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NAME | COPYRIGHT | DESCRIPTION | HISTORY EXPANSION | PROGRAMMING WITH HISTORY FUNCTIONS | History Functions | FILES | SEE ALSO | AUTHORS | BUG REPORTS | COLOPHON |
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HISTORY(3) Library Functions Manual HISTORY(3)
history - GNU History Library
The GNU History Library is Copyright (C) 1989-2025 by the Free
Software Foundation, Inc.
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 when composing new ones.
The History library provides functions that allow applications to
their history, the set of previously-typed lines, which it keeps
in a list. Applications can choose which lines to save into a
history list, how many commands to save, save a history list to a
file, read a history list from a file, and display lines from the
history in various formats.
The history library supports a history expansion feature that is
identical to the history expansion in bash. This section
describes what syntax features are available.
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 is usually performed immediately after a
complete line is read. It takes place in two parts. The first is
to determine which history list entry to use during substitution.
The second is to select portions of that entry to include into the
current one.
The entry selected from the history is the event, and the portions
of that entry that are acted upon are words. Various modifiers
are available to manipulate the selected words. The entry is
split into words in the same fashion as bash does when reading
input, so that several words that would otherwise be separated are
considered one word when surrounded by quotes (see the description
of history_tokenize() below). The event designator selects the
event, the optional word designator selects words from the event,
and various optional modifiers are available to manipulate the
selected words.
History expansions are introduced by the appearance of the history
expansion character, which is ! by default. History expansions
may appear anywhere in the input, but do not nest.
Only backslash (\) and single quotes can quote the history
expansion character.
There is a special abbreviation for substitution, active when the
quick substitution character (default ^) is the first character on
the line. It selects the previous history list entry, using an
event designator equivalent to !!, and substitutes one string for
another in that entry. It is described below under Event
Designators. This is the only history expansion that does not
begin with the history expansion character.
Event Designators
An event designator is a reference to an entry in the history
list. The event designator consists of the portion of the word
beginning with the history expansion character and ending with the
word designator if present, or the end of the word. Unless the
reference is absolute, events are relative to the current position
in the history list.
! Start a history substitution, except when followed by a
blank, newline, carriage return, =, or (.
!n Refer to history list entry n.
!-n Refer to the current entry minus n.
!! Refer to the previous entry. This is a synonym for “!-1”.
!string
Refer to the most recent command preceding the current
position in the history list starting with string.
!?string[?]
Refer to the most recent command preceding the current
position in the history list containing string. The
trailing ? may be omitted if string is followed immediately
by a newline. If string is missing, this uses the string
from the most recent search; it is an error if there is no
previous search string.
^string1^string2^
Quick substitution. Repeat the previous command, replacing
string1 with string2. Equivalent to
“!!:s^string1^string2^” (see Modifiers below).
!# The entire command line typed so far.
Word Designators
Word designators are used to select desired words from the event.
They are optional; if the word designator isn't supplied, the
history expansion uses the entire 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.
0 (zero)
The zeroth word. For the shell, and many other
applications, this is the command word.
n The nth word.
^ The first argument: word 1.
$ The last word. This is usually the last argument, but
expands to the zeroth word if there is only one word in the
line.
% The first word matched by the most recent “?string?”
search, if the search string begins with a character that
is part of a word. By default, searches begin at the end
of each line and proceed to the beginning, so the first
word matched is the one closest to the end of the line.
x-y A range of words; “-y” abbreviates “0-y”.
* All of the words but the zeroth. This is a synonym for
“1-$”. It is not an error to use * if there is just one
word in the event; it expands to the empty string in that
case.
x* Abbreviates x-$.
x- Abbreviates x-$ like x*, but omits the last word. If x is
missing, it defaults to 0.
If a word designator is supplied without an event specification,
the previous command is used as the event, equivalent to !!.
Modifiers
After the optional word designator, the expansion may include a
sequence of one or more of the following modifiers, each preceded
by a “:”. These modify, or edit, the word or words selected from
the history event.
h Remove a trailing filename component, leaving only the
head.
t Remove all leading filename components, leaving the tail.
r Remove a trailing suffix of the form .xxx, leaving the
basename.
e Remove all but the trailing suffix.
p Print the new command but do not execute it.
q Quote the substituted words, escaping further
substitutions.
x Quote the substituted words as with q, but break into words
at blanks and newlines. The q and x modifiers are mutually
exclusive; expansion uses the last one supplied.
s/old/new/
Substitute new for the first occurrence of old in the event
line. Any character may be used as the delimiter in place
of /. The final delimiter is optional if it is the last
character of the event line. A single backslash quotes the
delimiter in old and new. If & appears in new, it is
replaced with old. A single backslash quotes the &. If
old is null, it is set to the last old substituted, or, if
no previous history substitutions took place, the last
string in a !?string[?] search. If new is null, each
matching old is deleted.
& Repeat the previous substitution.
g Cause changes to be applied over the entire event line.
This is used in conjunction with “:s” (e.g.,
“:gs/old/new/”) or “:&”. If used with “:s”, any delimiter
can be used in place of /, and the final delimiter is
optional if it is the last character of the event line. An
a may be used as a synonym for g.
G Apply the following “s” or “&” modifier once to each word
in the event line.
This section describes how to use the History library in other
programs.
Introduction to History
A 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 identical to the history substitution provided by
bash.
The programmer can also 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.
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;
} HIST_ENTRY;
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
structure:
/*
* A structure used to pass around the current state of the history.
