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 

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

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

       #include 

       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 || _POSIX_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 charac-
       ters of this element (aside from the initial '-')  are  option  charac-
       ters.   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 argu-
       ment 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 argu-
       ment, 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 exten-
       sions.)	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 non-options 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 non-option argument is encountered.  If the first
       character of optstring is '-', then  each  non-option  argv-element  is
       handled	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 non-zero (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  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 argu-
	      ment.

       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 char-
	      acter.)	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  charac-
       ter  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 parame-
       ter.

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

       __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
	      .  SUSv1 permitted the declaration to appear in	either
	         or  .   POSIX.1-2001  marked  the  use  of
	       for this purpose as  LEGACY.   POSIX.1-2001  does  not
	      allow the declaration to appear in .

       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  pro-
       gram  options:  -n, with no associated value; and -t val, which expects
       an associated value.

       #include 
       #include 
       #include 

       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\n",
			   argv[0]);
		   exit(EXIT_FAILURE);
	       }
	   }

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

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

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

	   /* Other code omitted */

	   exit(EXIT_SUCCESS);
       }

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

       #include      /* for printf */
       #include     /* for exit */
       #include 

       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("\n");
		   break;

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

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

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

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

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

	       case '?':
		   break;

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

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

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getsubopt(3), feature_test_macros(7)

COLOPHON
       This  page  is  part of release 3.22 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				  2008-08-29			     GETOPT(3)