Info Catalog make: Eval Function make: Functions make: Flavor Function

make: Origin Function

 
 8.10 The 'origin' Function
 ==========================
 
 The 'origin' function is unlike most other functions in that it does not
 operate on the values of variables; it tells you something _about_ a
 variable.  Specifically, it tells you where it came from.
 
    The syntax of the 'origin' function is:
 
      $(origin VARIABLE)
 
    Note that VARIABLE is the _name_ of a variable to inquire about, not
 a _reference_ to that variable.  Therefore you would not normally use a
 '$' or parentheses when writing it.  (You can, however, use a variable
 reference in the name if you want the name not to be a constant.)
 
    The result of this function is a string telling you how the variable
 VARIABLE was defined:
 
 'undefined'
 
      if VARIABLE was never defined.
 
 'default'
 
      if VARIABLE has a default definition, as is usual with 'CC' and so
      on.  Variables Used by Implicit Rules Implicit Variables.
      Note that if you have redefined a default variable, the 'origin'
      function will return the origin of the later definition.
 
 'environment'
 
      if VARIABLE was inherited from the environment provided to 'make'.
 
 'environment override'
 
      if VARIABLE was inherited from the environment provided to 'make',
      and is overriding a setting for VARIABLE in the makefile as a
      result of the '-e' option (Summary of Options Options
      Summary.).
 
 'file'
 
      if VARIABLE was defined in a makefile.
 
 'command line'
 
      if VARIABLE was defined on the command line.
 
 'override'
 
      if VARIABLE was defined with an 'override' directive in a makefile
      (The 'override' Directive Override Directive.).
 
 'automatic'
 
      if VARIABLE is an automatic variable defined for the execution of
      the recipe for each rule (Automatic Variables).
 
    This information is primarily useful (other than for your curiosity)
 to determine if you want to believe the value of a variable.  For
 example, suppose you have a makefile 'foo' that includes another
 makefile 'bar'.  You want a variable 'bletch' to be defined in 'bar' if
 you run the command 'make -f bar', even if the environment contains a
 definition of 'bletch'.  However, if 'foo' defined 'bletch' before
 including 'bar', you do not want to override that definition.  This
 could be done by using an 'override' directive in 'foo', giving that
 definition precedence over the later definition in 'bar'; unfortunately,
 the 'override' directive would also override any command line
 definitions.  So, 'bar' could include:
 
      ifdef bletch
      ifeq "$(origin bletch)" "environment"
      bletch = barf, gag, etc.
      endif
      endif
 
 If 'bletch' has been defined from the environment, this will redefine
 it.
 
    If you want to override a previous definition of 'bletch' if it came
 from the environment, even under '-e', you could instead write:
 
      ifneq "$(findstring environment,$(origin bletch))" ""
      bletch = barf, gag, etc.
      endif
 
    Here the redefinition takes place if '$(origin bletch)' returns
 either 'environment' or 'environment override'.  Functions for
 String Substitution and Analysis Text Functions.
 

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