GETOPT(3C) Standard C Library Functions GETOPT(3C)


NAME


getopt - command option parsing

SYNOPSIS


SVID3, XPG3
#include <stdio.h>

int getopt(int argc, char * const argv[], const char *optstring);


extern char *optarg;


extern int optind, opterr, optopt;


POSIX.2, XPG4, SUS, SUSv2, SUSv3
#include <unistd.h>

int getopt(int argc, char * const argv[], const char *optstring);


extern char *optarg;


extern int optind, opterr, optopt;


DESCRIPTION


The getopt() function is a command line parser that can be used by
applications that follow Basic Utility Syntax Guidelines 3, 4, 5, 6, 7,
9, and 10 which parallel those defined by application portability
standards (see Intro(1)). It can also be used by applications which
additionally follow the Command Line Interface Paradigm (CLIP) syntax
extension guidelines 15, 16, and 17. It partially enforces guideline 18
by requiring that every option has a short-name, but it allows multiple
long-names to be associated with an option. The remaining guidelines are
not addressed by getopt() and are the responsibility of the application.


The argc and argv arguments are the argument count and argument array as
passed to main (see exec(2)). The optstring argument specifies the
acceptable options. For utilities wanting to conform to the Basic Utility
Syntax Guidelines, optstring is a string of recognized option characters.
All option characters allowed by Utility Syntax Guideline 3 are allowed
in optstring. If a character is followed by a colon (:), the option is
expected to have an option-argument, which can be separated from it by
white space. Utilities wanting to conform to the extended CLIP
guidelines can specify long-option equivalents to short options by
following the short-option character (and optional colon) with a sequence
of strings, each enclosed in parentheses, that specify the long-option
aliases.


The getopt() function returns the short-option character in optstring
that corresponds to the next option found in argv.


The getopt() function places in optind the argv index of the next
argument to be processed. The optind variable is external and is
initialized to 1 before the first call to getopt(). The getopt() function
sets the variable optarg to point to the start of the option-argument as
follows:

o If the option is a short option and that character is the last
character in the argument, then optarg contains the next
element of argv, and optind is incremented by 2.

o If the option is a short option and that character is not the
last character in the argument, then optarg points to the
string following the option character in that argument, and
optind is incremented by 1.

o If the option is a long option and the character equals is not
found in the argument, then optarg contains the next element
of argv, and optind is incremented by 2.

o If the option is a long option and the character equals is
found in the argument, then optarg points to the string
following the equals character in that argument and optind is
incremented by 1.


In all cases, if the resulting value of optind is not less than argc,
this indicates a missing option-argument and getopt() returns an error
indication.


When all options have been processed (that is, up to the first operand),
getopt() returns -1. The special option "--"(two hyphens) can be used to
delimit the end of the options; when it is encountered, -1 is returned
and "--" is skipped. This is useful in delimiting non-option arguments
that begin with "-" (hyphen).


If getopt() encounters a short-option character or a long-option string
not described in the opstring argument, it returns the question-mark (?)
character. If it detects a missing option-argument, it also returns the
question-mark (?) character, unless the first character of the optstring
argument was a colon (:), in which case getopt() returns the colon (:)
character. For short options, getopt() sets the variable optopt to the
option character that caused the error. For long options, optopt is set
to the hyphen (-) character and the failing long option can be identified
through argv[optind-1]. If the application has not set the variable
opterr to 0 and the first character of optstring is not a colon (:),
getopt() also prints a diagnostic message to stderr.

RETURN VALUES


The getopt() function returns the short-option character associated with
the option recognized.


A colon (:) is returned if getopt() detects a missing argument and the
first character of optstring was a colon (:).


A question mark (?) is returned if getopt() encounters an option not
specified in optstring or detects a missing argument and the first
character of optstring was not a colon (:).


Otherwise, getopt() returns -1 when all command line options are parsed.

ERRORS


No errors are defined.

