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



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

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 opterr, optind, 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 POSIX.1-2017, 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[].
       If the application sets optind to zero before calling getopt(), the
       behavior is unspecified. 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
       <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, unless the stderr stream has wide orientation, in
       which case the behavior is undefined.

       The getopt() function need not 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
       If the application has not set the variable opterr to 0, the first
       character of optstring is not a <colon>, and a write error occurs while
       getopt() is printing a diagnostic message to stderr, then the error
       indicator for stderr shall be set; but getopt() shall still succeed and
       the value of errno after getopt() is unspecified.

       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 <stdio.h>
           #include <stdlib.h>
           #include <unistd.h>

           int
           main(int argc, char *argv[ ])
           {
               int c;
               int bflg = 0, aflg = 0, errflg = 0;
               char *ifile;
               char *ofile;
               . . .
               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++;
                       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

   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>
           ...
           const char *Options = "hdbtl";
           ...
           int dbtype, 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 characters is only
       possible when such characters can be represented as type int.

       Applications which use wide-character output functions with stderr
       should ensure that any calls to getopt() do not write to stderr, either
       by setting opterr to 0 or by ensuring the first character of optstring
       is always a <colon>.

       While ferror(stderr) may be used to detect failures to write a
       diagnostic to stderr when getopt() returns ''??'', the value of errno is
       unspecified in such a condition. Applications desiring more control
       over handling write failures should set opterr to 0 and independently
       perform output to stderr, rather than relying on getopt() to do the
       output.

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> characters 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 POSIX.1-2017, Section 12.2, Utility
       Syntax Guidelines, <unistd.h>

       The Shell and Utilities volume of POSIX.1-2017, getopts

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            GETOPT(3)
