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-@node Getopt, Argp, , Parsing Program Arguments
-@section Parsing program options using @code{getopt}
-
-The @code{getopt} and @code{getopt_long} functions automate some of the
-chore involved in parsing typical unix command line options.
-
-@menu
-* Using Getopt:: Using the @code{getopt} function.
-* Example of Getopt:: An example of parsing options with @code{getopt}.
-* Getopt Long Options:: GNU suggests utilities accept long-named
- options; here is one way to do.
-* Getopt Long Option Example:: An example of using @code{getopt_long}.
-@end menu
-
-@node Using Getopt, Example of Getopt, , Getopt
-@subsection Using the @code{getopt} function
-
-Here are the details about how to call the @code{getopt} function. To
-use this facility, your program must include the header file
-@file{unistd.h}.
-@pindex unistd.h
-
-@comment unistd.h
-@comment POSIX.2
-@deftypevar int opterr
-If the value of this variable is nonzero, then @code{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, @code{getopt}
-does not print any messages, but it still returns the character @code{?}
-to indicate an error.
-@end deftypevar
-
-@comment unistd.h
-@comment POSIX.2
-@deftypevar int optopt
-When @code{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.
-@end deftypevar
-
-@comment unistd.h
-@comment POSIX.2
-@deftypevar int optind
-This variable is set by @code{getopt} to the index of the next element
-of the @var{argv} array to be processed. Once @code{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 @code{1}.
-@end deftypevar
-
-@comment unistd.h
-@comment POSIX.2
-@deftypevar {char *} optarg
-This variable is set by @code{getopt} to point at the value of the
-option argument, for those options that accept arguments.
-@end deftypevar
-
-@comment unistd.h
-@comment POSIX.2
-@deftypefun int getopt (int @var{argc}, char *const *@var{argv}, const char *@var{options})
-@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
-@c Swapping elements of passed-in argv may be partial in case of
-@c cancellation. Gettext brings about a whole lot of AS and AC safety
-@c issues. The getopt API involves returning values in the
-@c non-thread-specific optarg variable, which adds another thread-safety
-@c issue. Given print_errors, it may output errors to stderr, which may
-@c self-deadlock, leak locks, or encounter (in a signal handler) or
-@c leave (in case of cancellation) stderr in an inconsistent state.
-@c Various implicit, indirect uses of malloc, in uses of memstream and
-@c asprintf for error-printing, bring about the usual malloc issues.
-@c
-@c _getopt_internal
-@c _getopt_internal_r
-@c gettext
-@c _getopt_initialize
-@c getenv
-@c open_memstream
-@c lockfile, unlockfile, __fxprintf -> stderr
-@c asprintf
-The @code{getopt} function gets the next option argument from the
-argument list specified by the @var{argv} and @var{argc} arguments.
-Normally these values come directly from the arguments received by
-@code{main}.
-
-The @var{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 (@samp{:}) to indicate that it takes a
-required argument. If an option character is followed by two colons
-(@samp{::}), its argument is optional; this is a GNU extension.
-
-@code{getopt} has three ways to deal with options that follow
-non-options @var{argv} elements. The special argument @samp{--} forces
-in all cases the end of option scanning.
-
-@itemize @bullet
-@item
-The default is to permute the contents of @var{argv} while scanning it
-so that eventually all the non-options are at the end. This allows
-options to be given in any order, even with programs that were not
-written to expect this.
-
-@item
-If the @var{options} argument string begins with a hyphen (@samp{-}), this
-is treated specially. It permits arguments that are not options to be
-returned as if they were associated with option character @samp{\1}.
-
-@item
-POSIX demands the following behavior: the first non-option stops option
-processing. This mode is selected by either setting the environment
-variable @code{POSIXLY_CORRECT} or beginning the @var{options} argument
-string with a plus sign (@samp{+}).
-@end itemize
-
-The @code{getopt} function returns the option character for the next
-command line option. When no more option arguments are available, it
-returns @code{-1}. There may still be more non-option arguments; you
-must compare the external variable @code{optind} against the @var{argc}
-parameter to check this.
