NAME
getopt - get option letter from argv
SYNOPSIS
int getopt(argc, argv, optstring)
int argc;
char **argv;
char *optstring;
extern char *optarg;
extern int optind;
DESCRIPTION
Getopt returns the next option letter in argv that matches a
letter in optstring. Optstring is a string of recognized
option letters; if a letter is followed by a colon, the
option is expected to have an argument that may or may not
be separated from it by white space. Optarg is set to point
to the start of the option argument on return from getopt.
Getopt places in optind the argv index of the next argument
to be processed. Because optind is external, it is normally
initialized to zero automatically before the first call to
getopt.
When all options have been processed (i.e., up to the first
non-option argument), getopt returns EOF. The special
option -- may be used to delimit the end of the options; EOF
will be returned, and -- will be skipped.
DIAGNOSTICS
Getopt prints an error message on stderr and returns a ques-
tion mark (?) when it encounters an option letter not
included in optstring.
EXAMPLE
The following code fragment shows how one might process the
arguments for a command that can take the mutually exclusive
options a and b, and the options f and o, both of which
require arguments:
main(argc, argv)
int argc;
char **argv;
{
int c;
extern int optind;
extern char *optarg;
.
.
.
while ((c = getopt(argc, argv, "abf:o:")) != EOF)
switch (c) {
case `a':
if (bflg)
errflg++;
else
aflg++;
break;
case `b':
if (aflg)
errflg++;
else
bproc();
break;
case `f':
ifile = optarg;
break;
case `o':
ofile = optarg;
break;
case `?':
default:
errflg++;
break;
}
if (errflg) {
fprintf(stderr, "Usage: ...");
exit(2);
}
for (; optind < argc; optind++) {
.
.
.
}
.
.
.
}
HISTORY
Written by Henry Spencer, working from a Bell Labs manual
page. Modified by Keith Bostic to behave more like the Sys-
tem V version.
BUGS
It is not obvious how `-' standing alone should be treated;
this version treats it as a non-option argument, which is
not always right.
Option arguments are allowed to begin with `-'; this is rea-
sonable but reduces the amount of error checking possible.
Getopt is quite flexible but the obvious price must be paid:
there is much it could do that it doesn't, like checking
mutually exclusive options, checking type of option argu-
ments, etc.