NAME¶

SYNOPSIS¶

#include <unistd.h>

int getopt(int argc, char * const argv[],
           const char *optstring);

extern char *optarg;
extern int optind, opterr, optopt;

#include <getopt.h>

int getopt_long(int argc, char * const argv[],
           const char *optstring,
           const struct option *longopts, int *longindex);

int getopt_long_only(int argc, char * const argv[],
           const char *optstring,
           const struct option *longopts, int *longindex);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
getopt_long(), getopt_long_only(): _GNU_SOURCE

DESCRIPTION¶

The variable optind is the index of the next element to be processed in argv. The system initializes this value to 1. The caller can reset it to 1 to restart scanning of the same argv, or when scanning a new argument vector.

If getopt() finds another option character, it returns that character, updating the external variable optind and a static variable nextchar so that the next call to getopt() can resume the scan with the following option character or argv-element.

If there are no more option characters, getopt() returns -1. Then optind is the index in argv of the first argv-element that is not an option.

optstring is a string containing the legitimate option characters. If such a character is followed by a colon, the option requires an argument, so getopt() places a pointer to the following text in the same argv-element, or the text of the following argv-element, in optarg. Two colons mean an option takes an optional arg; if there is text in the current argv-element (i.e., in the same word as the option name itself, for example, "-oarg"), then it is returned in optarg, otherwise optarg is set to zero. This is a GNU extension. If optstring contains W followed by a semicolon, then -W foo is treated as the long option --foo. (The -W option is reserved by POSIX.2 for implementation extensions.) This behavior is a GNU extension, not available with libraries before glibc 2.

By default, getopt() permutes the contents of argv as it scans, so that eventually all the nonoptions are at the end. Two other modes are also implemented. If the first character of optstring is '+' or the environment variable POSIXLY_CORRECT is set, then option processing stops as soon as a nonoption argument is encountered. If the first character of optstring is '-', then each nonoption argv-element is handled as if it were the argument of an option with character code 1. (This is used by programs that were written to expect options and other argv-elements in any order and that care about the ordering of the two.) The special argument "--" forces an end of option-scanning regardless of the scanning mode.

While processing the option list, getopt() can detect two kinds of errors: (1) an option character that was not specified in optstring and (2) a missing option argument (i.e., an option at the end of the command line without an expected argument). Such errors are handled and reported as follows:

• By default, getopt() prints an error message on standard error, places the erroneous option character in optopt, and returns '?' as the function result.
• If the caller has set the global variable opterr to zero, then getopt() does not print an error message. The caller can determine that there was an error by testing whether the function return value is '?'. (By default, opterr has a nonzero value.)
• If the first character (following any optional '+' or '-' described above) of optstring is a colon (':'), then getopt() likewise does not print an error message. In addition, it returns ':' instead of '?' to indicate a missing option argument. This allows the caller to distinguish the two different types of errors.

struct option {
    const char *name;
    int         has_arg;
    int        *flag;
    int         val;
};

RETURN VALUE¶

getopt_long() and getopt_long_only() also return the option character when a short option is recognized. For a long option, they return val if flag is NULL, and 0 otherwise. Error and -1 returns are the same as for getopt(), plus '?' for an ambiguous match or an extraneous parameter.

ENVIRONMENT¶

POSIXLY_CORRECT

If this is set, then option processing stops as soon as a nonoption argument is encountered.

_<PID>_GNU_nonoption_argv_flags_

This variable was used by bash(1) 2.0 to communicate to glibc which arguments are the results of wildcard expansion and so should not be considered as options. This behavior was removed in bash(1) version 2.01, but the support remains in glibc.

ATTRIBUTES¶

CONFORMING TO¶

getopt():

POSIX.1-2001, POSIX.1-2008, and POSIX.2, provided the environment variable POSIXLY_CORRECT is set. Otherwise, the elements of argv aren't really const, because we permute them. We pretend they're const in the prototype to be compatible with other systems.

The use of '+' and '-' in optstring is a GNU extension.

On some older implementations, getopt() was declared in <stdio.h>. SUSv1 permitted the declaration to appear in either <unistd.h> or <stdio.h>. POSIX.1-1996 marked the use of <stdio.h> for this purpose as LEGACY. POSIX.1-2001 does not require the declaration to appear in <stdio.h>.

getopt_long() and getopt_long_only():

These functions are GNU extensions.

NOTES¶

EXAMPLE¶

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
int
main(int argc, char *argv[])
{
    int flags, opt;
    int nsecs, tfnd;
    nsecs = 0;
    tfnd = 0;
    flags = 0;
    while ((opt = getopt(argc, argv, "nt:")) != -1) {
        switch (opt) {
        case 'n':
            flags = 1;
            break;
        case 't':
            nsecs = atoi(optarg);
            tfnd = 1;
            break;
        default: /* '?' */
            fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",
                    argv[0]);
            exit(EXIT_FAILURE);
        }
    }
    printf("flags=%d; tfnd=%d; nsecs=%d; optind=%d\n",
            flags, tfnd, nsecs, optind);
    if (optind >= argc) {
        fprintf(stderr, "Expected argument after options\n");
        exit(EXIT_FAILURE);
    }
    printf("name argument = %s\n", argv[optind]);
    /* Other code omitted */
    exit(EXIT_SUCCESS);
}

SEE ALSO¶

COLOPHON¶