1HISTORY(3) Library Functions Manual HISTORY(3)
2
6 history - GNU History Library
7
9 The GNU History Library is Copyright (C) 1989-2020 by the Free Software
10 Foundation, Inc.
11
13 Many programs read input from the user a line at a time. The GNU His‐
14 tory library is able to keep track of those lines, associate arbitrary
15 data with each line, and utilize information from previous lines in
16 composing new ones.
17
19 The history library supports a history expansion feature that is iden‐
20 tical to the history expansion in bash. This section describes what
21 syntax features are available.
22 History expansions introduce words from the history list into the input
24 stream, making it easy to repeat commands, insert the arguments to a
25 previous command into the current input line, or fix errors in previous
26 commands quickly.
27 History expansion is usually performed immediately after a complete
29 line is read. It takes place in two parts. The first is to determine
30 which line from the history list to use during substitution. The sec‐
31 ond is to select portions of that line for inclusion into the current
32 one. The line selected from the history is the event, and the portions
33 of that line that are acted upon are words. Various modifiers are
34 available to manipulate the selected words. The line is broken into
35 words in the same fashion as bash does when reading input, so that sev‐
36 eral words that would otherwise be separated are considered one word
37 when surrounded by quotes (see the description of history_tokenize()
38 below). History expansions are introduced by the appearance of the
39 history expansion character, which is ! by default. Only backslash (\)
40 and single quotes can quote the history expansion character.
41 Event Designators
43 An event designator is a reference to a command line entry in the his‐
44 tory list. Unless the reference is absolute, events are relative to
45 the current position in the history list.
46 ! Start a history substitution, except when followed by a blank,
48 newline, = or (.
49 !n Refer to command line n.
50 !-n Refer to the current command minus n.
51 !! Refer to the previous command. This is a synonym for `!-1'.
52 !string
53 Refer to the most recent command preceding the current position
54 in the history list starting with string.
55 !?string[?]
56 Refer to the most recent command preceding the current position
57 in the history list containing string. The trailing ? may be
58 omitted if string is followed immediately by a newline. If
59 string is missing, the string from the most recent search is
60 used; it is an error if there is no previous search string.
61 ^string1^string2^
62 Quick substitution. Repeat the last command, replacing string1
63 with string2. Equivalent to ``!!:s^string1^string2^'' (see Mod‐
64 ifiers below).
65 !# The entire command line typed so far.
66 Word Designators
68 Word designators are used to select desired words from the event. A :
69 separates the event specification from the word designator. It may be
70 omitted if the word designator begins with a ^, $, *, -, or %. Words
71 are numbered from the beginning of the line, with the first word being
72 denoted by 0 (zero). Words are inserted into the current line sepa‐
73 rated by single spaces.
74 0 (zero)
76 The zeroth word. For the shell, this is the command word.
77 n The nth word.
78 ^ The first argument. That is, word 1.
79 $ The last word. This is usually the last argument, but will ex‐
80 pand to the zeroth word if there is only one word in the line.
81 % The first word matched by the most recent `?string?' search, if
82 the search string begins with a character that is part of a
83 word.
84 x-y A range of words; `-y' abbreviates `0-y'.
85 * All of the words but the zeroth. This is a synonym for `1-$'.
86 It is not an error to use * if there is just one word in the
87 event; the empty string is returned in that case.
88 x* Abbreviates x-$.
89 x- Abbreviates x-$ like x*, but omits the last word. If x is miss‐
90 ing, it defaults to 0.
91 If a word designator is supplied without an event specification, the
93 previous command is used as the event.
94 Modifiers
96 After the optional word designator, there may appear a sequence of one
97 or more of the following modifiers, each preceded by a `:'. These mod‐
98 ify, or edit, the word or words selected from the history event.
99 h Remove a trailing file name component, leaving only the head.
101 t Remove all leading file name components, leaving the tail.
102 r Remove a trailing suffix of the form .xxx, leaving the basename.
103 e Remove all but the trailing suffix.
104 p Print the new command but do not execute it.
105 q Quote the substituted words, escaping further substitutions.
106 x Quote the substituted words as with q, but break into words at
107 blanks and newlines. The q and x modifiers are mutually exclu‐
108 sive; the last one supplied is used.
109 s/old/new/
110 Substitute new for the first occurrence of old in the event
111 line. Any character may be used as the delimiter in place of /.
112 The final delimiter is optional if it is the last character of
113 the event line. The delimiter may be quoted in old and new with
114 a single backslash. If & appears in new, it is replaced by old.
