getopt
function
Here are the details about how to call the getopt
function. To
use this facility, your program must include the header file
`unistd.h'.
getopt
prints an
error message to the standard error stream if it encounters an unknown
option character or an option with a missing required argument. This is
the default behavior. If you set this variable to zero, getopt
does not print any messages, but it still returns the character ?
to indicate an error.
getopt
encounters an unknown option character or an option
with a missing required argument, it stores that option character in
this variable. You can use this for providing your own diagnostic
messages.
getopt
to the index of the next element
of the argv array to be processed. Once getopt
has found
all of the option arguments, you can use this variable to determine
where the remaining non-option arguments begin. The initial value of
this variable is 1
.
getopt
to point at the value of the
option argument, for those options that accept arguments.
getopt
function gets the next option argument from the
argument list specified by the argv and argc arguments.
Normally these values come directly from the arguments received by
main
.
The options argument is a string that specifies the option characters that are valid for this program. An option character in this string can be followed by a colon (`:') to indicate that it takes a required argument. If an option character is followed by two colons (`::'), its argument is optional; this is a GNU extension.
getopt
has three ways to deal with options that follow
non-options argv elements. The special argument `--' forces
in all cases the end of option scanning.
POSIXLY_CORRECT
or beginning the options argument
string with a plus sign (`+').
The getopt
function returns the option character for the next
command line option. When no more option arguments are available, it
returns -1
. There may still be more non-option arguments; you
must compare the external variable optind
against the argc
parameter to check this.
If the option has an argument, getopt
returns the argument by
storing it in the variable optarg. You don't ordinarily need to
copy the optarg
string, since it is a pointer into the original
argv array, not into a static area that might be overwritten.
If getopt
finds an option character in argv that was not
included in options, or a missing option argument, it returns
`?' and sets the external variable optopt
to the actual
option character. If the first character of options is a colon
(`:'), then getopt
returns `:' instead of `?' to
indicate a missing option argument. In addition, if the external
variable opterr
is nonzero (which is the default), getopt
prints an error message.
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