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


       #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
       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

       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
       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

       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

       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.


       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


              If this is set, then  option  processing  stops  as  soon  as  a
              nonoption 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
       '+'  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.)


       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.


       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>

       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>

       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)

               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);

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



       getsubopt(3), feature_test_macros(7)


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