ne_buffer
     This is the line gathered so far.  You are welcome to modify the
     contents of the line, but see *note Allowing Undoing::.  The
     function 'rl_extend_line_buffer' is available to increase the
     memory allocated to 'rl_line_buffer'.

 -- Variable: int rl_point
     The offset of the current cursor position in 'rl_line_buffer' (the
     _point_).

 -- Variable: int rl_end
     The number of characters present in 'rl_line_buffer'.  When
     'rl_point' is at the end of the line, 'rl_point' and 'rl_end' are
     equal.

 -- Variable: int rl_mark
     The MARK (saved position) in the current line.  If set, the mark
     and point define a _region_.

 -- Variable: int rl_done
     Setting this to a non-zero value causes Readline to return the
     current line immediately.  Readline will set this variable when it
     has read a key sequence bound to 'accept-line' and is about to
     return the line to the caller.

 -- Variable: int rl_eof_found
     Readline will set this variable when it has read an EOF character
     (e.g., the stty 'EOF' character) on an empty line or encountered a
     read error and is about to return a NULL line to the caller.

 -- Variable: int rl_num_chars_to_read
     Setting this to a positive value before calling 'readline()' causes
     Readline to return after accepting that many characters, rather
     than reading up to a character bound to 'accept-line'.

 -- Variable: int rl_pending_input
     Setting this to a value makes it the next keystroke read.  This is
     a way to stuff a single character into the input stream.

 -- Variable: int rl_dispatching
     Set to a non-zero value if a function is being called from a key
     binding; zero otherwise.  Application functions can test this to
     discover whether they were called directly or by Readline's
     dispatching mechanism.

 -- Variable: int rl_erase_empty_line
     Setting this to a non-zero value causes Readline to completely
     erase the current line, including any prompt, any time a newline is
     typed as the only character on an otherwise-empty line.  The cursor
     is moved to the beginning of the newly-blank line.

 -- Variable: char * rl_prompt
     The prompt Readline uses.  This is set from the argument to
     'readline()', and should not be assigned to directly.  The
     'rl_set_prompt()' function (*note Redisplay::) may be used to
     modify the prompt string after calling 'readline()'.

 -- Variable: char * rl_display_prompt
     The string displayed as the prompt.  This is usually identical to
     RL_PROMPT, but may be changed temporarily by functions that use the
     prompt string as a message area, such as incremental search.

 -- Variable: int rl_already_prompted
     If an application wishes to display the prompt itself, rather than
     have Readline do it the first time 'readline()' is called, it
     should set this variable to a non-zero value after displaying the
     prompt.  The prompt must also be passed as the argument to
     'readline()' so the redisplay functions can update the display
     properly.  The calling application is responsible for managing the
     value; Readline never sets it.

 -- Variable: const char * rl_library_version
     The version number of this revision of the library.

 -- Variable: int rl_readline_version
     An integer encoding the current version of the library.  The
     encoding is of the form 0xMMMM, where MM is the two-digit major
     version number, and MM is the two-digit minor version number.  For
     example, for Readline-4.2, 'rl_readline_version' would have the
     value 0x0402.

 -- Variable: int rl_gnu_readline_p
     Always set to 1, denoting that this is GNU Readline rather than
     some emulation.

 -- Variable: const char * rl_terminal_name
     The terminal type, used for initialization.  If not set by the
     application, Readline sets this to the value of the 'TERM'
     environment variable the first time it is called.

 -- Variable: const char * rl_readline_name
     This variable is set to a unique name by each application using
     Readline.  The value allows conditional parsing of the inputrc file
     (*note Conditional Init Constructs::).

 -- Variable: FILE * rl_instream
     The stdio stream from which Readline reads input.  If 'NULL',
     Readline defaults to STDIN.

 -- Variable: FILE * rl_outstream
     The stdio stream to which Readline performs output.  If 'NULL',
     Readline defaults to STDOUT.

