| GETOPT(3) | Library Functions Manual | GETOPT(3) | 
getopt —
#include <unistd.h>
extern char *optarg;
  
  extern int optind;
  
  extern int optopt;
  
  extern int opterr;
  
  extern int optreset;
int
  
  getopt(int
    argc, char * const
    argv[], const char
    *optstring);
getopt() function incrementally parses a command
  line argument list argv and returns the next
  known option character. An option character is
  known if it has been specified in the string of accepted
  option characters, optstring.
The option string optstring may contain the
    following elements: individual characters, and characters followed by a
    colon to indicate an option argument is to follow. If an individual
    character is followed by two colons, then the option argument is optional;
    optarg is set to the rest of the current
    argv word, or NULL if there
    were no more characters in the current word. This is a
    NetBSD extension. For example, an option string
    “x” recognizes an option
    “-x”, and an option string
    “x:” recognizes an option and argument
    “-x argument”.
    It does not matter to getopt() if a following
    argument has leading whitespace.
On return from getopt(),
    optarg points to an option argument, if it is
    anticipated, and the variable optind contains the
    index to the next argv argument for a subsequent call
    to getopt(). The variable
    optopt saves the last known option
    character returned by getopt().
The variables opterr and
    optind are both initialized to 1. The
    optind variable may be set to another value before a
    set of calls to getopt() in order to skip over more
    or less argv entries.
In order to use getopt() to evaluate
    multiple sets of arguments, or to evaluate a single set of arguments
    multiple times, the variable optreset must be set to 1
    before the second and each additional set of calls to
    getopt(), and the variable
    optind must be reinitialized.
The getopt() function returns -1 when the
    argument list is exhausted. The interpretation of options in the argument
    list may be cancelled by the option “--” (double dash) which
    causes getopt() to signal the end of argument
    processing and return -1. When all options have been processed (i.e., up to
    the first non-option argument), getopt() returns
  -1.
getopt() function returns the next known option
  character in optstring. If
  getopt() encounters a character not found in
  optstring or if it detects a missing option argument, it
  returns ‘?’ (question mark). If optstring
  has a leading ‘:’ then a missing option argument causes
  ‘:’ to be returned instead of ‘?’. In either case,
  the variable optopt is set to the character that caused
  the error. The getopt() function returns -1 when the
  argument list is exhausted.
extern char *optarg;
extern int optind;
int bflag, ch, fd;
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)) < 0) {
			(void)fprintf(stderr,
			    "myname: %s: %s\n", optarg, strerror(errno));
			exit(1);
		}
		break;
	case '?':
	default:
		usage();
	}
}
argc -= optind;
argv += optind;
getopt() function encounters a character not
  found in the string optstring or detects a missing
  option argument it writes an error message to stderr and
  returns ‘?’. Setting opterr to a zero will
  disable these error messages. If optstring has a leading
  ‘:’ then a missing option argument causes a ‘:’ to
  be returned in addition to suppressing any error messages.
Option arguments are allowed to begin with ‘-’; this is reasonable but reduces the amount of error checking possible.
getopt() function multiple times. This is an
  extension to the IEEE Std 1003.2
  (“POSIX.2”) specification.
getopt() function appeared in
  4.3BSD.
getopt() function was once specified to return
  EOF instead of -1. This was changed by
  IEEE Std 1003.2-1992 (“POSIX.2”) to
  decouple getopt() from
  <stdio.h>.
A single dash (‘-’) may be specified as a character
    in optstring, however it should
    never have an argument associated with it. This allows
    getopt() to be used with programs that expect
    ‘-’ as an option flag. This practice is wrong, and should not
    be used in any current development. It is provided for backward
    compatibility only. Care should be taken not to use
    ‘-’ as the first character in optstring
    to avoid a semantic conflict with GNU getopt(),
    which assigns different meaning to an optstring that
    begins with a ‘-’. By default, a single dash causes
    getopt() to return -1.
It is also possible to handle digits as option letters. This
    allows getopt() to be used with programs that expect
    a number (“-3”) as an option. This
    practice is wrong, and should not be used in any current development. It is
    provided for backward compatibility only. The following
    code fragment works in most cases.
int ch;
long length;
char *p;
while ((ch = getopt(argc, argv, "0123456789")) != -1) {
	switch (ch) {
	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 = ch - '0';
		else
			length = strtol(argv[optind] + 1, NULL, 10);
		break;
	}
}
| June 5, 2014 | NetBSD 10.0 |