GETOPT(3) BSD 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
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 charac-
ters, optstring.
The option string optstring may contain the following elements: individu-
al 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 argu-
ment ``-x argument''. It does not matter to getopt() if a following argu-
ment 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 variable opterr and optind are both initialized to 1. In order to
use getopt() to evaluate multiple sets of arguments, or to evaluate a
single set of arguments multiple times, optind must be initialized to the
number of argv entries to be skipped in each evaluation.
The getopt() function returns an EOF when the argument list is exhausted,
or a non-recognized option is encountered. 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 error message `?'
to the stderr. Setting opterr to a zero will disable these error mes-
sages.
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: unable to read file %s.\n", optarg);
exit(1) ;
}
break;
case '?':
default:
usage();
}
argc -= optind;
argv += optind;
HISTORY
The getopt() function appeared 4.3BSD.
BUGS
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 an character in optstring, howev-
er 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 develop-
ment. It is provided for backward compatibility only. By default, a sin-
gle 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 op-
tion. This practice is wrong, and should not be used in any current de-
velopment. It is provided for backward compatibility only. The following
code fragment works fairly well.
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;
}
}
4.3 Berkeley Distribution March 26, 1993 2