115 A single backslash will quote the &. If old is null, it is set
116 to the last old substituted, or, if no previous history substi‐
117 tutions took place, the last string in a !?string[?] search.
118 If new is null, each matching old is deleted.
119 & Repeat the previous substitution.
120 g Cause changes to be applied over the entire event line. This is
121 used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.
122 If used with `:s', any delimiter can be used in place of /, and
123 the final delimiter is optional if it is the last character of
124 the event line. An a may be used as a synonym for g.
125 G Apply the following `s' or `&' modifier once to each word in the
126 event line.
127
129 This section describes how to use the History library in other pro‐
130 grams.
131 Introduction to History
133 A programmer using the History library has available functions for re‐
134 membering lines on a history list, associating arbitrary data with a
135 line, removing lines from the list, searching through the list for a
136 line containing an arbitrary text string, and referencing any line in
137 the list directly. In addition, a history expansion function is avail‐
138 able which provides for a consistent user interface across different
139 programs.
140 The user using programs written with the History library has the bene‐
142 fit of a consistent user interface with a set of well-known commands
143 for manipulating the text of previous lines and using that text in new
144 commands. The basic history manipulation commands are identical to the
145 history substitution provided by bash.
146 The programmer can also use the readline library, which includes some
148 history manipulation by default, and has the added advantage of command
149 line editing.
150 Before declaring any functions using any functionality the History li‐
152 brary provides in other code, an application writer should include the
153 file <readline/history.h> in any file that uses the History library's
154 features. It supplies extern declarations for all of the library's
155 public functions and variables, and declares all of the public data
156 structures.
157 History Storage
159 The history list is an array of history entries. A history entry is
160 declared as follows:
161 typedef void * histdata_t;
163 typedef struct _hist_entry {
165 char *line;
166 char *timestamp;
167 histdata_t data;
168 } HIST_ENTRY;
169 The history list itself might therefore be declared as
171 HIST_ENTRY ** the_history_list;
173 The state of the History library is encapsulated into a single struc‐
175 ture:
176 /*
178 * A structure used to pass around the current state of the history.
179 */
180 typedef struct _hist_state {
181 HIST_ENTRY **entries; /* Pointer to the entries themselves. */
182 int offset; /* The location pointer within this array. */
183 int length; /* Number of elements within this array. */
184 int size; /* Number of slots allocated to this array. */
185 int flags;
186 } HISTORY_STATE;
187 If the flags member includes HS_STIFLED, the history has been stifled.
189
191 This section describes the calling sequence for the various functions
192 exported by the GNU History library.
193 Initializing History and State Management
195 This section describes functions used to initialize and manage the
196 state of the History library when you want to use the history functions
197 in your program.
198 void using_history (void)
200 Begin a session in which the history functions might be used. This
201 initializes the interactive variables.
202 HISTORY_STATE * history_get_history_state (void)
204 Return a structure describing the current state of the input history.
205 void history_set_history_state (HISTORY_STATE *state)
207 Set the state of the history list according to state.
208 History List Management
211 These functions manage individual entries on the history list, or set
212 parameters managing the list itself.
213 void add_history (const char *string)
215 Place string at the end of the history list. The associated data field
216 (if any) is set to NULL. If the maximum number of history entries has
217 been set using stifle_history(), and the new number of history entries
218 would exceed that maximum, the oldest history entry is removed.
219 void add_history_time (const char *string)
221 Change the time stamp associated with the most recent history entry to
222 string.
223 HIST_ENTRY * remove_history (int which)
225 Remove history entry at offset which from the history. The removed el‐
226 ement is returned so you can free the line, data, and containing struc‐
227 ture.
228 histdata_t free_history_entry (HIST_ENTRY *histent)
230 Free the history entry histent and any history library private data as‐
231 sociated with it. Returns the application-specific data so the caller
232 can dispose of it.
233 HIST_ENTRY * replace_history_entry (int which, const char *line, hist‐
235 data_t data)
236 Make the history entry at offset which have line and data. This re‐
237 turns the old entry so the caller can dispose of any application-spe‐
238 cific data. In the case of an invalid which, a NULL pointer is re‐
239 turned.
240 void clear_history (void)
242 Clear the history list by deleting all the entries.
243 void stifle_history (int max)
245 Stifle the history list, remembering only the last max entries. The
246 history list will contain only max entries at a time.
247 int unstifle_history (void)
249 Stop stifling the history. This returns the previously-set maximum
250 number of history entries (as set by stifle_history()). history was
251 stifled. The value is positive if the history was stifled, negative if
252 it wasn't.
