NAME

getopt − get option letter from argument vector

SYNTAX

int getopt (argc, argv, optstring)
int argc;
char ∗∗argv;
char ∗optstring;

extern char ∗optarg;
extern int optind;

DESCRIPTION

The getopt subroutine returns the next option letter in argv that matches a letter in optstring. The 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.  The optarg is set to point to the start of the option argument on return from getopt.

The 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

The getopt prints an error message on stderr and returns a question 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;
bufsiza = 512;
break;
case ′?′:
errflg++;
}
if (errflg) {
fprintf (stderr, "usage: . . . ");
exit (2);
}
for ( ; optind < argc; optind++) {
if (access (argv[optind], 4)) {
.
.
.
}