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.\" @(#)getopt.3 6.16 (Berkeley) 4/19/91
.Nd get option letter from argv
.Fn getopt "int argc" "char * const *argv" "const char *optstring"
if it has been specified in the string of accepted option characters,
may contain the following characters; letters and
letters followed by a colon to indicate an option argument
is to follow. It does not matter to
if a following argument has leading white space.
points to an option argument, if it is anticipated,
contains the index to the next
argument for a subsequent call
are both initialized to 1.
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
must be initialized to the number of argv entries to be skipped in each
when the argument list is exhausted, or a non-recognized
The interpretation of options in the argument list may be cancelled
(double dash) which causes
to signal the end of argument processing and return an
When all options have been processed (i.e., up to the first non-option
function encounters a character not found in the string
a missing option argument
to a zero will disable these error messages.
while ((ch = getopt(argc, argv, "bf:")) != EOF)
if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
"myname: unable to read file %s.\en", optarg);
Option arguments are allowed to begin with
reduces the amount of error checking possible.
may be specified as an character in
have an argument associated with it.
to be used with programs that expect
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
By default, a single dash causes
This is, we believe, compatible with System V.
It is also possible to handle digits as option letters.
to be used with programs that expect a number
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
The following code fragment works fairly well.
.Bd -literal -offset indent
while ((c = getopt(argc, argv, "0123456789")) != EOF)
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
if (p[0] == '-' && p[1] == ch && !p[2])
length = atoi(argv[optind] + 1);