Next: , Previous: Setting, Up: Using Variables  6.6 Appending
More Text to Variables  Often it is useful to add more text to
the value of a variable already defined. You do this with a line
containing ‘+=’, like this:       objects += another.o  This
takes the value of the variable objects, and adds the text
‘another.o’ to it (preceded by a single space). Thus:
objects = main.o foo.o bar.o utils.o      objects += another.o
sets objects to ‘main.o foo.o bar.o utils.o another.o’.  Using
‘+=’ is similar to:       objects = main.o foo.o bar.o utils.o
objects := $(objects) another.o   When the variable in question
has not been defined before, ‘+=’ acts just like normal ‘=’: it
defines a recursively-expanded variable. However, when there is
a previous definition, exactly what ‘+=’ does depends on what
flavor of variable you defined originally. See The Two Flavors
of Variables, for an explanation of the two flavors of
variables.  When you add to a variable's value with ‘+=’, make
acts essentially as if y