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| Standard C Library Functions | getopt(3C) |
| | getopt - get option letter from argument vector |
SYNOPSIS
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#include <stdlib.h> int getopt(int argc, char * const *argv, const char *optstring, extern char *optarg;
extern int optind, opterr, optopt;
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The getopt() function returns the next option letter in argv that matches a letter in optstring. It supports all the rules of the command syntax standard (see intro(1)). Since all new commands are intended to adhere to the command syntax standard, they should use getopts(1), getopt(3C) or getsubopt(3C) to parse positional
parameters and check for options that are legal for that command.
The optstring argument must contain the option letters the command using getopt() will recognize; if a letter is followed by a colon, the option is expected to have an argument, or group of arguments, which may be separated from it by white space. The optarg argument is set to point to the start of the option argument on return from getopt().
The getopt() function places in optind the argv index of the next argument to be processed. optind is external and is initialized to 1 before the first call to getopt(). When all options have
been processed (that is, up to the first non-option argument), getopt() returns EOF. The special option "--" (two hyphens) may be used to delimit the end of the options; when it is encountered, EOF is returned and "--"' is skipped. This is useful in delimiting non-option arguments that begin with "-" (hyphen).
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The getopt() function prints an error message on the standard error and returns a "?" (question mark) when it encounters an option letter not included in optstring or no argument after an option that expects one. This error
message may be disabled by setting opterr to 0. The value of the character that caused the error is in optopt.
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If the application is linked with -lintl, then messages printed from this function are in the native language specified by the LC_MESSAGES locale category; see setlocale(3C).
The getopt() function does not fully check for mandatory arguments; that is, given an option string a:b and the input -a -b, getopt() assumes that -b is the mandatory argument
to the -a option and not that -a is missing a mandatory argument.
It is a violation of the command syntax standard (see intro(1)) for options with arguments to be grouped with other options, as in cmd -abo filename , where a and b are options, o is an option that requires an argument, and filename is the argument to o. Although this syntax is permitted in the current implementation, it should
not be used because it may not be supported in future releases. The correct syntax to use is:
cmd -ab -o filename.
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| | Example 1. Example on how one might process the arguments for a command.
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The following code fragment shows how one might process the arguments for a command that can take the mutually exclusive options a and b, and the option o, which requires an argument:
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#include <stdlib.h>
#include <stdio.h>
main (int argc, char **argv)
{
int c;
extern char *optarg;
extern int optind;
int aflg = 0;
int bflg = 0;
int errflg = 0;
char *ofile = NULL;
while ((c = getopt(argc, argv, "abo:")) != EOF)
switch (c) {
case 'a':
if (bflg)
errflg++;
else
aflg++;
break;
case 'b':
if (aflg)
errflg++;
else
bflg++;
break;
case 'o':
ofile = optarg;
(void)printf("ofile = %s\n", ofile);
break;
case '?':
errflg++;
}
if (errflg) {
(void)fprintf(stderr,
"usage: cmd [-a|-b] [-o <filename>] files...\n");
exit (2);
}
for ( ; optind < argc; optind++)
(void)printf("%s\n", argv[optind]);
return 0;
}
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See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Unsafe |
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