Re: about :: sign and % sign problems

[Paul D. Smith]

%% Lin George <address@hidden> writes:

  >> foo:: bar ; echo Update due to bar

  >> foo:: baz ; echo Update due to baz
   
  lg> Good example! I think the effect is the same as the following
  lg> statements (I think either bar or baz is out of date, foo will be
  lg> remade.),
   
  lg> foo: bar baz ; echo something

But this doesn't do the same thing.

In my example above, "Update due to bar" will be printed if foo is out
of date with respect to bar, and "Update due to baz" will be printed if
foo is out of date with respect to baz.  If neither is out of date,
nothing is printed.  If both are out of date, both are printed.

In your example, "something" is printed if either or both of bar and baz
are out of date.

  lg> except that it is not easy to detect whether foo is remade by bar
  lg> or remade by baz. Is that correct?

No, it's easy to tell which prerequisites were out of date.  Look up the
$? variable in the GNU make manual.

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