path: root/lib/libc/stdlib/getopt_long.3

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.\"     @(#)getopt.3	8.5 (Berkeley) 4/27/95
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.Dd $Mdocdate: January 13 2020 $
.Dt GETOPT_LONG 3
.Os
.Sh NAME
.Nm getopt_long ,
.Nm getopt_long_only
.Nd get long options from command line argument list
.Sh SYNOPSIS
.In getopt.h
.Vt extern char *optarg;
.Vt extern int optind;
.Vt extern int optopt;
.Vt extern int opterr;
.Vt extern int optreset;
.Ft int
.Fn getopt_long "int argc" "char * const *argv" "const char *optstring" "const struct option *longopts" "int *longindex"
.Ft int
.Fn getopt_long_only "int argc" "char * const *argv" "const char *optstring" "const struct option *longopts" "int *longindex"
.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 -offset indent
$ 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
By default,
.Fn getopt_long
permutes
.Ar argv
such that all option arguments are evaluated before any non-options arguments.
If the first character of
.Fa optstring
is a plus sign
.Pq Ql +
or if the environment variable
.Ev POSIXLY_CORRECT
is set, then
.Ar argv
is processed in order and option processing stops as soon as the first
non-option argument is encountered.
.Pp
The
.Fn getopt_long
call requires an array to be initialized describing the long
options.
Each element of the array is a structure:
.Bd -literal -offset indent
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:
.Pp
.Bl -tag -width "optional_argument" -compact -offset indent
.It Dv no_argument
no argument to the option is expected.
.It Dv required_argument
an argument to the option is required.
.It Dv 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 longindex
field is not
.Dv NULL ,
then the integer pointed to by it will be set to the index of the long
option relative to
.Fa longopts .
.Pp
The last element of the
.Fa longopts
array has to be filled with zeroes.
.Pp
The
.Fn getopt_long_only
function behaves identically to
.Fn getopt_long
with the exception that long options may start with
.Sq -
in addition to
.Sq -- .
If an option starting with
.Sq -
does not match a long option but does match a single-character option,
the single-character option is returned.
.Sh RETURN VALUES
If the
.Fa flag
field in
.Li struct option
is
.Dv NULL ,
.Fn getopt_long
and
.Fn getopt_long_only
return the value specified in the
.Fa val
field, which is usually just the corresponding short option.
If
.Fa flag
is not
.Dv NULL ,
these functions return 0 and store
.Fa val
in the location pointed to by
.Fa flag .
These functions return
.Sq \&:
if there was a missing option argument,
.Sq \&?
if the user specified an unknown or ambiguous option, and
\-1 when the argument list has been exhausted.
.Sh IMPLEMENTATION DIFFERENCES
This section describes differences to the GNU implementation
found in glibc-2.1.3:
.Bl -bullet
.It
handling of
.Ql -
within the option string (not the first character):
.Bl -tag -width "OpenBSD"
.It GNU
treats a
.Ql -
on the command line as a non-argument.
.It OpenBSD
a
.Ql -
within the option string matches a
.Ql -
(single dash) on the command line.
This functionality is provided for backward compatibility with
programs, such as
.Xr su 1 ,
that use
.Ql -
as an option flag.
This practice is wrong, and should not be used in any current development.
.El
.It
handling of
.Ql ::
in the option string in the presence of
.Ev POSIXLY_CORRECT :
.Bl -tag -width "OpenBSD"
.It Both
GNU and
.Ox
ignore
.Ev POSIXLY_CORRECT
here and take
.Ql ::
to mean the preceding option takes an optional argument.
.El
.It
return value in case of missing argument if first character
(after
.Ql +
or
.Ql - )
in the option string is not
.Ql \&: :
.Bl -tag -width "OpenBSD"
.It GNU
returns
.Ql \&?
.It OpenBSD
returns
.Ql \&:
(since
.Ox Ns 's
.Xr getopt 3
does).
.El
.It
handling of
.Ql --a
in
.Xr getopt 3 :
.Bl -tag -width "OpenBSD"
.It GNU
parses this as option
.Ql - ,
option
.Ql a .
.It OpenBSD
parses this as
.Ql -- ,
and returns \-1 (ignoring the
.Ql a )
(because the original
.Fn getopt
did.)
.El
.It
setting of
.Va optopt
for long options with
.Va flag
.No non- Ns Dv NULL :
.Bl -tag -width "OpenBSD"
.It GNU
sets
.Va optopt
to
.Va val .
.It OpenBSD
sets
.Va optopt
to 0 (since
.Va val
would never be returned).
.El
.It
handling of
.Ql -W
with
.Ql W;
in the option string in
.Xr getopt 3
(not
.Fn getopt_long ) :
.Bl -tag -width "OpenBSD"
.It GNU
causes a segmentation fault.
.It OpenBSD
no special handling is done;
.Ql W;
is interpreted as two separate options, neither of which take an argument.
.El
.It
setting of
.Va optarg
for long options without an argument that are invoked via
.Ql -W
(with
.Ql W;
in the option string):
.Bl -tag -width "OpenBSD"
.It GNU
sets
.Va optarg
to the option name (the argument of
.Ql -W ) .
.It OpenBSD
sets
.Va optarg
to
.Dv NULL
(the argument of the long option).
.El
.It
handling of
.Ql -W
with an argument that is not (a prefix to) a known long option
(with
.Ql W;
in the option string):
.Bl -tag -width "OpenBSD"
.It GNU
returns
.Ql -W
with
.Va optarg
set to the unknown option.
.It OpenBSD
treats this as an error (unknown option) and returns
.Ql \&?
with
.Va optopt
set to 0 and
.Va optarg
set to
.Dv NULL
(as GNU's man page documents).
.El
.It
The error messages are different.
.It
.Ox
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
.Va optind
relative to current positions) are the same, though.
(We do fewer variable swaps.)
.El
.Sh ENVIRONMENT
.Bl -tag -width Ev
.It Ev POSIXLY_CORRECT
If set, option processing stops when the first non-option is found and
a leading
.Sq +
in the
.Ar optstring
is ignored.
.El
.Sh EXAMPLES
.Bd -literal
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)) == -1)
			err(1, "unable to open %s", optarg);
		break;
	case 0:
		if (daggerset)
			fprintf(stderr, "Buffy will use her dagger to "
			    "apply fluoride to dracula's teeth\en");
		break;
	default:
		usage();
	}
argc -= optind;
argv += optind;
.Ed
.Sh SEE ALSO
.Xr getopt 3
.Sh HISTORY
The
.Fn getopt_long
and
.Fn getopt_long_only
functions first appeared in GNU libiberty.
This implementation first appeared in
.Ox 3.3 .
.Sh BUGS
The
.Ar argv
argument is not really
.Dv const
as its elements may be permuted (unless
.Ev POSIXLY_CORRECT
is set).