Re: Pattern rules with % matching empty string?

[Philip Guenther]

On Thu, Apr 23, 2020 at 10:55 PM Glen Huang <address@hidden> wrote:

> I’m trying to do something like this:
>
> remote-bin-host%: bin
>         scp $< host$*:$<
>         touch $@
>
> to update files in remote hosts.
>
> It works for remote-bin-host1, remote-bin-host2, etc, but not
> remote-bin-host. It seems % won’t match empty string.
>

This is the documented behavior of pattern rules.  To quote the info pages:

10.5 Defining and Redefining Pattern Rules
==========================================

You define an implicit rule by writing a "pattern rule".  A pattern
rule looks like an ordinary rule, except that its target contains the
character `%' (exactly one of them).  The target is considered a
pattern for matching file names; the `%' can match any nonempty
substring, while other characters match only themselves.


Note: "nonempty"


I tried mixing static and pattern rule like this to make it work:
>
> remote-bin-host remote-bin-host%: bin
>         scp $< host$*:$<
>         touch $@
>
> And make complains such mixture is deprecated.
>

Right, because pattern rules mean with multiple targets have a magic
meaning, making what they mean when mixed with non-pattern targets
ambiguous.


Is there a clean way to write it without splitting the rule and duplicating
> most of the receipt?
>

Put the commands for the rule in a variable and have two rules, one pattern
and one not, that both use the variable as their entire recipe.


Philip Guenther