1getopt(3) Library Functions Manual getopt(3)
2
6 getopt, getopt_long, getopt_long_only, optarg, optind, opterr, optopt -
7 Parse command-line options
8
10 Standard C library (libc, -lc)
11
13 #include <unistd.h>
14 int getopt(int argc, char *argv[],
16 const char *optstring);
17 extern char *optarg;
19 extern int optind, opterr, optopt;
20 #include <getopt.h>
22 int getopt_long(int argc, char *argv[],
24 const char *optstring,
25 const struct option *longopts, int *longindex);
26 int getopt_long_only(int argc, char *argv[],
27 const char *optstring,
28 const struct option *longopts, int *longindex);
29 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
31 getopt():
33 _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
34 getopt_long(), getopt_long_only():
36 _GNU_SOURCE
37
39 The getopt() function parses the command-line arguments. Its arguments
40 argc and argv are the argument count and array as passed to the main()
41 function on program invocation. An element of argv that starts with
42 '-' (and is not exactly "-" or "--") is an option element. The charac‐
43 ters of this element (aside from the initial '-') are option charac‐
44 ters. If getopt() is called repeatedly, it returns successively each
45 of the option characters from each of the option elements.
46 The variable optind is the index of the next element to be processed in
48 argv. The system initializes this value to 1. The caller can reset it
49 to 1 to restart scanning of the same argv, or when scanning a new argu‐
50 ment vector.
51 If getopt() finds another option character, it returns that character,
53 updating the external variable optind and a static variable nextchar so
54 that the next call to getopt() can resume the scan with the following
55 option character or argv-element.
56 If there are no more option characters, getopt() returns -1. Then
58 optind is the index in argv of the first argv-element that is not an
59 option.
60 optstring is a string containing the legitimate option characters. A
62 legitimate option character is any visible one byte ascii(7) character
63 (for which isgraph(3) would return nonzero) that is not '-', ':', or
64 ';'. If such a character is followed by a colon, the option requires
65 an argument, so getopt() places a pointer to the following text in the
66 same argv-element, or the text of the following argv-element, in op‐
67 targ. Two colons mean an option takes an optional arg; if there is
68 text in the current argv-element (i.e., in the same word as the option
69 name itself, for example, "-oarg"), then it is returned in optarg, oth‐
70 erwise optarg is set to zero. This is a GNU extension. If optstring
71 contains W followed by a semicolon, then -W foo is treated as the long
72 option --foo. (The -W option is reserved by POSIX.2 for implementation
73 extensions.) This behavior is a GNU extension, not available with li‐
74 braries before glibc 2.
75 By default, getopt() permutes the contents of argv as it scans, so that
77 eventually all the nonoptions are at the end. Two other scanning modes
78 are also implemented. If the first character of optstring is '+' or
79 the environment variable POSIXLY_CORRECT is set, then option processing
80 stops as soon as a nonoption argument is encountered. If '+' is not
81 the first character of optstring, it is treated as a normal option. If
82 POSIXLY_CORRECT behaviour is required in this case optstring will con‐
83 tain two '+' symbols. If the first character of optstring is '-', then
84 each nonoption argv-element is handled as if it were the argument of an
85 option with character code 1. (This is used by programs that were
86 written to expect options and other argv-elements in any order and that
87 care about the ordering of the two.) The special argument "--" forces
88 an end of option-scanning regardless of the scanning mode.
89 While processing the option list, getopt() can detect two kinds of er‐
91 rors: (1) an option character that was not specified in optstring and
92 (2) a missing option argument (i.e., an option at the end of the com‐
93 mand line without an expected argument). Such errors are handled and
94 reported as follows:
95 • By default, getopt() prints an error message on standard error,
97 places the erroneous option character in optopt, and returns '?' as
98 the function result.
99 • If the caller has set the global variable opterr to zero, then
101 getopt() does not print an error message. The caller can determine
102 that there was an error by testing whether the function return value
103 is '?'. (By default, opterr has a nonzero value.)
104 • If the first character (following any optional '+' or '-' described
106 above) of optstring is a colon (':'), then getopt() likewise does
107 not print an error message. In addition, it returns ':' instead of
108 '?' to indicate a missing option argument. This allows the caller
109 to distinguish the two different types of errors.
