1GETOPT(3) Linux Programmer's Manual GETOPT(3)
2
6 getopt, getopt_long, getopt_long_only, optarg, optind, opterr, optopt -
7 Parse command-line options
8
10 #include <unistd.h>
11 int getopt(int argc, char * const argv[],
13 const char *optstring);
14 extern char *optarg;
16 extern int optind, opterr, optopt;
17 #include <getopt.h>
19 int getopt_long(int argc, char * const argv[],
21 const char *optstring,
22 const struct option *longopts, int *longindex);
23 int getopt_long_only(int argc, char * const argv[],
25 const char *optstring,
26 const struct option *longopts, int *longindex);
27 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
29 getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
31 getopt_long(), getopt_long_only(): _GNU_SOURCE
32
34 The getopt() function parses the command-line arguments. Its arguments
35 argc and argv are the argument count and array as passed to the main()
36 function on program invocation. An element of argv that starts with
37 '-' (and is not exactly "-" or "--") is an option element. The charac‐
38 ters of this element (aside from the initial '-') are option charac‐
39 ters. If getopt() is called repeatedly, it returns successively each
40 of the option characters from each of the option elements.
41 The variable optind is the index of the next element to be processed in
43 argv. The system initializes this value to 1. The caller can reset it
44 to 1 to restart scanning of the same argv, or when scanning a new argu‐
45 ment vector.
46 If getopt() finds another option character, it returns that character,
48 updating the external variable optind and a static variable nextchar so
49 that the next call to getopt() can resume the scan with the following
50 option character or argv-element.
51 If there are no more option characters, getopt() returns -1. Then
53 optind is the index in argv of the first argv-element that is not an
54 option.
55 optstring is a string containing the legitimate option characters. If
57 such a character is followed by a colon, the option requires an argu‐
58 ment, so getopt() places a pointer to the following text in the same
59 argv-element, or the text of the following argv-element, in optarg.
60 Two colons mean an option takes an optional arg; if there is text in
61 the current argv-element (i.e., in the same word as the option name
62 itself, for example, "-oarg"), then it is returned in optarg, otherwise
63 optarg is set to zero. This is a GNU extension. If optstring contains
64 W followed by a semicolon, then -W foo is treated as the long option
65 --foo. (The -W option is reserved by POSIX.2 for implementation exten‐
66 sions.) This behavior is a GNU extension, not available with libraries
67 before glibc 2.
68 By default, getopt() permutes the contents of argv as it scans, so that
70 eventually all the nonoptions are at the end. Two other modes are also
71 implemented. If the first character of optstring is '+' or the envi‐
72 ronment variable POSIXLY_CORRECT is set, then option processing stops
73 as soon as a nonoption argument is encountered. If the first character
74 of optstring is '-', then each nonoption argv-element is handled as if
75 it were the argument of an option with character code 1. (This is used
76 by programs that were written to expect options and other argv-elements
77 in any order and that care about the ordering of the two.) The special
78 argument "--" forces an end of option-scanning regardless of the scan‐
79 ning mode.
80 If getopt() does not recognize an option character, it prints an error
82 message to stderr, stores the character in optopt, and returns '?'.
83 The calling program may prevent the error message by setting opterr to
84 0.
85 If getopt() finds an option character in argv that was not included in
87 optstring, or if it detects a missing option argument, it returns '?'
88 and sets the external variable optopt to the actual option character.
89 If the first character (following any optional '+' or '-' described
90 above) of optstring is a colon (':'), then getopt() returns ':' instead
91 of '?' to indicate a missing option argument. If an error was
92 detected, and the first character of optstring is not a colon, and the
93 external variable opterr is nonzero (which is the default), getopt()
94 prints an error message.
95 getopt_long() and getopt_long_only()
97 The getopt_long() function works like getopt() except that it also
98 accepts long options, started with two dashes. (If the program accepts
99 only long options, then optstring should be specified as an empty
100 string (""), not NULL.) Long option names may be abbreviated if the
101 abbreviation is unique or is an exact match for some defined option. A
102 long option may take a parameter, of the form --arg=param or --arg
103 param.
104 longopts is a pointer to the first element of an array of struct option
106 declared in <getopt.h> as
107 struct option {
109 const char *name;
110 int has_arg;
111 int *flag;
112 int val;
113 };
114 The meanings of the different fields are:
116 name is the name of the long option.
118 has_arg
120 is: no_argument (or 0) if the option does not take an argument;
121 required_argument (or 1) if the option requires an argument; or
122 optional_argument (or 2) if the option takes an optional argu‐
123 ment.
124 flag specifies how results are returned for a long option. If flag
126 is NULL, then getopt_long() returns val. (For example, the
127 calling program may set val to the equivalent short option char‐
128 acter.) Otherwise, getopt_long() returns 0, and flag points to
129 a variable which is set to val if the option is found, but left
130 unchanged if the option is not found.
131 val is the value to return, or to load into the variable pointed to
133 by flag.
134 The last element of the array has to be filled with zeros.
136 If longindex is not NULL, it points to a variable which is set to the
138 index of the long option relative to longopts.
139 getopt_long_only() is like getopt_long(), but '-' as well as "--" can
141 indicate a long option. If an option that starts with '-' (not "--")
142 doesn't match a long option, but does match a short option, it is
143 parsed as a short option instead.
144
146 If an option was successfully found, then getopt() returns the option
147 character. If all command-line options have been parsed, then getopt()
148 returns -1. If getopt() encounters an option character that was not in
149 optstring, then '?' is returned. If getopt() encounters an option with
150 a missing argument, then the return value depends on the first charac‐
151 ter in optstring: if it is ':', then ':' is returned; otherwise '?' is
152 returned.
