The GNU History Library is Copyright (C) 1989-2001 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 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 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.
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, 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:
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 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.
1void (using_history, void, )
Begin a session in which the history functions might be used. This
initializes the interactive variables.
1HISTORY_STATE * (history_get_history_state, void, )
Return a structure describing the current state of the input history.
1void (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.
1void (add_history, const char *string, )
Place string at the end of the history list. The associated data
field (if any) is set to NULL.
1HIST_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.
3HIST_ENTRY * (replace_history_entry, int which, const char *line)
Make the history entry at offset which have line and data.
This returns the old entry so you can dispose of the data. In the case
of an invalid which, a NULL pointer is returned.
1void (clear_history, void, )
Clear the history list by deleting all the entries.
1void (stifle_history, int max, )
Stifle the history list, remembering only the last max entries.
1int (unstifle_history, void, )
Stop stifling the history. This returns the previous amount the
history was stifled. The value is positive if the history was
stifled, negative if it wasn't.
1int (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.
1HIST_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.
1int (where_history, void, )
Returns the offset of the current history element.
1HIST_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.
1HIST_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.
1int (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.
1int (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.
1HIST_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.
1HIST_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.
2int (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.
2int (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.
3int (history_search_pos, const char *string, int direction)
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.
1int (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.
3int (read_history_range, const char *filename, int from)
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.
1int (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.
2int (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.
2int (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.
2int (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.
3char * (get_history_event, const char *string, int *cindex)
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.
1char ** (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.
3char * (history_arg_extract, int first, int last)
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.
inthistory_base
The logical offset of the first entry in the history list.
inthistory_length
The number of entries currently stored in the history list.
inthistory_max_entries
The maximum number of history entries. This must be changed using
stifle_history().
charhistory_expansion_char
The character that introduces a history event. The default is !.
Setting this to 0 inhibits history expansion.
charhistory_subst_char
The character that invokes word substitution if found at the start of
a line. The default is ^.
charhistory_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.
inthistory_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.
FILES
~/.history
Default filename for reading and writing saved history
SEE ALSO
The Gnu Readline Library, Brian Fox and Chet Ramey
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.