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

       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 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.
       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.

       While  processing the option list, getopt() can detect two kinds of er-
       rors: (1) an option character that was not specified in  optstring  and
       (2)  a  missing option argument (i.e., an option at the end of the com-
       mand line without an expected argument).  Such errors are  handled  and
       reported as follows:

       *  By  default,  getopt()  prints  an  error message on standard error,
          places the erroneous option character in optopt, and returns '?'  as
          the function result.

       *  If  the  caller  has  set  the  global variable opterr to zero, then
          getopt() does not print an error message.  The caller can  determine
          that there was an error by testing whether the function return value
          is '?'.  (By default, opterr has a nonzero value.)

       *  If the first character (following any optional '+' or '-'  described
          above)  of  optstring  is a colon (':'), then getopt() likewise does
          not print an error message.  In addition, it returns ':' instead  of
          '?'  to  indicate a missing option argument.  This allows the caller
          to distinguish the two different types of errors.

   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

       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
              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.

       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.

       For an  explanation  of  the  terms  used  in  this  section,  see  at-

       |Interface                | Attribute     | Value                     |
       |getopt(), getopt_long(), | Thread safety | MT-Unsafe race:getopt env |
       |getopt_long_only()       |               |                           |
              POSIX.1-2001, POSIX.1-2008, and POSIX.2, provided  the  environ-
              ment  variable  POSIXLY_CORRECT is set.  Otherwise, the elements
              of argv aren't really const, because we permute them.   We  pre-
              tend  they're const in the prototype to be compatible with other

              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.1-1996  marked  the  use   of
              <stdio.h> for this purpose as LEGACY.  POSIX.1-2001 does not re-
              quire 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 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>

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

               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++]);


       getopt(1), getsubopt(3)

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GNU                               2019-03-06                         GETOPT(3)
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