xref: /netbsd-src/lib/libc/stdlib/getopt_long.3 (revision b4852c3567bdc1c13cfb849248c5a43f3ed56363)

.\"	$NetBSD: getopt_long.3,v 1.22 2022/01/04 19:36:16 uwe Exp $
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.\"     @(#)getopt.3	8.5 (Berkeley) 4/27/95
.\"
.Dd December 9, 2018
.Dt GETOPT_LONG 3
.Os
.Sh NAME
.Nm getopt_long
.Nd get long options from command line argument list
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In getopt.h
.Ft int
.Fn getopt_long "int argc" "char * const *argv" "const char *optstring" "struct option *long_options" "int *index"
.Sh DESCRIPTION
The
.Fn getopt_long
function is similar to
.Xr getopt 3
but it accepts options in two forms: words and characters.
The
.Fn getopt_long
function provides a superset of the functionality of
.Xr getopt 3 .
.Fn getopt_long
can be used in two ways.
In the first way, every long option understood by the program has a
corresponding short option, and the option structure is only used to
translate from long options to short options.
When used in this fashion,
.Fn getopt_long
behaves identically to
.Xr getopt 3 .
This is a good way to add long option processing to an existing program
with the minimum of rewriting.
.Pp
In the second mechanism, a long option sets a flag in the
.Fa option
structure passed, or will store a pointer to the command line argument
in the
.Fa option
structure passed to it for options that take arguments.
Additionally, the long option's argument may be specified as a single
argument with an equal sign, e.g.
.Bd -literal
myprogram --myoption=somevalue
.Ed
.Pp
When a long option is processed the call to
.Fn getopt_long
will return 0.
For this reason, long option processing without
shortcuts is not backwards compatible with
.Xr getopt 3 .
.Pp
It is possible to combine these methods, providing for long options
processing with short option equivalents for some options.
Less frequently used options would be processed as long options only.
.Pp
Abbreviated long option names are accepted when
.Fn getopt_long
processes long options if the abbreviation is unique.
An exact match is always preferred for a defined long option.
.Pp
The
.Fn getopt_long
call requires a structure to be initialized describing the long options.
The structure is:
.Bd -literal
struct option {
	char *name;
	int has_arg;
	int *flag;
	int val;
};
.Ed
.Pp
The
.Fa name
field should contain the option name without the leading double dash.
.Pp
The
.Fa has_arg
field should be one of:
.Bl -tag -width "optional_argument"
.It Li no_argument
no argument to the option is expected.
.It Li required_argument
an argument to the option is required.
.It Li optional_argument
an argument to the option may be presented.
.El
.Pp
If
.Fa flag
is not
.Dv NULL ,
then the integer pointed to by it will be set to the value in the
.Fa val
field.
If the
.Fa flag
field is
.Dv NULL ,
then the
.Fa val
field will be returned.
Setting
.Fa flag
to
.Dv NULL
and setting
.Fa val
to the corresponding short option will make this function act just
like
.Xr getopt 3 .
.Pp
If the
.Fa index
argument is not
.Dv NULL ,
the integer it points to will be set to the index of the long option
in the
.Fa long_options
array.
.Pp
The last element of the
.Fa long_options
array has to be filled with zeroes (see
.Sx EXAMPLES
section).
.Sh EXAMPLES
.Bd -literal -compact
extern char *optarg;
extern int optind;
int bflag, ch, fd;
int daggerset;

/* options descriptor */
static struct option longopts[] = {
	{ "buffy",	no_argument,		NULL, 		'b' },
	{ "fluoride",	required_argument,	NULL, 	       	'f' },
	{ "daggerset",	no_argument,		&daggerset,	1 },
	{ NULL,		0,			NULL, 		0 }
};

bflag = 0;
while ((ch = getopt_long(argc, argv, "bf:", longopts, NULL)) != -1)
	switch (ch) {
	case 'b':
		bflag = 1;
		break;
	case 'f':
		if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
			(void)fprintf(stderr,
			    "myname: %s: %s\en", optarg, strerror(errno));
			exit(1);
		}
		break;
	case 0:
		if(daggerset) {
			fprintf(stderr,"Buffy will use her dagger to "
				       "apply fluoride to dracula's teeth\en");
		}
		break;
	case '?':
	default:
		usage();
}
argc -= optind;
argv += optind;
.Ed
.Sh IMPLEMENTATION DIFFERENCES
This section describes differences to the GNU implementation
found in glibc-2.1.3:
.Bl -tag -width "xxx"
.It Li o
handling of - as first char of option string in presence of
environment variable POSIXLY_CORRECT:
.Bl -tag -width "NetBSD"
.It Li GNU
ignores POSIXLY_CORRECT and returns non-options as
arguments to option '\e1'.
.It Li NetBSD
honors POSIXLY_CORRECT and stops at the first non-option.
.El
.It Li o
handling of :: in options string in presence of POSIXLY_CORRECT:
.Bl -tag -width "NetBSD"
.It Li Both
GNU and NetBSD ignore POSIXLY_CORRECT here and take :: to
mean the preceding option takes an optional argument.
.El
.It Li o
return value in case of missing argument if first character
(after + or -) in option string is not ':':
.Bl -tag -width "NetBSD"
.It Li GNU
returns '?'
.It NetBSD
returns ':' (since NetBSD's getopt does).
.El
.It Li o
handling of --a in getopt:
.Bl -tag -width "NetBSD"
.It Li GNU
parses this as option '-', option 'a'.
.It Li NetBSD
parses this as '--', and returns \-1 (ignoring the a).
(Because the original getopt does.)
.El
.It Li o
setting of optopt for long options with flag !=
.Dv NULL :
.Bl -tag -width "NetBSD"
.It Li GNU
sets optopt to val.
.It Li NetBSD
sets optopt to 0 (since val would never be returned).
.El
.It Li o
handling of -W with W; in option string in getopt (not getopt_long):
.Bl -tag -width "NetBSD"
.It Li GNU
causes a segfault.
.It Li NetBSD
returns \-1, with optind pointing past the argument of -W
(as if `-W arg' were `--arg', and thus '--' had been found).
.\" How should we treat W; in the option string when called via
.\" getopt?  Ignore the ';' or treat it as a ':'? Issue a warning?
.El
.It Li o
setting of optarg for long options without an argument that are
invoked via -W (W; in option string):
.Bl -tag -width "NetBSD"
.It Li GNU
sets optarg to the option name (the argument of -W).
.It Li NetBSD
sets optarg to
.Dv NULL
(the argument of the long option).
.El
.It Li o
handling of -W with an argument that is not (a prefix to) a known
long option (W; in option string):
.Bl -tag -width "NetBSD"
.It Li GNU
returns -W with optarg set to the unknown option.
.It Li NetBSD
treats this as an error (unknown option) and returns '?' with
optopt set to 0 and optarg set to
.Dv NULL
(as GNU's man page documents).
.El
.It Li o
The error messages are different.
.It Li o
NetBSD does not permute the argument vector at the same points in
the calling sequence as GNU does.
The aspects normally used by the caller
(ordering after \-1 is returned, value of optind relative
to current positions) are the same, though.
(We do fewer variable swaps.)
.El
.Sh SEE ALSO
.Xr getopt 3
.Sh HISTORY
The
.Fn getopt_long
function first appeared in GNU libiberty.
The first
.Nx
implementation appeared in 1.5.
.Sh BUGS
The implementation can completely replace
.Xr getopt 3 ,
but right now we are using separate code.
.Pp
The
.Fa argv
argument is not really const.