Re: Defining a macro if it is NOT yet defined

[Jeff Johnson <jbj JBJ ORG>]

On Sun, Jan 27, 2002 at 07:05:05PM +0100, Alexander Skwar wrote:
> Hello.
> 
> I'm trying to hack together a SPEC file which should build identically
> on RedHat, Mandrake and Debian machines.  However, for the Mandrake
> build, I'd like to use some predefined macros (like %{update_menus}).
> Now, since I'd put %{update_menus} in the %post scriptlet, I want to
> have a "real" value there, and not just %{update_menus}, so that when a
> Mandrake user installs this package which is built on a Debian PC (where
> %update_menus is not defined) he'll still get the "real" value of
> %%update_menus.
> 
> What I'm looking for is a way to %define a macro, if it's not yet
> defined.  So something likd ifndef would be of good use here.
> 
> I'm currently trying something like:
> 
> %if %(echo %{?update_menus:1})
>         # do nothing - update_menus is already defined
> %else
>         %define update_menus some value here
> %endif
> 
> But that's not working :(  If %update_menus is already defined, the TRUE
> part is executed (which contains nothing but the comment).  However, if
> update_menus is not defined, I'll get this error message:
> 
> error: /home/askwar/rpm/SPECS/test.spec:41: parseExpressionBoolean returns -1
> 
> Is there a way to do this?
> 
> ---- a little later... ----
> 
> Ah!  I figured it out.  I now have:
> 
> %if !%(test "%{?update_menus:1}" = 1 && echo 1 || echo 0)
>         %define update_menus some value
> %endif
> 
> However, that's a little "clumsy".  Is there a shorter way to do this?

IIRC this is gonna break (at least with some versions of rpm, I forget).

Remember macros have absolutely no context, so %define is recognized in
comments, in strings, on the false branch of %if conditions, *everywhere*.

However, you can test for existence, and then, if not defined, set a default
thusly

	%{!?update_menus: %define update_menus some_value}

73 de Jeff

-- 
Jeff Johnson	ARS N3NPQ
jbj@jbj.org	(jbj@redhat.com)
Chapel Hill, NC