6.4 How Variables Get Their Values

Variables can get values in several different ways:

• You can specify an overriding value when you run make. See section Overriding Variables.

• You can specify a value in the makefile, either with an assignment (see section Setting Variables) or with a verbatim definition (see section Defining Variables Verbatim).

• Variables in the environment become make variables. See section Variables from the Environment.

• Several automatic variables are given new values for each rule. Each of these has a single conventional use. See section Automatic Variables.

• Several variables have constant initial values. See section Variables Used by Implicit Rules.