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This is, produced by makeinfo version 4.7 from
This document describes the GNU History library (version 5.1-beta1,
11 November 2005), a programming tool that provides a consistent user
interface for recalling lines of previously typed input.
Copyright (C) 1988-2004 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.1 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
being "A GNU Manual," and with the Back-Cover Texts as in (a)
below. A copy of the license is included in the section entitled
"GNU Free Documentation License."
(a) The FSF's Back-Cover Text is: "You have freedom to copy and
modify this GNU Manual, like GNU software. Copies published by
the Free Software Foundation raise funds for GNU development."
* History: (history). The GNU history library API.

File:, Node: Top, Next: Using History Interactively, Up: (dir)
GNU History Library
This document describes the GNU History library, a programming tool that
provides a consistent user interface for recalling lines of previously
typed input.
* Menu:
* Using History Interactively:: GNU History User's Manual.
* Programming with GNU History:: GNU History Programmer's Manual.
* Copying This Manual:: Copying This Manual.
* Concept Index:: Index of concepts described in this manual.
* Function and Variable Index:: Index of externally visible functions
and variables.

File:, Node: Using History Interactively, Next: Programming with GNU History, Prev: Top, Up: Top
1 Using History Interactively
This chapter describes how to use the GNU History Library interactively,
from a user's standpoint. It should be considered a user's guide. For
information on using the GNU History Library in your own programs,
*note Programming with GNU History::.
* Menu:
* History Interaction:: What it feels like using History as a user.

File:, Node: History Interaction, Up: Using History Interactively
1.1 History Expansion
The History library provides a history expansion feature that is similar
to the history expansion provided by `csh'. This section describes the
syntax used to manipulate the history information.
History expansions introduce words from the history list into the
input stream, making it easy to repeat commands, insert the arguments
to a previous command into the current input line, or fix errors in
previous commands quickly.
History expansion takes place in two parts. The first is to
determine which line from the history list should be used during
substitution. The second is to select portions of that line for
inclusion into the current one. The line selected from the history is
called the "event", and the portions of that line that are acted upon
are called "words". Various "modifiers" are available to manipulate
the selected words. The line is broken into words in the same fashion
that Bash does, so that several words surrounded by quotes are
considered one word. History expansions are introduced by the
appearance of the history expansion character, which is `!' by default.
* Menu:
* Event Designators:: How to specify which history line to use.
* Word Designators:: Specifying which words are of interest.
* Modifiers:: Modifying the results of substitution.

File:, Node: Event Designators, Next: Word Designators, Up: History Interaction
1.1.1 Event Designators
An event designator is a reference to a command line entry in the
history list.
Start a history substitution, except when followed by a space, tab,
the end of the line, or `='.
Refer to command line N.
Refer to the command N lines back.
Refer to the previous command. This is a synonym for `!-1'.
Refer to the most recent command starting with STRING.
Refer to the most recent command containing STRING. The trailing
`?' may be omitted if the STRING is followed immediately by a
Quick Substitution. Repeat the last command, replacing STRING1
with STRING2. Equivalent to `!!:s/STRING1/STRING2/'.
The entire command line typed so far.

File:, Node: Word Designators, Next: Modifiers, Prev: Event Designators, Up: History Interaction
1.1.2 Word Designators
Word designators are used to select desired words from the event. A
`:' separates the event specification from the word designator. It may
be omitted if the word designator begins with a `^', `$', `*', `-', or
`%'. Words are numbered from the beginning of the line, with the first
word being denoted by 0 (zero). Words are inserted into the current
line separated by single spaces.
For example,
designates the preceding command. When you type this, the
preceding command is repeated in toto.
designates the last argument of the preceding command. This may be
shortened to `!$'.
designates the second argument of the most recent command starting
with the letters `fi'.
Here are the word designators:
`0 (zero)'
The `0'th word. For many applications, this is the command word.
The Nth word.
The first argument; that is, word 1.
The last argument.
The word matched by the most recent `?STRING?' search.
A range of words; `-Y' abbreviates `0-Y'.
All of the words, except the `0'th. This is a synonym for `1-$'.
It is not an error to use `*' if there is just one word in the
event; the empty string is returned in that case.
Abbreviates `X-$'
Abbreviates `X-$' like `X*', but omits the last word.
If a word designator is supplied without an event specification, the
previous command is used as the event.

