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(make.info)Values

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How Variables Get Their Values
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   Variables can get values in several different ways:

   * You can specify an overriding value when you run `make'.  Note:
     Overriding Variables.

   * You can specify a value in the makefile, either with an assignment
     (Note: Setting Variables.) or with a verbatim definition
     (Note: Defining Variables Verbatim.).

   * Variables in the environment become `make' variables.  Note:
     Variables from the Environment.

   * Several "automatic" variables are given new values for each rule.
     Each of these has a single conventional use.  Note: Automatic
     Variables.

   * Several variables have constant initial values.  Note: Variables
     Used by Implicit Rules.