subgetopt(3) C Library Functions subgetopt(3)
NAME
subgetopt - get option character from command line
SYNTAX
#include <subgetopt.h>
char *sgoptarg;
int sgoptind;
int sgoptpos;
int sgoptdone;
int sgoptproblem;
int sgopt(argc,argv,opts);
int argc;
char **argv;
char *opts;
DESCRIPTION
sgopt returns the next valid command-line option character
from argv.
Valid option characters are listed in the opts string. opts
may be empty. A character in opts may be followed by a
colon, in which case it takes an option argument. Avoid
using the characters ?, :, and - as option characters.
Below option argument is abbreviated as optarg and command-
line argument is abbreviated as cmdarg.
Options are listed in cmdargs which begin with a minus sign.
Several options which do not take optargs may be combined
into one cmdarg.
An option which takes an optarg may be handled in two ways.
If it appears at the very end of a cmdarg, then the entire
next cmdarg is the optarg. But if there are any characters
in the cmdarg after the option character, then those charac-
ters form the optarg. The optarg is returned in sgoptarg.
Next time sgopt looks at the cmdarg which follows the
optarg.
If a cmdarg does not begin with a hyphen, or if it is a lone
hyphen not followed by any characters, or if it begins with
two hyphens, then it terminates option processing, and sgopt
returns an appropriate code. If there are two hyphens,
sgopt will advance attention to the next cmdarg, so it can
be called again to read further options.
PROPER USAGE
sgoptproblem should be used only when sgopt returns ?.
sgoptind and sgoptpos are defined all the time. sgoptarg is
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defined all the time; it is null unless sgopt has just
returned an option with optarg.
sgopt is typically used as follows.
#include <subgetopt.h>
main(argc,argv) int argc; char **argv; { int opt;
while ((opt = sgopt(argc,argv,"a:s")) != sgoptdone)
switch(opt) {
case 'a':
printf("opt a with optarg %s\n",sgoptarg); break;
case 's':
printf("opt s with no optarg\n"); break;
case '?':
if (argv[sgoptind] && (sgoptind < argc))
printf("illegal opt %c\n",sgoptproblem);
else
printf("missing arg, opt %c\n",sgoptproblem);
exit(1);
}
argv += sgoptind;
while (*argv) printf("argument %s\n",*argv++);
exit(0);
}
The end of the command line is marked by either argc, or a
null pointer in argv, whichever comes first. Normally these
two markers coincide, so it is redundant to test for both
argv[sgoptind] and sgoptind < argc. The above code shows
both tests as an illustration.
Multiple option sets: One useful technique is to call sgopt
with a primary opts until it returns EOF, then call sgopt
with a secondary opts until it returns EOF. The user can
provide primary options, then a double hyphen, and then sec-
ondary options. No special handling is needed if some or
all of the options are omitted. The same technique can be
used for any number of option sets in series.
Multiple command lines: Before parsing a new argv, make sure
to set sgoptind and sgoptpos back to 1 and 0.
PARSING STAGES
sgopt keeps track of its position in argv with sgoptind and
sgoptpos, which are initialized to 1 and 0. It looks at
argv[sgoptind][sgoptpos] and following characters.
sgopt indicates that no more options are available by
returning sgoptdone, which is initialized to SUBGETOPTDONE,
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which is defined as -1.
sgopt begins by setting optarg to null.
Ending conditions: If argv is null, or sgoptind is larger
than argc, or the current cmdarg argv[sgoptind] is null,
then sgopt returns optdone.
Stage one: If the current character is zero, sgopt moves to
the beginning of the next cmdarg. It then checks the ending
conditions again.
Stage two: If the current position is the begining of the
cmdarg, sgopt checks whether the current character is a
minus sign. If not it returns optdone. It then moves to
the next character. If that character is zero, sgopt moves
back to the beginning of the cmdarg, and returns sgoptdone.
If the character is a minus sign, sgopt moves to the begin-
ning of the next cmdarg, and returns sgoptdone.
Stage three: sgopt records the current character, c, and
moves to the next character. There are three possibilities:
(1) c is an option character without optarg in opts, or (2)
c is an option character with optarg in opts, or (3) c does
not appear in opts.
(1) If c appears as an option character without optarg in
opts, sgopt returns c.
(2) If c appears as an option character with optarg in opts,
sgopt sets sgoptarg to the current position, and moves to
the next cmdarg. If sgoptarg is nonempty, sgopt returns c.
Then sgopt sets sgoptarg to the current cmdarg. If the cur-
rent cmdarg is null, or past argc, sgopt sets sgoptproblem
to c and returns ?. Otherwise sgopt moves to the next argu-
ment and returns c.
(2) If c does not appear in opts, sgopt sets sgoptproblem to
c and returns ?.
SYNTAX NOTE
sgopt is actually a macro abbreviation for subgetopt. The
external sg variables are also macros for subget. These
macros are defined in <subgetopt.h>, unless SUBGETOPTNOSHORT
is defined when <subgetopt.h> is included.
VERSION
subgetopt version 0.9, 931129.
AUTHOR
Placed into the public domain by Daniel J. Bernstein.
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