getopt(3p) — Linux manual page

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.1‐2017, 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         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.

       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         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.1‐2017, Section 12.2,
       Utility Syntax Guidelines, unistd.h(0p)

       The Shell and Utilities volume of POSIX.1‐2017, getopts(1p)

COPYRIGHT         top

       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(3P)

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