253 int history_is_stifled (void)
255 Returns non-zero if the history is stifled, zero if it is not.
256 Information About the History List
259 These functions return information about the entire history list or in‐
260 dividual list entries.
261 HIST_ENTRY ** history_list (void)
263 Return a NULL terminated array of HIST_ENTRY * which is the current in‐
264 put history. Element 0 of this list is the beginning of time. If
265 there is no history, return NULL.
266 int where_history (void)
268 Returns the offset of the current history element.
269 HIST_ENTRY * current_history (void)
271 Return the history entry at the current position, as determined by
272 where_history(). If there is no entry there, return a NULL pointer.
273 HIST_ENTRY * history_get (int offset)
275 Return the history entry at position offset. The range of valid values
276 of offset starts at history_base and ends at history_length - 1. If
277 there is no entry there, or if offset is outside the valid range, re‐
278 turn a NULL pointer.
279 time_t history_get_time (HIST_ENTRY *)
281 Return the time stamp associated with the history entry passed as the
282 argument.
283 int history_total_bytes (void)
285 Return the number of bytes that the primary history entries are using.
286 This function returns the sum of the lengths of all the lines in the
287 history.
288 Moving Around the History List
291 These functions allow the current index into the history list to be set
292 or changed.
293 int history_set_pos (int pos)
295 Set the current history offset to pos, an absolute index into the list.
296 Returns 1 on success, 0 if pos is less than zero or greater than the
297 number of history entries.
298 HIST_ENTRY * previous_history (void)
300 Back up the current history offset to the previous history entry, and
301 return a pointer to that entry. If there is no previous entry, return
302 a NULL pointer.
303 HIST_ENTRY * next_history (void)
305 If the current history offset refers to a valid history entry, incre‐
306 ment the current history offset. If the possibly-incremented history
307 offset refers to a valid history entry, return a pointer to that entry;
308 otherwise, return a NULL pointer.
309 Searching the History List
312 These functions allow searching of the history list for entries con‐
313 taining a specific string. Searching may be performed both forward and
314 backward from the current history position. The search may be an‐
315 chored, meaning that the string must match at the beginning of the his‐
316 tory entry.
317 int history_search (const char *string, int direction)
319 Search the history for string, starting at the current history offset.
320 If direction is less than 0, then the search is through previous en‐
321 tries, otherwise through subsequent entries. If string is found, then
322 the current history index is set to that history entry, and the value
323 returned is the offset in the line of the entry where string was found.
324 Otherwise, nothing is changed, and a -1 is returned.
325 int history_search_prefix (const char *string, int direction)
327 Search the history for string, starting at the current history offset.
328 The search is anchored: matching lines must begin with string. If di‐
329 rection is less than 0, then the search is through previous entries,
330 otherwise through subsequent entries. If string is found, then the
331 current history index is set to that entry, and the return value is 0.
332 Otherwise, nothing is changed, and a -1 is returned.
333 int history_search_pos (const char *string, int direction, int pos)
335 Search for string in the history list, starting at pos, an absolute in‐
336 dex into the list. If direction is negative, the search proceeds back‐
337 ward from pos, otherwise forward. Returns the absolute index of the
338 history element where string was found, or -1 otherwise.
339 Managing the History File
342 The History library can read the history from and write it to a file.
343 This section documents the functions for managing a history file.
344 int read_history (const char *filename)
346 Add the contents of filename to the history list, a line at a time. If
347 filename is NULL, then read from ~/.history. Returns 0 if successful,
348 or errno if not.
349 int read_history_range (const char *filename, int from, int to)
351 Read a range of lines from filename, adding them to the history list.
352 Start reading at line from and end at to. If from is zero, start at
353 the beginning. If to is less than from, then read until the end of the
354 file. If filename is NULL, then read from ~/.history. Returns 0 if
355 successful, or errno if not.
356 int write_history (const char *filename)
358 Write the current history to filename, overwriting filename if neces‐
359 sary. If filename is NULL, then write the history list to ~/.history.
360 Returns 0 on success, or errno on a read or write error.
361 int append_history (int nelements, const char *filename)
364 Append the last nelements of the history list to filename. If filename
365 is NULL, then append to ~/.history. Returns 0 on success, or errno on
366 a read or write error.
367 int history_truncate_file (const char *filename, int nlines)
369 Truncate the history file filename, leaving only the last nlines lines.
370 If filename is NULL, then ~/.history is truncated. Returns 0 on suc‐
371 cess, or errno on failure.