110 getopt_long() and getopt_long_only()
112 The getopt_long() function works like getopt() except that it also ac‐
113 cepts long options, started with two dashes. (If the program accepts
114 only long options, then optstring should be specified as an empty
115 string (""), not NULL.) Long option names may be abbreviated if the
116 abbreviation is unique or is an exact match for some defined option. A
117 long option may take a parameter, of the form --arg=param or --arg
118 param.
119 longopts is a pointer to the first element of an array of struct option
121 declared in <getopt.h> as
122 struct option {
124 const char *name;
125 int has_arg;
126 int *flag;
127 int val;
128 };
129 The meanings of the different fields are:
131 name is the name of the long option.
133 has_arg
135 is: no_argument (or 0) if the option does not take an argument;
136 required_argument (or 1) if the option requires an argument; or
137 optional_argument (or 2) if the option takes an optional argu‐
138 ment.
139 flag specifies how results are returned for a long option. If flag
141 is NULL, then getopt_long() returns val. (For example, the
142 calling program may set val to the equivalent short option char‐
143 acter.) Otherwise, getopt_long() returns 0, and flag points to
144 a variable which is set to val if the option is found, but left
145 unchanged if the option is not found.
146 val is the value to return, or to load into the variable pointed to
148 by flag.
149 The last element of the array has to be filled with zeros.
151 If longindex is not NULL, it points to a variable which is set to the
153 index of the long option relative to longopts.
154 getopt_long_only() is like getopt_long(), but '-' as well as "--" can
156 indicate a long option. If an option that starts with '-' (not "--")
157 doesn't match a long option, but does match a short option, it is
158 parsed as a short option instead.
159
161 If an option was successfully found, then getopt() returns the option
162 character. If all command-line options have been parsed, then getopt()
163 returns -1. If getopt() encounters an option character that was not in
164 optstring, then '?' is returned. If getopt() encounters an option with
165 a missing argument, then the return value depends on the first charac‐
166 ter in optstring: if it is ':', then ':' is returned; otherwise '?' is
167 returned.
168 getopt_long() and getopt_long_only() also return the option character
170 when a short option is recognized. For a long option, they return val
171 if flag is NULL, and 0 otherwise. Error and -1 returns are the same as
172 for getopt(), plus '?' for an ambiguous match or an extraneous parame‐
173 ter.
174
176 POSIXLY_CORRECT
177 If this is set, then option processing stops as soon as a nonop‐
178 tion argument is encountered.
179 _<PID>_GNU_nonoption_argv_flags_
181 This variable was used by bash(1) 2.0 to communicate to glibc
182 which arguments are the results of wildcard expansion and so
183 should not be considered as options. This behavior was removed
184 in bash(1) 2.01, but the support remains in glibc.
185
187 For an explanation of the terms used in this section, see at‐
188 tributes(7).
189 ┌───────────────────┬───────────────┬──────────────────────────────────┐
191 │Interface │ Attribute │ Value │
192 ├───────────────────┼───────────────┼──────────────────────────────────┤
193 │getopt(), │ Thread safety │ MT-Unsafe race:getopt env │
194 │getopt_long(), │ │ │
195 │getopt_long_only() │ │ │
196 └───────────────────┴───────────────┴──────────────────────────────────┘
197
199 POSIX specifies that the argv array argument should be const, but these
200 functions permute its elements unless the environment variable POSIX‐
201 LY_CORRECT is set. const is used in the actual prototype to be compat‐
202 ible with other systems; however, this page doesn't show the qualifier,
203 to avoid confusing readers.
204
206 getopt()
207 POSIX.1-2008.
208 getopt_long()
210 getopt_long_only()
211 GNU.
212 The use of '+' and '-' in optstring is a GNU extension.
214
216 getopt()
217 POSIX.1-2001, and POSIX.2.
218 On some older implementations, getopt() was declared in <stdio.h>.
220 SUSv1 permitted the declaration to appear in either <unistd.h> or
221 <stdio.h>. POSIX.1-1996 marked the use of <stdio.h> for this purpose
222 as LEGACY. POSIX.1-2001 does not require the declaration to appear in
223 <stdio.h>.
