getopt(3) contains the following sample code for parsing -<number>
options:

int length;
char *p;

while ((c = getopt(argc, argv, "0123456789")) != -1) {
        switch (c) {
        case '0': case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
                p = argv[optind - 1];
                if (p[0] == '-' && p[1] == ch && !p[2])
                        length = atoi(++p);
                else
                        length = atoi(argv[optind] + 1);
                break;
        }
}

Can anyone explain what the second branch of the "if" is for, and how to
trigger it?  For bonus points, explain how to add an extra option (say,
"-a") in such a way that an argument of "-a0" doesn't cause a segfault
there.

[ Background: I'm trying to clean up split(1), which contains similar
  code, and can be segfaulted by running "split --1". ]

-- 
Ben Harris                                                   <bjh21@netbsd.org>
Portmaster, NetBSD/acorn26           <URL:http://www.netbsd.org/Ports/acorn26/>