Below is the output of man history on Ubuntu 26.04.1
As far as I can tell it is unrelated to the history command running on my
computer as seen in the text of the filed bug above. What gives?
HISTORY(3)
Library Functions Manual
HISTORY(3)
NAME
history - GNU History Library
COPYRIGHT
The GNU History Library is Copyright (C) 1989-2025 by the Free Software
Foundation, Inc.
DESCRIPTION
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.
H
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.
HISTORY EXPANSION
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.
PROGRAMMING WITH HISTORY FUNCTIONS
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.
History Functions
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 maxi‐
mum, 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 de‐
limit 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
charac‐
ters 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.
FILES
~/.history
Default filename for reading and writing saved history
SEE ALSO
The Gnu Readline Library, Brian Fox and Chet Ramey
The Gnu History Library, Brian Fox and Chet Ramey
bash(1)
readline(3)
AUTHORS
Brian Fox, Free Software Foundation
[email protected]
Chet Ramey, Case Western Reserve University
[email protected]
BUG REPORTS
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 [email protected]. If you have a fix, you are welcome to mail that as
well! Suggestions and “philosophical” bug reports may be mailed to
[email protected] or
posted to the Usenet newsgroup gnu.bash.bug.
Comments and bug reports concerning this manual page should be
directed to [email protected].
GNU History 8.3
2024 December 31
HISTORY(3)
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https://bugs.launchpad.net/bugs/2167133
Title:
command 'history -c' is not documented
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