PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

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

NAME         top

       getopt, optarg, opterr, optind, optopt — command option parsing

SYNOPSIS         top

       #include <unistd.h>

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

DESCRIPTION         top

       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.1‐2008, 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.

       The getopt() function need not be thread-safe.

RETURN VALUE         top

       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         top

       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         top

   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         top

       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.

       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         top

       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         top

       None.

SEE ALSO         top

       exec(1p)

       The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility
       Syntax Guidelines, unistd.h(0p)

       The Shell and Utilities volume of POSIX.1‐2008, getopts(1p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                          GETOPT(3P)

Pages that refer to this page: stdio.h(0p)unistd.h(0p)getopts(1p)getsubopt(3p)optarg(3p)