getopt_long, getopt_long_only - get long options from command line argument
list
#include <getopt.h>
extern char *optarg;
extern int optind;
extern int optopt;
extern int opterr;
extern int optreset;
int
getopt_long(int argc, char * const *argv, const char
*optstring,
const struct option *longopts, int *longindex);
int
getopt_long_only(int argc, char * const *argv, const char
*optstring,
const struct option *longopts, int *longindex);
The getopt_long() function is similar to getopt(3) but it
accepts options
in two forms: words and characters. The getopt_long() function provides
a superset of the functionality of getopt(3). 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, getopt_long() behaves identically to getopt(3).
This is a good
way to add long option processing to an existing program
with the minimum
of rewriting.
In the second mechanism, a long option sets a flag in the
option structure
passed, or will store a pointer to the command line argument in the
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.
myprogram --myoption=somevalue
When a long option is processed the call to getopt_long()
will return 0.
For this reason, long option processing without shortcuts is
not backwards
compatible with getopt(3).
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.
The getopt_long() call requires a structure to be initialized describing
the long options. The structure is:
struct option {
char *name;
int has_arg;
int *flag;
int val;
};
The name field should contain the option name without the
leading double
dash.
The has_arg field should be one of:
no_argument no argument to the option is expect.
required_argument an argument to the option is required.
optional_argument an argument to the option may be presented.
If flag is not NULL, then the integer pointed to by it will
be set to the
value in the val field. If the flag field is NULL, then the
val field
will be returned. Setting flag to NULL and setting val to
the corresponding
short option will make this function act just like
getopt(3).
If the longindex field is not NULL, then the integer pointed
to by it
will be set to the index of the long option relative to
longopts.
The last element of the longopts array has to be filled with
zeroes.
The getopt_long_only() function behaves identically to
getopt_long() with
the exception that long options may start with `-' in addition to `--'.
If an option starting with `-' does not match a long option
but does
match a single-character option, the single-character option
is returned.
If the flag field in struct option is NULL, getopt_long()
and
getopt_long_only() return the value specified in the val
field, which is
usually just the corresponding short option. If flag is not
NULL, these
functions return 0 and store val in the location pointed to
by flag.
These functions return `:' if there was a missing option argument, `?' if
the user specified an unknown or ambiguous option, and -1
when the argument
list has been exhausted.
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
teeth0);
}
break;
default:
usage();
}
argc -= optind;
argv += optind;
IMPLEMENTATION DIFFERENCES [Toc] [Back] This section describes differences to the GNU implementation
found in
glibc-2.1.3:
o handling of - as first char of option string in presence of environment
variable POSIXLY_CORRECT:
GNU ignores POSIXLY_CORRECT and returns non-options as arguments
to option '1'.
OpenBSD honors POSIXLY_CORRECT and stops at the first
non-option.
o handling of - within the option string (not the first
character):
GNU treats a `-' on the command line as a non-argument.
OpenBSD a `-' within the option string matches a `-'
(single dash)
on the command line. This functionality is
provided for
backward compatibility with programs, such as
su(1), that
use `-' as an option flag. This practice is
wrong, and
should not be used in any current development.
o handling of :: in options string in presence of POSIXLY_CORRECT:
Both GNU and OpenBSD ignore POSIXLY_CORRECT here
and take :: to
mean the preceding option takes an optional
argument.
o return value in case of missing argument if first character (after +
or -) in option string is not ':':
GNU returns '?'
OpenBSD returns ':' (since OpenBSD's getopt does).
o handling of --a in getopt:
GNU parses this as option '-', option 'a'.
OpenBSD parses this as '--', and returns -1 (ignoring
the a). (Because
the original getopt does.)
o setting of optopt for long options with flag != NULL:
GNU sets optopt to val.
OpenBSD sets optopt to 0 (since val would never be returned).
o handling of -W with W; in option string in getopt (not
getopt_long):
GNU causes a segfault.
OpenBSD no special handling is done; ``W;'' is interpreted as two
separate options, neither of which take an argument.
o setting of optarg for long options without an argument
that are invoked
via -W (W; in option string):
GNU sets optarg to the option name (the argument
of -W).
OpenBSD sets optarg to NULL (the argument of the long
option).
o handling of -W with an argument that is not (a prefix
to) a known
long option (W; in option string):
GNU returns -W with optarg set to the unknown option.
OpenBSD treats this as an error (unknown option) and
returns '?'
with optopt set to 0 and optarg set to NULL
(as GNU's man
page documents).
o The error messages are different.
o OpenBSD 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.)
POSIXLY_CORRECT If set, option processing stops when the
first non-option
is found and a leading `-' or `+' in
the optstring
is ignored.
getopt(3)
The getopt_long() and getopt_long_only() functions first appeared in GNU
libiberty. This implementation first appeared in OpenBSD
3.3.
The argv argument is not really const as its elements may be
permuted
(unless POSIXLY_CORRECT is set).
OpenBSD 3.6 April 1, 2000
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