GETOPT(3)						     Linux Programmer's Manual							 GETOPT(3)

NAME

       getopt, getopt_long, getopt_long_only, optarg, optind, opterr, optopt - Parse command-line options

SYNOPSIS

       #include <unistd.h>

       int getopt(int argc, char * const argv[],
		  const char *optstring);

       extern char *optarg;
       extern int optind, opterr, optopt;

       #include <getopt.h>

       int getopt_long(int argc, char * const argv[],
		  const char *optstring,
		  const struct option *longopts, int *longindex);

       int getopt_long_only(int argc, char * const argv[],
		  const char *optstring,
		  const struct option *longopts, int *longindex);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
       getopt_long(), getopt_long_only(): _GNU_SOURCE

DESCRIPTION

       The  getopt()  function	parses	the command-line arguments.  Its arguments argc and argv are the argument count and array as passed to the
       main() function on program invocation.  An element of argv that starts with '-' (and is not exactly "-" or "--") is an option element.  The
       characters  of  this element (aside from the initial '-') are option characters.  If getopt() is called repeatedly, it returns successively
       each of the option characters from each of the option elements.

       The variable optind is the index of the next element to be processed in argv.  The system initializes this value  to  1.   The  caller  can
       reset it to 1 to restart scanning of the same argv, or when scanning a new argument vector.

       If getopt() finds another option character, it returns that character, updating the external variable optind and a static variable nextchar
       so that the next call to getopt() can resume the scan with the following option character or argv-element.

       If there are no more option characters, getopt() returns -1.  Then optind is the index in argv of the first argv-element  that  is  not	an
       option.

       optstring  is  a  string  containing  the legitimate option characters.	If such a character is followed by a colon, the option requires an
       argument, so getopt() places a pointer to the following text in the same argv-element, or  the  text  of  the  following  argv-element,	in
       optarg.	 Two  colons  mean  an	option	takes an optional arg; if there is text in the current argv-element (i.e., in the same word as the
       option name itself, for example, "-oarg"), then it is returned in optarg, otherwise optarg is set to zero.  This is a  GNU  extension.	If
       optstring  contains  W followed by a semicolon, then -W foo is treated as the long option --foo.  (The -W option is reserved by POSIX.2 for
       implementation extensions.)  This behavior is a GNU extension, not available with libraries before glibc 2.

       By default, getopt() permutes the contents of argv as it scans, so that eventually all the nonoptions are at the end.  Two other modes  are
       also  implemented.   If	the first character of optstring is '+' or the environment variable POSIXLY_CORRECT is set, then option processing
       stops as soon as a nonoption argument is encountered.  If the first character of optstring is '-', then each nonoption argv-element is han-
       dled  as  if  it  were  the argument of an option with character code 1.  (This is used by programs that were written to expect options and
       other argv-elements in any order and that care about the ordering of the two.)  The special argument "--" forces an end of  option-scanning
       regardless of the scanning mode.

       If  getopt() does not recognize an option character, it prints an error message to stderr, stores the character in optopt, and returns '?'.
       The calling program may prevent the error message by setting opterr to 0.

       If getopt() finds an option character in argv that was not included in optstring, or if it detects a missing option  argument,  it  returns
       '?'  and  sets  the  external  variable	optopt	to the actual option character.  If the first character (following any optional '+' or '-'
       described above) of optstring is a colon (':'), then getopt() returns ':' instead of '?' to indicate a  missing	option	argument.   If	an
       error  was  detected,  and  the	first  character  of  optstring  is not a colon, and the external variable opterr is nonzero (which is the
       default), getopt() prints an error message.

   getopt_long() and getopt_long_only()
       The getopt_long() function works like getopt() except that it also accepts long options, started with two dashes.  (If the program  accepts
       only  long  options,  then  optstring  should be specified as an empty string (""), not NULL.)  Long option names may be abbreviated if the
       abbreviation is unique or is an exact match for some defined option.  A long option may take a parameter, of the form --arg=param or  --arg
       param.

       longopts is a pointer to the first element of an array of struct option declared in <getopt.h> as

	   struct option {
	       const char *name;
	       int	   has_arg;
	       int	  *flag;
	       int	   val;
	   };

       The meanings of the different fields are:

       name   is the name of the long option.

       has_arg
	      is:  no_argument	(or  0)  if  the option does not take an argument; required_argument (or 1) if the option requires an argument; or
	      optional_argument (or 2) if the option takes an optional argument.

       flag   specifies how results are returned for a long option.  If flag is NULL, then getopt_long() returns val.  (For example,  the  calling
	      program  may  set  val to the equivalent short option character.)  Otherwise, getopt_long() returns 0, and flag points to a variable
	      which is set to val if the option is found, but left unchanged if the option is not found.

       val    is the value to return, or to load into the variable pointed to by flag.

       The last element of the array has to be filled with zeros.

       If longindex is not NULL, it points to a variable which is set to the index of the long option relative to longopts.

       getopt_long_only() is like getopt_long(), but '-' as well as "--" can indicate a long option.  If an option that starts with '-' (not "--")
       doesn't match a long option, but does match a short option, it is parsed as a short option instead.

