GETOPT_LONG(3) Library Functions Manual GETOPT_LONG(3)
NAME
getopt_long, getopt_long_only – get long options from command line
argument list
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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);
DESCRIPTION
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). The 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, 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 expected
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.
RETURN VALUES
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 and
error messages are suppressed, ‘?’ 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 ‘?’. Specifying ‘:’ in optstr will cause the
error message to be suppressed and ‘:’ to be returned instead.
In addition to ‘:’, a leading ‘+’ or ‘-’ in optstr also has special
meaning. If either of these are specified, they must appear before ‘:’.
A leading ‘+’ indicates that processing should be halted at the first
non-option argument, matching the default behavior of getopt(3). The
default behavior without ‘+’ is to permute non-option arguments to the
end of argv.
A leading ‘-’ indicates that all non-option arguments should be treated
as if they are arguments to a literal ‘1’ flag (i.e., the function call
will return the value 1, rather than the char literal '1').
ENVIRONMENT
POSIXLY_CORRECT If set, option processing stops when the first non-
option is found and a leading ‘-’ or ‘+’ in the
optstring is ignored.
EXAMPLES
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\n");
}
break;
default:
usage();
}
}
argc -= optind;
argv += optind;
IMPLEMENTATION DIFFERENCES
This section describes differences to the GNU implementation found in
glibc-2.1.3:
• Setting of optopt for long options with flag != NULL:
GNU sets optopt to val.
BSD sets optopt to 0 (since val would never be returned).
• 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’).
BSD sets optarg to NULL (the argument of the long option).
• 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.
BSD 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).
• BSD 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.)
SEE ALSO
getopt(3)
HISTORY
The getopt_long() and getopt_long_only() functions first appeared in the
GNU libiberty library. The first BSD implementation of getopt_long()
appeared in NetBSD 1.5, the first BSD implementation of
getopt_long_only() in OpenBSD 3.3. FreeBSD first included getopt_long()
in FreeBSD 5.0, getopt_long_only() in FreeBSD 5.2.
BUGS
The argv argument is not really const as its elements may be permuted
(unless POSIXLY_CORRECT is set).
The implementation can completely replace getopt(3), but right now we are
using separate code.
getopt_long makes the assumption that the first argument should always be
skipped because it's typically the program name. As a result, setting
optind to 0 will indicate that getopt_long should reset, and optind will
be set to 1 in the process. This behavior differs from getopt(3), which
will handle an optind value of 0 as expected and process the first
element.
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