What does "%if 0%{?..." mean

[Jos Vos]

On Sat, Jan 17, 2009 at 02:09:31PM -0800, Jonathan Ryshpan wrote:

> I have a spec file with this text.
>         %if 0%{?build_jack_svn}
>         %define jack_revision 3190
>         %define jack_version 0.116.1
>         %define jack_svndate 20081206.171018
>         %else
>         %define jack_version 0.116.1
>         %endif
> 
> What does all this do?  I can't find the form "%if 0%{?mac}" defined
> anywhere.  I assume it means the macro mac exists and has the value 0 
> -- is this correct?

No.

The "0%{?build_jack_svn}" expands to "0X" where "X" is the value of
the %{build_jack_svn} macro if this macro is defined, or it expands
to "0" if the %{build_jack_svn} macro is not defined.

-- 
--    Jos Vos <jos at xos.nl>
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