getopt

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
       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.  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.

       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.

       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
              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 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
       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.

ENVIRONMENT
       POSIXLY_CORRECT
              If this is set, then option processing stops as soon as a
              nonoption 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.

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

       ┌─────────────────────────┬───────────────┬───────────────────────────┐
       │Interface                Attribute     Value                     │
       ├─────────────────────────┼───────────────┼───────────────────────────┤
       │getopt(), getopt_long(), │ Thread safety │ MT-Unsafe race:getopt env │
       │getopt_long_only()       │               │                           │
       └─────────────────────────┴───────────────┴───────────────────────────┘
CONFORMING TO
       getopt():
              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 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.1-1996 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.

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.)

EXAMPLE
   getopt()
       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>

       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; nsecs=%d; optind=%d\n",
                   flags, tfnd, nsecs, 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
       getopt(1), getsubopt(3)

COLOPHON
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       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



GNU                               2019-03-06                         GETOPT(3)