plan9 man page for arg

ARG(2)								System Calls Manual							    ARG(2)

NAME
       ARGBEGIN, ARGEND, ARGC, ARGF, arginit, argopt - process option letters from argv

SYNOPSIS
       #include <u.h>
       #include <libc.h>

       ARGBEGIN {
       char *ARGF();
       Rune ARGC();
       } ARGEND

       extern char *argv0;

       /* Alef only */

       Arg  *arginit(int argc, byte **argv);

       Rune argopt(Arg *arg);

       byte *argf(Arg *arg);

DESCRIPTION
       These  macros  assume the names argc and argv are in scope; see exec(2).  ARGBEGIN and ARGEND surround code for processing program options.
       The code should be the cases of a C switch on option characters; it is executed once for each option character.	Options end after an argu-
       ment --, before an argument -, or before an argument that doesn't begin with -.

       ARGC() returns the current option character.

       ARGF()  returns	the current option argument: a pointer to the rest of the option string if not empty, or the next argument in argv if any,
       or 0.  ARGF must be called just once for each option that takes an argument.

       After ARGBEGIN, argv0 is a copy of argv[0] (conventionally the name of the program).

       After ARGEND, argv points at a zero-terminated list of the remaining argc arguments.

   Alef
       The Alef argument processing routines are unrelated.  Instead, an aggr called Arg is initialized by a call to arginit.  Successive calls to
       argopt  return  successive  option  characters,	or  zero at the end of the options.  After a call to argopt, argf will return any argument
       string associated with the option.

EXAMPLES
       This C program can take option b and option f, which requires an argument.

	      #include <u.h>
	      #include <libc.h>
	      void
	      main(int argc, char *argv[])
	      {
		      char *f;
		      print("%s", argv[0]);
		      ARGBEGIN {
		      case 'b':
			      print(" -b");
			      break;
		      case 'f':
			      print(" -f(%s)", (f=ARGF())? f: "no arg");
			      break;
		      default:
			      print(" badflag('%c')", ARGC());
		      } ARGEND
		      print(" %d args:", argc);
		      while(*argv)
			      print(" '%s'", *argv++);
		      print("
");
		      exits(0);
	      }

       Here is the output for the run prog -bffile1 -r -f file2 arg1 arg2

	      prog -b -f(file1) badflag('r') -f(file2) 2 args: 'arg1' 'arg2'

       This Alef program accepts options b and, with an attached file name, f.

	      #include <alef.h>
	      void
	      main(int argc, byte **argv)
	      {
		      int a, ac, bflag;
		      byte *file;
		      Arg *arg;

		      arg = arginit(argc, argv);
		      while(ac = argopt(arg)) switch(ac){
		      case 'b':
			      bflag = 1;
			      break;
		      case 'f':
			      file = argf(arg);
			      break;
		      }
		      for(a=0; a<arg->ac; a++)
			      print("argument %s
", arg->av[a]);
	      }

SOURCE
       /sys/include/libc.h

																	    ARG(2)