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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 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 it-
       self, 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 nonoptions are at the	end.  Two other	modes are also
       implemented.   If  the first character of optstring is '+' or the envi-
       ronment 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	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	 scan-
       ning 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 de-
       tected, 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  ac-
       cepts  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 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	nonop-
	      tion 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 al-
	      low 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
   getopt()
       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	<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\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);
       }

   getopt_long()
       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",     required_argument, 0,  0	},
		   {"append",  no_argument,	  0,  0	},
		   {"delete",  required_argument, 0,  0	},
		   {"verbose", no_argument,	  0,  0	},
		   {"create",  required_argument, 0, 'c'},
		   {"file",    required_argument, 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)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       http://www.kernel.org/doc/man-pages/.

GNU				  2014-05-09			     GETOPT(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON

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