EXAMPLES


Example 1: Parsing Command Line Options




The following code fragment shows how you might process the arguments for
a utility that can take the mutually-exclusive options a and b and the
options f and o, both of which require arguments:


#include <unistd.h>

int
main(int argc, char *argv[ ])
{
int c;
int bflg, aflg, errflg;
char *ifile;
char *ofile;
extern char *optarg;
extern int optind, optopt;
...
while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
switch(c) {
case 'a':
if (bflg)
errflg++;
else
aflg++;
break;
case 'b':
if (aflg)
errflg++;
else {
bflg++;
bproc();
}
break;
case 'f':
ifile = optarg;
break;
case 'o':
ofile = optarg;
break;
case ':': /* -f or -o without operand */
fprintf(stderr,
"Option -%c requires an operand\n", optopt);
errflg++;
break;
case '?':
fprintf(stderr,
"Unrecognized option: -%c\n", optopt);
errflg++;
}
}
if (errflg) {
fprintf(stderr, "usage: ... ");
exit(2);
}
for ( ; optind < argc; optind++) {
if (access(argv[optind], R_OK)) {
...
}


This code accepts any of the following as equivalent:


cmd -ao arg path path
cmd -a -o arg path path
cmd -o arg -a path path
cmd -a -o arg -- path path
cmd -a -oarg path path
cmd -aoarg path path


Example 2: Check Options and Arguments.




The following example parses a set of command line options and prints
messages to standard output for each option and argument that it
encounters.


#include <unistd.h>
#include <stdio.h>
...
int c;
char *filename;
extern char *optarg;
extern int optind, optopt, opterr;
...
while ((c = getopt(argc, argv, ":abf:")) != -1) {
switch(c) {
case 'a':
printf("a is set\n");
break;
case 'b':
printf("b is set\n");
break;
case 'f':
filename = optarg;
printf("filename is %s\n", filename);
break;
case ':':
printf("-%c without filename\n", optopt);
break;
case '?':
printf("unknown arg %c\n", optopt);
break;
}
}


This example can be expanded to be CLIP-compliant by substituting the
following string for the optstring argument:


:a(ascii)b(binary)f:(in-file)o:(out-file)V(version)?(help)


and by replacing the '?' case processing with:


case 'V':
fprintf(stdout, "cmd 1.1\n");
exit(0);
case '?':
if (optopt == '?') {
print_help();
exit(0);
}
if (optopt == '-')
fprintf(stderr,
"unrecognized option: %s\n", argv[optind-1]);
else
fprintf(stderr,
"unrecognized option: -%c\n", optopt);
errflg++;
break;


and by replacing the ':' case processing with:


case ':': /* -f or -o without operand */
if (optopt == '-')
fprintf(stderr,
"Option %s requires an operand\n", argv[optind-1]);
else
fprintf(stderr,
"Option -%c requires an operand\n", optopt);
errflg++;
break;


While not encouraged by the CLIP specification, multiple long-option
aliases can also be assigned as shown in the following example:


:a(ascii)b(binary):(in-file)(input)o:(outfile)(output)V(version)?(help)


ENVIRONMENT VARIABLES


See environ(5) for descriptions of the following environment variables
that affect the execution of getopt(): LANG, LC_ALL, and LC_MESSAGES.

LC_CTYPE
Determine the locale for the interpretation of sequences of
bytes as characters in optstring.


USAGE


The getopt() function does not fully check for mandatory arguments
because there is no unambiguous algorithm to do so. 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. Indeed, the only time a missing option-argument can be
reliably detected is when the option is the final option on the command
line and is not followed by any command arguments.


It is a violation of the Basic Utility 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


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+
|MT-Level | Unsafe |
+--------------------+-----------------+
|Standard | See below. |
+--------------------+-----------------+


For the Basic Utility Command syntax is Standard, see standards(5).

SEE ALSO


Intro(1), getopt(1), getopts(1), getopt_long(3C), getsubopt(3C),
gettext(3C), setlocale(3C), attributes(5), environ(5), standards(5)


July 17, 2018 GETOPT(3C)