1GETOPT(3P) POSIX Programmer's Manual GETOPT(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 getopt, optarg, opterr, optind, optopt — command option parsing
13
15 #include <unistd.h>
16 int getopt(int argc, char * const argv[], const char *optstring);
18 extern char *optarg;
19 extern int opterr, optind, optopt;
20
22 The getopt() function is a command-line parser that shall follow Util‐
23 ity Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in the Base Definitions
24 volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
25 The parameters argc and argv are the argument count and argument array
27 as passed to main() (see exec()). The argument optstring is a string
28 of recognized option characters; if a character is followed by a
29 <colon>, the option takes an argument. All option characters allowed by
30 Utility Syntax Guideline 3 are allowed in optstring. The implementa‐
31 tion may accept other characters as an extension.
32 The variable optind is the index of the next element of the argv[] vec‐
34 tor to be processed. It shall be initialized to 1 by the system, and
35 getopt() shall update it when it finishes with each element of argv[].
36 If the application sets optind to zero before calling getopt(), the
37 behavior is unspecified. When an element of argv[] contains multiple
38 option characters, it is unspecified how getopt() determines which
39 options have already been processed.
40 The getopt() function shall return the next option character (if one is
42 found) from argv that matches a character in optstring, if there is one
43 that matches. If the option takes an argument, getopt() shall set the
44 variable optarg to point to the option-argument as follows:
45 1. If the option was the last character in the string pointed to by an
47 element of argv, then optarg shall contain the next element of
48 argv, and optind shall be incremented by 2. If the resulting value
49 of optind is greater than argc, this indicates a missing option-
50 argument, and getopt() shall return an error indication.
51 2. Otherwise, optarg shall point to the string following the option
53 character in that element of argv, and optind shall be incremented
54 by 1.
55 If, when getopt() is called:
57 argv[optind] is a null pointer
60 *argv[optind] is not the character -
61 argv[optind] points to the string "-"
62 getopt() shall return -1 without changing optind. If:
64 argv[optind] points to the string "--"
67 getopt() shall return -1 after incrementing optind.
69 If getopt() encounters an option character that is not contained in
71 optstring, it shall return the <question-mark> ('?') character. If it
72 detects a missing option-argument, it shall return the <colon> charac‐
73 ter (':') if the first character of optstring was a <colon>, or a
74 <question-mark> character ('?') otherwise. In either case, getopt()
75 shall set the variable optopt to the option character that caused the
76 error. If the application has not set the variable opterr to 0 and the
77 first character of optstring is not a <colon>, getopt() shall also
78 print a diagnostic message to stderr in the format specified for the
79 getopts utility, unless the stderr stream has wide orientation, in
80 which case the behavior is undefined.
81 The getopt() function need not be thread-safe.
83
85 The getopt() function shall return the next option character specified
86 on the command line.
87 A <colon> (':') shall be returned if getopt() detects a missing argu‐
89 ment and the first character of optstring was a <colon> (':').
90 A <question-mark> ('?') shall be returned if getopt() encounters an
92 option character not in optstring or detects a missing argument and the
93 first character of optstring was not a <colon> (':').
94 Otherwise, getopt() shall return -1 when all command line options are
96 parsed.
97
99 If the application has not set the variable opterr to 0, the first
100 character of optstring is not a <colon>, and a write error occurs while
101 getopt() is printing a diagnostic message to stderr, then the error
102 indicator for stderr shall be set; but getopt() shall still succeed and
103 the value of errno after getopt() is unspecified.
104 The following sections are informative.
106
108 Parsing Command Line Options
109 The following code fragment shows how you might process the arguments
110 for a utility that can take the mutually-exclusive options a and b and
111 the options f and o, both of which require arguments:
112 #include <stdio.h>
115 #include <stdlib.h>
116 #include <unistd.h>
117 int
119 main(int argc, char *argv[ ])
120 {
121 int c;
122 int bflg = 0, aflg = 0, errflg = 0;
123 char *ifile;
124 char *ofile;
125 . . .
