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\"     @(#)getopt.3     8.5 (Berkeley) 4/27/95
\"
Dd June 5, 2014
Dt GETOPT 3
Os
Sh NAME
Nm getopt
Nd get option character from command line argument list
Sh LIBRARY
Lb libc
Sh SYNOPSIS
In unistd.h
Vt extern char *optarg;
Vt extern int   optind;
Vt extern int   optopt;
Vt extern int   opterr;
Vt extern int   optreset;
Ft int
Fn getopt "int argc" "char * const argv[]" "const char *optstring"
Sh DESCRIPTION
The
Fn getopt
function incrementally parses a command line argument list
Fa argv
and returns the next
Em known
option character.
An option character is
Em known
if it has been specified in the string of accepted option characters,
Fa optstring .
Pp
The option string
Fa optstring
may contain the following elements: individual characters, and
characters followed by a colon to indicate an option argument
is to follow.
If an individual character is followed by two colons, then the
option argument is optional;
Va optarg
is set to the rest of the current
Va argv
word, or
Dv NULL
if there were no more characters in the current word.
This is a
Nx
extension.
For example, an option string
Qq x
recognizes an option
Dq Fl x ,
and an option string
Qq x:
recognizes an option and argument
Dq Fl x Ar argument .
It does not matter to
Fn getopt
if a following argument has leading whitespace.
Pp
On return from
Fn getopt ,
Va optarg
points to an option argument, if it is anticipated,
and the variable
Va optind
contains the index to the next
Fa argv
argument for a subsequent call
to
Fn getopt .
The variable
Va optopt
saves the last
Em known
option character returned by
Fn getopt .
Pp
The variables
Va opterr
and
Va optind
are both initialized to 1.
The
Va optind
variable may be set to another value before a set of calls to
Fn getopt
in order to skip over more or less argv entries.
Pp
In order to use
Fn getopt
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
the variable
Va optreset
must be set to 1 before the second and each additional set of calls to
Fn getopt ,
and the variable
Va optind
must be reinitialized.
Pp
The
Fn getopt
function returns \-1 when the argument list is exhausted.
The interpretation of options in the argument list may be cancelled
by the option
Dq --
(double dash) which causes
Fn getopt
to signal the end of argument processing and return \-1.
When all options have been processed (i.e., up to the first non-option
argument),
Fn getopt
returns \-1.
Sh RETURN VALUES
The
Fn getopt
function returns the next known option character in
Fa optstring .
If
Fn getopt
encounters a character not found in
Fa optstring
or if it detects a missing option argument,
it returns
Sq \&?
(question mark).
If
Fa optstring
has a leading
Sq \&:
then a missing option argument causes
Sq \&:
to be returned instead of
Sq \&? .
In either case, the variable
Va optopt
is set to the character that caused the error.
The
Fn getopt
function returns \-1 when the argument list is exhausted.
Sh EXAMPLES
Bd -literal -compact
extern char *optarg;
extern int optind;
int bflag, ch, fd;

bflag = 0;
while ((ch = getopt(argc, argv, "bf:")) != -1) {
       switch (ch) {
       case 'b':
               bflag = 1;
               break;
       case 'f':
               if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
                       (void)fprintf(stderr,
                           "myname: %s: %s\en", optarg, strerror(errno));
                       exit(1);
               }
               break;
       case '?':
       default:
               usage();
       }
}
argc -= optind;
argv += optind;
Ed
Sh RETURN VALUES
If the
Fn getopt
function encounters a character not found in the string
Fa optstring
or detects
a missing option argument it writes an error message to
Em stderr
and returns
Sq \&? .
Setting
Va opterr
to a zero will disable these error messages.
If
Fa optstring
has a leading
Sq \&:
then a missing option argument causes a
Sq \&:
to be returned in addition to suppressing any error messages.
Pp
Option arguments are allowed to begin with
Sq - ;
this is reasonable but reduces the amount of error checking possible.
Sh SEE ALSO
Xr getopt 1 ,
Xr getopt_long 3 ,
Xr getsubopt 3
Sh STANDARDS
The
Va optreset
variable was added to make it possible to call the
Fn getopt
function multiple times.
This is an extension to the
St -p1003.2
specification.
Sh HISTORY
The
Fn getopt
function appeared in
Bx 4.3 .
Sh BUGS
The
Fn getopt
function was once specified to return
Dv EOF
instead of \-1.
This was changed by
St -p1003.2-92
to decouple
Fn getopt
from
In stdio.h .
Pp
A single dash
Pq Sq -
may be specified as a character in
Fa optstring ,
however it should
Em never
have an argument associated with it.
This allows
Fn getopt
to be used with programs that expect
Sq -
as an option flag.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
Em only .
Care should be taken not to use
Sq -
as the first character in
Fa optstring
to avoid a semantic conflict with
Tn GNU
Fn getopt ,
which assigns different meaning to an
Fa optstring
that begins with a
Sq - .
By default, a single dash causes
Fn getopt
to return \-1.
Pp
It is also possible to handle digits as option letters.
This allows
Fn getopt
to be used with programs that expect a number
Pq Dq Li \-3
as an option.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
Em only .
The following code fragment works in most cases.
Bd -literal -offset indent
int ch;
long length;
char *p;

while ((ch = getopt(argc, argv, "0123456789")) != -1) {
       switch (ch) {
       case '0': case '1': case '2': case '3': case '4':
       case '5': case '6': case '7': case '8': case '9':
               p = argv[optind - 1];
               if (p[0] == '-' && p[1] == ch && !p[2])
                       length = ch - '0';
               else
                       length = strtol(argv[optind] + 1, NULL, 10);
               break;
       }
}
Ed

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