RETURN VALUE

       If  an  option  was  successfully  found,  then	getopt() returns the option character.	If all command-line options have been parsed, then
       getopt() returns -1.  If getopt() encounters an option character that was not in optstring, then '?' is returned.  If  getopt()	encounters
       an  option  with a missing argument, then the return value depends on the first character in optstring: if it is ':', then ':' is returned;
       otherwise '?' is returned.

       getopt_long() and getopt_long_only() also return the option character when a short option is recognized.  For a long  option,  they  return
       val  if flag is NULL, and 0 otherwise.  Error and -1 returns are the same as for getopt(), plus '?' for an ambiguous match or an extraneous
       parameter.

ENVIRONMENT

       POSIXLY_CORRECT
	      If this is set, then option processing stops as soon as a nonoption argument is encountered.

       _<PID>_GNU_nonoption_argv_flags_
	      This variable was used by bash(1) 2.0 to communicate to glibc which arguments are the results of wildcard expansion  and	so  should
	      not be considered as options.  This behavior was removed in bash(1) version 2.01, but the support remains in glibc.

CONFORMING TO

       getopt():
	      POSIX.2  and  POSIX.1-2001, provided the environment variable POSIXLY_CORRECT is set.  Otherwise, the elements of argv aren't really
	      const, because we permute them.  We pretend they're const in the prototype to be compatible with other systems.

	      The use of '+' and '-' in optstring is a GNU extension.

	      On some older implementations, getopt() was declared in <stdio.h>.  SUSv1 permitted the declaration to appear in	either	<unistd.h>
	      or  <stdio.h>.  POSIX.1-2001 marked the use of <stdio.h> for this purpose as LEGACY.  POSIX.1-2001 does not allow the declaration to
	      appear in <stdio.h>.

       getopt_long() and getopt_long_only():
	      These functions are GNU extensions.

NOTES

       A program that scans multiple argument vectors, or rescans the same vector more than once, and wants to make use of GNU extensions such	as
       '+'  and  '-'  at  the  start  of optstring, or changes the value of POSIXLY_CORRECT between scans, must reinitialize getopt() by resetting
       optind to 0, rather than the traditional value of 1.  (Resetting to 0 forces the invocation of  an  internal  initialization  routine  that
       rechecks POSIXLY_CORRECT and checks for GNU extensions in optstring.)

BUGS

       The  POSIX.2 specification of getopt() has a technical error described in POSIX.2 Interpretation 150.  The GNU implementation (and probably
       all other implementations) implements the correct behavior rather than that specified.

EXAMPLE

       The following trivial example program uses getopt() to handle two program options: -n, with no associated value; and -t val, which  expects
       an associated value.

       #include <unistd.h>
       #include <stdlib.h>
       #include <stdio.h>

       int
       main(int argc, char *argv[])
       {
	   int flags, opt;
	   int nsecs, tfnd;

	   nsecs = 0;
	   tfnd = 0;
	   flags = 0;
	   while ((opt = getopt(argc, argv, "nt:")) != -1) {
	       switch (opt) {
	       case 'n':
		   flags = 1;
		   break;
	       case 't':
		   nsecs = atoi(optarg);
		   tfnd = 1;
		   break;
	       default: /* '?' */
		   fprintf(stderr, "Usage: %s [-t nsecs] [-n] name
",
			   argv[0]);
		   exit(EXIT_FAILURE);
	       }
	   }

	   printf("flags=%d; tfnd=%d; optind=%d
", flags, tfnd, optind);

	   if (optind >= argc) {
	       fprintf(stderr, "Expected argument after options
");
	       exit(EXIT_FAILURE);
	   }

	   printf("name argument = %s
", argv[optind]);

	   /* Other code omitted */

	   exit(EXIT_SUCCESS);
       }

       The following example program illustrates the use of getopt_long() with most of its features.

       #include <stdio.h>     /* for printf */
       #include <stdlib.h>    /* for exit */
       #include <getopt.h>

       int
       main(int argc, char **argv)
       {
	   int c;
	   int digit_optind = 0;

	   while (1) {
	       int this_option_optind = optind ? optind : 1;
	       int option_index = 0;
	       static struct option long_options[] = {
		   {"add", 1, 0, 0},
		   {"append", 0, 0, 0},
		   {"delete", 1, 0, 0},
		   {"verbose", 0, 0, 0},
		   {"create", 1, 0, 'c'},
		   {"file", 1, 0, 0},
		   {0, 0, 0, 0}
	       };

	       c = getopt_long(argc, argv, "abc:d:012",
			long_options, &option_index);
	       if (c == -1)
		   break;

	       switch (c) {
	       case 0:
		   printf("option %s", long_options[option_index].name);
		   if (optarg)
		       printf(" with arg %s", optarg);
		   printf("
");
		   break;

	       case '0':
	       case '1':
	       case '2':
		   if (digit_optind != 0 && digit_optind != this_option_optind)
		     printf("digits occur in two different argv-elements.
");
		   digit_optind = this_option_optind;
		   printf("option %c
", c);
		   break;

	       case 'a':
		   printf("option a
");
		   break;

	       case 'b':
		   printf("option b
");
		   break;

	       case 'c':
		   printf("option c with value '%s'
", optarg);
		   break;

	       case 'd':
		   printf("option d with value '%s'
", optarg);
		   break;

	       case '?':
		   break;

	       default:
		   printf("?? getopt returned character code 0%o ??
", c);
	       }
	   }

	   if (optind < argc) {
	       printf("non-option ARGV-elements: ");
	       while (optind < argc)
		   printf("%s ", argv[optind++]);
	       printf("
");
	   }

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       getsubopt(3), feature_test_macros(7)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2010-02-03								 GETOPT(3)