*/
typedef struct _hist_state {
HIST_ENTRY **entries; /* Pointer to entry records. */
int offset; /* The current record. */
int length; /* Number of records in list. */
int size; /* Number of records allocated. */
int flags;
} HISTORY_STATE;
If the flags member includes HS_STIFLED, the history has been
stifled.
This section describes the calling sequence for the various
functions exported by the GNU History library.
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.
void using_history (void)
Begin a session in which the history functions might be used.
This initializes the interactive variables.
HISTORY_STATE * history_get_history_state (void)
Return a structure describing the current state of the input
history.
void history_set_history_state (HISTORY_STATE *state)
Set the state of the history list according to state.
History List Management
These functions manage individual entries on the history list, or
set parameters managing the list itself.
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. If the maximum number of history
entries has been set using stifle_history(), and the new number of
history entries would exceed that maximum, the oldest history
entry is removed.
void add_history_time (const char *string)
Change the time stamp associated with the most recent history
entry to string.
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.
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.
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.
void clear_history (void)
Clear the history list by deleting all the entries.
void stifle_history (int max)
Stifle the history list, remembering only the last max entries.
The history list will contain only max entries at a time.
int unstifle_history (void)
Stop stifling the history. This returns the previously-set
maximum number of history entries (as set by stifle_history()).
history was stifled. The value is positive if the history was
stifled, negative if it wasn't.
int history_is_stifled (void)
Returns non-zero if the history is stifled, zero if it is not.
Information About the History List
These functions return information about the entire history list
or individual list entries.
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.
int where_history (void)
Returns the offset of the current history element.
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
pointer.
HIST_ENTRY * history_get (int offset)
Return the history entry at position offset. The range of valid
values of offset starts at history_base and ends at history_length
- 1. If there is no entry there, or if offset is outside the
valid range, return a NULL pointer.
time_t history_get_time (HIST_ENTRY *)
Return the time stamp associated with the history entry passed as
the argument.
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.
Moving Around the History List
These functions allow the current index into the history list to
be set or changed.
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.
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.
HIST_ENTRY * next_history (void)
If the current history offset refers to a valid history entry,
increment the current history offset. If the possibly-incremented
history offset refers to a valid history entry, return a pointer
to that entry; otherwise, return a NULL pointer.
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.
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
the function returns -1.
int history_search_prefix (const char *string, int direction)
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 the
function returns -1.
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.
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.
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.
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.
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
error.
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.
int history_truncate_file (const char *filename, int nlines)
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.
History Expansion
These functions implement history expansion.
int history_expand (const char *string, char **output)
Expand string, placing the result into output, a pointer to a
string. Returns:
0 If no expansions took place (or, if the only change
in the text was the removal of escape characters
preceding the history expansion character);
1 if expansions did take place;
-1 if there was an error in expansion;
2 if the returned line should be displayed, but not
executed, as with the :p modifier.
If an error occurred in expansion, then output contains a
descriptive error message.
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.
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.
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
history_tokenize().
History Variables
This section describes the externally-visible variables exported
by the GNU History Library.
int history_base
The logical offset of the first entry in the history list.
int history_length
The number of entries currently stored in the history list.
int history_max_entries
The maximum number of history entries. This must be changed using
stifle_history().
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. The current timestamp
format uses the value of history_comment_char to delimit timestamp
entries in the history file. If that variable does not have a
value (the default), the history library will not write
timestamps.
char history_expansion_char
The character that introduces a history event. The default is !.
Setting this to 0 inhibits history expansion.
char history_subst_char
The character that invokes word substitution if found at the start
of a line. The default is ^.
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.
char * history_word_delimiters
The characters that separate tokens for history_tokenize(). The
default value is " \t\n()<>;&|".
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, \r, and =.
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.
int history_quotes_inhibit_expansion
If non-zero, the history expansion code implements shell-like
quoting: single-quoted words are not scanned for the history
expansion character or the history comment character, and double-
quoted words may have history expansion performed, since single
quotes are not special within double quotes. The default value is
0.
int history_quoting_state
An application may set this variable to indicate that the current
line being expanded is subject to existing quoting. If set to ',
history expansion assumes that the line is single-quoted and
inhibit expansion until it reads an unquoted closing single quote;
if set to ", history expansion assumes the line is double quoted
until it reads an unquoted closing double quote. If set to zero,
the default, history expansion assumes the line is not quoted and
treats quote characters within the line as described above. This
is only effective if history_quotes_inhibit_expansion is set.
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.
~/.history
Default filename for reading and writing saved history
The Gnu Readline Library, Brian Fox and Chet Ramey
The Gnu History Library, Brian Fox and Chet Ramey
bash(1)
readline(3)
Brian Fox, Free Software Foundation
bfox@gnu.org
Chet Ramey, Case Western Reserve University
chet.ramey@case.edu
If you find a bug in the history library, you should report it.
But first, you should make sure that it really is a bug, and that
it appears in the latest version of the history library that you
have.
Once you have determined that a bug actually exists, mail a bug
report to bug-readline@gnu.org. If you have a fix, you are
welcome to mail that as well! Suggestions and “philosophical” bug
reports may be mailed to bug-readline@gnu.org or posted to the
Usenet newsgroup gnu.bash.bug.
Comments and bug reports concerning this manual page should be
directed to chet.ramey@case.edu.
This page is part of the readline (GNU Readline library) project.
Information about the project can be found at
⟨http://www.gnu.org/software/readline/⟩. If you have a bug report
for this manual page, see
⟨http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html#Bugs⟩.
This page was obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/readline.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-07-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
GNU History 8.3 2024 December 31 HISTORY(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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