1# $NetBSD: varmod-assign-shell.mk,v 1.4 2022/01/10 20:32:29 rillig Exp $
2#
3# Tests for the variable modifier '::!=', which assigns the output of a shell
4# command to the variable, but only if the command exited successfully.  This
5# is different from the other places that capture the output of an external
6# command (variable assignment operator '!=', expression modifier ':sh',
7# expression modifier ':!...!'), which also use the output when the shell
8# command fails or crashes.
9#
10# The variable modifier '::!=' and its close relatives have been around since
11# var.c 1.45 from 2000-06-01.
12#
13# Before 2020.08.25.21.16.53, the variable modifier '::!=' had a bug for
14# unsuccessful commands, it put the previous value of the variable into the
15# error message instead of the command that was executed.  That's where the
16# counterintuitive error message 'make: "previous" returned non-zero status'
17# comes from.
18#
19# BUGS
20#	Even though the variable modifier '::!=' produces an error message,
21#	the exit status of make is still 0.
22#
23#	Having an error message instead of a warning like for the variable
24#	assignment operator '!=' is another unnecessary inconsistency.
25
26DIRECT=		previous
27DIRECT!=	echo output; false
28
29ASSIGNED=	previous
30.MAKEFLAGS: -dv			# to see the actual command
31_:=		${ASSIGNED::!=echo output; ${:Ufalse}}
32.MAKEFLAGS: -d0
33
34all:
35	@echo DIRECT=${DIRECT:Q}
36	@echo ASSIGNED=${ASSIGNED:Q}
37