-
-If the option has an argument, @code{getopt} returns the argument by
-storing it in the variable @var{optarg}. You don't ordinarily need to
-copy the @code{optarg} string, since it is a pointer into the original
-@var{argv} array, not into a static area that might be overwritten.
-
-If @code{getopt} finds an option character in @var{argv} that was not
-included in @var{options}, or a missing option argument, it returns
-@samp{?} and sets the external variable @code{optopt} to the actual
-option character. If the first character of @var{options} is a colon
-(@samp{:}), then @code{getopt} returns @samp{:} instead of @samp{?} to
-indicate a missing option argument. In addition, if the external
-variable @code{opterr} is nonzero (which is the default), @code{getopt}
-prints an error message.
-@end deftypefun
-
-@node Example of Getopt
-@subsection Example of Parsing Arguments with @code{getopt}
-
-Here is an example showing how @code{getopt} is typically used. The
-key points to notice are:
-
-@itemize @bullet
-@item
-Normally, @code{getopt} is called in a loop. When @code{getopt} returns
-@code{-1}, indicating no more options are present, the loop terminates.
-
-@item
-A @code{switch} statement is used to dispatch on the return value from
-@code{getopt}. In typical use, each case just sets a variable that
-is used later in the program.
-
-@item
-A second loop is used to process the remaining non-option arguments.
-@end itemize
-
-@smallexample
-@include testopt.c.texi
-@end smallexample
-
-Here are some examples showing what this program prints with different
-combinations of arguments:
-
-@smallexample
-% testopt
-aflag = 0, bflag = 0, cvalue = (null)
-
-% testopt -a -b
-aflag = 1, bflag = 1, cvalue = (null)
-
-% testopt -ab
-aflag = 1, bflag = 1, cvalue = (null)
-
-% testopt -c foo
-aflag = 0, bflag = 0, cvalue = foo
-
-% testopt -cfoo
-aflag = 0, bflag = 0, cvalue = foo
-
-% testopt arg1
-aflag = 0, bflag = 0, cvalue = (null)
-Non-option argument arg1
-
-% testopt -a arg1
-aflag = 1, bflag = 0, cvalue = (null)
-Non-option argument arg1
-
-% testopt -c foo arg1
-aflag = 0, bflag = 0, cvalue = foo
-Non-option argument arg1
-
-% testopt -a -- -b
-aflag = 1, bflag = 0, cvalue = (null)
-Non-option argument -b
-
-% testopt -a -
-aflag = 1, bflag = 0, cvalue = (null)
-Non-option argument -
-@end smallexample
-
-@node Getopt Long Options
-@subsection Parsing Long Options with @code{getopt_long}
-
-To accept GNU-style long options as well as single-character options,
-use @code{getopt_long} instead of @code{getopt}. This function is
-declared in @file{getopt.h}, not @file{unistd.h}. You should make every
-program accept long options if it uses any options, for this takes
-little extra work and helps beginners remember how to use the program.
-
-@comment getopt.h
-@comment GNU
-@deftp {Data Type} {struct option}
-This structure describes a single long option name for the sake of
-@code{getopt_long}. The argument @var{longopts} must be an array of
-these structures, one for each long option. Terminate the array with an
-element containing all zeros.
-
-The @code{struct option} structure has these fields:
-
-@table @code
-@item const char *name
-This field is the name of the option. It is a string.
-
-@item int has_arg
-This field says whether the option takes an argument. It is an integer,
-and there are three legitimate values: @w{@code{no_argument}},
-@code{required_argument} and @code{optional_argument}.
-
-@item int *flag
-@itemx int val
-These fields control how to report or act on the option when it occurs.
-
-If @code{flag} is a null pointer, then the @code{val} is a value which
-identifies this option. Often these values are chosen to uniquely
-identify particular long options.
-
-If @code{flag} is not a null pointer, it should be the address of an
-@code{int} variable which is the flag for this option. The value in
-@code{val} is the value to store in the flag to indicate that the option
-was seen.