224
226 A program that scans multiple argument vectors, or rescans the same
227 vector more than once, and wants to make use of GNU extensions such as
228 '+' and '-' at the start of optstring, or changes the value of POSIX‐
229 LY_CORRECT between scans, must reinitialize getopt() by resetting
230 optind to 0, rather than the traditional value of 1. (Resetting to 0
231 forces the invocation of an internal initialization routine that
232 rechecks POSIXLY_CORRECT and checks for GNU extensions in optstring.)
233 Command-line arguments are parsed in strict order meaning that an op‐
235 tion requiring an argument will consume the next argument, regardless
236 of whether that argument is the correctly specified option argument or
237 simply the next option (in the scenario the user mis-specifies the com‐
238 mand line). For example, if optstring is specified as "1n:" and the
239 user specifies the command line arguments incorrectly as prog -n -1,
240 the -n option will be given the optarg value "-1", and the -1 option
241 will be considered to have not been specified.
242
244 getopt()
245 The following trivial example program uses getopt() to handle two pro‐
246 gram options: -n, with no associated value; and -t val, which expects
247 an associated value.
248 #include <stdio.h>
250 #include <stdlib.h>
251 #include <unistd.h>
252 int
254 main(int argc, char *argv[])
255 {
256 int flags, opt;
257 int nsecs, tfnd;
258 nsecs = 0;
260 tfnd = 0;
261 flags = 0;
262 while ((opt = getopt(argc, argv, "nt:")) != -1) {
263 switch (opt) {
264 case 'n':
265 flags = 1;
266 break;
267 case 't':
268 nsecs = atoi(optarg);
269 tfnd = 1;
270 break;
271 default: /* '?' */
272 fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",
273 argv[0]);
274 exit(EXIT_FAILURE);
275 }
276 }
277 printf("flags=%d; tfnd=%d; nsecs=%d; optind=%d\n",
279 flags, tfnd, nsecs, optind);
280 if (optind >= argc) {
282 fprintf(stderr, "Expected argument after options\n");
283 exit(EXIT_FAILURE);
284 }
285 printf("name argument = %s\n", argv[optind]);
287 /* Other code omitted */
289 exit(EXIT_SUCCESS);
291 }
292 getopt_long()
294 The following example program illustrates the use of getopt_long() with
295 most of its features.
296 #include <getopt.h>
298 #include <stdio.h> /* for printf */
299 #include <stdlib.h> /* for exit */
300 int
302 main(int argc, char *argv[])
303 {
304 int c;
305 int digit_optind = 0;
306 while (1) {
308 int this_option_optind = optind ? optind : 1;
309 int option_index = 0;
310 static struct option long_options[] = {
311 {"add", required_argument, 0, 0 },
312 {"append", no_argument, 0, 0 },
313 {"delete", required_argument, 0, 0 },
314 {"verbose", no_argument, 0, 0 },
315 {"create", required_argument, 0, 'c'},
316 {"file", required_argument, 0, 0 },
317 {0, 0, 0, 0 }
318 };
319 c = getopt_long(argc, argv, "abc:d:012",
321 long_options, &option_index);
322 if (c == -1)
323 break;
324 switch (c) {
326 case 0:
327 printf("option %s", long_options[option_index].name);
328 if (optarg)
329 printf(" with arg %s", optarg);
330 printf("\n");
331 break;
332 case '0':
334 case '1':
335 case '2':
336 if (digit_optind != 0 && digit_optind != this_option_optind)
337 printf("digits occur in two different argv-elements.\n");
338 digit_optind = this_option_optind;
339 printf("option %c\n", c);
340 break;
341 case 'a':
343 printf("option a\n");
344 break;
345 case 'b':
347 printf("option b\n");
348 break;
349 case 'c':
351 printf("option c with value '%s'\n", optarg);
352 break;
353 case 'd':
355 printf("option d with value '%s'\n", optarg);
356 break;
357 case '?':
359 break;
360 default:
362 printf("?? getopt returned character code 0%o ??\n", c);
363 }
364 }
365 if (optind < argc) {
367 printf("non-option ARGV-elements: ");
368 while (optind < argc)
369 printf("%s ", argv[optind++]);
370 printf("\n");
371 }
372 exit(EXIT_SUCCESS);
374 }
375
377 getopt(1), getsubopt(3)
378Linux man-pages 6.04 2023-04-03 getopt(3)