%% Manoj Srivastava <[EMAIL PROTECTED]> writes:
ms> In some cases, GNU make ignores some double-colon rules when dry-run.
ms> Assumed this Makefile is given
ms> install.man:: foo.1
ms> @echo install foo.1
ms> install.man:: foo.2
ms> @echo install foo.2
ms> install.man::
ms> @echo install done
ms> I've got the following results
ms> % make -n install.man
ms> echo install foo.1
ms> echo install done
ms> I expect "echo install foo.2", but make dry-run shows not to
ms> run "install foo.2".
ms> However, if I run make actually
ms> % make install.man
ms> install foo.1
ms> install foo.2
ms> install done
ms> "install foo.2" is executed. Is this an intentional behavior or a
ms> bug of GNU make?
It is intentional behavior. When GNU make runs with -n it must assume
that your command script does what you say it will do: since it doesn't
run the script itself it can't know what the script _really_ does.
For a rule like this:
install.man:: foo.1
<some script>
GNU make _must_ assume that <some script> updates the target
"install.man"... how can it know that it really doesn't?
So, when you run with -n it assumes that the target is now updated,
which automatically makes it newer than "foo.2", so the rule depending
on "foo.2" does not get run.
The last install.man rule is run because there is a special condition
for double-colon rules, that if they have no prerequisites the command
is run even if the target exists (see the section "Double-Colon Rules"
in the GNU make manual).
However, double-colon rules that _DO_ have prerequisites are only
invoked if the prerequisites are newer than the target, just as with
normal rules.
You can see the behavior "make -n" is emulating without using -n if you
have your scripts actually create the target your makefile says it will:
install.man:: foo.1
@echo install foo.1
touch $@
install.man:: foo.2
@echo install foo.2
touch $@
install.man::
@echo install done
touch $@
$ make -n
install foo.1
install done
$ make
install foo.1
install done
ms> Note that pmake run as I expected
ms> % pmake -n install.man
ms> echo install foo.1
ms> echo install foo.2
ms> echo install done
Most likely pmake behaves differently; it may always run all
double-colon scripts, even if there's a satisfied prerequisite
relationship.
Try the above makefile with the touch lines in it: does it run all three
rules even though the touch lines exist?
--
-------------------------------------------------------------------------------
Paul D. Smith <[EMAIL PROTECTED]> Find some GNU make tips at:
http://www.gnu.org http://make.paulandlesley.org
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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