-@end table
-@end deftp
-
-@comment getopt.h
-@comment GNU
-@deftypefun int getopt_long (int @var{argc}, char *const *@var{argv}, const char *@var{shortopts}, const struct option *@var{longopts}, int *@var{indexptr})
-@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
-@c Same issues as getopt.
-Decode options from the vector @var{argv} (whose length is @var{argc}).
-The argument @var{shortopts} describes the short options to accept, just as
-it does in @code{getopt}. The argument @var{longopts} describes the long
-options to accept (see above).
-
-When @code{getopt_long} encounters a short option, it does the same
-thing that @code{getopt} would do: it returns the character code for the
-option, and stores the option's argument (if it has one) in @code{optarg}.
-
-When @code{getopt_long} encounters a long option, it takes actions based
-on the @code{flag} and @code{val} fields of the definition of that
-option.
-
-If @code{flag} is a null pointer, then @code{getopt_long} returns the
-contents of @code{val} to indicate which option it found. You should
-arrange distinct values in the @code{val} field for options with
-different meanings, so you can decode these values after
-@code{getopt_long} returns. If the long option is equivalent to a short
-option, you can use the short option's character code in @code{val}.
-
-If @code{flag} is not a null pointer, that means this option should just
-set a flag in the program. The flag is a variable of type @code{int}
-that you define. Put the address of the flag in the @code{flag} field.
-Put in the @code{val} field the value you would like this option to
-store in the flag. In this case, @code{getopt_long} returns @code{0}.
-
-For any long option, @code{getopt_long} tells you the index in the array
-@var{longopts} of the options definition, by storing it into
-@code{*@var{indexptr}}. You can get the name of the option with
-@code{@var{longopts}[*@var{indexptr}].name}. So you can distinguish among
-long options either by the values in their @code{val} fields or by their
-indices. You can also distinguish in this way among long options that
-set flags.
-
-When a long option has an argument, @code{getopt_long} puts the argument
-value in the variable @code{optarg} before returning. When the option
-has no argument, the value in @code{optarg} is a null pointer. This is
-how you can tell whether an optional argument was supplied.
-
-When @code{getopt_long} has no more options to handle, it returns
-@code{-1}, and leaves in the variable @code{optind} the index in
-@var{argv} of the next remaining argument.
-@end deftypefun
-
-Since long option names were used before @code{getopt_long}
-was invented there are program interfaces which require programs
-to recognize options like @w{@samp{-option value}} instead of
-@w{@samp{--option value}}. To enable these programs to use the GNU
-getopt functionality there is one more function available.
-
-@comment getopt.h
-@comment GNU
-@deftypefun int getopt_long_only (int @var{argc}, char *const *@var{argv}, const char *@var{shortopts}, const struct option *@var{longopts}, int *@var{indexptr})
-@safety{@prelim{}@mtunsafe{@mtasurace{:getopt} @mtsenv{}}@asunsafe{@ascuheap{} @ascuintl{} @asulock{} @asucorrupt{}}@acunsafe{@acsmem{} @aculock{} @acucorrupt{}}}
-@c Same issues as getopt.
-
-The @code{getopt_long_only} function is equivalent to the
-@code{getopt_long} function but it allows the user of the
-application to pass long options with only @samp{-} instead of
-@samp{--}. The @samp{--} prefix is still recognized but instead of
-looking through the short options if a @samp{-} is seen it is first
-tried whether this parameter names a long option. If not, it is parsed
-as a short option.
-
-Assuming @code{getopt_long_only} is used starting an application with
-
-@smallexample
- app -foo
-@end smallexample
-
-@noindent
-the @code{getopt_long_only} will first look for a long option named
-@samp{foo}. If this is not found, the short options @samp{f}, @samp{o},
-and again @samp{o} are recognized.
-@end deftypefun
-
-@node Getopt Long Option Example
-@subsection Example of Parsing Long Options with @code{getopt_long}
-
-@smallexample
-@include longopt.c.texi
-@end smallexample