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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 ``` ``````# SPDX-License-Identifier: GPL-2.0 # Shorthand warning = \$(warning-if,y,\$(1)) # Simply expanded variable. X := 1 SIMPLE := \$(X) X := 2 \$(warning,SIMPLE = \$(SIMPLE)) # Recursively expanded variable. X := 1 RECURSIVE = \$(X) X := 2 \$(warning,RECURSIVE = \$(RECURSIVE)) # Append something to a simply expanded variable. Y := 3 SIMPLE += \$(Y) Y := 4 \$(warning,SIMPLE = \$(SIMPLE)) # Append something to a recursively expanded variable. Y := 3 RECURSIVE += \$(Y) Y := 4 \$(warning,RECURSIVE = \$(RECURSIVE)) # Use += operator to an undefined variable. # This works as a recursively expanded variable. Y := 3 UNDEFINED_VARIABLE += \$(Y) Y := 4 \$(warning,UNDEFINED_VARIABLE = \$(UNDEFINED_VARIABLE)) # You can use variable references for the lefthand side of assignment statement. X := A Y := B \$(X)\$(Y) := 5 \$(warning,AB = \$(AB)) # User-defined function. greeting = \$(1), my name is \$(2). \$(warning,\$(greeting,Hello,John)) # The number of arguments is not checked for user-defined functions. # If some arguments are optional, it is useful to pass fewer parameters. # \$(2) will be blank in this case. \$(warning,\$(greeting,Hello)) # Unreferenced parameters are just ignored. \$(warning,\$(greeting,Hello,John,ignored,ignored)) ``````