make: "varmod-assign-shell.mk" line 21: warning: Command "echo output; (exit 13)" exited with status 13 Global: _ = # (empty) Var_Parse: ${ASSIGNED::!=echo output; ${:U(exit 13)}} (eval-keep-dollar-and-undefined) Evaluating modifier ${ASSIGNED::...} on value "previous" (eval-keep-dollar-and-undefined, regular) Modifier part: "echo output; (exit 13)" Capturing the output of command "echo output; (exit 13)" make: "varmod-assign-shell.mk" line 26: warning: while evaluating variable "ASSIGNED" with value "previous": Command "echo output; (exit 13)" exited with status 13 Result of ${ASSIGNED::!=echo output; ${:U(exit 13)}} is "" (eval-keep-dollar-and-undefined, regular) Global: _ = # (empty) Global: .MAKEFLAGS = -r -k -d v -d Global: .MAKEFLAGS = -r -k -d v -d 0 DIRECT=output ASSIGNED=previous exit status 0