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Node:<a name="Missing">Missing</a>,
Next:<a rel="next" accesskey="n" href="Makefile-Conventions.html#Makefile%20Conventions">Makefile Conventions</a>,
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<h2 class="chapter">Incompatibilities and Missing Features</h2>

   <p>The <code>make</code> programs in various other systems support a few features
that are not implemented in GNU <code>make</code>.  The POSIX.2 standard
(<cite>IEEE Standard 1003.2-1992</cite>) which specifies <code>make</code> does not
require any of these features.

     <ul>
<li>A target of the form <code></code><var>file</var><code>((</code><var>entry</var><code>))</code> stands for a member
of archive file <var>file</var>.  The member is chosen, not by name, but by
being an object file which defines the linker symbol <var>entry</var>.

     <p>This feature was not put into GNU <code>make</code> because of the
nonmodularity of putting knowledge into <code>make</code> of the internal
format of archive file symbol tables.
See <a href="Archive-Symbols.html#Archive%20Symbols">Updating Archive Symbol Directories</a>.

     </p><li>Suffixes (used in suffix rules) that end with the character <code>~</code>
have a special meaning to System V <code>make</code>;
they refer to the SCCS file that corresponds
to the file one would get without the <code>~</code>.  For example, the
suffix rule <code>.c~.o</code> would make the file <code></code><var>n</var><code>.o</code> from
the SCCS file <code>s.</code><var>n</var><code>.c</code>.  For complete coverage, a whole
series of such suffix rules is required.
See <a href="Suffix-Rules.html#Suffix%20Rules">Old-Fashioned Suffix Rules</a>.

     <p>In GNU <code>make</code>, 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 <a href="Chained-Rules.html#Chained%20Rules">Chains of Implicit Rules</a>.

     </p><li>In System V and 4.3 BSD <code>make</code>, files found by <code>VPATH</code> search
(see <a href="Directory-Search.html#Directory%20Search">Searching Directories for Prerequisites</a>) have their names changed inside command
strings.  We feel it is much cleaner to always use automatic variables
and thus make this feature obsolete.

     <li>In some Unix <code>make</code>s, the automatic variable <code>$*</code> appearing in
the prerequisites of a rule has the amazingly strange "feature" of
expanding to the full name of the <em>target of that rule</em>.  We cannot
imagine what went on in the minds of Unix <code>make</code> developers to do
this; it is utterly inconsistent with the normal definition of <code>$*</code>.

     <li>In some Unix <code>make</code>s, implicit rule search
(see <a href="Implicit-Rules.html#Implicit%20Rules">Using Implicit Rules</a>) is apparently done for
<em>all</em> targets, not just those without commands.  This means you can
do:

     <pre class="example">          foo.o:
                  cc -c foo.c
          </pre>

     <p>and Unix <code>make</code> will intuit that <code>foo.o</code> depends on
<code>foo.c</code>.

     <p>We feel that such usage is broken.  The prerequisite properties of
<code>make</code> are well-defined (for GNU <code>make</code>, at least),
and doing such a thing simply does not fit the model.

     </p><li>GNU <code>make</code> 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.

     <li>It appears that in SVR4 <code>make</code>, a suffix rule can be specified with
no commands, and it is treated as if it had empty commands
(see <a href="Empty-Commands.html#Empty%20Commands">Empty Commands</a>).  For example:

     <pre class="example">          .c.a:
          </pre>

     <p>will override the built-in <code>.c.a</code> suffix rule.

     <p>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 <code>make</code>:

     <pre class="example">          .c.a: ;
          </pre>

     </p><li>Some versions of <code>make</code> invoke the shell with the <code>-e</code> flag,
except under <code>-k</code> (see <a href="Testing.html#Testing">Testing the Compilation of a Program</a>).  The <code>-e</code> 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.
</ul>

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