1@ignore 2This file documents the user interface to the GNU History library. 3 4Copyright (C) 1988-2020 Free Software Foundation, Inc. 5Authored by Brian Fox and Chet Ramey. 6 7Permission is granted to make and distribute verbatim copies of this manual 8provided the copyright notice and this permission notice are preserved on 9all copies. 10 11Permission is granted to process this file through Tex and print the 12results, provided the printed document carries copying permission notice 13identical to this one except for the removal of this paragraph (this 14paragraph not being relevant to the printed manual). 15 16Permission is granted to copy and distribute modified versions of this 17manual under the conditions for verbatim copying, provided also that the 18GNU Copyright statement is available to the distributee, and provided that 19the entire resulting derived work is distributed under the terms of a 20permission notice identical to this one. 21 22Permission is granted to copy and distribute translations of this manual 23into another language, under the above conditions for modified versions. 24@end ignore 25 26@node Programming with GNU History 27@chapter Programming with GNU History 28 29This chapter describes how to interface programs that you write 30with the @sc{gnu} History Library. 31It should be considered a technical guide. 32For information on the interactive use of @sc{gnu} History, @pxref{Using 33History Interactively}. 34 35@menu 36* Introduction to History:: What is the GNU History library for? 37* History Storage:: How information is stored. 38* History Functions:: Functions that you can use. 39* History Variables:: Variables that control behaviour. 40* History Programming Example:: Example of using the GNU History Library. 41@end menu 42 43@node Introduction to History 44@section Introduction to History 45 46Many programs read input from the user a line at a time. The @sc{gnu} 47History library is able to keep track of those lines, associate arbitrary 48data with each line, and utilize information from previous lines in 49composing new ones. 50 51A programmer using the History library has available functions 52for remembering lines on a history list, associating arbitrary data 53with a line, removing lines from the list, searching through the list 54for a line containing an arbitrary text string, and referencing any line 55in the list directly. In addition, a history @dfn{expansion} function 56is available which provides for a consistent user interface across 57different programs. 58 59The user using programs written with the History library has the 60benefit of a consistent user interface with a set of well-known 61commands for manipulating the text of previous lines and using that text 62in new commands. The basic history manipulation commands are similar to 63the history substitution provided by @code{csh}. 64 65The programmer can also use the Readline library, which 66includes some history manipulation by default, and has the added 67advantage of command line editing. 68 69Before declaring any functions using any functionality the History 70library provides in other code, an application writer should include 71the file @code{<readline/history.h>} in any file that uses the 72History library's features. It supplies extern declarations for all 73of the library's public functions and variables, and declares all of 74the public data structures. 75 76@node History Storage 77@section History Storage 78 79The history list is an array of history entries. A history entry is 80declared as follows: 81 82@example 83typedef void *histdata_t; 84 85typedef struct _hist_entry @{ 86 char *line; 87 char *timestamp; 88 histdata_t data; 89@} HIST_ENTRY; 90@end example 91 92The history list itself might therefore be declared as 93 94@example 95HIST_ENTRY **the_history_list; 96@end example 97 98The state of the History library is encapsulated into a single structure: 99 100@example 101/* 102 * A structure used to pass around the current state of the history. 103 */ 104typedef struct _hist_state @{ 105 HIST_ENTRY **entries; /* Pointer to the entries themselves. */ 106 int offset; /* The location pointer within this array. */ 107 int length; /* Number of elements within this array. */ 108 int size; /* Number of slots allocated to this array. */ 109 int flags; 110@} HISTORY_STATE; 111@end example 112 113If the flags member includes @code{HS_STIFLED}, the history has been 114stifled. 115 116@node History Functions 117@section History Functions 118 119This section describes the calling sequence for the various functions 120exported by the @sc{gnu} History library. 121 122@menu 123* Initializing History and State Management:: Functions to call when you 124 want to use history in a 125 program. 126* History List Management:: Functions used to manage the list 127 of history entries. 128* Information About the History List:: Functions returning information about 129 the history list. 130* Moving Around the History List:: Functions used to change the position 131 in the history list. 132* Searching the History List:: Functions to search the history list 133 for entries containing a string. 134* Managing the History File:: Functions that read and write a file 135 containing the history list. 136* History Expansion:: Functions to perform csh-like history 137 expansion. 138@end menu 139 140@node Initializing History and State Management 141@subsection Initializing History and State Management 142 143This section describes functions used to initialize and manage 144the state of the History library when you want to use the history 145functions in your program. 