515 lines
18 KiB
Text
515 lines
18 KiB
Text
@ignore
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This file documents the user interface to the GNU History library.
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Copyright (C) 1988, 1991, 1994, 1996 Free Software Foundation, Inc.
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Authored by Brian Fox and Chet Ramey.
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Permission is granted to make and distribute verbatim copies of this manual
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provided the copyright notice and this permission notice are preserved on
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all copies.
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Permission is granted to process this file through Tex and print the
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results, provided the printed document carries copying permission notice
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identical to this one except for the removal of this paragraph (this
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paragraph not being relevant to the printed manual).
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that the
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GNU Copyright statement is available to the distributee, and provided that
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the entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@end ignore
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@node Programming with GNU History
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@chapter Programming with GNU History
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This chapter describes how to interface programs that you write
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with the GNU History Library.
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It should be considered a technical guide.
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For information on the interactive use of GNU History, @pxref{Using
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History Interactively}.
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@menu
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* Introduction to History:: What is the GNU History library for?
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* History Storage:: How information is stored.
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* History Functions:: Functions that you can use.
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* History Variables:: Variables that control behaviour.
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* History Programming Example:: Example of using the GNU History Library.
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@end menu
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@node Introduction to History
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@section Introduction to History
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Many programs read input from the user a line at a time. The GNU History
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library is able to keep track of those lines, associate arbitrary data with
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each line, and utilize information from previous lines in composing new
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ones.
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The programmer using the History library has available functions
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for remembering lines on a history list, associating arbitrary data
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with a line, removing lines from the list, searching through the list
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for a line containing an arbitrary text string, and referencing any line
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in the list directly. In addition, a history @dfn{expansion} function
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is available which provides for a consistent user interface across
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different programs.
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The user using programs written with the History library has the
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benefit of a consistent user interface with a set of well-known
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commands for manipulating the text of previous lines and using that text
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in new commands. The basic history manipulation commands are similar to
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the history substitution provided by @code{csh}.
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If the programmer desires, he can use the Readline library, which
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includes some history manipulation by default, and has the added
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advantage of command line editing.
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@node History Storage
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@section History Storage
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The history list is an array of history entries. A history entry is
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declared as follows:
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@example
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typedef struct _hist_entry @{
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char *line;
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char *data;
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@} HIST_ENTRY;
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@end example
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The history list itself might therefore be declared as
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@example
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HIST_ENTRY **the_history_list;
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@end example
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The state of the History library is encapsulated into a single structure:
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@example
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/* A structure used to pass the current state of the history stuff around. */
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typedef struct _hist_state @{
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HIST_ENTRY **entries; /* Pointer to the entries themselves. */
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int offset; /* The location pointer within this array. */
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int length; /* Number of elements within this array. */
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int size; /* Number of slots allocated to this array. */
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int flags;
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@} HISTORY_STATE;
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@end example
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If the flags member includes @code{HS_STIFLED}, the history has been
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stifled.
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@node History Functions
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@section History Functions
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This section describes the calling sequence for the various functions
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present in GNU History.
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@menu
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* Initializing History and State Management:: Functions to call when you
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want to use history in a
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program.
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* History List Management:: Functions used to manage the list
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of history entries.
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* Information About the History List:: Functions returning information about
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the history list.
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* Moving Around the History List:: Functions used to change the position
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in the history list.
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* Searching the History List:: Functions to search the history list
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for entries containing a string.
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* Managing the History File:: Functions that read and write a file
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containing the history list.
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* History Expansion:: Functions to perform csh-like history
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expansion.
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@end menu
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@node Initializing History and State Management
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@subsection Initializing History and State Management
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This section describes functions used to initialize and manage
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the state of the History library when you want to use the history
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functions in your program.
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@deftypefun void using_history ()
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Begin a session in which the history functions might be used. This
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initializes the interactive variables.
