Info Catalog make: Multi-Line make: Using Variables make: Environment

make: Undefine Directive

 
 6.9 Undefining Variables
 ========================
 
 If you want to clear a variable, setting its value to empty is usually
 sufficient.  Expanding such a variable will yield the same result (empty
 string) regardless of whether it was set or not.  However, if you are
DONTPRINTYET  using the 'flavor' (Flavor Function) and 'origin' (*noteOrigin
DONTPRINTYET  using the 'flavor' (Flavor Function) and 'origin' (Origin

 Function) functions, there is a difference between a variable that was
 never set and a variable with an empty value.  In such situations you
 may want to use the 'undefine' directive to make a variable appear as if
 it was never set.  For example:
 
      foo := foo
      bar = bar
 
      undefine foo
      undefine bar
 
      $(info $(origin foo))
      $(info $(flavor bar))
 
    This example will print "undefined" for both variables.
 
    If you want to undefine a command-line variable definition, you can
 use the 'override' directive together with 'undefine', similar to how
 this is done for variable definitions:
 
      override undefine CFLAGS
 

Info Catalog make: Multi-Line make: Using Variables make: Environment