146 147@deftypefun void using_history (void) 148Begin a session in which the history functions might be used. This 149initializes the interactive variables. 150@end deftypefun 151 152@deftypefun {HISTORY_STATE *} history_get_history_state (void) 153Return a structure describing the current state of the input history. 154@end deftypefun 155 156@deftypefun void history_set_history_state (HISTORY_STATE *state) 157Set the state of the history list according to @var{state}. 158@end deftypefun 159 160@node History List Management 161@subsection History List Management 162 163These functions manage individual entries on the history list, or set 164parameters managing the list itself. 165 166@deftypefun void add_history (const char *string) 167Place @var{string} at the end of the history list. The associated data 168field (if any) is set to @code{NULL}. 169If the maximum number of history entries has been set using 170@code{stifle_history()}, and the new number of history entries would exceed 171that maximum, the oldest history entry is removed. 172@end deftypefun 173 174@deftypefun void add_history_time (const char *string) 175Change the time stamp associated with the most recent history entry to 176@var{string}. 177@end deftypefun 178 179@deftypefun {HIST_ENTRY *} remove_history (int which) 180Remove history entry at offset @var{which} from the history. The 181removed element is returned so you can free the line, data, 182and containing structure. 183@end deftypefun 184 185@deftypefun {histdata_t} free_history_entry (HIST_ENTRY *histent) 186Free the history entry @var{histent} and any history library private 187data associated with it. Returns the application-specific data 188so the caller can dispose of it. 189@end deftypefun 190 191@deftypefun {HIST_ENTRY *} replace_history_entry (int which, const char *line, histdata_t data) 192Make the history entry at offset @var{which} have @var{line} and @var{data}. 193This returns the old entry so the caller can dispose of any 194application-specific data. In the case 195of an invalid @var{which}, a @code{NULL} pointer is returned. 196@end deftypefun 197 198@deftypefun void clear_history (void) 199Clear the history list by deleting all the entries. 200@end deftypefun 201 202@deftypefun void stifle_history (int max) 203Stifle the history list, remembering only the last @var{max} entries. 204The history list will contain only @var{max} entries at a time. 205@end deftypefun 206 207@deftypefun int unstifle_history (void) 208Stop stifling the history. This returns the previously-set 209maximum number of history entries (as set by @code{stifle_history()}). 210The value is positive if the history was 211stifled, negative if it wasn't. 212@end deftypefun 213 214@deftypefun int history_is_stifled (void) 215Returns non-zero if the history is stifled, zero if it is not. 216@end deftypefun 217 218@node Information About the History List 219@subsection Information About the History List 220 221These functions return information about the entire history list or 222individual list entries. 223 224@deftypefun {HIST_ENTRY **} history_list (void) 225Return a @code{NULL} terminated array of @code{HIST_ENTRY *} which is the 226current input history. Element 0 of this list is the beginning of time. 227If there is no history, return @code{NULL}. 228@end deftypefun 229 230@deftypefun int where_history (void) 231Returns the offset of the current history element. 232@end deftypefun 233 234@deftypefun {HIST_ENTRY *} current_history (void) 235Return the history entry at the current position, as determined by 236@code{where_history()}. If there is no entry there, return a @code{NULL} 237pointer. 238@end deftypefun 239 240@deftypefun {HIST_ENTRY *} history_get (int offset) 241Return the history entry at position @var{offset}. 242The range of valid 243values of @var{offset} starts at @code{history_base} and ends at 244@var{history_length} - 1 (@pxref{History Variables}). 245If there is no entry there, or if @var{offset} is outside the valid 246range, return a @code{NULL} pointer. 247@end deftypefun 248 249@deftypefun time_t history_get_time (HIST_ENTRY *entry) 250Return the time stamp associated with the history entry @var{entry}. 251If the timestamp is missing or invalid, return 0. 252@end deftypefun 253 254@deftypefun int history_total_bytes (void) 255Return the number of bytes that the primary history entries are using. 256This function returns the sum of the lengths of all the lines in the 257history. 258@end deftypefun 259 260@node Moving Around the History List 261@subsection Moving Around the History List 262 263These functions allow the current index into the history list to be 264set or changed. 265 266@deftypefun int history_set_pos (int pos) 267Set the current history offset to @var{pos}, an absolute index 268into the list. 269Returns 1 on success, 0 if @var{pos} is less than zero or greater 270than the number of history entries. 271@end deftypefun 272 273@deftypefun {HIST_ENTRY *} previous_history (void) 274Back up the current history offset to the previous history entry, and 275return a pointer to that entry. If there is no previous entry, return 276a @code{NULL} pointer. 277@end deftypefun 278 279@deftypefun {HIST_ENTRY *} next_history (void) 280If the current history offset refers to a valid history entry, 281increment the current history offset. 