GETOPT(3) BSD Programmer's Manual GETOPT(3)
getopt - get option character from command line argument list
#include <unistd.h>
extern char *optarg;
extern int opterr;
extern int optind;
extern int optopt;
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 charac-
ters, optstring.
The option string optstring may contain the following elements: individu-
al characters, characters followed by a colon, and characters followed by
two colons. A character followed by a single colon indicates that an ar-
gument is to follow the option on the command line. Two colons indicates
that the argument is optional - this is an extension not covered by PO-
SIX. 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 whitespace;
except in the case where the argument is optional, denoted with two
colons, no leading whitespace is permitted.
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 larger than 0 before a set of calls
to getopt() in order to skip over more or less argv entries. An optind
value of 0 is reserved for compatibility with GNU getopt().
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 ar-
gument 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.
The following code accepts the options -b and -f argument and adjusts
argc and argv after option argument processing has completed.
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)) == -1)
err(1, "%s", optarg);
break;
default:
usage();
/* NOTREACHED */
}
}
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 mes-
sage to stderr and returns '?'. Setting opterr to a zero will disable
these error messages. If optstring has a leading ':' then a missing op-
tion 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 speci-
fied by IEEE Std 1003.1 ("POSIX.1").
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 optind variable is set to 0, getopt() will behave as if the
optreset variable has been set. This is for compatibility with GNU
getopt(). New code should use optreset instead.
o If the first character of optstring is a plus sign ('+'), it will be
ignored. This is for compatibility with GNU getopt() where it is re-
quired to cancel argument processing at the first non-option (like
everyone else does by default, including POSIX).
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 op-
tion 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.
Historic BSD versions of getopt() set optopt to the last option character
processed. However, this conflicts with IEEE Std 1003.1 ("POSIX.1") which
stipulates that optopt be set to the last character that caused an error.
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 and can handle mixed number and letter arguments.
int aflag = 0, bflag = 0, ch, lastch = '\0';
int length = -1, newarg = 1, prevoptind = 1;
while ((ch = getopt(argc, argv, "0123456789ab")) != -1) {
switch (ch) {
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
if (newarg || !isdigit(lastch))
length = 0;
else if (length > INT_MAX / 10)
usage();
length = (length * 10) + (ch - '0');
break;
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
default:
usage();
}
lastch = ch;
newarg = optind != prevoptind;
prevoptind = optind;
}
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