src/retval/retval.c

#include <ctype.h> /* isdigit(3) */
#include <sysexits.h> /* EX_USAGE */
#include <unistd.h> /* write(2) */
#include "libio.h" /* fdprint(3), parse_uint(3) */

static char *program_name = "retval";

int main(int argc, char *argv[]){
	unsigned int s;

	if(argc < 2){
usage:		write(2, "Usage: ", 7);
		fdprint(2, argv[0] == NULL ? program_name : argv[0]);
		write(2, " [status]\n", 10);
		return EX_USAGE;
	}

	for(s = 0; argv[1][s] != '\0'; ++s)
		if(!isdigit(argv[1][s]))
			goto usage;

	s = parse_uint(argv[1]);

	return s;
}