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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 Overriding Variables.
• You can specify a value in the makefile, either with an assignment (see Setting Variables) or with a verbatim definition (see Defining Multi-Line Variables).
• You can specify a short-lived value with the let function (see The let Function) or with the foreach function (see The foreach Function).
• Variables in the environment become make variables. See Variables from the Environment.
• Several automatic variables are given new values for each rule. Each of these has a single conventional use. See Automatic Variables.
• Several variables have constant initial values. See Variables Used by Implicit Rules.