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