Simply argument parsing

naki, 2026-07-15

I know that plan 9 has its own approach to parse argumets, but I've never really read those macros before

Now, when I've read them, I thought that having ARGEND is not really that good, and in fact this feels kind of redundant to me

So, I've made my own implementation. It consists of 2 macros:

• ARGS, which is an engine to traverse argv until the end or the double dash (--)
• ARG(ifnot), that fetches the next argument, and if noargument found then ifnot gets executed. I like to put errx() call there

Also, there's a variable param storing currently processed parameter and _arg being temporary storage for the ARG() macro

The code below is licensed under the public domain license, or isc license, as you wish:

/* these macros corrupt argc, argv, pointers 
 * stored at argv belonging to options */
char param, *_arg;
#define switchargs(argc, argv) for(++argv, --argc;\
	argv[0] && argv[0][0]=='-' && argv[0][1]\
	&& !(argv[0][1]=='-' && argv[0][2]=='\0' && argv++ && argc--);\
	++argv, --argc)\
	for(++argv[0]; argv[0][0];)\
	switch(param=argv[0]++[0])
#define getarg(argc, argv, ifnot) (argv[0][0]? 0:\
	argv[1]? ++argv, --argc:\
	(ifnot), _arg=argv[0], argv[0]="", _arg)

Also, that's the way how it's intended to be used:

int
main(int argc, char **argv)
{
	char *lopt;

	switchargs(argc, argv){
	break; case 'a': printf("flag a was triggered\n");
	break; case 'b': printf("b: %s\n", getarg(argc, argv, errx(1, "no argument for b")));
	break; case '-':
		lopt = getarg(argc, argv, 0);
		if (!strcmp(lopt, "long"))
			printf("long: %s\n", getarg(argc, argv, errx(1, "no argument for long")));
		else
			printf("some unknown long option was passed (%s)\n", lopt);
	break; default:  printf("something other was passed (%c)\n", param);
	}

	puts("args left:");
	for (; *argv; ++argv)
		puts(*argv);
}