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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) 1989-2020 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 in composing new ones.
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 line from the history list to use during
substitution. The second is to select portions of that line for
inclusion into the current one. The line selected from the
history is the event, and the portions of that line that are
acted upon are words. Various modifiers are available to
manipulate the selected words. The line is broken 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). History expansions are introduced by
the appearance of the history expansion character, which is ! by
default. Only backslash (\) and single quotes can quote the
history expansion character.
Event Designators
An event designator is a reference to a command line entry in the
history list. 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, = or (.
!n Refer to command line n.
!-n Refer to the current command minus n.
!! Refer to the previous command. 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, the
string from the most recent search is used; it is an error
if there is no previous search string.
^string1^string2^
Quick substitution. Repeat the last 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.
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, this is the command word.
n The nth word.
^ The first argument. That is, word 1.
$ The last word. This is usually the last argument, but
will expand 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.
x-y A range of words; `-y' abbreviates `0-y'.
* All of the words but the zeroth. This is a synonym for
`1-$'. It is not an error to use * if there is just one
word in the event; the empty string is returned in that
case.
x* Abbreviates x-$.
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.
Modifiers
After the optional word designator, there may appear 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 file name component, leaving only the
head.
t Remove all leading file name 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; the last one supplied is used.
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. 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 &. 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 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;
} 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 a -1 is returned.
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 a -1 is returned.
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 (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), timestamps will not be written.
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, double-quoted words are not scanned for the history
expansion character or the history comment character. The
default value is 0.
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
[email protected]
Chet Ramey, Case Western Reserve University
[email protected]
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 [email protected].
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 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-01-14.) 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
[email protected]
GNU History 8.1 2020 July 17 HISTORY(3)
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HTML rendering created 2024-06-26 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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