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. See section Updating Archive Symbol Directories.

• 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. See section Old-Fashioned 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. See section Chains of Implicit Rules.

• In System V make, the string `$$@' has the strange meaning that, in the prerequisites of a rule with multiple targets, it stands for the particular target that is being processed.

  This is not defined in GNU make because `$$' should always stand for an ordinary `$'.

  It is possible to get portions of this functionality through the use of static pattern rules (see section Static Pattern Rules). The System V make rule:

  $(targets): $$@.o lib.a

  can be replaced with the GNU make static pattern rule:

  $(targets): %: %.o lib.a

• In System V and 4.3 BSD make, files found by VPATH search (see section Searching Directories for Prerequisites) 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 makes, 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 makes, implicit rule search (see section Using 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 (see section 5.8 Using 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' (see section Testing the Compilation of a Program). 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.