File:, Node: Modifiers, Prev: Word Designators, Up: History Interaction
1.1.3 Modifiers
After the optional word designator, you can add a sequence of one or
more of the following modifiers, each preceded by a `:'.
Remove a trailing pathname component, leaving only the head.
Remove all leading pathname components, leaving the tail.
Remove a trailing suffix of the form `.SUFFIX', leaving the
Remove all but the trailing suffix.
Print the new command but do not execute it.
Substitute NEW for the first occurrence of OLD in the event line.
Any delimiter may be used in place of `/'. The delimiter may be
quoted in OLD and NEW with a single backslash. If `&' appears in
NEW, it is replaced by OLD. A single backslash will quote the
`&'. The final delimiter is optional if it is the last character
on the input line.
Repeat the previous substitution.
Cause changes to be applied over the entire event line. Used in
conjunction with `s', as in `gs/OLD/NEW/', or with `&'.
Apply the following `s' modifier once to each word in the event.

File:, Node: Programming with GNU History, Next: Copying This Manual, Prev: Using History Interactively, Up: Top
2 Programming with GNU History
This chapter describes how to interface programs that you write with
the GNU History Library. It should be considered a technical guide.
For information on the interactive use of GNU History, *note Using
History Interactively::.
* Menu:
* Introduction to History:: What is the GNU History library for?
* History Storage:: How information is stored.
* History Functions:: Functions that you can use.
* History Variables:: Variables that control behaviour.
* History Programming Example:: Example of using the GNU History Library.

File:, Node: Introduction to History, Next: History Storage, Up: Programming with GNU History
2.1 Introduction to History
Many programs read input from the user a line at a time. The GNU
History library is able to keep track of those lines, associate
arbitrary data with each line, and utilize information from previous
lines in composing new ones.
The programmer using the History library has available functions for
remembering lines on a history list, associating arbitrary data with a
line, removing lines from the list, searching through the list for a
line containing an arbitrary text string, and referencing any line in
the list directly. In addition, a history "expansion" function is
available which provides for a consistent user interface across
different programs.
The user using programs written with the History library has the
benefit of a consistent user interface with a set of well-known
commands for manipulating the text of previous lines and using that text
in new commands. The basic history manipulation commands are similar to
the history substitution provided by `csh'.
If the programmer desires, he can use the Readline library, which
includes some history manipulation by default, and has the added
advantage of command line editing.
Before declaring any functions using any functionality the History
library provides in other code, an application writer should include
the file `<readline/history.h>' in any file that uses the History
library's features. It supplies extern declarations for all of the
library's public functions and variables, and declares all of the
public data structures.

File:, Node: History Storage, Next: History Functions, Prev: Introduction to History, Up: Programming with GNU History
2.2 History Storage
The history list is an array of history entries. A history entry is
declared as follows:
typedef void *histdata_t;
typedef struct _hist_entry {
char *line;
char *timestamp;
histdata_t data;
The history list itself might therefore be declared as
HIST_ENTRY **the_history_list;
The state of the History library is encapsulated into a single
* A structure used to pass around the current state of the history.
typedef struct _hist_state {
HIST_ENTRY **entries; /* Pointer to the entries themselves. */
int offset; /* The location pointer within this array. */
int length; /* Number of elements within this array. */
int size; /* Number of slots allocated to this array. */
int flags;
If the flags member includes `HS_STIFLED', the history has been

File:, Node: History Functions, Next: History Variables, Prev: History Storage, Up: Programming with GNU History
2.3 History Functions
This section describes the calling sequence for the various functions
exported by the GNU History library.
* Menu:
* Initializing History and State Management:: Functions to call when you
want to use history in a
* History List Management:: Functions used to manage the list
of history entries.
* Information About the History List:: Functions returning information about
the history list.
* Moving Around the History List:: Functions used to change the position
in the history list.
* Searching the History List:: Functions to search the history list
for entries containing a string.
* Managing the History File:: Functions that read and write a file
containing the history list.
* History Expansion:: Functions to perform csh-like history

