( Makefile Contents

Info Catalog ( Makefiles ( Makefiles ( Makefile Names
 3.1 What Makefiles Contain
 Makefiles contain five kinds of things: "explicit rules", "implicit
 rules", "variable definitions", "directives", and "comments".  Rules,
 variables, and directives are described at length in later chapters.
    * An "explicit rule" says when and how to remake one or more files,
      called the rule's "targets".  It lists the other files that the
      targets depend on, called the "prerequisites" of the target, and
      may also give commands to use to create or update the targets.
       Writing Rules Rules.
    * An "implicit rule" says when and how to remake a class of files
      based on their names.  It describes how a target may depend on a
      file with a name similar to the target and gives commands to
      create or update such a target.   Using Implicit Rules
      Implicit Rules.
    * A "variable definition" is a line that specifies a text string
      value for a variable that can be substituted into the text later.
      The simple makefile example shows a variable definition for
      `objects' as a list of all object files ( Variables Make
      Makefiles Simpler Variables Simplify.).
    * A "directive" is a command for `make' to do something special while
      reading the makefile.  These include:
         * Reading another makefile ( Including Other Makefiles
         * Deciding (based on the values of variables) whether to use or
           ignore a part of the makefile ( Conditional Parts of
           Makefiles Conditionals.).
         * Defining a variable from a verbatim string containing
           multiple lines ( Defining Variables Verbatim Defining.).
    * `#' in a line of a makefile starts a "comment".  It and the rest
      of the line are ignored, except that a trailing backslash not
      escaped by another backslash will continue the comment across
      multiple lines.  A line containing just a comment (with perhaps
      spaces before it) is effectively blank, and is ignored.  If you
      want a literal `#', escape it with a backslash (e.g., `\#').
      Comments may appear on any line in the makefile, although they are
      treated specially in certain situations.
      Within a command script (if the line begins with a TAB character)
      the entire line is passed to the shell, just as with any other
      line that begins with a TAB.  The shell decides how to interpret
      the text: whether or not this is a comment is up to the shell.
      Within a `define' directive, comments are not ignored during the
      definition of the variable, but rather kept intact in the value of
      the variable.  When the variable is expanded they will either be
      treated as `make' comments or as command script text, depending on
      the context in which the variable is evaluated.
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