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@end deftypefun
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@deftypefun {HISTORY_STATE *} history_get_history_state ()
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Return a structure describing the current state of the input history.
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@end deftypefun
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@deftypefun void history_set_history_state (HISTORY_STATE *state)
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Set the state of the history list according to @var{state}.
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@end deftypefun
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@node History List Management
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@subsection History List Management
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These functions manage individual entries on the history list, or set
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parameters managing the list itself.
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@deftypefun void add_history (char *string)
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Place @var{string} at the end of the history list. The associated data
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field (if any) is set to @code{NULL}.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} remove_history (int which)
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Remove history entry at offset @var{which} from the history. The
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removed element is returned so you can free the line, data,
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and containing structure.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} replace_history_entry (int which, char *line, char *data)
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Make the history entry at offset @var{which} have @var{line} and @var{data}.
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This returns the old entry so you can dispose of the data. In the case
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of an invalid @var{which}, a @code{NULL} pointer is returned.
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@end deftypefun
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@deftypefun void clear_history ()
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Clear the history list by deleting all the entries.
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@end deftypefun
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@deftypefun void stifle_history (int max)
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Stifle the history list, remembering only the last @var{max} entries.
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@end deftypefun
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@deftypefun int unstifle_history ()
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Stop stifling the history. This returns the previous amount the
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history was stifled. The value is positive if the history was
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stifled, negative if it wasn't.
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@end deftypefun
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@deftypefun int history_is_stifled ()
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Returns non-zero if the history is stifled, zero if it is not.
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@end deftypefun
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@node Information About the History List
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@subsection Information About the History List
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These functions return information about the entire history list or
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individual list entries.
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@deftypefun {HIST_ENTRY **} history_list ()
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Return a @code{NULL} terminated array of @code{HIST_ENTRY} which is the
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current input history. Element 0 of this list is the beginning of time.
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If there is no history, return @code{NULL}.
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@end deftypefun
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@deftypefun int where_history ()
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Returns the offset of the current history element.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} current_history ()
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Return the history entry at the current position, as determined by
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@code{where_history ()}. If there is no entry there, return a @code{NULL}
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pointer.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} history_get (int offset)
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Return the history entry at position @var{offset}, starting from
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@code{history_base}. If there is no entry there, or if @var{offset}
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is greater than the history length, return a @code{NULL} pointer.
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@end deftypefun
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@deftypefun int history_total_bytes ()
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Return the number of bytes that the primary history entries are using.
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This function returns the sum of the lengths of all the lines in the
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history.
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@end deftypefun
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@node Moving Around the History List
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@subsection Moving Around the History List
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These functions allow the current index into the history list to be
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set or changed.
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@deftypefun int history_set_pos (int pos)
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Set the position in the history list to @var{pos}, an absolute index
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into the list.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} previous_history ()
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Back up the current history offset to the previous history entry, and
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return a pointer to that entry. If there is no previous entry, return
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a @code{NULL} pointer.
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@end deftypefun
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@deftypefun {HIST_ENTRY *} next_history ()
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Move the current history offset forward to the next history entry, and
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return the a pointer to that entry. If there is no next entry, return
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a @code{NULL} pointer.
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@end deftypefun
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@node Searching the History List
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@subsection Searching the History List
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@cindex History Searching
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These functions allow searching of the history list for entries containing
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a specific string. Searching may be performed both forward and backward
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from the current history position. The search may be @dfn{anchored},
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meaning that the string must match at the beginning of the history entry.
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@cindex anchored search
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@deftypefun int history_search (char *string, int direction)
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Search the history for @var{string}, starting at the current history
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offset. If @var{direction} < 0, then the search is through previous entries,
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else through subsequent. If @var{string} is found, then
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the current history index is set to that history entry, and the value
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returned is the offset in the line of the entry where
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@var{string} was found. Otherwise, nothing is changed, and a -1 is
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returned.