126 while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
127 switch(c) {
128 case 'a':
129 if (bflg)
130 errflg++;
131 else
132 aflg++;
133 break;
134 case 'b':
135 if (aflg)
136 errflg++;
137 else
138 bflg++;
139 break;
140 case 'f':
141 ifile = optarg;
142 break;
143 case 'o':
144 ofile = optarg;
145 break;
146 case ':': /* -f or -o without operand */
147 fprintf(stderr,
148 "Option -%c requires an operand\n", optopt);
149 errflg++;
150 break;
151 case '?':
152 fprintf(stderr,
153 "Unrecognized option: '-%c'\n", optopt);
154 errflg++;
155 }
156 }
157 if (errflg) {
158 fprintf(stderr, "usage: . . . ");
159 exit(2);
160 }
161 for ( ; optind < argc; optind++) {
162 if (access(argv[optind], R_OK)) {
163 . . .
164 }
165 This code accepts any of the following as equivalent:
167 cmd -ao arg path path
170 cmd -a -o arg path path
171 cmd -o arg -a path path
172 cmd -a -o arg -- path path
173 cmd -a -oarg path path
174 cmd -aoarg path path
175 Selecting Options from the Command Line
177 The following example selects the type of database routines the user
178 wants to use based on the Options argument.
179 #include <unistd.h>
182 #include <string.h>
183 ...
184 const char *Options = "hdbtl";
185 ...
186 int dbtype, c;
187 char *st;
188 ...
189 dbtype = 0;
190 while ((c = getopt(argc, argv, Options)) != -1) {
191 if ((st = strchr(Options, c)) != NULL) {
192 dbtype = st - Options;
193 break;
194 }
195 }
196
198 The getopt() function is only required to support option characters
199 included in Utility Syntax Guideline 3. Many historical implementations
200 of getopt() support other characters as options. This is an allowed
201 extension, but applications that use extensions are not maximally por‐
202 table. Note that support for multi-byte option characters is only pos‐
203 sible when such characters can be represented as type int.
204 Applications which use wide-character output functions with stderr
206 should ensure that any calls to getopt() do not write to stderr, either
207 by setting opterr to 0 or by ensuring the first character of optstring
208 is always a <colon>.
209 While ferror(stderr) may be used to detect failures to write a diagnos‐
211 tic to stderr when getopt() returns '?', the value of errno is unspeci‐
212 fied in such a condition. Applications desiring more control over han‐
213 dling write failures should set opterr to 0 and independently perform
214 output to stderr, rather than relying on getopt() to do the output.
215
217 The optopt variable represents historical practice and allows the
218 application to obtain the identity of the invalid option.
219 The description has been written to make it clear that getopt(), like
221 the getopts utility, deals with option-arguments whether separated from
222 the option by <blank> characters or not. Note that the requirements on
223 getopt() and getopts are more stringent than the Utility Syntax Guide‐
224 lines.
225 The getopt() function shall return -1, rather than EOF, so that
227 <stdio.h> is not required.
228 The special significance of a <colon> as the first character of opt‐
230 string makes getopt() consistent with the getopts utility. It allows an
231 application to make a distinction between a missing argument and an
232 incorrect option letter without having to examine the option letter. It
233 is true that a missing argument can only be detected in one case, but
234 that is a case that has to be considered.
235
237 None.
238
240 exec
241 The Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syn‐
243 tax Guidelines, <unistd.h>
244 The Shell and Utilities volume of POSIX.1‐2017, getopts
246
248 Portions of this text are reprinted and reproduced in electronic form
249 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
250 table Operating System Interface (POSIX), The Open Group Base Specifi‐
251 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
252 Electrical and Electronics Engineers, Inc and The Open Group. In the
253 event of any discrepancy between this version and the original IEEE and
254 The Open Group Standard, the original IEEE and The Open Group Standard
255 is the referee document. The original Standard can be obtained online
256 at http://www.opengroup.org/unix/online.html .
257 Any typographical or formatting errors that appear in this page are
259 most likely to have been introduced during the conversion of the source
260 files to man page format. To report such errors, see https://www.ker‐
261 nel.org/doc/man-pages/reporting_bugs.html .
262IEEE/The Open Group 2017 GETOPT(3P)