( Multiple Rules

Info Catalog ( Multiple Targets ( Rules ( Static Pattern
 4.11 Multiple Rules for One Target
 One file can be the target of several rules.  All the prerequisites
 mentioned in all the rules are merged into one list of prerequisites for
 the target.  If the target is older than any prerequisite from any rule,
 the commands are executed.
    There can only be one set of commands to be executed for a file.  If
 more than one rule gives commands for the same file, `make' uses the
 last set given and prints an error message.  (As a special case, if the
 file's name begins with a dot, no error message is printed.  This odd
 behavior is only for compatibility with other implementations of
 `make'... you should avoid using it).  Occasionally it is useful to
 have the same target invoke multiple commands which are defined in
 different parts of your makefile; you can use "double-colon rules"
 ( Double-Colon) for this.
    An extra rule with just prerequisites can be used to give a few extra
 prerequisites to many files at once.  For example, makefiles often have
 a variable, such as `objects', containing a list of all the compiler
 output files in the system being made.  An easy way to say that all of
 them must be recompiled if `config.h' changes is to write the following:
      objects = foo.o bar.o
      foo.o : defs.h
      bar.o : defs.h test.h
      $(objects) : config.h
    This could be inserted or taken out without changing the rules that
 really specify how to make the object files, making it a convenient
 form to use if you wish to add the additional prerequisite
    Another wrinkle is that the additional prerequisites could be
 specified with a variable that you set with a command argument to `make'
 ( Overriding Variables Overriding.).  For example,
      $(objects) : $(extradeps)
 means that the command `make extradeps=foo.h' will consider `foo.h' as
 a prerequisite of each object file, but plain `make' will not.
    If none of the explicit rules for a target has commands, then `make'
 searches for an applicable implicit rule to find some commands 
 Using Implicit Rules Implicit Rules.).
Info Catalog ( Multiple Targets ( Rules ( Static Pattern
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