File:, Node: Initializing History and State Management, Next: History List Management, Up: History Functions
2.3.1 Initializing History and State Management
This section describes functions used to initialize and manage the
state of the History library when you want to use the history functions
in your program.
-- Function: void using_history (void)
Begin a session in which the history functions might be used. This
initializes the interactive variables.
-- Function: HISTORY_STATE * history_get_history_state (void)
Return a structure describing the current state of the input
-- Function: void history_set_history_state (HISTORY_STATE *state)
Set the state of the history list according to STATE.

File:, Node: History List Management, Next: Information About the History List, Prev: Initializing History and State Management, Up: History Functions
2.3.2 History List Management
These functions manage individual entries on the history list, or set
parameters managing the list itself.
-- Function: void add_history (const char *string)
Place STRING at the end of the history list. The associated data
field (if any) is set to `NULL'.
-- Function: void add_history_time (const char *string)
Change the time stamp associated with the most recent history
entry to STRING.
-- Function: HIST_ENTRY * remove_history (int which)
Remove history entry at offset WHICH from the history. The
removed element is returned so you can free the line, data, and
containing structure.
-- Function: histdata_t free_history_entry (HIST_ENTRY *histent)
Free the history entry HISTENT and any history library private
data associated with it. Returns the application-specific data so
the caller can dispose of it.
-- Function: HIST_ENTRY * replace_history_entry (int which, const char
*line, histdata_t data)
Make the history entry at offset WHICH have LINE and DATA. This
returns the old entry so the caller can dispose of any
application-specific data. In the case of an invalid WHICH, a
`NULL' pointer is returned.
-- Function: void clear_history (void)
Clear the history list by deleting all the entries.
-- Function: void stifle_history (int max)
Stifle the history list, remembering only the last MAX entries.
-- Function: int unstifle_history (void)
Stop stifling the history. This returns the previously-set
maximum number of history entries (as set by `stifle_history()').
The value is positive if the history was stifled, negative if it
-- Function: int history_is_stifled (void)
Returns non-zero if the history is stifled, zero if it is not.

File:, Node: Information About the History List, Next: Moving Around the History List, Prev: History List Management, Up: History Functions
2.3.3 Information About the History List
These functions return information about the entire history list or
individual list entries.
-- Function: HIST_ENTRY ** history_list (void)
Return a `NULL' terminated array of `HIST_ENTRY *' which is the
current input history. Element 0 of this list is the beginning of
time. If there is no history, return `NULL'.
-- Function: int where_history (void)
Returns the offset of the current history element.
-- Function: HIST_ENTRY * current_history (void)
Return the history entry at the current position, as determined by
`where_history()'. If there is no entry there, return a `NULL'
-- Function: HIST_ENTRY * history_get (int offset)
Return the history entry at position OFFSET, starting from
`history_base' (*note History Variables::). If there is no entry
there, or if OFFSET is greater than the history length, return a
`NULL' pointer.
-- Function: time_t history_get_time (HIST_ENTRY *entry)
Return the time stamp associated with the history entry ENTRY.
-- Function: int history_total_bytes (void)
Return the number of bytes that the primary history entries are
using. This function returns the sum of the lengths of all the
lines in the history.

File:, Node: Moving Around the History List, Next: Searching the History List, Prev: Information About the History List, Up: History Functions
2.3.4 Moving Around the History List
These functions allow the current index into the history list to be set
or changed.
-- Function: int history_set_pos (int pos)
Set the current history offset to POS, an absolute index into the
list. Returns 1 on success, 0 if POS is less than zero or greater
than the number of history entries.
-- Function: HIST_ENTRY * previous_history (void)
Back up the current history offset to the previous history entry,
and return a pointer to that entry. If there is no previous
entry, return a `NULL' pointer.
-- Function: HIST_ENTRY * next_history (void)
Move the current history offset forward to the next history entry,
and return the a pointer to that entry. If there is no next
entry, return a `NULL' pointer.

