.TH ARG 2
.SH NAME
ARG \(mi process option letters from argv
.SH SYNOPSIS
.nf
.B #include <libc.h>
.B ARGBEGIN {
.B } ARGEND
.B char *ARGF();
.B Rune ARGC();
.PP
.B extern char *argv0;
.fi
.SH DESCRIPTION
Command-line arguments to programs (see
.IR exec (2))
are conventionally arranged as a set of
.I options
\(em strings beginning with a
.B -
(minus sign)
\(em followed by plain arguments such as file names.
The
.B ARG
macros provide a convenient means for processing these options.
Option characters appear in nonempty clusters preceded by 
.BR - .
After options processing is terminated
(by an argument not starting with
.BR - ,
or by the argument
.B --
which is then skipped,
or by the argument
.BR - ),
execution resumes after the
.BR ARGEND .
.PP
The body of a
.B switch
statement should be put between
.B ARGBEGIN{
and
.BR }ARGEND ;
it is executed once for each option character
(the character itself may be referenced by
.BR ARGC() ).
If an option takes a string argument
(that is, the rest of the current option string or if that is empty,
the next argument),
it can be referenced by
.BR ARGF() .
After
.BR ARGEND ,
.I argv
points at a zero-terminated list of the remaining
.I argc
arguments.
.PP
.B ARGBEGIN
also sets up
.I argv0
to point at
.B argv[0]
(conventionally the name of the program).
.PP
.SH EXAMPLES
This program processes arguments
for a command that can take option
.B b
and option
.BR f ,
which requires an argument.
.PP
.EX
.ta \w'12345678'u +\w'12345678'u +\w'12345678'u +\w'12345678'u +\w'12345678'u
#include <u.h>
#include <libc.h>

main(int argc, char *argv[])
{
	char *f;

	print("%s", argv[0]);
	ARGBEGIN{
	case 'b':	print(" -b"); break;
	case 'f':	f = ARGF(); print(" -f(%s)", f?f:"no arg"); break;
	default:	print(" badflag('%c')", ARGC()); break;
	}ARGEND
	print(" %d args:", argc);
	while(*argv)
		print(" '%s'", *argv++);
	print("\en");
	exits(0);
}
.EE
When this program is run as
.EX
	prog -bffile1 -r -f file2 arg1 argn
.EE
it yields
.EX
	prog -b -f(file1) badflag('r') -f(file2) 2 args: 'arg1' 'argn'
.EE
.SH DIAGNOSTICS
.B ARGF()
returns 0 on error.