optarg(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.

   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
   0.

   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
   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.1-2001  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.

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

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   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/.

---

More Linux Commands

---