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 optind, opterr, optopt;
20
23 The getopt() function is a command-line parser that shall follow Util‐
24 ity Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in the Base Definitions
25 volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide‐
26 lines.
27 The parameters argc and argv are the argument count and argument array
29 as passed to main() (see exec()). The argument optstring is a string of
30 recognized option characters; if a character is followed by a colon,
31 the option takes an argument. All option characters allowed by Utility
32 Syntax Guideline 3 are allowed in optstring. The implementation may
33 accept other characters as an extension.
34 The variable optind is the index of the next element of the argv[] vec‐
36 tor to be processed. It shall be initialized to 1 by the system, and
37 getopt() shall update it when it finishes with each element of argv[].
38 When an element of argv[] contains multiple option characters, it is
39 unspecified how getopt() determines which options have already been
40 processed.
41 The getopt() function shall return the next option character (if one is
43 found) from argv that matches a character in optstring, if there is one
44 that matches. If the option takes an argument, getopt() shall set the
45 variable optarg to point to the option-argument as follows:
46 1. If the option was the last character in the string pointed to by an
48 element of argv, then optarg shall contain the next element of
49 argv, and optind shall be incremented by 2. If the resulting value
50 of optind is greater than argc, this indicates a missing option-
51 argument, and getopt() shall return an error indication.
52 2. Otherwise, optarg shall point to the string following the option
54 character in that element of argv, and optind shall be incremented
55 by 1.
56 If, when getopt() is called:
58 argv[optind] is a null pointer*
61 argv[optind] is not the character -
62 argv[optind] points to the string "-"
63 getopt() shall return -1 without changing optind. If:
65 argv[optind] points to the string "--"
68 getopt() shall return -1 after incrementing optind.
70 If getopt() encounters an option character that is not contained in
72 optstring, it shall return the question-mark ( '?' ) character. If it
73 detects a missing option-argument, it shall return the colon character
74 ( ':' ) if the first character of optstring was a colon, or a question-
75 mark character ( '?' ) otherwise. In either case, getopt() shall set
76 the variable optopt to the option character that caused the error. If
77 the application has not set the variable opterr to 0 and the first
78 character of optstring is not a colon, getopt() shall also print a
79 diagnostic message to stderr in the format specified for the getopts
80 utility.
81 The getopt() function need not be reentrant. A function that is not
83 required to be reentrant is not required to be thread-safe.
84
86 The getopt() function shall return the next option character specified
87 on the command line.
88 A colon ( ':' ) shall be returned if getopt() detects a missing argu‐
90 ment and the first character of optstring was a colon ( ':' ).
91 A question mark ( '?' ) shall be returned if getopt() encounters an
93 option character not in optstring or detects a missing argument and the
94 first character of optstring was not a colon ( ':' ).
95 Otherwise, getopt() shall return -1 when all command line options are
97 parsed.
98
100 No errors are defined.
101 The following sections are informative.
103
105 Parsing Command Line Options
106 The following code fragment shows how you might process the arguments
107 for a utility that can take the mutually-exclusive options a and b and
108 the options f and o, both of which require arguments:
109 #include <unistd.h>
112 int
115 main(int argc, char *argv[ ])
116 {
117 int c;
118 int bflg, aflg, errflg;
119 char *ifile;
120 char *ofile;
121 extern char *optarg;
122 extern int optind, optopt;
123 . . .
124 while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
125 switch(c) {
126 case 'a':
127 if (bflg)
128 errflg++;
129 else
130 aflg++;
131 break;
132 case 'b':
133 if (aflg)
134 errflg++;
135 else {
136 bflg++;
137 bproc();
138 }
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 Checking Options and Arguments
177 The following example parses a set of command line options and prints
178 messages to standard output for each option and argument that it
179 encounters.
180 #include <unistd.h>
183 #include <stdio.h>
184 ...
185 int c;
186 char *filename;
187 extern char *optarg;
188 extern int optind, optopt, opterr;
189 ...
190 while ((c = getopt(argc, argv, ":abf:")) != -1) {
191 switch(c) {
192 case 'a':
193 printf("a is set\n");
194 break;
195 case 'b':
196 printf("b is set\n");
197 break;
198 case 'f':
199 filename = optarg;
200 printf("filename is %s\n", filename);
201 break;
202 case ':':
203 printf("-%c without filename\n", optopt);
204 break;
205 case '?':
206 printf("unknown arg %c\n", optopt);
207 break;
208 }
209 }
210 Selecting Options from the Command Line
212 The following example selects the type of database routines the user
213 wants to use based on the Options argument.
214 #include <unistd.h>
217 #include <string.h>
218 ...
219 char *Options = "hdbtl";
220 ...
221 int dbtype, i;
222 char c;
223 char *st;
224 ...
225 dbtype = 0;
226 while ((c = getopt(argc, argv, Options)) != -1) {
227 if ((st = strchr(Options, c)) != NULL) {
228 dbtype = st - Options;
229 break;
230 }
231 }
232
234 The getopt() function is only required to support option characters
235 included in Utility Syntax Guideline 3. Many historical implementations
236 of getopt() support other characters as options. This is an allowed
237 extension, but applications that use extensions are not maximally por‐
238 table. Note that support for multi-byte option characters is only pos‐
239 sible when such characters can be represented as type int.
240
242 The optopt variable represents historical practice and allows the
243 application to obtain the identity of the invalid option.
244 The description has been written to make it clear that getopt(), like
246 the getopts utility, deals with option-arguments whether separated from
247 the option by <blank>s or not. Note that the requirements on getopt()
248 and getopts are more stringent than the Utility Syntax Guidelines.
249 The getopt() function shall return -1, rather than EOF, so that
251 <stdio.h> is not required.
252 The special significance of a colon as the first character of optstring
254 makes getopt() consistent with the getopts utility. It allows an appli‐
255 cation to make a distinction between a missing argument and an incor‐
256 rect option letter without having to examine the option letter. It is
257 true that a missing argument can only be detected in one case, but that
258 is a case that has to be considered.
259
261 None.
262
264 exec(), the Base Definitions volume of IEEE Std 1003.1-2001,
265 <unistd.h>, the Shell and Utilities volume of IEEE Std 1003.1-2001
266
268 Portions of this text are reprinted and reproduced in electronic form
269 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
270 -- Portable Operating System Interface (POSIX), The Open Group Base
271 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
272 Electrical and Electronics Engineers, Inc and The Open Group. In the
273 event of any discrepancy between this version and the original IEEE and
274 The Open Group Standard, the original IEEE and The Open Group Standard
275 is the referee document. The original Standard can be obtained online
276 at http://www.opengroup.org/unix/online.html .
277IEEE/The Open Group 2003 GETOPT(3P)