GETOPT(3) BSD Library Functions Manual GETOPT(3)
NAME
getopt -- get option character from command line argument list
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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);
DESCRIPTION
The 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. 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 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 argu-ments arguments
ments 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.
RETURN VALUES
The 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.
EXAMPLES
#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;
DIAGNOSTICS
If the getopt() function encounters a character not found in the string optstring or detects a missing
option argument it writes an error message to the 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.
SEE ALSO
getopt(1), getopt_long(3), getsubopt(3)
STANDARDS
The optreset variable was added to make it possible to call the getopt() function multiple times. This
is an extension to the IEEE Std 1003.2 (``POSIX.2'') specification.
HISTORY
The getopt() function appeared in 4.3BSD.
BUGS
The 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 argu-ment argument
ment 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 cur-rent current
rent 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;
}
BSD April 27, 1995 BSD
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