3.6 Other Special Variables

GNU make also supports a special variable. Note that any value you assign to this variable will be ignored; it will always return its special value.

The first special variable is .VARIABLES. When expanded, the value consists of a list of the names of all global variables defined in all makefiles read up until that point. This includes variables which have empty values, as well as built-in variables (see section Variables Used by Implicit Rules), but does not include any variables which are only defined in a target-specific context.