Variables A variable is a name defined in a makefile to represent a string of text, called the variable's value . These values are substituted by explicit request into targets, dependencies, commands, and other parts of the makefile. Variables can represent lists of file names, options to pass to compilers, programs to run, directories to look in for source files, directories to write output in, or anything else you can imagine.
Variable names are case-sensitive.
The names foo , FOO , and Foo all refer to different variables. A few variables have names that are a single punctuation character or just a few characters. These are the automatic variables , and they have particular specialized uses. See Automatic . Reference How to use the value of a variable.