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@end deftypefun
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@deftypefun int history_search_prefix (char *string, int direction)
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Search the history for @var{string}, starting at the current history
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offset. The search is anchored: matching lines must begin with
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@var{string}. If @var{direction} < 0, then the search is through previous
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entries, else through subsequent. If @var{string} is found, then the
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current history index is set to that entry, and the return value is 0.
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Otherwise, nothing is changed, and a -1 is returned.
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@end deftypefun
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@deftypefun int history_search_pos (char *string, int direction, int pos)
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Search for @var{string} in the history list, starting at @var{pos}, an
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absolute index into the list. If @var{direction} is negative, the search
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proceeds backward from @var{pos}, otherwise forward. Returns the absolute
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index of the history element where @var{string} was found, or -1 otherwise.
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@end deftypefun
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@node Managing the History File
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@subsection Managing the History File
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The History library can read the history from and write it to a file.
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This section documents the functions for managing a history file.
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@deftypefun int read_history (char *filename)
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Add the contents of @var{filename} to the history list, a line at a
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time. If @var{filename} is @code{NULL}, then read from
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@file{~/.history}. Returns 0 if successful, or errno if not.
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@end deftypefun
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@deftypefun int read_history_range (char *filename, int from, int to)
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Read a range of lines from @var{filename}, adding them to the history list.
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Start reading at line @var{from} and end at @var{to}. If
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@var{from} is zero, start at the beginning. If @var{to} is less than
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@var{from}, then read until the end of the file. If @var{filename} is
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@code{NULL}, then read from @file{~/.history}. Returns 0 if successful,
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or @code{errno} if not.
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@end deftypefun
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@deftypefun int write_history (char *filename)
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Write the current history to @var{filename}, overwriting @var{filename}
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if necessary. If @var{filename} is
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@code{NULL}, then write the history list to @file{~/.history}. Values
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returned are as in @code{read_history ()}.
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@end deftypefun
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@deftypefun int append_history (int nelements, char *filename)
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Append the last @var{nelements} of the history list to @var{filename}.
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@end deftypefun
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@deftypefun int history_truncate_file (char *filename, int nlines)
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Truncate the history file @var{filename}, leaving only the last
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@var{nlines} lines.
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@end deftypefun
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@node History Expansion
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@subsection History Expansion
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These functions implement @code{csh}-like history expansion.
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@deftypefun int history_expand (char *string, char **output)
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Expand @var{string}, placing the result into @var{output}, a pointer
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to a string (@pxref{History Interaction}). Returns:
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@table @code
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@item 0
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If no expansions took place (or, if the only change in
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the text was the de-slashifying of the history expansion
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character);
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@item 1
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if expansions did take place;
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@item -1
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if there was an error in expansion;
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@item 2
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if the returned line should only be displayed, but not executed,
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as with the @code{:p} modifier (@pxref{Modifiers}).
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@end table
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If an error ocurred in expansion, then @var{output} contains a descriptive
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error message.
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@end deftypefun
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@deftypefun {char *} history_arg_extract (int first, int last, char *string)
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Extract a string segment consisting of the @var{first} through @var{last}
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arguments present in @var{string}. Arguments are broken up as in Bash.
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@end deftypefun
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@deftypefun {char *} get_history_event (char *string, int *cindex, int qchar)
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Returns the text of the history event beginning at @var{string} +
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@var{*cindex}. @var{*cindex} is modified to point to after the event
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specifier. At function entry, @var{cindex} points to the index into
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@var{string} where the history event specification begins. @var{qchar}
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is a character that is allowed to end the event specification in addition
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to the ``normal'' terminating characters.
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@end deftypefun
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@deftypefun {char **} history_tokenize (char *string)
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Return an array of tokens parsed out of @var{string}, much as the
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shell might. The tokens are split on white space and on the
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characters @code{()<>;&|$}, and shell quoting conventions are
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obeyed.
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@end deftypefun
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@node History Variables
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@section History Variables
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This section describes the externally visible variables exported by
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the GNU History Library.
