( Rules

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 4 Writing Rules
 A "rule" appears in the makefile and says when and how to remake
 certain files, called the rule's "targets" (most often only one per
 rule).  It lists the other files that are the "prerequisites" of the
 target, and "commands" to use to create or update the target.
    The order of rules is not significant, except for determining the
 "default goal": the target for `make' to consider, if you do not
 otherwise specify one.  The default goal is the target of the first
 rule in the first makefile.  If the first rule has multiple targets,
 only the first target is taken as the default.  There are two
 exceptions: a target starting with a period is not a default unless it
 contains one or more slashes, `/', as well; and, a target that defines
 a pattern rule has no effect on the default goal.  ( Defining and
 Redefining Pattern Rules Pattern Rules.)
    Therefore, we usually write the makefile so that the first rule is
 the one for compiling the entire program or all the programs described
 by the makefile (often with a target called `all').   Arguments to
 Specify the Goals Goals.


* Rule Example                An example explained.
* Rule Syntax                 General syntax explained.
* Prerequisite Types          There are two types of prerequisites.
* Wildcards                   Using wildcard characters such as `*'.
* Directory Search            Searching other directories for source files.
* Phony Targets               Using a target that is not a real file's name.
* Force Targets               You can use a target without commands
                                   or prerequisites to mark other targets
                                   as phony.
* Empty Targets               When only the date matters and the
                                   files are empty.
* Special Targets             Targets with special built-in meanings.
* Multiple Targets            When to make use of several targets in a rule.
* Multiple Rules              How to use several rules with the same target.
* Static Pattern              Static pattern rules apply to multiple targets
                                   and can vary the prerequisites according to
                                   the target name.
* Double-Colon                How to use a special kind of rule to allow
                                   several independent rules for one target.
* Automatic Prerequisites     How to automatically generate rules giving
                                   prerequisites from source files themselves.
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