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.\" @(#)getopt.3 8.4 (Berkeley) 4/19/94
.Nd get option character from command line argument list
.Fn getopt "int argc" "char * const *argv" "const char *optstring"
function incrementally parses a command line argument list
if it has been specified in the string of accepted option characters,
may contain the following elements: individual characters, and
characters followed by a colon to indicate an option argument
For example, an option string
recognizes an option and argument
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
option character returned by
are both initialized to 1.
variable may be set to another value before a set of calls to
in order to skip over more or less argv entries.
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
must be set to 1 before the second and each additional set of calls to
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 it writes an error message and returns
to a zero will disable these error messages.
then a missing option argument causes a
to be returned in addition to suppressing any error messages.
Option arguments are allowed to begin with
reduces the amount of error checking possible.
variable was added to make it possible to call the
This is an extension to the
while ((ch = getopt(argc, argv, "bf:")) != EOF)
if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
"myname: %s: %s\en", optarg, strerror(errno));
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 in most cases.
.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);