Tweaking the program name for <err.h> functions

[Alejandro Colomar]

[TO += musl]

Hi!

On Fri, Mar 08, 2024 at 01:30:51AM +0100, Guillem Jover wrote:
> That is not portable because the BSDs do not support that variable.
> But all BSDs for which I've got a checkout (FreeBSD, NetBSD, OpenBSD,
> DragonflyBSD) support changing it via setprogname(), but that's not
> available in glibc (libbsd provides it though).
> 
> libbsd and cosmopolitan libc support setting it via setprogname() or
> program_invocation_short_name.
> 
> musl libc supports setting it via program_invocation_short_name.
> 
> uclibc might support __progname and/or program_invocation_short_name
> depending on how it has been configured, but it does not support
> setting the err(3) program name via those.

Hmmm.

	$ cat err.c 
	#define _GNU_SOURCE
	#include <bsd/stdlib.h>
	#include <err.h>
	#include <errno.h>
	#include <error.h>


	int
	main(void)
	{
		program_invocation_name = "foo";
		program_invocation_short_name = "bar";
		setprogname("baz");

		error(0, errno, "fmt string");
		err(1, "fmt2");
	}
	$ cc -Wall -Wextra err.c -lbsd
	$ ./a.out 
	foo: fmt string
	baz: fmt2: Success

This would already be portable enough for what I want, except that
libbsd isn't very welcome in some OSes as a core library.  I guess I'll
need libc support.

> 
> > Maybe it would be interesting to get the BSDs to support these pointers?
> 
> They already have a way to control the program name though. (And
> it seems to me that using functions instead of global variables is
> superior. :)

Indeed.  I didn't know about such function.  I'll reformulate my
original suggestion to this other one:

How about adding setprogname(3) (and getprogname(3)) to GNU and musl
libc?

> 
> Thanks,
> Guillem

Have a lovely night!
Alex

-- 
<https://www.alejandro-colomar.es/>
Looking for a remote C programming job at the moment.
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