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           #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


           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
           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.
           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
           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
           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.
                  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-
           flag   specifies how results are returned for a long option.   If  flag
           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.


           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
           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-


                  If this is set, then option processing stops as soon as a nonop-
                  tion argument is encountered.
                  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.


                  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.


           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
           gram  options:  -n, with no associated value; and -t val, which expects
           an associated value.
           #include <unistd.h>
           #include <stdlib.h>
           #include <stdio.h>
           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;
                   case 't':
                       nsecs = atoi(optarg);
                       tfnd = 1;
                   default: /* '?' */
                       fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",
               printf("flags=%d; tfnd=%d; optind=%d\n", flags, tfnd, optind);
               if (optind >= argc) {
                   fprintf(stderr, "Expected argument after options\n");
               printf("name argument = %s\n", argv[optind]);
               /* Other code omitted */
           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>
                       {"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)
                   switch (c) {
                   case 0:
                       printf("option %s", long_options[option_index].name);
                       if (optarg)
                           printf(" with arg %s", optarg);
                   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);
                   case 'a':
                       printf("option a\n");
                   case 'b':
                       printf("option b\n");
                   case 'c':
                       printf("option c with value '%s'\n", optarg);
                   case 'd':
                       printf("option d with value '%s'\n", optarg);
                   case '?':
                       printf("?? getopt returned character code 0%o ??\n", c);

    GNU 2010-11-01 GETOPT(3)


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