getopt(3C)getopt(3C)NAMEgetopt - get option letter from argument vector
SYNOPSIS
#include <unistd.h>
int getopt (int argc, char * const argv[], const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;
extern void getoptreset (void);
DESCRIPTIONgetopt 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.
optstring must contain the option letters that 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. optarg is set to point to the start of
the option argument on return from getopt.
getopt 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 (i.e., up to the
first non-option argument), getopt returns -1. The special option ``--''
(two hyphens) may 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).
getoptreset can be used to reset all the internal state of getopt so that
it may be used again on a different set of arguments.
EXAMPLE
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:
#include <unistd.h>
main (int argc, char *argv[])
{
int c;
extern char *optarg;
extern int optind;
int aflg = 0;
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int bflg = 0;
int errflg = 0;
char *ofile = NULL;
while ((c = getopt(argc, argv, "abo:")) != -1)
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<file>] files...\n");
exit (2);
}
for ( ; optind < argc; optind++)
(void)printf("%s\n", argv[optind]);
return 0;
}
FILES
/usr/lib/locale/locale/LC_MESSAGES/uxlibc
language-specific message file [See LANG on environ(5).]
SEE ALSOgetopts(1), intro(1), getsubopt(3C), pfmt(3C), setlabel(3C)RETURN VALUE
The getopt function returns the next option character specified on the
command line.
A colon character ``:'' is returned if getopt detects a missing argument
and the first character of optstring was a colon character ``:''.
A question mark character ``?'' is returned if getopt encounters an
option character not in optstring or detects a missing argument and the
first character of optstring was not a colon character ``:''.
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Otherwise getopt returns -1 when all command line options are parsed.
DIAGNOSTICS
If getopt detects a missing option-argument, it returns the ``:'' colon
character if the first character of optstring was a colon, or a ``?''
(question mark) character otherwise. If the application has not set the
variable opterr to zero and the first character of optstring is not a
colon, getopt also prints a diagnostic message in the standard error
format. The value of the character that caused the error is in optopt.
The label defined by a call to setlabel(3C) will be used if available;
otherwise the name of the utility (argv[0]) will be used. Remember to
set the environment variable (NOMSGSEVERITY=1) for X/Open conformance.
Also, the environment variable (NOMSGLABEL) must be not defined in order
for setlabel(3C) to print labels.
NOTES
The library routine getopt 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 option -a 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
-aboxxx file, where a and b are options, o is an option that requires an
argument, and xxx 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 is cmd -ab -o
xxx file.
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