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@deftypevar int history_base
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The logical offset of the first entry in the history list.
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@end deftypevar
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@deftypevar int history_length
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The number of entries currently stored in the history list.
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@end deftypevar
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@deftypevar int max_input_history
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The maximum number of history entries. This must be changed using
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@code{stifle_history ()}.
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@end deftypevar
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@deftypevar char history_expansion_char
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The character that starts a history event. The default is @samp{!}.
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@end deftypevar
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@deftypevar char history_subst_char
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The character that invokes word substitution if found at the start of
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a line. The default is @samp{^}.
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@end deftypevar
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@deftypevar char history_comment_char
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During tokenization, if this character is seen as the first character
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of a word, then it and all subsequent characters up to a newline are
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ignored, suppressing history expansion for the remainder of the line.
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This is disabled by default.
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@end deftypevar
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@deftypevar {char *} history_no_expand_chars
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The list of characters which inhibit history expansion if found immediately
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following @var{history_expansion_char}. The default is whitespace and
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@samp{=}.
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@end deftypevar
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@deftypevar {char *} history_search_delimiter_chars
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The list of additional characters which can delimit a history search
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string, in addition to whitespace, @samp{:} and @samp{?} in the case of
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a substring search. The default is empty.
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@end deftypevar
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@deftypevar int history_quotes_inhibit_expansion
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If non-zero, single-quoted words are not scanned for the history expansion
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character. The default value is 0.
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@end deftypevar
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@deftypevar {Function *} history_inhibit_expansion_function
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This should be set to the address of a function that takes two arguments:
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a @code{char *} (@var{string}) and an integer index into that string (@var{i}).
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It should return a non-zero value if the history expansion starting at
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@var{string[i]} should not be performed; zero if the expansion should
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be done.
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It is intended for use by applications like Bash that use the history
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expansion character for additional purposes.
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By default, this variable is set to NULL.
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@end deftypevar
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@node History Programming Example
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@section History Programming Example
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The following program demonstrates simple use of the GNU History Library.
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@smallexample
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main ()
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@{
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char line[1024], *t;
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int len, done = 0;
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line[0] = 0;
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using_history ();
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while (!done)
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@{
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printf ("history$ ");
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fflush (stdout);
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t = fgets (line, sizeof (line) - 1, stdin);
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if (t && *t)
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@{
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len = strlen (t);
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if (t[len - 1] == '\n')
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t[len - 1] = '\0';
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@}
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if (!t)
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strcpy (line, "quit");
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if (line[0])
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@{
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char *expansion;
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int result;
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result = history_expand (line, &expansion);
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if (result)
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fprintf (stderr, "%s\n", expansion);
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if (result < 0 || result == 2)
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@{
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free (expansion);
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continue;
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@}
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add_history (expansion);
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strncpy (line, expansion, sizeof (line) - 1);
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free (expansion);
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@}
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if (strcmp (line, "quit") == 0)
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done = 1;
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else if (strcmp (line, "save") == 0)
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write_history ("history_file");
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else if (strcmp (line, "read") == 0)
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read_history ("history_file");
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else if (strcmp (line, "list") == 0)
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@{
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register HIST_ENTRY **the_list;
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register int i;
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the_list = history_list ();
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if (the_list)
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for (i = 0; the_list[i]; i++)
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printf ("%d: %s\n", i + history_base, the_list[i]->line);
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@}
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else if (strncmp (line, "delete", 6) == 0)
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@{
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int which;
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if ((sscanf (line + 6, "%d", &which)) == 1)
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@{
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HIST_ENTRY *entry = remove_history (which);
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if (!entry)
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fprintf (stderr, "No such entry %d\n", which);
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else
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@{
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free (entry->line);
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free (entry);
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@}
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@}
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else
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@{
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fprintf (stderr, "non-numeric arg given to `delete'\n");
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@}
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@}
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@}
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@}
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@end smallexample
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