153 getopt_long() and getopt_long_only() also return the option character
155 when a short option is recognized. For a long option, they return val
156 if flag is NULL, and 0 otherwise. Error and -1 returns are the same as
157 for getopt(), plus '?' for an ambiguous match or an extraneous parame‐
158 ter.
159
161 POSIXLY_CORRECT
162 If this is set, then option processing stops as soon as a nonop‐
163 tion argument is encountered.
164 _<PID>_GNU_nonoption_argv_flags_
166 This variable was used by bash(1) 2.0 to communicate to glibc
167 which arguments are the results of wildcard expansion and so
168 should not be considered as options. This behavior was removed
169 in bash(1) version 2.01, but the support remains in glibc.
170
172 getopt():
173 POSIX.2 and POSIX.1-2001, provided the environment variable
174 POSIXLY_CORRECT is set. Otherwise, the elements of argv aren't
175 really const, because we permute them. We pretend they're const
176 in the prototype to be compatible with other systems.
177 The use of '+' and '-' in optstring is a GNU extension.
179 On some older implementations, getopt() was declared in
181 <stdio.h>. SUSv1 permitted the declaration to appear in either
182 <unistd.h> or <stdio.h>. POSIX.1-2001 marked the use of
183 <stdio.h> for this purpose as LEGACY. POSIX.1-2001 does not
184 allow the declaration to appear in <stdio.h>.
185 getopt_long() and getopt_long_only():
187 These functions are GNU extensions.
188
190 A program that scans multiple argument vectors, or rescans the same
191 vector more than once, and wants to make use of GNU extensions such as
192 '+' and '-' at the start of optstring, or changes the value of
193 POSIXLY_CORRECT between scans, must reinitialize getopt() by resetting
194 optind to 0, rather than the traditional value of 1. (Resetting to 0
195 forces the invocation of an internal initialization routine that
196 rechecks POSIXLY_CORRECT and checks for GNU extensions in optstring.)
197
199 The POSIX.2 specification of getopt() has a technical error described
200 in POSIX.2 Interpretation 150. The GNU implementation (and probably
201 all other implementations) implements the correct behavior rather than
202 that specified.
203
205 The following trivial example program uses getopt() to handle two pro‐
206 gram options: -n, with no associated value; and -t val, which expects
207 an associated value.
208 #include <unistd.h>
210 #include <stdlib.h>
211 #include <stdio.h>
212 int
214 main(int argc, char *argv[])
215 {
216 int flags, opt;
217 int nsecs, tfnd;
218 nsecs = 0;
220 tfnd = 0;
221 flags = 0;
222 while ((opt = getopt(argc, argv, "nt:")) != -1) {
223 switch (opt) {
224 case 'n':
225 flags = 1;
226 break;
227 case 't':
228 nsecs = atoi(optarg);
229 tfnd = 1;
230 break;
231 default: /* '?' */
232 fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",
233 argv[0]);
234 exit(EXIT_FAILURE);
235 }
236 }
237 printf("flags=%d; tfnd=%d; optind=%d\n", flags, tfnd, optind);
239 if (optind >= argc) {
241 fprintf(stderr, "Expected argument after options\n");
242 exit(EXIT_FAILURE);
243 }
244 printf("name argument = %s\n", argv[optind]);
246 /* Other code omitted */
248 exit(EXIT_SUCCESS);
250 }
251 The following example program illustrates the use of getopt_long() with
253 most of its features.
254 #include <stdio.h> /* for printf */
256 #include <stdlib.h> /* for exit */
257 #include <getopt.h>
258 int
260 main(int argc, char **argv)
261 {
262 int c;
263 int digit_optind = 0;
264 while (1) {
266 int this_option_optind = optind ? optind : 1;
267 int option_index = 0;
268 static struct option long_options[] = {
269 {"add", required_argument, 0, 0 },
270 {"append", no_argument, 0, 0 },
271 {"delete", required_argument, 0, 0 },
272 {"verbose", no_argument, 0, 0 },
273 {"create", required_argument, 0, 'c'},
274 {"file", required_argument, 0, 0 },
275 {0, 0, 0, 0 }
276 };
277 c = getopt_long(argc, argv, "abc:d:012",
279 long_options, &option_index);
280 if (c == -1)
281 break;
282 switch (c) {
284 case 0:
285 printf("option %s", long_options[option_index].name);
286 if (optarg)
287 printf(" with arg %s", optarg);
288 printf("\n");
289 break;
290 case '0':
292 case '1':
293 case '2':
294 if (digit_optind != 0 && digit_optind != this_option_optind)
295 printf("digits occur in two different argv-elements.\n");
296 digit_optind = this_option_optind;
297 printf("option %c\n", c);
298 break;
299 case 'a':
301 printf("option a\n");
302 break;
303 case 'b':
305 printf("option b\n");
306 break;
307 case 'c':
309 printf("option c with value '%s'\n", optarg);
310 break;
311 case 'd':
313 printf("option d with value '%s'\n", optarg);
314 break;
315 case '?':
317 break;
318 default:
320 printf("?? getopt returned character code 0%o ??\n", c);
321 }
322 }
323 if (optind < argc) {
325 printf("non-option ARGV-elements: ");
326 while (optind < argc)
327 printf("%s ", argv[optind++]);
328 printf("\n");
329 }
330 exit(EXIT_SUCCESS);
332 }
333
335 getsubopt(3)
336
338 This page is part of release 3.53 of the Linux man-pages project. A
339 description of the project, and information about reporting bugs, can
340 be found at http://www.kernel.org/doc/man-pages/.
341GNU 2010-11-01 GETOPT(3)