282If the possibly-incremented history offset refers to a valid history 283entry, return a pointer to that entry; 284otherwise, return a @code{BNULL} pointer. 285@end deftypefun 286 287@node Searching the History List 288@subsection Searching the History List 289@cindex History Searching 290 291These functions allow searching of the history list for entries containing 292a specific string. Searching may be performed both forward and backward 293from the current history position. The search may be @dfn{anchored}, 294meaning that the string must match at the beginning of the history entry. 295@cindex anchored search 296 297@deftypefun int history_search (const char *string, int direction) 298Search the history for @var{string}, starting at the current history offset. 299If @var{direction} is less than 0, then the search is through 300previous entries, otherwise through subsequent entries. 301If @var{string} is found, then 302the current history index is set to that history entry, and the value 303returned is the offset in the line of the entry where 304@var{string} was found. Otherwise, nothing is changed, and a -1 is 305returned. 306@end deftypefun 307 308@deftypefun int history_search_prefix (const char *string, int direction) 309Search the history for @var{string}, starting at the current history 310offset. The search is anchored: matching lines must begin with 311@var{string}. If @var{direction} is less than 0, then the search is 312through previous entries, otherwise through subsequent entries. 313If @var{string} is found, then the 314current history index is set to that entry, and the return value is 0. 315Otherwise, nothing is changed, and a -1 is returned. 316@end deftypefun 317 318@deftypefun int history_search_pos (const char *string, int direction, int pos) 319Search for @var{string} in the history list, starting at @var{pos}, an 320absolute index into the list. If @var{direction} is negative, the search 321proceeds backward from @var{pos}, otherwise forward. Returns the absolute 322index of the history element where @var{string} was found, or -1 otherwise. 323@end deftypefun 324 325@node Managing the History File 326@subsection Managing the History File 327 328The History library can read the history from and write it to a file. 329This section documents the functions for managing a history file. 330 331@deftypefun int read_history (const char *filename) 332Add the contents of @var{filename} to the history list, a line at a time. 333If @var{filename} is @code{NULL}, then read from @file{~/.history}. 334Returns 0 if successful, or @code{errno} if not. 335@end deftypefun 336 337@deftypefun int read_history_range (const char *filename, int from, int to) 338Read a range of lines from @var{filename}, adding them to the history list. 339Start reading at line @var{from} and end at @var{to}. 340If @var{from} is zero, start at the beginning. If @var{to} is less than 341@var{from}, then read until the end of the file. If @var{filename} is 342@code{NULL}, then read from @file{~/.history}. Returns 0 if successful, 343or @code{errno} if not. 344@end deftypefun 345 346@deftypefun int write_history (const char *filename) 347Write the current history to @var{filename}, overwriting @var{filename} 348if necessary. 349If @var{filename} is @code{NULL}, then write the history list to 350@file{~/.history}. 351Returns 0 on success, or @code{errno} on a read or write error. 352@end deftypefun 353 354@deftypefun int append_history (int nelements, const char *filename) 355Append the last @var{nelements} of the history list to @var{filename}. 356If @var{filename} is @code{NULL}, then append to @file{~/.history}. 357Returns 0 on success, or @code{errno} on a read or write error. 358@end deftypefun 359 360@deftypefun int history_truncate_file (const char *filename, int nlines) 361Truncate the history file @var{filename}, leaving only the last 362@var{nlines} lines. 363If @var{filename} is @code{NULL}, then @file{~/.history} is truncated. 364Returns 0 on success, or @code{errno} on failure. 365@end deftypefun 366 367@node History Expansion 368@subsection History Expansion 369 370These functions implement history expansion. 371 372@deftypefun int history_expand (char *string, char **output) 373Expand @var{string}, placing the result into @var{output}, a pointer 374to a string (@pxref{History Interaction}). Returns: 375@table @code 376@item 0 377If no expansions took place (or, if the only change in 378the text was the removal of escape characters preceding the history expansion 379character); 380@item 1 381if expansions did take place; 382@item -1 383if there was an error in expansion; 384@item 2 385if the returned line should be displayed, but not executed, 386as with the @code{:p} modifier (@pxref{Modifiers}). 387@end table 388 389If an error occurred in expansion, then @var{output} contains a descriptive 390error message. 391@end deftypefun 392 393@deftypefun {char *} get_history_event (const char *string, int *cindex, int qchar) 394Returns the text of the history event beginning at @var{string} + 395@var{*cindex}. @var{*cindex} is modified to point to after the event 396specifier. At function entry, @var{cindex} points to the index into 397@var{string} where the history event specification begins. @var{qchar} 398is a character that is allowed to end the event specification in addition 399to the ``normal'' terminating characters. 400@end deftypefun 401 402@deftypefun {char **} history_tokenize (const char *string) 403Return an array of tokens parsed out of @var{string}, much as the 404shell might. The tokens are split on the characters in the 405@var{history_word_delimiters} variable, 406and shell quoting conventions are obeyed as described below. 