File:, Node: Searching the History List, Next: Managing the History File, Prev: Moving Around the History List, Up: History Functions
2.3.5 Searching the History List
These functions allow searching of the history list for entries
containing a specific string. Searching may be performed both forward
and backward from the current history position. The search may be
"anchored", meaning that the string must match at the beginning of the
history entry.
-- Function: int history_search (const char *string, int direction)
Search the history for STRING, starting at the current history
offset. If DIRECTION is less than 0, then the search is through
previous entries, otherwise through subsequent entries. If STRING
is found, then the current history index is set to that history
entry, and the value returned is the offset in the line of the
entry where STRING was found. Otherwise, nothing is changed, and
a -1 is returned.
-- Function: int history_search_prefix (const char *string, int
Search the history for STRING, starting at the current history
offset. The search is anchored: matching lines must begin with
STRING. If DIRECTION is less than 0, then the search is through
previous entries, otherwise through subsequent entries. If STRING
is found, then the current history index is set to that entry, and
the return value is 0. Otherwise, nothing is changed, and a -1 is
-- Function: int history_search_pos (const char *string, int
direction, int pos)
Search for STRING in the history list, starting at POS, an
absolute index into the list. If DIRECTION is negative, the search
proceeds backward from POS, otherwise forward. Returns the
absolute index of the history element where STRING was found, or
-1 otherwise.

File:, Node: Managing the History File, Next: History Expansion, Prev: Searching the History List, Up: History Functions
2.3.6 Managing the History File
The History library can read the history from and write it to a file.
This section documents the functions for managing a history file.
-- Function: int read_history (const char *filename)
Add the contents of FILENAME to the history list, a line at a time.
If FILENAME is `NULL', then read from `~/.history'. Returns 0 if
successful, or `errno' if not.
-- Function: int read_history_range (const char *filename, int from,
int to)
Read a range of lines from FILENAME, adding them to the history
list. Start reading at line FROM and end at TO. If FROM is zero,
start at the beginning. If TO is less than FROM, then read until
the end of the file. If FILENAME is `NULL', then read from
`~/.history'. Returns 0 if successful, or `errno' if not.
-- Function: int write_history (const char *filename)
Write the current history to FILENAME, overwriting FILENAME if
necessary. If FILENAME is `NULL', then write the history list to
`~/.history'. Returns 0 on success, or `errno' on a read or write
-- Function: int append_history (int nelements, const char *filename)
Append the last NELEMENTS of the history list to FILENAME. If
FILENAME is `NULL', then append to `~/.history'. Returns 0 on
success, or `errno' on a read or write error.
-- Function: int history_truncate_file (const char *filename, int
Truncate the history file FILENAME, leaving only the last NLINES
lines. If FILENAME is `NULL', then `~/.history' is truncated.
Returns 0 on success, or `errno' on failure.

File:, Node: History Expansion, Prev: Managing the History File, Up: History Functions
2.3.7 History Expansion
These functions implement history expansion.
-- Function: int history_expand (char *string, char **output)
Expand STRING, placing the result into OUTPUT, a pointer to a
string (*note History Interaction::). Returns:
If no expansions took place (or, if the only change in the
text was the removal of escape characters preceding the
history expansion character);
if expansions did take place;
if there was an error in expansion;
if the returned line should be displayed, but not executed,
as with the `:p' modifier (*note Modifiers::).
If an error ocurred in expansion, then OUTPUT contains a
descriptive error message.
-- Function: char * get_history_event (const char *string, int
*cindex, int qchar)
Returns the text of the history event beginning at STRING +
*CINDEX. *CINDEX is modified to point to after the event
specifier. At function entry, CINDEX points to the index into
STRING where the history event specification begins. QCHAR is a
character that is allowed to end the event specification in
addition to the "normal" terminating characters.
-- Function: char ** history_tokenize (const char *string)
Return an array of tokens parsed out of STRING, much as the shell
might. The tokens are split on the characters in the
HISTORY_WORD_DELIMITERS variable, and shell quoting conventions
are obeyed.
-- Function: char * history_arg_extract (int first, int last, const
char *string)
Extract a string segment consisting of the FIRST through LAST
arguments present in STRING. Arguments are split using