 -- Variable: int rl_prefer_env_winsize
     If non-zero, Readline gives values found in the 'LINES' and
     'COLUMNS' environment variables greater precedence than values
     fetched from the kernel when computing the screen dimensions.

 -- Variable: rl_command_func_t * rl_last_func
     The address of the last command function Readline executed.  May be
     used to test whether or not a function is being executed twice in
     succession, for example.

 -- Variable: rl_hook_func_t * rl_startup_hook
     If non-zero, this is the address of a function to call just before
     'readline' prints the first prompt.

 -- Variable: rl_hook_func_t * rl_pre_input_hook
     If non-zero, this is the address of a function to call after the
     first prompt has been printed and just before 'readline' starts
     reading input characters.

 -- Variable: rl_hook_func_t * rl_event_hook
     If non-zero, this is the address of a function to call periodically
     when Readline is waiting for terminal input.  By default, this will
     be called at most ten times a second if there is no keyboard input.

 -- Variable: rl_getc_func_t * rl_getc_function
     If non-zero, Readline will call indirectly through this pointer to
     get a character from the input stream.  By default, it is set to
     'rl_getc', the default Readline character input function (*note
     Character Input::).  In general, an application that sets
     RL_GETC_FUNCTION should consider setting RL_INPUT_AVAILABLE_HOOK as
     well.

 -- Variable: rl_hook_func_t * rl_signal_event_hook
     If non-zero, this is the address of a function to call if a read
     system call is interrupted when Readline is reading terminal input.

 -- Variable: rl_hook_func_t * rl_timeout_event_hook
     If non-zero, this is the address of a function to call if Readline
     times out while reading input.

 -- Variable: rl_hook_func_t * rl_input_available_hook
     If non-zero, Readline will use this function's return value when it
     needs to determine whether or not there is available input on the
     current input source.  The default hook checks 'rl_instream'; if an
     application is using a different input source, it should set the
     hook appropriately.  Readline queries for available input when
     implementing intra-key-sequence timeouts during input and
     incremental searches.  This may use an application-specific timeout
     before returning a value; Readline uses the value passed to
     'rl_set_keyboard_input_timeout()' or the value of the user-settable
     KEYSEQ-TIMEOUT variable.  This is designed for use by applications
     using Readline's callback interface (*note Alternate Interface::),
     which may not use the traditional 'read(2)' and file descriptor
     interface, or other applications using a different input mechanism.
     If an application uses an input mechanism or hook that can
     potentially exceed the value of KEYSEQ-TIMEOUT, it should increase
     the timeout or set this hook appropriately even when not using the
     callback interface.  In general, an application that sets
     RL_GETC_FUNCTION should consider setting RL_INPUT_AVAILABLE_HOOK as
     well.

 -- Variable: rl_voidfunc_t * rl_redisplay_function
     If non-zero, Readline will call indirectly through this pointer to
     update the display with the current contents of the editing buffer.
     By default, it is set to 'rl_redisplay', the default Readline
     redisplay function (*note Redisplay::).

 -- Variable: rl_vintfunc_t * rl_prep_term_function
     If non-zero, Readline will call indirectly through this pointer to
     initialize the terminal.  The function takes a single argument, an
     'int' flag that says whether or not to use eight-bit characters.
     By default, this is set to 'rl_prep_terminal' (*note Terminal
     Management::).

 -- Variable: rl_voidfunc_t * rl_deprep_term_function
     If non-zero, Readline will call indirectly through this pointer to
     reset the terminal.  This function should undo the effects of
     'rl_prep_term_function'.  By default, this is set to
     'rl_deprep_terminal' (*note Terminal Management::).

 -- Variable: Keymap rl_executing_keymap
     This variable is set to the keymap (*note Keymaps::) in which the
     currently executing Readline function was found.

 -- Variable: Keymap rl_binding_keymap
     This variable is set to the keymap (*note Keymaps::) in which the
     last key binding occurred.

 -- Variable: char * rl_executing_macro
     This variable is set to the text of any currently-executing macro.

