File: make.info,  Node: Values,  Next: Setting,  Prev: Advanced,  Up: Using Variables

6.4 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: Overriding.

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

   * You can specify a short-lived value with the 'let' function (*note
     Let Function::) or with the 'foreach' function (*note Foreach
     Function::).

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