File:, Node: History Variables, Next: History Programming Example, Prev: History Functions, Up: Programming with GNU History
2.4 History Variables
This section describes the externally-visible variables exported by the
GNU History Library.
-- Variable: int history_base
The logical offset of the first entry in the history list.
-- Variable: int history_length
The number of entries currently stored in the history list.
-- Variable: int history_max_entries
The maximum number of history entries. This must be changed using
-- Variable: int history_write_timestamps
If non-zero, timestamps are written to the history file, so they
can be preserved between sessions. The default value is 0,
meaning that timestamps are not saved.
-- Variable: char history_expansion_char
The character that introduces a history event. The default is `!'.
Setting this to 0 inhibits history expansion.
-- Variable: char history_subst_char
The character that invokes word substitution if found at the start
of a line. The default is `^'.
-- Variable: char history_comment_char
During tokenization, if this character is seen as the first
character of a word, then it and all subsequent characters up to a
newline are ignored, suppressing history expansion for the
remainder of the line. This is disabled by default.
-- Variable: char * history_word_delimiters
The characters that separate tokens for `history_tokenize()'. The
default value is `" \t\n()<>;&|"'.
-- Variable: char * history_search_delimiter_chars
The list of additional characters which can delimit a history
search string, in addition to space, TAB, `:' and `?' in the case
of a substring search. The default is empty.
-- Variable: char * history_no_expand_chars
The list of characters which inhibit history expansion if found
immediately following HISTORY_EXPANSION_CHAR. The default is
space, tab, newline, carriage return, and `='.
-- Variable: int history_quotes_inhibit_expansion
If non-zero, single-quoted words are not scanned for the history
expansion character. The default value is 0.
-- Variable: rl_linebuf_func_t * history_inhibit_expansion_function
This should be set to the address of a function that takes two
arguments: a `char *' (STRING) and an `int' index into that string
(I). It should return a non-zero value if the history expansion
starting at STRING[I] should not be performed; zero if the
expansion should be done. It is intended for use by applications
like Bash that use the history expansion character for additional
purposes. By default, this variable is set to `NULL'.

File:, Node: History Programming Example, Prev: History Variables, Up: Programming with GNU History
2.5 History Programming Example
The following program demonstrates simple use of the GNU History
#include <stdio.h>
#include <readline/history.h>
main (argc, argv)
int argc;
char **argv;
char line[1024], *t;
int len, done = 0;
line[0] = 0;
using_history ();
while (!done)
printf ("history$ ");
fflush (stdout);
t = fgets (line, sizeof (line) - 1, stdin);
if (t && *t)
len = strlen (t);
if (t[len - 1] == '\n')
t[len - 1] = '\0';
if (!t)
strcpy (line, "quit");
if (line[0])
char *expansion;
int result;
result = history_expand (line, &expansion);
if (result)
fprintf (stderr, "%s\n", expansion);
if (result < 0 || result == 2)
free (expansion);
add_history (expansion);
strncpy (line, expansion, sizeof (line) - 1);
free (expansion);
if (strcmp (line, "quit") == 0)
done = 1;
else if (strcmp (line, "save") == 0)
write_history ("history_file");
else if (strcmp (line, "read") == 0)
read_history ("history_file");
else if (strcmp (line, "list") == 0)
register HIST_ENTRY **the_list;
register int i;
the_list = history_list ();
if (the_list)
for (i = 0; the_list[i]; i++)
printf ("%d: %s\n", i + history_base, the_list[i]->line);
else if (strncmp (line, "delete", 6) == 0)
int which;
if ((sscanf (line + 6, "%d", &which)) == 1)
HIST_ENTRY *entry = remove_history (which);
if (!entry)
fprintf (stderr, "No such entry %d\n", which);
free (entry->line);
free (entry);
fprintf (stderr, "non-numeric arg given to `delete'\n");

File:, Node: Copying This Manual, Next: Concept Index, Prev: Programming with GNU History, Up: Top
Appendix A Copying This Manual
* Menu:
* GNU Free Documentation License:: License for copying this manual.

