@node getopt, misc
@subheading Syntax

@example
#include <unistd.h>

int getopt(int argc, char * const *argv, const char *options);
extern char *optarg;
extern int optind, opterr, optopt;
@end example

@subheading Description

Parse options from the command line.  The @var{options} are a string of
valid option characters.  If a given option takes a parameter, that
character should be followed by a colon.

For each valid switch, this function sets @code{optarg} to the argument
(if the switch takes one), sets @code{optind} to the index in @var{argv}
that it is using, sets @code{optopt} to the option letter found, and
returns the option letter found.

If an unexpected option is found, @code{getopt} will return @code{?},
and if @code{opterr} is nonzero, will print an error message to stderr. 

The special option @code{--} indicates that no more options follow on
the command line, and cause @code{getopt} to stop looking. 

@subheading Return Value

The option found, or -1 if no more options.

@subheading Portability

@portability !ansi, posix

@subheading Example

@example
int c;
opterr = 0;
while ((c=getopt(argc, argv, "vbf:")) != -1)
@{
  switch (c)
  @{
    case 'v':
      verbose_flag ++;
      break;
    case 'b':
      binary_flag ++;
      break;
    case 'f':
      output_filename = optarg;
      break;
    case '?':
      printf("Unknown option %c\n", optopt);
      usage();
      exit(1);
  @}
@}
@end example