man/man3c/getopt_long.3c

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.Dd August 10, 2020
.Dt GETOPT_LONG 3C
.Os
.Sh NAME
.Nm getopt_long ,
.Nm getopt_long_clip ,
.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 ;
.Ft int
.Fo getopt_long
.Fa "int argc"
.Fa "char * const *argv"
.Fa "const char *optstring"
.Fa "const struct option *longopts"
.Fa "int *longindex"
.Fc
.Ft int
.Fo getopt_long_only
.Fa "int argc"
.Fa "char * const *argv"
.Fa "const char *optstring"
.Fa "const struct option *longopts"
.Fa "int *longindex"
.Fc
.Ft int
.Fo getopt_long_clip
.Fa "int argc"
.Fa "char * const *argv"
.Fa "const char *optstring"
.Fa "const struct option *longopts"
.Fa "int *longindex"
.Fc
.Sh DESCRIPTION
The
.Fn getopt_long
function is similar to
.Xr getopt 3C
but it accepts options in two forms: short options and long options.
Short options are the traditional option flags that use a hyphen followed
by a single character.
This is the only form of option that is portable and it is supported by
.Xr getopt 3C .
Note, some implementation of
.Xr getopt 3C
do support non-standard extensions for long options; however, these are
not portable and not considered in this manual page.
Common example of short options are:
.Fl a ,
.Fl l ,
and
.Fl r .
Long options use two hyphen characters are generally full words.
The long versions of the above might be:
.Fl -all ,
.Fl -list ,
and
.Fl -recursive .
.Pp
The
.Fn getopt_long
function can be used to:
.Bl -enum
.It
Support an option with both short and long forms.
.It
Support an option with only a short form.
.It
Support an option with only a long form.
.El
.Pp
To have a short option selected, as with
.Xr getopt 3C ,
it must be listed in
.Fa optstring .
Long options are instead listed in the
.Fa longopts
array.
For an option to have both a short and long form it must be present in
both
.Fa optstring
and
.Fa longopts .
.Pp
Long options can be handled in two different 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 3C .
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 3C .
.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
In
.Fn getopt_long
and
.Fn getopt_long_only ,
.Fa optstring
acts similar to
.Fa optstring
in
.Xr getopt 3C ,
listing the set of supported short option flags.
In addition,
.Fa optstring
can begin with
.Ql +
or
.Ql - .
If
.Fa optstring
begins with
.Ql + ,
the first non-option terminates option processing.
This is equivalent to setting the environment variable
.Ev POSIXLY_CORRECT .
If
.Fa optstring
begins with
.Ql - ,
non-options are treated as options to the argument
.Ql \e1 .
.Pp
If
.Fa optstring
does not begin with
.Ql +
and
.Ev POSIXLY_CORRECT
is not set, if
.Ql W\&;
appears in
.Fa optstring ,
.Ql "-W myoption"
is treated the same as
.Ql "--myoption"
and
.Va optarg
is set to
.Ql myoption .
.Pp
In
.Fn getopt_long_clip ,
.Ql +
and
.Ql -
are ignored at the beginning of a string.
.Pp
The
.Fn getopt_long ,
.Fn getopt_long_only ,
and
.Fn getopt_long_clip
functions require 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
.Fa name
field should contain the option name without the leading double hyphen.
.Pp
The
.Fa 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
.Fa flag
is not
.Dv NULL ,
then the integer pointed to by it will be set to the
value in the
.Fa val
field and
.Va optopt
will be set to
.Sy 0 .
If the
.Fa flag
field is
.Dv NULL ,
then the
.Fa val
field will be returned and
.Va optopt
is set to the value in the
.Fa val
field.
Setting
.Fa flag
to
.Dv NULL
and setting
.Fa val
to the corresponding short option will make this function act just
like
.Xr getopt 3C .
.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.
.Pp
The
.Fn getopt_long_clip
function is a variation of
.Fn getopt_long
except that options must also adhere to the Sun CLIP specification.
Specifically, the major differences from
.Fn getopt_long
are:
.Bl -bullet -offset indent
.It
All option arguments are required
.Po
.Dv optional_argument
is treated the same as
.Dv required_argument
.Pc .
.It
Long options cannot be abbreviated on the command line.
.It
Long options must use a double hyphen
.Pq Ql -- .
.It
Option processing stops at the first non-option.
.It
All long options must have an equivalent short option (single character) and
vice-versa.
.It
A leading
.Ql +
or
.Ql -
in
.Fa optstring
is ignored.
.Fa optstring
is treated as if it began after the leading
.Ql +
or
.Ql - .
.El
.Pp
On each call to
.Fn getopt_long ,
.Fn getopt_long_only ,
or
.Fn getopt_long ,
.Va optind
is set to the
.Va argv
index of the
.Em next
argument to be processed.
.Va optind
is initialized to
.Sy 1
prior to the first invocation of
.Fn getopt_long ,
.Fn getopt_long_only ,
or
.Fn getopt_long_clip .
.Pp
If
.Va opterr
is set to a non-zero value and
.Fa optstring
does not start with
.Ql \&: ,
.Fn getopt_long ,
.Fn getopt_long_only ,
and
.Fn getopt_long_clip
will print an error message to
.Sy stderr
when an error or invalid option is encountered.
.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 .
These functions return
.Ql \&:
if there was a missing option argument,
.Ql \&?
if the user specified an unknown or ambiguous option, and
\-1 when the argument list has been exhausted.
.Pp
If a long option to
.Fn getopt_long_clip
is missing its equivalent short option (or vice-versa),\-1 is returned on the
first call to
.Fn getopt_long_clip ,
and
.Dv errno
is set to
.Er EINVAL .
If
.Va opterr
is set to a non-zero value and
.Fa optstring
does not start with
.Ql \&: ,
an error message will be written to
.Sy stderr .
.Pp
If
.Fa optstring
does not start with
.Ql \&:
and
.Fn getopt_long ,
.Fn getopt_long_only ,
or
.Fn getopt_long_clip
return
.Ql \&:
or
.Ql \&? ,
if
.Va opterr
is set to a non-zero value, an error message is written to
.Dv stderr .
.Sh ENVIRONMENT
The following environment variables can effect the execution of
.Nm getopt_long ,
.Nm getopt_long_only ,
and
.Nm getopt_long_clip :
.Ev LANG ,
.Ev LC_ALL ,
.Ev LC_MESSAGES .
See
.Xr environ 5 .
.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 USAGE
Similar to
.Xr getopt 3C ,
since there is no unambiguous way to detect a missing option-argument except when the
option is the last option on the command line, the
.Fn getopt_long ,
.Fn getopt_long_only ,
and
.Fn getopt_long_clip
functions cannot fully check for mandatory arguments.
For example, the option string
.Ql ho\&:
with an input of
.Ql Fl o Fl h
will assume that
.Ql Fl h
is the required argument to
.Fl o
instead of assuming that
.Fl o
is missing its option-argument.
.Pp
Like
.Xr getopt 3C ,
grouping options taking or requiring arguments with other options is a violation of the
Basic Utility Command syntax standard (see
.Xr Intro 1 ) .
For example, given the option string
.Ql cde\&: ,
running:
.Pp
.Dl cmd Fl cde Ar ieio
.Pp
is incorrect.
Current versions of
.Nm getopt_long ,
.Nm getopt_long_only ,
and
.Nm getopt_long_clip
accept this, however future versions may not support this.
The correct invocation would be:
.Pp
.Dl cmd Fl cd Fl e Ar ieio
.Sh EXAMPLES
.Sy Example 1
Basic usage of
.Fn getopt_long .
.Pp
In this example, the short options,
.Fl b
and
.Fl f
are treated the same way as their corresponding long options
.Fl -buffy
and
.Fl -fluoride .
The long option
.Fl -daggerset
is only matched as a long option.
.Pp
.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
.Pp
.Sy Example 2
Mixing short-only and long-only options.
.Pp
This example has a program that uses both short and long options and
always causes the option to be handled in a way that is similar to
.Xr getopt 3C
regardless of if it is short or long.
Options that are only long options are assigned a character value that
is outside of the common 8-bit range
.Po
starting at
.Dv USHRT_MAX
+ 1.
.Pc
This allows them to still integrate into a normal
.Xr getopt 3C
style option processing loop.
.Pp
In the following code,
.Fl s
is only usable as a short option while
.Fl -long-only
is only usable as a long option, hence
.Fl s
is only specified in
.Fa optstring
and
.Fl -long-only
is only specified in the
.Fa longopts
.Vt option
array.
.Pp
.Bd -literal -compact
#include <getopt.h>
#include <stdio.h>
#include <limits.h>

