xref: /freebsd/lib/libc/stdlib/getopt_long.3 (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)

.\"	$OpenBSD: getopt_long.3,v 1.10 2004/01/06 23:44:28 fgsch Exp $
.\"	$NetBSD: getopt_long.3,v 1.14 2003/08/07 16:43:40 agc Exp $
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.Dd December 24, 2022
.Dt GETOPT_LONG 3
.Os
.Sh NAME
.Nm getopt_long ,
.Nm getopt_long_only
.Nd get long options from command line argument list
.Sh LIBRARY
.Lb libc
.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
.Fo getopt_long
.Fa "int argc" "char * const *argv" "const char *optstring"
.Fa "const struct option *longopts" "int *longindex"
.Fc
.Ft int
.Fo getopt_long_only
.Fa "int argc" "char * const *argv" "const char *optstring"
.Fa "const struct option *longopts" "int *longindex"
.Fc
.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 .
The
.Fn getopt_long
function
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
.Vt option
structure passed, or will store a pointer to the command line argument
in the
.Vt 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.,
.Pp
.Dl "myprogram --myoption=somevalue"
.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
The
.Fn getopt_long
call requires a structure to be initialized describing the long
options.
The structure is:
.Bd -literal -offset indent
struct option {
	char *name;
	int has_arg;
	int *flag;
	int val;
};
.Ed
.Pp
The
.Va name
field should contain the option name without the leading double dash.
.Pp
The
.Va has_arg
field should be one of:
.Pp
.Bl -tag -width ".Dv optional_argument" -offset indent -compact
.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
.Va flag
is not
.Dv NULL ,
then the integer pointed to by it will be set to the
value in the
.Va val
field.
If the
.Va flag
field is
.Dv NULL ,
then the
.Va val
field will be returned.
Setting
.Va flag
to
.Dv NULL
and setting
.Va 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
.Ql -
in addition to
.Ql -- .
If an option starting with
.Ql -
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
.Vt "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 .
.Pp
These functions return
.Ql \&:
if there was a missing option argument and error messages are suppressed,
.Ql \&?
if the user specified an unknown or ambiguous option, and
\-1 when the argument list has been exhausted.
The default behavior when a missing option argument is encountered is to write
an error and return
.Ql \&? .
Specifying
.Ql \&:
in
.Fa optstr
will cause the error message to be suppressed and
.Ql \&:
to be returned instead.
.Pp
In addition to
.Ql \&: ,
a leading
.Ql \&+
or
.Ql \&-
in
.Fa optstr
also has special meaning.
If either of these are specified, they must appear before
.Ql \&: .
.Pp
A leading
.Ql \&+
indicates that processing should be halted at the first non-option argument,
matching the default behavior of
.Xr getopt 3 .
The default behavior without
.Ql \&+
is to permute non-option arguments to the end of
.Fa argv .
.Pp
A leading
.Ql \&-
indicates that all non-option arguments should be treated as if they are
arguments to a literal
.Ql \&1
flag (i.e., the function call will return the value 1, rather than the char
literal '1').
.Sh ENVIRONMENT
.Bl -tag -width ".Ev POSIXLY_CORRECT"
.It Ev POSIXLY_CORRECT
If set, option processing stops when the first non-option is found and
a leading
.Ql -
or
.Ql +
in the
.Fa optstring
is ignored.
.El
.Sh EXAMPLES
.Bd -literal -compact
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,		\*[Am]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 IMPLEMENTATION DIFFERENCES
This section describes differences to the
.Tn GNU
implementation
found in glibc-2.1.3:
.Bl -bullet
.\" .It
.\" Handling of
.\" .Ql -
.\" as first char of option string in presence of
.\" environment variable
.\" .Ev POSIXLY_CORRECT :
.\" .Bl -tag -width ".Bx"
.\" .It Tn GNU
.\" ignores
.\" .Ev POSIXLY_CORRECT
.\" and returns non-options as
.\" arguments to option '\e1'.
