getopt(3C)

NAME

getopt(), optarg, opterr, optind, optopt — get option letter from argument vector

SYNOPSIS

#include <unistd.h>

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

extern char *optarg;

extern int optind, opterr, optopt;

DESCRIPTION

getopt() returns the next option letter in argv (starting from argv[1]) that matches a letter in optstring. argc and argv are the argument count and argument array as passed to main(). optstring is a string of recognized option characters; if a character is followed by a colon, the option takes an argument which may or may not be separated from it by whitespace.

optind is the index of the next element of the argv[] vector to be processed. It is initialized to 1 by the system, and getopt() updates it when it finishes with each element of argv[].

getopt() returns the next option character from argv that matches a character in optstring, if there is one that matches. If the option takes an argument, getopt() sets the variable optarg to point to the option argument as follows:

If the option was the last character in the string pointed to by an element of argv, then optarg contains the next element of argv, and optind is incremented by 2. If the resulting value of optind is greater than or equal to argc, this indicates a missing option argument, and getopt() returns an error indication.
Otherwise, optarg points to the string following the option character in that element of argv, and optind is incremented by 1.

If, when getopt() is called, argv[optind] is NULL, or the string pointed to by argv[optind] either does not begin with the character - or consists only of the character -, getopt() returns -1 without changing optind. If argv[optind] points to the string --, getopt() returns -1 after incrementing optind.

If getopt() encounters an option character that is not contained in optstring, it returns the question-mark (?) character. If it detects a missing option argument, it returns the colon character (:) if the first character of optstring was a colon, or a question-mark character otherwise. In either case, getopt() sets the variable optopt to the option character that caused the error. If the application has not set the variable opterr to zero and the first character of optstring is not a colon, getopt() also prints a diagnostic message to standard error.

The special option -- can be used to delimit the end of the options; -1 is returned, and -- is skipped.

RETURN VALUE

getopt() returns the next option character specified on the command line. A colon (:) is returned if getopt() detects a missing argument and the first character of optstring was a colon (:).

A question-mark (?) is returned if getopt() encounters an option character not in optstring or detects a missing argument and the first character of optstring was not a colon (:).

Otherwise, getopt() returns -1 when all command line options have been parsed.

EXTERNAL INFLUENCES

Locale

The LC_CTYPE category determines the interpretation of option letters as single and/or multi-byte characters.

International Code Set Support

Single- and multibyte character code sets are supported.

ERRORS

getopt() fails under the following conditions:

[EILSEQ]: An invalid multibyte character sequence was encountered during option processing.

EXAMPLES

The following code fragment shows to process arguments for a command that can take the mutually exclusive options a and b, and the options f and o, both of which require arguments:

#include <stdio.h>
#include <unistd.h>
main (int argc, char *argv[])
{
    int c;
    int bflg, aflg, errflg;
    extern char *optarg;
    extern int optind, optopt;
    .
    .
    .
    while ((c = getopt(argc, argv, ":abf:o:")) != -1)
        switch (c) {
        case 'a':
            if (bflg)
                errflg++;
            else
                aflg++;
            break;
        case 'b':
            if (aflg)
                errflg++;
            else {
                bflg++;
                bproc( );
            }
            break;
        case 'f':
            ifile = optarg;
            break;
        case 'o':
            ofile = optarg;
            break;
        case ':':        /* -f or -o without arguments */
            fprintf(stderr, "Option -%c requires an argument\n",
                optopt);
            errflg++;
            break;
        case '?':
            fprintf(stderr, "Unrecognized option: - %c\n",
                optopt);
            errflg++;
        }
    if (errflg) {
        fprintf(stderr, "usage: . . . ");
        exit (2);
    }
    for ( ; optind < argc; optind++) {
        if (access(argv[optind], 4)) {
    .
    .
    .
}

WARNINGS

Options can be any ASCII characters except colon (:), question mark (?), or null (\0).

STANDARDS CONFORMANCE

getopt(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

optarg: AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

opterr: AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

optind: AES, SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

optopt: AES, SVID3, XPG4, POSIX.2