| GETOPT(3) | Library Functions Manual | GETOPT(3) |
getopt —
#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);
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 POSIX. 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 argument processing
and return -1. When all options have been processed (i.e., up to the first
non-option argument), getopt() returns -1.
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.
-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();
}
}
argc -= optind;
argv += optind;
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() function implements a superset of the
functionality specified by IEEE Std 1003.1
(“POSIX.1”).
The following extensions are supported:
getopt() function multiple times.getopt() will behave as if the
optreset variable has been set. This is for
compatibility with GNU getopt(). New code should
use optreset instead.+’), it will be ignored. This is
for compatibility with GNU getopt().-’), non-options will be returned
as arguments to the option character
‘\1’. This is for compatibility with
GNU getopt().-’) 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.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.
getopt() function appeared in
4.3BSD.
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;
}
| January 4, 2016 | OpenBSD-current |