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man:optarg

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 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
     option.
     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
     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 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
     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 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
     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 argu-
            ment.
     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.

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  charac-
     ter  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 parame-
     ter.

ENVIRONMENT

     POSIXLY_CORRECT
            If this is set, then option processing stops as soon as a nonop-
            tion 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).
     allbox;  lbw24  lb  lb  l  l l.  Interface Attribute Value T{ getopt(),
     getopt_long(),   getopt_long_only()    T}   Thread    safety  MT-Unsafe
     race:getopt env

CONFORMING TO

     getopt():
            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
            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 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>
     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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GNU 2017-09-15 GETOPT(3)

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