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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.
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.
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.
If a word designator is supplied without an event specification, the previous command is used as the event.
After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a ‘:’.
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.
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.
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.
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.
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.
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.
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.
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.
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:
If an error ocurred in expansion, then output contains a descriptive error message.
- If no expansions took place (or, if the only change in the text was the removal of escape characters preceding the history expansion character);
- if expansions did take place;
- -1
- if there was an error in expansion;
- if the returned line should be displayed, but not executed, as with the :p modifier.
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().
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_wite_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, 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.
Chet Ramey, Case Western Reserve University
chet@ins.CWRU.Edu
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.