1make: "varmod-assign-shell.mk" line 21: warning: Command "echo output; (exit 13)" exited with status 13 2Global: _ = # (empty) 3Var_Parse: ${ASSIGNED::!=echo output; ${:U(exit 13)}} (eval-keep-dollar-and-undefined) 4Evaluating modifier ${ASSIGNED::...} on value "previous" (eval-keep-dollar-and-undefined, regular) 5Modifier part: "echo output; (exit 13)" 6Capturing the output of command "echo output; (exit 13)" 7make: "varmod-assign-shell.mk" line 26: warning: Command "echo output; (exit 13)" exited with status 13 8Result of ${ASSIGNED::!=echo output; ${:U(exit 13)}} is "" (eval-keep-dollar-and-undefined, regular) 9Global: _ = # (empty) 10Global: .MAKEFLAGS = -r -k -d v -d 11Global: .MAKEFLAGS = -r -k -d v -d 0 12DIRECT=output 13ASSIGNED=previous 14exit status 0 15