On 05/20/2009 03:23 AM, Panu Matilainen wrote:
Apologies for missing this when the recommendation of %global over
%define in Fedora guidelines was being discussed, but better late than
never...
https://fedoraproject.org/wiki/Packaging/Guidelines#.25global_preferred_over_.25define
says "The two macro defining statements behave the same when they are a
the top level of rpm's nesting level" but this is not correct:
The body of a %global macro is expanded at definition time, whereas the
body of a %define is expanded only when used. For many uses it doesn't
make any difference but identical they are not, even on top level - for
example see the attached example spec:
$ rpmbuild -bp macroex.spec 2>/dev/null|grep ^case
case1: first - second
case2: second - %{xxx}
Another example of this difference (in case of parametrized macros):
https://bugzilla.redhat.com/show_bug.cgi?id=495658
Hi Panu, How does this look? (Note, I haven't tested any of this code
yet as I'm running out the door. I wrote it just from how I understand
your message and bz#495658). Also note that I don't know what causes
rpm to clear the %defines that have been defined. If you can fill that
in that would be great. If it's too complex, we can figure out some way
to rephrase around it.
"""
%global and %define are both used to define macros inside rpm spec
files. We generally prefer using %global over %define.
%define created macros when they are used in nested macro expansions
(like in %{!?foo: ... } constructs theoretically only lasts until the
end brace (local scope), while %global definitions have global scope.
However, rpm currently doesn't clear the scope for the macros unless
[Accurate information needed here]. So %define'd macros often last
throughout a spec file. However, when they don't, it's often
non-obvious why the spec file is failing as the failure is caused by
something changing in another part of the spec file.
%global has another major difference from %define that can cause
problems when you first write the macro. %global is evaluated at the
time that it is written whereas %define is evaluated separately
everytime it occurs in a spec file. As an example, if you do the
following in a spec file::
<pre>
%build
%global foo FOO
%global bar %foo
%define baz %foo
echo %{bar} - %{baz}
%global foo FOOBAR
echo %{bar} - %{baz}
You get this:
FOO - FOO
FOO - FOOBAR
</pre>
One place this becomes apparent is parameterized macros:
<pre>
%build
%global print_arg echo "Hello %1"
%print_arg World
</pre>
because the %1 is evaluated when print_arg is defined, this prints
<code>Hello</code> rather than "Hello World".
Escaping the % fixes this usage:
<pre>
%global print_arg echo "Hello %%1"
</pre>
"""
-Toshio
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