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

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 initialized 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 character in optstring, if there is
       one that matches. If the option takes an argument, getopt() shall set the variable 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 contain 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 ques-
       tion-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
", optopt);
				  errflg++;
				  break;
		      case '?':
				  fprintf(stderr,
					  "Unrecognized option: -%c
", 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
");
		      break;
		  case 'b':
		      printf("b is set
");
		      break;
		  case 'f':
		      filename = optarg;
		      printf("filename is %s
", filename);
		      break;
		  case ':':
		      printf("-%c without filename
", optopt);
		      break;
		  case '?':
		      printf("unknown arg %c
", 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 argument.

	      #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  por-
       table. Note that support for multi-byte option characters 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  Guide-
       lines.

       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, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications 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 Standard, 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(P)