On Monday 30 July 2007 01:00, David A. Greene wrote:
> Say I have a rule with an ignored-error action:
>
> some_file:
> -$(DO_SOMETHING) > $@
>
> Is there a way to test for existence of some_file from another rule?
>
> For example:
>
> some_rule : some_file
> $(if $(DO_EXISTENCE_TEST_HERE),$(DO_GOODSTUFF),$(DO_BADSTUFF))
>
> $(wildcard some_file) doesn't always seem to be reliable.
>
> Ideas?
All right, I believe I'm completely on the wrong path here because $(if) and
$(wildcard) aren't useful in rule actions since they get expanded when
the Makefile is parsed, not when the rule is invoked.
However, that doesn't explain behavior that I've seen where
$(if $(wildcard)) _does_ actually work in rule actions. Sometimes.
The case I'm looking at is something like this (much simplified):
define generate_rules
file1_dep:
Do something to create some_file_created_by_file1_dep
Some stuff to create file1_dep
file1: file1_dep
$$(if $$(wildcard some_file_created_by_file1_dep),$$(eval VAR := true), \
$$(eval VAR=false)
endef
This does actually seem to work. Sometimes. i.e. in some cases VAR is set
to "true." Other times VAR is set to "false." I don't know why sometimes and
not never. It seems to depend somewhat on where/when generate_rules is
invoked. Is there some odd interaction between macro expansion and variable
evaluation possible?
-Dave
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