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The `override' Directive
If a variable has been set with a command argument (Note: Overriding
Variables.), then ordinary assignments in the makefile are
ignored. If you want to set the variable in the makefile even though
it was set with a command argument, you can use an `override'
directive, which is a line that looks like this:
override VARIABLE = VALUE
override VARIABLE := VALUE
To append more text to a variable defined on the command line, use:
override VARIABLE += MORE TEXT
Note: Appending More Text to Variables.
The `override' directive was not invented for escalation in the war
between makefiles and command arguments. It was invented so you can
alter and add to values that the user specifies with command arguments.
For example, suppose you always want the `-g' switch when you run the
C compiler, but you would like to allow the user to specify the other
switches with a command argument just as usual. You could use this
override CFLAGS += -g
You can also use `override' directives with `define' directives.
This is done as you might expect:
override define foo
Note: Defining Variables Verbatim.
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