makefile tricks

make, GNUmake

VAR=ABC $(DEF) # lazy variable, expands at use (may differ at different usages)
VAR:=ABC $(DEF) # expands right away

# how to run executable and get its output into variable
A1:=$(shell $(EXE1))

# how to get content of file into variable
VAR:=`cat xyz` # does not expand right away, remains as 'cat xyz' until use
VAR:=$(shell cat xyz) # calls and expands right away into contents of the file xyz