GETOPT(3) UNIX Programmer's Manual GETOPT(3) NAME getopt - get option character from command line argument list SYNOPSIS #include <stdlib.h> extern char *optarg; extern int optind; extern int optopt; extern int opterr; extern int optreset; int getopt(argc, argv, optstring) int argc; char **argv; char *optstring; DESCRIPTION The getopt() function incrementally parses a command line argument list argv and returns the next known option charac- ter. 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 ele- ments: individual characters, and characters followed by a colon to indicate an option argument is to follow. 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 white space. On return from getopt(), optarg points to an option argu- ment, 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 variable 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 argu- ments, 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 an EOF when the argument list is exhausted, or a non-recognized option is encountered. Printed 11/26/99 January 12, 1996 1 GETOPT(3) UNIX Programmer's Manual GETOPT(3) 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 an EOF. When all options have been processed (i.e., up to the first non-option argument), getopt() returns EOF. DIAGNOSTICS If the getopt() function encounters a character not found in the string optarg or detects a missing option argument it writes an error message and returns `?' to the stderr. Set- ting 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 rea- sonable but reduces the amount of error checking possible. EXTENSIONS The optreset variable was added to make it possible to call the getopt() function multiple times. This is an extension to the IEEE Std1003.2 (``POSIX'') specification. EXAMPLE extern char *optarg; extern int optind; int bflag, ch, fd; bflag = 0; while ((ch = getopt(argc, argv, "bf:")) != EOF) 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; HISTORY The getopt() function appeared 4.3BSD. Printed 11/26/99 January 12, 1996 2 GETOPT(3) UNIX Programmer's Manual GETOPT(3) BUGS A single dash ``-'' may be specified as an character in opt- string , 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 pro- vided for backward compatibility only . By default, a single dash causes getopt() to return EOF. This is, we believe, compatible with System V. 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 pro- vided for backward compatibility only. The following code fragment works in most cases. int length; char *p; while ((c = getopt(argc, argv, "0123456789")) != EOF) 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; } } Printed 11/26/99 January 12, 1996 3