 -- Variable: int rl_executing_key
     The key that caused the dispatch to the currently-executing
     Readline function.

 -- Variable: char * rl_executing_keyseq
     The full key sequence that caused the dispatch to the
     currently-executing Readline function.

 -- Variable: int rl_key_sequence_length
     The number of characters in RL_EXECUTING_KEYSEQ.

 -- Variable: int rl_readline_state
     A variable with bit values that encapsulate the current Readline
     state.  A bit is set with the 'RL_SETSTATE' macro, and unset with
     the 'RL_UNSETSTATE' macro.  Use the 'RL_ISSTATE' macro to test
     whether a particular state bit is set.  Current state bits include:

     'RL_STATE_NONE'
          Readline has not yet been called, nor has it begun to
          initialize.
     'RL_STATE_INITIALIZING'
          Readline is initializing its internal data structures.
     'RL_STATE_INITIALIZED'
          Readline has completed its initialization.
     'RL_STATE_TERMPREPPED'
          Readline has modified the terminal modes to do its own input
          and redisplay.
     'RL_STATE_READCMD'
          Readline is reading a command from the keyboard.
     'RL_STATE_METANEXT'
          Readline is reading more input after reading the meta-prefix
          character.
     'RL_STATE_DISPATCHING'
          Readline is dispatching to a command.
     'RL_STATE_MOREINPUT'
          Readline is reading more input while executing an editing
          command.
     'RL_STATE_ISEARCH'
          Readline is performing an incremental history search.
     'RL_STATE_NSEARCH'
          Readline is performing a non-incremental history search.
     'RL_STATE_SEARCH'
          Readline is searching backward or forward through the history
          for a string.
     'RL_STATE_NUMERICARG'
          Readline is reading a numeric argument.
     'RL_STATE_MACROINPUT'
          Readline is currently getting its input from a
          previously-defined keyboard macro.
     'RL_STATE_MACRODEF'
          Readline is currently reading characters defining a keyboard
          macro.
     'RL_STATE_OVERWRITE'
          Readline is in overwrite mode.
     'RL_STATE_COMPLETING'
          Readline is performing word completion.
     'RL_STATE_SIGHANDLER'
          Readline is currently executing the readline signal handler.
     'RL_STATE_UNDOING'
          Readline is performing an undo.
     'RL_STATE_INPUTPENDING'
          Readline has input pending due to a call to
          'rl_execute_next()'.
     'RL_STATE_TTYCSAVED'
          Readline has saved the values of the terminal's special
          characters.
     'RL_STATE_CALLBACK'
          Readline is currently using the alternate (callback) interface
          (*note Alternate Interface::).
     'RL_STATE_VIMOTION'
          Readline is reading the argument to a vi-mode "motion"
          command.
     'RL_STATE_MULTIKEY'
          Readline is reading a multiple-keystroke command.
     'RL_STATE_VICMDONCE'
          Readline has entered vi command (movement) mode at least one
          time during the current call to 'readline()'.
     'RL_STATE_DONE'
          Readline has read a key sequence bound to 'accept-line' and is
          about to return the line to the caller.
     'RL_STATE_TIMEOUT'
          Readline has timed out (it did not receive a line or specified
          number of characters before the timeout duration specified by
          'rl_set_timeout' elapsed) and is returning that status to the
          caller.
     'RL_STATE_EOF'
          Readline has read an EOF character (e.g., the stty 'EOF'
          character) or encountered a read error and is about to return
          a NULL line to the caller.

 -- Variable: int rl_explicit_arg
     Set to a non-zero value if an explicit numeric argument was
     specified by the user.  Only valid in a bindable command function.

 -- Variable: int rl_numeric_arg
     Set to the value of any numeric argument explicitly specified by
     the user before executing the current Readline function.  Only
     valid in a bindable command function.

 -- Variable: int rl_editing_mode
     Set to a value denoting Readline's current editing mode.  A value
     of 1 means Readline is currently in emacs mode; 0 means that vi
     mode is active.