372 History Expansion
375 These functions implement history expansion.
376 int history_expand (char *string, char **output)
378 Expand string, placing the result into output, a pointer to a string.
379 Returns:
380 0 If no expansions took place (or, if the only change in
381 the text was the removal of escape characters preceding
382 the history expansion character);
383 1 if expansions did take place;
384 -1 if there was an error in expansion;
385 2 if the returned line should be displayed, but not exe‐
386 cuted, as with the :p modifier.
387 If an error occurred in expansion, then output contains a descriptive
388 error message.
389 char * get_history_event (const char *string, int *cindex, int qchar)
391 Returns the text of the history event beginning at string + *cindex.
392 *cindex is modified to point to after the event specifier. At function
393 entry, cindex points to the index into string where the history event
394 specification begins. qchar is a character that is allowed to end the
395 event specification in addition to the ``normal'' terminating charac‐
396 ters.
397 char ** history_tokenize (const char *string)
399 Return an array of tokens parsed out of string, much as the shell
400 might. The tokens are split on the characters in the history_word_de‐
401 limiters variable, and shell quoting conventions are obeyed.
402 char * history_arg_extract (int first, int last, const char *string)
404 Extract a string segment consisting of the first through last arguments
405 present in string. Arguments are split using history_tokenize().
406 History Variables
409 This section describes the externally-visible variables exported by the
410 GNU History Library.
411 int history_base
413 The logical offset of the first entry in the history list.
414 int history_length
416 The number of entries currently stored in the history list.
417 int history_max_entries
419 The maximum number of history entries. This must be changed using sti‐
420 fle_history().
421 int history_write_timestamps
423 If non-zero, timestamps are written to the history file, so they can be
424 preserved between sessions. The default value is 0, meaning that time‐
425 stamps are not saved. The current timestamp format uses the value of
426 history_comment_char to delimit timestamp entries in the history file.
427 If that variable does not have a value (the default), timestamps will
428 not be written.
429 char history_expansion_char
431 The character that introduces a history event. The default is !. Set‐
432 ting this to 0 inhibits history expansion.
433 char history_subst_char
435 The character that invokes word substitution if found at the start of a
436 line. The default is ^.
437 char history_comment_char
439 During tokenization, if this character is seen as the first character
440 of a word, then it and all subsequent characters up to a newline are
441 ignored, suppressing history expansion for the remainder of the line.
442 This is disabled by default.
443 char * history_word_delimiters
445 The characters that separate tokens for history_tokenize(). The de‐
446 fault value is " \t\n()<>;&|".
447 char * history_no_expand_chars
449 The list of characters which inhibit history expansion if found immedi‐
450 ately following history_expansion_char. The default is space, tab,
451 newline, \r, and =.
452 char * history_search_delimiter_chars
454 The list of additional characters which can delimit a history search
455 string, in addition to space, tab, : and ? in the case of a substring
456 search. The default is empty.
457 int history_quotes_inhibit_expansion
459 If non-zero, double-quoted words are not scanned for the history expan‐
460 sion character or the history comment character. The default value is
461 0.
462 rl_linebuf_func_t * history_inhibit_expansion_function
464 This should be set to the address of a function that takes two argu‐
465 ments: a char * (string) and an int index into that string (i). It
466 should return a non-zero value if the history expansion starting at
467 string[i] should not be performed; zero if the expansion should be
468 done. It is intended for use by applications like bash that use the
469 history expansion character for additional purposes. By default, this
470 variable is set to NULL.
471
473 ~/.history
474 Default filename for reading and writing saved history
475
477 The Gnu Readline Library, Brian Fox and Chet Ramey
478 The Gnu History Library, Brian Fox and Chet Ramey
479 bash(1)
480 readline(3)
481
483 Brian Fox, Free Software Foundation
484 bfox@gnu.org
485 Chet Ramey, Case Western Reserve University
487 chet.ramey@case.edu
488
490 If you find a bug in the history library, you should report it. But
491 first, you should make sure that it really is a bug, and that it ap‐
492 pears in the latest version of the history library that you have.
493 Once you have determined that a bug actually exists, mail a bug report
495 to bug-readline@gnu.org. If you have a fix, you are welcome to mail
496 that as well! Suggestions and `philosophical' bug reports may be
497 mailed to bug-readline@gnu.org or posted to the Usenet newsgroup
498 gnu.bash.bug.
499 Comments and bug reports concerning this manual page should be directed
501 to chet.ramey@case.edu.
502GNU History 8.1 2020 July 17 HISTORY(3)