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GETOPT(3P)                 POSIX Programmer's Manual                GETOPT(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       getopt, optarg, opterr, optind, optopt - command option parsing

SYNOPSIS
       #include <unistd.h>

       int getopt(int argc, char * const argv[], const char *optstring);
       extern char *optarg;
       extern int optind, opterr, optopt;


DESCRIPTION
       The  getopt()  function  is a command-line parser that shall follow Utility Syntax Guidelines 3, 4, 5, 6, 7, 9,
       and 10 in the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.

       The parameters argc and argv are the argument count and argument array as passed to main()  (see  exec()).  The
       argument  optstring  is  a  string  of recognized option characters; if a character is followed by a colon, the
       option takes an argument. All option characters allowed by Utility Syntax Guideline 3 are allowed in optstring.
       The implementation may accept other characters as an extension.

       The variable optind is the index of the next element of the argv[] vector to be processed. It shall be initial-
       ized to 1 by the system, and getopt() shall update it when it finishes with each element  of  argv[].  When  an
       element  of argv[] contains multiple option characters, it is unspecified how getopt() determines which options
       have already been processed.

       The getopt() function shall return the next option character (if one is found) from argv that matches a charac-
       ter  in  optstring, if there is one that matches. If the option takes an argument, getopt() shall set the vari-
       able optarg to point to the option-argument as follows:

        1. If the option was the last character in the string pointed to by an element of argv, then optarg shall con-
           tain  the  next  element of argv, and optind shall be incremented by 2. If the resulting value of optind is
           greater than argc, this indicates a missing option-argument, and getopt() shall return an error indication.


        2. Otherwise,  optarg  shall  point  to the string following the option character in that element of argv, and
           optind shall be incremented by 1.


       If, when getopt() is called:


              argv[optind]  is a null pointer*
              argv[optind]  is not the character -
              argv[optind]  points to the string "-"

       getopt() shall return -1 without changing optind. If:


              argv[optind]   points to the string "--"

       getopt() shall return -1 after incrementing optind.

       If getopt() encounters an option character that is not contained in optstring, it shall  return  the  question-
       mark ( '?' ) character. If it detects a missing option-argument, it shall return the colon character ( ':' ) if
       the first character of optstring was a colon, or a question-mark character ( '?' ) otherwise. In  either  case,
       getopt()  shall  set  the variable optopt to the option character that caused the error. If the application has
       not set the variable opterr to 0 and the first character of optstring is not a colon, getopt() shall also print
       a diagnostic message to stderr in the format specified for the getopts utility.

       The getopt() function need not be reentrant. A function that is not required to be reentrant is not required to
       be thread-safe.

RETURN VALUE
       The getopt() function shall return the next option character specified on the command line.

       A colon ( ':' ) shall be returned if getopt() detects a missing argument and the first character  of  optstring
       was a colon ( ':' ).

       A  question  mark  (  '?'  )  shall  be returned if getopt() encounters an option character not in optstring or
       detects a missing argument and the first character of optstring was not a colon ( ':' ).

       Otherwise, getopt() shall return -1 when all command line options are parsed.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   Parsing Command Line Options
       The following code fragment shows how you might process the arguments for a utility that can take the mutually-
       exclusive options a and b and the options f and o, both of which require arguments:


              #include <unistd.h>


              int
              main(int argc, char *argv[ ])
              {
                  int c;
                  int bflg, aflg, errflg;
                  char *ifile;
                  char *ofile;
                  extern char *optarg;
                  extern int optind, optopt;
                  . . .
                  while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
                      switch(c) {
                      case 'a':
                          if (bflg)
                              errflg++;
                          else
                              aflg++;
                          break;
                      case 'b':
                          if (aflg)
                              errflg++;
                          else {
                              bflg++;
                              bproc();
                          }
                          break;
                      case 'f':
                          ifile = optarg;
                          break;
                      case 'o':
                          ofile = optarg;
                          break;
                          case ':':       /* -f or -o without operand */
                                  fprintf(stderr,
                                          "Option -%c requires an operand\n", optopt);
                                  errflg++;
                                  break;
                      case '?':
                                  fprintf(stderr,
                                          "Unrecognized option: -%c\n", optopt);
                          errflg++;
                      }
                  }
                  if (errflg) {
                      fprintf(stderr, "usage: . . . ");
                      exit(2);
                  }
                  for ( ; optind < argc; optind++) {
                      if (access(argv[optind], R_OK)) {
                  . . .
              }

       This code accepts any of the following as equivalent:


              cmd -ao arg path path
              cmd -a -o arg path path
              cmd -o arg -a path path
              cmd -a -o arg -- path path
              cmd -a -oarg path path
              cmd -aoarg path path

   Checking Options and Arguments
       The  following  example  parses  a  set of command line options and prints messages to standard output for each
       option and argument that it encounters.


              #include <unistd.h>
              #include <stdio.h>
              ...
              int c;
              char *filename;
              extern char *optarg;
              extern int optind, optopt, opterr;
              ...
              while ((c = getopt(argc, argv, ":abf:")) != -1) {
                  switch(c) {
                  case 'a':
                      printf("a is set\n");
                      break;
                  case 'b':
                      printf("b is set\n");
                      break;
                  case 'f':
                      filename = optarg;
                      printf("filename is %s\n", filename);
                      break;
                  case ':':
                      printf("-%c without filename\n", optopt);
                      break;
                  case '?':
                      printf("unknown arg %c\n", optopt);
                      break;
                  }
              }

   Selecting Options from the Command Line
       The following example selects the type of database routines the user wants to use based on  the  Options  argu-
       ment.


              #include <unistd.h>
              #include <string.h>
              ...
              char *Options = "hdbtl";
              ...
              int dbtype, i;
              char c;
              char *st;
              ...
              dbtype = 0;
              while ((c = getopt(argc, argv, Options)) != -1) {
                  if ((st = strchr(Options, c)) != NULL) {
                      dbtype = st - Options;
                      break;
                  }
              }

APPLICATION USAGE
       The  getopt()  function  is  only required to support option characters included in Utility Syntax Guideline 3.
       Many historical implementations of getopt() support other characters as options. This is an allowed  extension,
       but  applications that use extensions are not maximally portable. Note that support for multi-byte option char-
       acters is only possible when such characters can be represented as type int.

RATIONALE
       The optopt variable represents historical practice and allows the application to obtain  the  identity  of  the
       invalid option.

       The  description  has been written to make it clear that getopt(), like the getopts utility, deals with option-
       arguments whether separated from the option by <blank>s or not. Note that  the  requirements  on  getopt()  and
       getopts are more stringent than the Utility Syntax Guidelines.

       The getopt() function shall return -1, rather than EOF, so that <stdio.h> is not required.

       The  special  significance  of  a  colon as the first character of optstring makes getopt() consistent with the
       getopts utility. It allows an application to make a distinction between a missing  argument  and  an  incorrect
       option  letter  without  having  to  examine  the option letter. It is true that a missing argument can only be
       detected in one case, but that is a case that has to be considered.

FUTURE DIRECTIONS
       None.

SEE ALSO
       exec(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>, the  Shell  and  Utilities  volume  of
       IEEE Std 1003.1-2001

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                           GETOPT(3P)