You can take a look at top comment in /usr/lib/rpm/macros Not sure what it means, however :)

Cheers

On Fri, Aug 31, 2012 at 11:33 PM, Björn Persson bjorn@xn--rombobjrn-67a.sewrote:

As maintainer of fedora-gnat-project-common I sometimes work on RPM macros for use in Ada packages. Every time I define a new macro I have trouble deciding whether its name should begin with an underscore or not. I know that there is some technical difference but I've never quite understood what practical difference it makes.

I've been trying to imitate macros with a similar function, so I defined _GNAT_project_dir with a leading underscore in analogy with _libdir and others. Macros containing command line flags for build tools I've defined without a leading underscore in analogy with optflags, but then there are _smp_mflags and the hardening macros which have the underscore, and __global_cflags and __global_ldflags even have two leading underscores.

Could someone explain what difference a leading underscore makes and give some guidance on when I should use it?

Is a double leading underscore functionally different from a single one, or is that just some kind of naming convention?

Björn Persson

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On 09/01/2012 12:33 AM, Björn Persson wrote:

As maintainer of fedora-gnat-project-common I sometimes work on RPM macros for use in Ada packages. Every time I define a new macro I have trouble deciding whether its name should begin with an underscore or not. I know that there is some technical difference but I've never quite understood what practical difference it makes.

I've been trying to imitate macros with a similar function, so I defined _GNAT_project_dir with a leading underscore in analogy with _libdir and others. Macros containing command line flags for build tools I've defined without a leading underscore in analogy with optflags, but then there are _smp_mflags and the hardening macros which have the underscore, and __global_cflags and __global_ldflags even have two leading underscores.

Could someone explain what difference a leading underscore makes and give some guidance on when I should use it?

Is a double leading underscore functionally different from a single one, or is that just some kind of naming convention?

A name is just a name, there's no functional difference. Once upon a time in a faraway galaxy there might have been, but that's nothing you need to worry about. These days its just a naming convention, albeit a rather blurry one.

The bottom line: as long as your macros are "namespaced" (such as your GNAT/_GNAT prefix) to limit the possibility of clashes with others, you're technically free to call them whatever you want. Following existing conventions is not a bad idea though.

- Panu -