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 13 Incompatibilities and Missing Features
 *****************************************
 
 The `make' programs in various other systems support a few features
 that are not implemented in GNU `make'.  The POSIX.2 standard (`IEEE
 Standard 1003.2-1992') which specifies `make' does not require any of
 these features.
 
    * A target of the form `FILE((ENTRY))' stands for a member of
      archive file FILE.  The member is chosen, not by name, but by
      being an object file which defines the linker symbol ENTRY.
 
      This feature was not put into GNU `make' because of the
      nonmodularity of putting knowledge into `make' of the internal
      format of archive file symbol tables.   Updating Archive
      Symbol Directories Archive Symbols.
 
    * Suffixes (used in suffix rules) that end with the character `~'
      have a special meaning to System V `make'; they refer to the SCCS
      file that corresponds to the file one would get without the `~'.
      For example, the suffix rule `.c~.o' would make the file `N.o' from
      the SCCS file `s.N.c'.  For complete coverage, a whole series of
      such suffix rules is required.   Old-Fashioned Suffix Rules
      Suffix Rules.
 
      In GNU `make', this entire series of cases is handled by two
      pattern rules for extraction from SCCS, in combination with the
      general feature of rule chaining.   Chains of Implicit Rules
      Chained Rules.
 
    * In System V and 4.3 BSD `make', files found by `VPATH' search
      ( Searching Directories for Prerequisites Directory Search.)
      have their names changed inside command strings.  We feel it is
      much cleaner to always use automatic variables and thus make this
      feature obsolete.
 
    * In some Unix `make's, the automatic variable `$*' appearing in the
      prerequisites of a rule has the amazingly strange "feature" of
      expanding to the full name of the _target of that rule_.  We cannot
      imagine what went on in the minds of Unix `make' developers to do
      this; it is utterly inconsistent with the normal definition of
      `$*'.  
 
    * In some Unix `make's, implicit rule search ( Using Implicit
      Rules Implicit Rules.) is apparently done for _all_ targets, not
      just those without commands.  This means you can do:
 
           foo.o:
                   cc -c foo.c
 
      and Unix `make' will intuit that `foo.o' depends on `foo.c'.
 
      We feel that such usage is broken.  The prerequisite properties of
      `make' are well-defined (for GNU `make', at least), and doing such
      a thing simply does not fit the model.
 
    * GNU `make' does not include any built-in implicit rules for
      compiling or preprocessing EFL programs.  If we hear of anyone who
      is using EFL, we will gladly add them.
 
    * It appears that in SVR4 `make', a suffix rule can be specified with
      no commands, and it is treated as if it had empty commands (
      Empty Commands).  For example:
 
           .c.a:
 
      will override the built-in `.c.a' suffix rule.
 
      We feel that it is cleaner for a rule without commands to always
      simply add to the prerequisite list for the target.  The above
      example can be easily rewritten to get the desired behavior in GNU
      `make':
 
           .c.a: ;
 
    * Some versions of `make' invoke the shell with the `-e' flag,
      except under `-k' ( Testing the Compilation of a Program
      Testing.).  The `-e' flag tells the shell to exit as soon as any
      program it runs returns a nonzero status.  We feel it is cleaner to
      write each shell command line to stand on its own and not require
      this special treatment.
 

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