enum longopt_chars {
        LONG_ONLY = USHRT_MAX +1
};

static struct option longopts[] = {
        { "all", no_argument, NULL, 'a' },
        { "list", no_argument, NULL, 'l' },
        { "long-only", no_argument, NULL, LONG_ONLY },
        { "output", required_argument, NULL, 'o' },
        { NULL }
};

int
main(int argc, char *argv[])
{
        int ch;

        while ((ch = getopt_long(argc, argv, "alo:s", longopts,
            NULL)) != -1) {
                switch (ch) {
                case 'a':
                        printf("found -a\en");
                        break;
                case 'l':
                        printf("found -l\en");
                        break;
                case 'o':
                        printf("found -o: %s\en", optarg);
                        break;
                case 's':
                        printf("found -s\en");
                        break;
                case LONG_ONLY:
                        printf("found --long-only\en");
                        break;
                default:
                        break;
                }
        }

        return (0);
}
.Ed
.Sh ERRORS
The
.Fn getopt_long_clip
function will fail if:
.Bl -tag -width EINVAL
.It Er EINVAL
A short option is missing a corresponding long option, or vice-versa.
.El
.Pp
There are no errors defined for
.Fn getopt_long
and
.Fn getopt_long_only .
.Sh IMPLEMENTATION DIFFERENCES
While the illumos implementations of
.Nm getopt_long
and
.Nm getopt_long_only
are broadly compatible with other implementations, the following edge cases
have historically been known to vary among implementations:
.Bl -bullet
.It
The setting of
.Va optopt
for long options with
.Fa flag
!=
.Dv NULL
in
.Vt struct option .
In illumos,
.Va optopt
is set to 0 (since
.Fa val
would never be returned).
.It
The setting of
.Va optarg
for long options without an argument that are
invoked via
.Ql -W
.Ql ( W\&;
in
.Fa optstring ) .
illumos sets
.Va optarg
to the option name (the argument of
.Ql -W ) .
.It
The handling of
.Ql -W
with an argument that is not (a prefix to) a known
long option
.Ql ( W\&;
in
.Fa optstring ) .
illumos treats this as an error (unknown option) and returns
.Ql \&?
with
.Va optopt
set to 0 and
.Va optarg
set to
.Dv NULL .
.It
illumos
may not permute the argument vector at the same points in
the calling sequence as other implementations.
The aspects normally used by
the caller (ordering after \-1 is returned, the value of
.Va optind
relative
to current positions) are the same, though.
(We often do fewer variable swaps.)
.El
.Sh INTERFACE STABILITY
Committed
.Sh MT-LEVEL
Unsafe
.Sh SEE ALSO
.Xr getopt 3C
.Sh BUGS
The
.Fa argv
argument is not really
.Vt const
as its elements may be permuted (unless
.Ev POSIXLY_CORRECT
is set).