getopt -- get option character from command line argument list
Standard C Library (libc, -lc)
#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);
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 variable 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, or
`?' if 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 -1. When all options have been processed (i.e., up to the first
non-option argument), getopt() returns -1.
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.
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.
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)
err(1, "%s", optarg);
break;
case '?':
default:
usage();
}
argc -= optind;
argv += optind;
The getopt() function appeared in 4.3BSD.
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 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. By default, a
single dash causes getopt() to return -1. 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
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 (but not all) cases.
int 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 = strtol(++p, &ep, 10);
else if (argv[optind] && argv[optind][1] == ch) {
length = strtol((p = argv[optind] + 1),
&ep, 10);
optind++;
optreset = 1;
} else
usage();
if (*ep != ' ')
errx(EX_USAGE, "illegal number -- %s", p);
break;
}
FreeBSD 5.2.1 April 27, 1995 FreeBSD 5.2.1 [ Back ] |
