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:
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 ‘$’ or parentheses when writing it. (You can, however, use a variable reference in the name if you want the name not to be a constant.)
The result of this function is a string telling you how the variable variable was defined:
CCand so on. See Variables Used by Implicit Rules. Note that if you have redefined a default variable, the
originfunction will return the origin of the later definition.
make, and is overriding a setting for variable in the makefile as a result of the ‘-e’ option (see Summary of Options).
overridedirective in a makefile (see The
This information is primarily useful (other than for your curiosity) to
determine if you want to believe the value of a variable. For example,
suppose you have a makefile foo that includes another makefile
bar. You want a variable
bletch to be defined in bar
if you run the command ‘make -f bar’, even if the environment contains
a definition of
bletch. However, if foo defined
bletch before including bar, you do not want to override that
definition. This could be done by using an
override directive in
foo, giving that definition precedence over the later definition in
bar; unfortunately, the
override directive would also
override any command line definitions. So, bar could
ifdef bletch ifeq "$(origin bletch)" "environment" bletch = barf, gag, etc. endif endif
bletch has been defined from the environment, this will redefine
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’. See Functions for String Substitution and Analysis.