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)):

           _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE

       getopt_long(), getopt_long_only():

       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 option.

       optstring is a string containing the legitimate option characters.  A
       legitimate option character is any visible one byte ascii(7) character
       (for which isgraph(3) would return nonzero) that is not '-', ':', or ';'.
       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 scanning 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 '+' is not the first
       character of optstring, it is treated as a normal option.  If
       POSIXLY_CORRECT behaviour is required in this case optstring will contain
       two '+' symbols.  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.

       While processing the option list, getopt() can detect two kinds of
       errors: (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 command
       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
       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 <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 argument.

       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

       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 parameter.

              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.

       For an explanation of the terms used in this section, see attributes(7).

       │Interface          Attribute     Value                              │
       │getopt(),          │ Thread safety │ MT-Unsafe race:getopt env          │
       │getopt_long(),     │               │                                    │
       │getopt_long_only() │               │                                    │

              POSIX.1-2001, POSIX.1-2008, and POSIX.2, provided the environment
              variable POSIXLY_CORRECT is set.  Otherwise, the elements of argv
              aren't really const, because these functions permute them.
              Nevertheless, const is used 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.1-1996 marked the use of <stdio.h> for this
              purpose as LEGACY.  POSIX.1-2001 does not require 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.)

       Command-line arguments are parsed in strict order meaning that an option
       requiring an argument will consume the next argument, regardless of
       whether that argument is the correctly specified option argument or
       simply the next option (in the scenario the user mis-specifies the
       command line).  For example, if optstring is specified as "1n:" and the
       user specifies the command line arguments incorrectly as prog -n -1, the
       -n option will be given the optarg value "-1", and the -1 option will be
       considered to have not been 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; 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                                2021-08-27                          GETOPT(3)