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researchv10 Dan Cross

.TH GETOPT 3
.CT 2 data_man
.SH NAME
getopt \(mi get option letter from argv
.SH SYNOPSIS
.nf
.B int getopt (argc, argv, optstring)
.B int argc;
.B char **argv;
.B char *optstring;
.PP
.B extern char *optarg;
.B extern int optind;
.B extern int opterr;
.fi
.SH DESCRIPTION
.I Getopt
returns the next option letter in
.I argv
that matches a letter in
.IR optstring .
.I Optstring
is a string of recognized option letters;
if a letter is followed by a colon, the option
is expected to have an argument, which may or
may not be separated from it by white space.
.I Optarg
is set to point to the start of the option argument, if any.
.PP
.I Optind,
initially 1, holds the index in
.I argv
of the next argument to be processed.
When
.I opterr
is nonzero (the default state), errors cause
diagnostic messages.
.PP
Option letters appear in nonempty clusters preceded by 
.BR - .
The special option
.L --
may be used to mark the end of the options.
.SH EXAMPLES
This fragment processes arguments
for a command that can take option
.B a
and option
.BR f ,
which requires an argument.
.PP
.EX
.ta \w'12345678'u +\w'12345678'u
main (argc, argv) char **argv;
{
	int c, errflg = 0;
	extern int optind;
	extern char *optarg, *ifile;
	while((c = getopt(argc, argv, "af:")) != -1)
		switch (c){
		case 'a':  aflg=1; break;
		case 'f':  ifile = optarg; break;
		case '?':  errflg=1; break;
		}
	if(errflg){
		fprintf(stderr, "usage: . . . ");
		exit(2);
	}
	for( ; optind < argc; optind++){
		if(access(argv[optind], 4)){
			...
		}
	}
	...
}
.EE
.SH SEE ALSO
.IR getflags (3)
.SH DIAGNOSTICS
When all options have been processed,
\-1 is returned;
.I optind
refers to the first non-option argument.
.br
When 
.I getopt
encounters an option letter not included in
.I optstring
or finds an option argument missing, it prints a diagnostic on
.B stderr
under control of
.I opterr
and returns a question mark
.LR ? .

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