GETOPT(3) | Library Functions Manual | GETOPT(3) |
getopt
—
#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);
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. If an individual
character is followed by two colons, then the option argument is optional;
optarg is set to the rest of the current
argv word, or NULL
if there
were no more characters in the current word. This is a
NetBSD extension. 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.
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 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.
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.
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: %s\n", optarg, strerror(errno)); exit(1); } break; case '?': 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 multiple times. This is an
extension to the IEEE Std 1003.2
(“POSIX.2”) specification.
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>
.
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
(),
which assigns different meaning to an optstring that
begins with a ‘-’. By default, a single dash causes
getopt
() to return -1.
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 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; } }
June 5, 2014 | NetBSD 9.0 |