int bflag, ch, fd;
char *filename;

bflag = 0;
while ((ch = getopt(argc, argv, "bf:")) != -1) {
        switch (ch) {
                case 'b':
                        bflag = 1;
                        break;
                case 'f':
                        if ((fd = open(optarg, O_RDONLY, 0)) == -1)
                                err(1, "%s", optarg);
                        break;
                default:
                        usage();
                        /* NOTREACHED */
                }
        }

argc -= optind;
argv += optind;

if (argc > 0)
        filename = *argv;

/* and so on */

int ch, tabs = 0;
char *file = NULL;

while ((ch = getopt(argc, argc, "t:") != -1)
        switch (ch) {
        case 't':
                tabs = atoi(optarg);
                break;
        default:
                /* do nothing */
                break;
        }

argc -= optind;
argv += optind;

if (argc)
        file = *argv;

argc -= optind;
argv += optind;

#include <err.h>
#include /* ... */

extern  char *__progname;
FILE   *fd[3];        /* we expect 3 file names as arguments */
int     i;

/* getopt() part skipped, see above */
/* argv[0] -- first arg after getopt, argv[1] -- second arg after getopt, and so on */

if (argc != 3)
        errx(1, "usage: %s [args] first second third\n", __progname);

for (i = 0; i < 3; i++) {
        fd[i] = fopen(argv[i], "r");
        if (fd[i] == NULL)
                err(1, "something went terribly wrong, panic!");
}

for(int i=0;i<argc;++i){
int fd=open(argv[i],O_RDONLY);
if(fd<0)...//тут должна быть обработка ошибок...
//какие- то действия
close(fd);
}