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HISTORY(3) HISTORY(3)
NAME
history - GNU History Library
COPYRIGHT
The GNU History Library is Copyright (C) 1989-2002 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 uti-
lize information from previous lines in composing new
ones.
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 cur-
rent 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 modi-
fiers 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 oth-
erwise be separated are considered one word when sur-
rounded by quotes (see the description of history_tok-
enize() 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 com-
mand 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 specifi-
cation, 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 sub-
stitutions.
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 back-
slash. 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.
PROGRAMMING WITH HISTORY FUNCTIONS
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, associ-
ating 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 inter-
face 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 previ-
ous 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 edit-
ing.
Before declaring any functions using any functionality the
History library provides in other code, an application
writer should include the file in any
file that uses the History library's features. It sup-
plies 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 his-
tory 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.
History Functions
This section describes the calling sequence for the vari-
ous 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 associ-
ated data field (if any) is set to NULL.
void add_history_time (const char *string)
Change the time stamp associated with the most recent his-
tory 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 sti-
fle_history()). history was stifled. The value is posi-
tive 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 his-
tory 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 his-
tory 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 his-
tory 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 sub-
sequent 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 direc-
tion)
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 man-
aging 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 ~/.his-
tory. 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 file-
name 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 file-
name 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'' termi-
nating 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 expan-
sion.
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 his-
tory expansion for the remainder of the line. This is
disabled by default.
char * history_word_delimiters
The characters that separate tokens for history_tok-
enize(). 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 his-
tory 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 per-
formed; 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 his-
tory
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
bfox@gnu.org
Chet Ramey, Case Western Reserve University
chet@ins.CWRU.Edu
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 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-read-
line@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.
GNU History 5.0 2003 July 31 HISTORY(3)