generate arbitrary strings, as in ${:Ufallback}. 8 9# Until 2020-08-22 it was possible to assign a value to the variable with 10# the empty name, leading to all kinds of unexpected effects. 11?= default 12= assigned # undefined behavior until 2020-08-22 13+= appended 14:= subst 15!= echo 'shell-output' 16 17# The .for loop expands the expression ${i} to ${:U1}, ${:U2} and so on. 18# This only works if the variable with the empty name is guaranteed to 19# be undefined. 20.for i in 1 2 3 21NUMBERS+= ${i} 22.endfor 23 24all: 25 @echo out: ${:Ufallback} 26 @echo out: ${NUMBERS} 27