File:, Node: GNU Free Documentation License, Up: Copying This Manual
A.1 GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
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This License is a kind of "copyleft", which means that derivative
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We have designed this License in order to use it for manuals for
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File:, Node: Concept Index, Next: Function and Variable Index, Prev: Copying This Manual, Up: Top
Appendix B Concept Index
* Menu:
* anchored search: Searching the History List.
(line 10)
* event designators: Event Designators. (line 6)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* history events: Event Designators. (line 7)
* history expansion: History Interaction. (line 6)
* History Searching: Searching the History List.
(line 6)

File:, Node: Function and Variable Index, Prev: Concept Index, Up: Top
Appendix C Function and Variable Index
* Menu:
* add_history: History List Management.
(line 10)
* add_history_time: History List Management.
(line 14)
* append_history: Managing the History File.
(line 29)
* clear_history: History List Management.
(line 35)
* current_history: Information About the History List.
(line 18)
* free_history_entry: History List Management.
(line 23)
* get_history_event: History Expansion. (line 31)
* history_arg_extract: History Expansion. (line 46)
* history_base: History Variables. (line 10)
* history_comment_char: History Variables. (line 33)
* history_expand: History Expansion. (line 9)
* history_expansion_char: History Variables. (line 25)
* history_get: Information About the History List.
(line 23)
* history_get_history_state: Initializing History and State Management.
(line 15)
* history_get_time: Information About the History List.
(line 29)
* history_inhibit_expansion_function: History Variables. (line 57)
* history_is_stifled: History List Management.
(line 47)
* history_length: History Variables. (line 13)
* history_list: Information About the History List.
(line 10)
* history_max_entries: History Variables. (line 16)
* history_no_expand_chars: History Variables. (line 48)
* history_quotes_inhibit_expansion: History Variables. (line 53)
* history_search: Searching the History List.
(line 13)
* history_search_delimiter_chars: History Variables. (line 43)
* history_search_pos: Searching the History List.
(line 33)
* history_search_prefix: Searching the History List.
(line 23)
* history_set_history_state: Initializing History and State Management.
(line 19)
* history_set_pos: Moving Around the History List.
(line 10)
* history_subst_char: History Variables. (line 29)
* history_tokenize: History Expansion. (line 39)
* history_total_bytes: Information About the History List.
(line 32)
* history_truncate_file: Managing the History File.
(line 35)
* history_word_delimiters: History Variables. (line 39)
* history_write_timestamps: History Variables. (line 20)
* next_history: Moving Around the History List.
(line 20)
* previous_history: Moving Around the History List.
(line 15)
* read_history: Managing the History File.
(line 10)
* read_history_range: Managing the History File.
(line 16)
* remove_history: History List Management.
(line 18)
* replace_history_entry: History List Management.
(line 29)
* stifle_history: History List Management.
(line 38)
* unstifle_history: History List Management.
(line 41)
* using_history: Initializing History and State Management.
(line 11)
* where_history: Information About the History List.
(line 15)
* write_history: Managing the History File.
(line 23)

Tag Table:
Node: Top1323
Node: Using History Interactively1948
Node: History Interaction2456
Node: Event Designators3880
Node: Word Designators4815
Node: Modifiers6454
Node: Programming with GNU History7681
Node: Introduction to History8413
Node: History Storage10103
Node: History Functions11238
Node: Initializing History and State Management12227
Node: History List Management13039
Node: Information About the History List15071
Node: Moving Around the History List16568
Node: Searching the History List17569
Node: Managing the History File19501
Node: History Expansion21321
Node: History Variables23229
Node: History Programming Example26035
Node: Copying This Manual28712
Node: GNU Free Documentation License28972
Node: Concept Index51378
Node: Function and Variable Index52218

End Tag Table