(I'm reading the manual for version 3.79)
At the end of Node: Multiple Rules, I think it'd be useful to have a
reference to Node: Double-Colon, since double-colon rules are another way to
have multiple rules all with the same target.
Here's how I came across this:
I have a hierarchy of projects with a top-level makefile. A very few of the
lower-level Makefiles have targets named `check', which (as you'd expect)
run some self-tests. I wanted to be able to type `make check' at the top of
the hierarchy, and have all of the self-tests run, in the projects that
*had* self tests, and in the other projects, I wanted nothing to happen.
I first tried simply having the top-level `check' target invoke make
recursively on its children. But that caused errors ("no rule to make
target check") in the projects that had no `check' target.
I then read Node: Overriding Makefiles, and was considering implementing its
suggestion, when somebody suggested that I use double-colon rules instead.
Double-colon rules seemed like a cleaner way to do what I wanted, so I'm now
using them. (The top-level makefile has a double-colon rule with the target
`check', with no prerequisistes and no commands; the few lower-level
makefiles that have self-tests each have their own double-colon rule with
the target `check', but whose prerequisites are the binary that gets made in
that directory, and whose command invokes the self-tests; the lower-level
makefiles in projects that lack self-tests simply have no rule at all for
`check').
However, I wish the manual had suggested them in Node: Multiple Rules; had
it done so, I would have saved some time.
Thanks
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