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#include <unistd.h>extern char *optarg;
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
GNU
extension.
For example, an option string
amp;"x"
recognizes an option
"
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.
#include <unistd.h> 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;
Option arguments are allowed to begin with "-"; this is reasonable but reduces the amount of error checking possible.
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 ‘amp;-’ 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 ‘amp;-’. 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 ("amp;-amp;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, *ep;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'; ep = ""; } else if (argv[optind] argv[optind][1] == ch) { length = strtol((p = argv[optind] + 1), ep, 10); optind++; optreset = 1; } else usage(); if (*ep != '\0') errx(EX_USAGE, "illegal number -- %s", p); break; }
GETOPT (3) | June 5, 2014 |
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