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history − GNU History Library
The GNU History Library is Copyright (C) 1989-2002 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.
|
! |
Start a history substitution, except when followed by a blank, newline, = or (. | ||
|
!n |
Refer to command line n. | ||
|
!−n |
Refer to the current command line minus n. | ||
|
!! |
Refer to the previous command. This is a synonym for ’!−1’. |
!string
Refer to the most recent command starting with string.
!?string[?]
Refer to the most recent command containing string. The trailing ? may be omitted if string is followed immediately by a newline.
^ 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 argument. | ||
|
% |
The word matched by the most recent ’?string?’ search. | ||
|
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 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 ’:’.
|
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. |
s/old/new/
Substitute new for the first occurrence of old in the event line. Any delimiter can be used 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.
|
& |
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’ modifier once to each word in the event line. |
This section describes how to use the History library in other programs.
Introduction
to History
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 identical to the history substitution provided by bash.
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.
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.
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.
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, starting
from history_base. If there is no entry there, or if
offset is greater than the history length, 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)
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.
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 ocurred 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.
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, single-quoted words are not scanned for the
history expansion 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
bfox@gnu.org
Chet Ramey,
Case Western Reserve University
chet@ins.CWRU.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@ins.CWRU.Edu.
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history(3) | |