Conditional Macro Definitions

A conditional macro definition is a line of the form:

target-list := macro = value

which assigns the given value to the indicated macro while make is processing the target named target-list and its dependencies.

Each word in target-list can contain one % pattern; make must know which targets the definition applies to, so you cannot use a conditional macro definition to alter a target name.

The following lines give CFLAGS an appropriate value for processing each program variant.

debug := CFLAGS= -g 
profile := CFLAGS= -pg -O

Notice that when you use a reference to a conditional macro in the dependency list, that reference must be delayed (by prepending a second $). Otherwise, make expands the reference before the correct value has been assigned. When it encounters a (possibly) incorrect reference of this sort, make issues a warning.