getopt - get option character from command line argument
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#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, characters followed by a colon, and characters followed by
two colons. A character followed by a single colon indicates that an argument
is to follow the option on the command line. Two
colons indicates
that the argument is optional--this is an extension not covered by POSIXFor
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
whitespace.
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 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 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.
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.
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.
POSIXLY_CORRECT If set, a leading `-' in optstring is ignored.
extern char *optarg;
extern int optind;
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: %s0, optarg, strerror(errno));
exit(1);
}
break;
case '?':
default:
usage();
}
}
argc -= optind;
argv += optind;
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 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.
getopt(1), getopt_long(3), getsubopt(3)
The getopt() function implements a superset of the functionality specified
by IEEE Std 1003.1 (``POSIX'').
The following extensions are supported:
o The optreset variable was added to make it possible to
call the
getopt() function multiple times.
o If the first character of optstring is a plus sign
(`+'), it will be
ignored. This is for compatibility with GNU getopt().
o If the first character of optstring is a dash (`-'),
non-options
will be returned as arguments to the option character
`1'. This is
for compatibility with GNU getopt().
o 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. Care should be taken not to use `-' as the first
character in
optstring to avoid a semantic conflict with GNU
getopt() semantics
(see above). By default, a single dash causes getopt()
to return
-1.
Unlike GNU getopt(), OpenBSD does not permute the argument
vector to allow
non-options to be interspersed with options on the command line.
Programs requiring this behavior should use getopt_long(3)
instead. Because
of this (and unlike GNU), the OpenBSD getopt() supports optional
arguments separated by whitespace.
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>.
It is 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 cases.
int ch;
long length;
char *p;
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';
else
length = strtol(argv[optind] +
1, NULL, 10);
break;
}
}
OpenBSD 3.6 December 17, 2002
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