.\" .It Bx
.\" honors
.\" .Ev POSIXLY_CORRECT
.\" and stops at the first non-option.
.\" .El
.\" .It
.\" Handling of
.\" .Ql -
.\" within the option string (not the first character):
.\" .Bl -tag -width ".Bx"
.\" .It Tn GNU
.\" treats a
.\" .Ql -
.\" on the command line as a non-argument.
.\" .It Bx
.\" 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 options string in presence of
.\" .Ev POSIXLY_CORRECT :
.\" .Bl -tag -width ".Bx"
.\" .It Both
.\" .Tn GNU
.\" and
.\" .Bx
.\" 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 option string is not
.\" .Ql \&: :
.\" .Bl -tag -width ".Bx"
.\" .It Tn GNU
.\" returns
.\" .Ql \&?
.\" .It Bx
.\" returns
.\" .Ql \&:
.\" (since
.\" .Bx Ns 's
.\" .Fn getopt
.\" does).
.\" .El
.\" .It
.\" Handling of
.\" .Ql --a
.\" in getopt:
.\" .Bl -tag -width ".Bx"
.\" .It Tn GNU
.\" parses this as option
.\" .Ql - ,
.\" option
.\" .Ql a .
.\" .It Bx
.\" parses this as
.\" .Ql -- ,
.\" and returns \-1 (ignoring the
.\" .Ql a ) .
.\" (Because the original
.\" .Fn getopt
.\" does.)
.\" .El
.It
Setting of
.Va optopt
for long options with
.Va flag
!=
.Dv NULL :
.Bl -tag -width ".Bx"
.It Tn GNU
sets
.Va optopt
to
.Va val .
.It Bx
sets
.Va optopt
to 0 (since
.Va val
would never be returned).
.El
.\" .It
.\" Handling of
.\" .Ql -W
.\" with
.\" .Ql W;
.\" in option string in
.\" .Fn getopt
.\" (not
.\" .Fn getopt_long ) :
.\" .Bl -tag -width ".Bx"
.\" .It Tn GNU
.\" causes a segfault.
.\" .It Bx
.\" 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
.Ql ( W;
in option string):
.Bl -tag -width ".Bx"
.It Tn GNU
sets
.Va optarg
to the option name (the argument of
.Ql -W ) .
.It Bx
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
.Ql ( W;
in option string):
.Bl -tag -width ".Bx"
.It Tn GNU
returns
.Ql -W
with
.Va optarg
set to the unknown option.
.It Bx
treats this as an error (unknown option) and returns
.Ql \&?
with
.Va optopt
set to 0 and
.Va optarg
set to
.Dv NULL
(as
.Tn GNU Ns 's
man page documents).
.El
.\" .It
.\" The error messages are different.
.It
.Bx
does not permute the argument vector at the same points in
the calling sequence as
.Tn 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 SEE ALSO
.Xr getopt 3
.Sh HISTORY
The
.Fn getopt_long
and
.Fn getopt_long_only
functions first appeared in the
.Tn GNU
libiberty library.
The first
.Bx
implementation of
.Fn getopt_long
appeared in
.Nx 1.5 ,
the first
.Bx
implementation of
.Fn getopt_long_only
in
.Ox 3.3 .
.Fx
first included
.Fn getopt_long
in
.Fx 5.0 ,
.Fn getopt_long_only
in
.Fx 5.2 .
.Sh BUGS
The
.Fa argv
argument is not really
.Vt const
as its elements may be permuted (unless
.Ev POSIXLY_CORRECT
is set).
.Pp
The implementation can completely replace
.Xr getopt 3 ,
but right now we are using separate code.
.Pp
.Nm
makes the assumption that the first argument should always be skipped because
it's typically the program name.
As a result, setting
.Va optind
to 0 will indicate that
.Nm
should reset, and
.Va optind
will be set to 1 in the process.
This behavior differs from
.Xr getopt 3 ,
which will handle an
.Va optind
value of 0 as expected and process the first element.