407@end deftypefun 408 409@deftypefun {char *} history_arg_extract (int first, int last, const char *string) 410Extract a string segment consisting of the @var{first} through @var{last} 411arguments present in @var{string}. Arguments are split using 412@code{history_tokenize}. 413@end deftypefun 414 415@node History Variables 416@section History Variables 417 418This section describes the externally-visible variables exported by 419the @sc{gnu} History Library. 420 421@deftypevar int history_base 422The logical offset of the first entry in the history list. 423@end deftypevar 424 425@deftypevar int history_length 426The number of entries currently stored in the history list. 427@end deftypevar 428 429@deftypevar int history_max_entries 430The maximum number of history entries. This must be changed using 431@code{stifle_history()}. 432@end deftypevar 433 434@deftypevar int history_write_timestamps 435If non-zero, timestamps are written to the history file, so they can be 436preserved between sessions. The default value is 0, meaning that 437timestamps are not saved. 438 439The current timestamp format uses the value of @var{history_comment_char} 440to delimit timestamp entries in the history file. If that variable does 441not have a value (the default), timestamps will not be written. 442@end deftypevar 443 444@deftypevar char history_expansion_char 445The character that introduces a history event. The default is @samp{!}. 446Setting this to 0 inhibits history expansion. 447@end deftypevar 448 449@deftypevar char history_subst_char 450The character that invokes word substitution if found at the start of 451a line. The default is @samp{^}. 452@end deftypevar 453 454@deftypevar char history_comment_char 455During tokenization, if this character is seen as the first character 456of a word, then it and all subsequent characters up to a newline are 457ignored, suppressing history expansion for the remainder of the line. 458This is disabled by default. 459@end deftypevar 460 461@deftypevar {char *} history_word_delimiters 462The characters that separate tokens for @code{history_tokenize()}. 463The default value is @code{" \t\n()<>;&|"}. 464@end deftypevar 465 466@deftypevar {char *} history_search_delimiter_chars 467The list of additional characters which can delimit a history search 468string, in addition to space, TAB, @samp{:} and @samp{?} in the case of 469a substring search. The default is empty. 470@end deftypevar 471 472@deftypevar {char *} history_no_expand_chars 473The list of characters which inhibit history expansion if found immediately 474following @var{history_expansion_char}. The default is space, tab, newline, 475carriage return, and @samp{=}. 476@end deftypevar 477 478@deftypevar int history_quotes_inhibit_expansion 479If non-zero, the history expansion code implements shell-like quoting: 480single-quoted words are not scanned for the history expansion 481character or the history comment character, and double-quoted words may 482have history expansion performed, since single quotes are not special 483within double quotes. 484The default value is 0. 485@end deftypevar 486 487@deftypevar int history_quoting_state 488An application may set this variable to indicate that the current line 489being expanded is subject to existing quoting. If set to @samp{'}, the 490history expansion function will assume that the line is single-quoted and 491inhibit expansion until it reads an unquoted closing single quote; if set 492to @samp{"}, history expansion will assume the line is double quoted until 493it reads an unquoted closing double quote. If set to zero, the default, 494the history expansion function will assume the line is not quoted and 495treat quote characters within the line as described above. 496This is only effective if @var{history_quotes_inhibit_expansion} is set. 497@end deftypevar 498 499@deftypevar {rl_linebuf_func_t *} history_inhibit_expansion_function 500This should be set to the address of a function that takes two arguments: 501a @code{char *} (@var{string}) 502and an @code{int} index into that string (@var{i}). 503It should return a non-zero value if the history expansion starting at 504@var{string[i]} should not be performed; zero if the expansion should 505be done. 506It is intended for use by applications like Bash that use the history 507expansion character for additional purposes. 508By default, this variable is set to @code{NULL}. 509@end deftypevar 510 511@node History Programming Example 512@section History Programming Example 513 514The following program demonstrates simple use of the @sc{gnu} History Library. 515 516@smallexample 517#include <stdio.h> 518#include <readline/history.h> 519 520main (argc, argv) 521 int argc; 522 char **argv; 523@{ 524 char line[1024], *t; 525 int len, done = 0; 526 527 line[0] = 0; 528 529 using_history (); 530 while (!done) 531 @{ 532 printf ("history$ "); 533 fflush (stdout); 534 t = fgets (line, sizeof (line) - 1, stdin); 535 if (t && *t) 536 @{ 537 len = strlen (t); 538 if (t[len - 1] == '\n') 539 t[len - 1] = '\0'; 540 @} 541 542 if (!t) 543 strcpy (line, "quit"); 544 545 if (line[0]) 546 @{ 547 char *expansion; 548 int result; 549 550 result = history_expand (line, &expansion); 551 if (result) 552 fprintf (stderr, "%s\n", expansion); 553 554 if (result < 0 || result == 2) 555 @{ 556 free (expansion); 557 continue; 558 @} 559 560 add_history (expansion); 561 strncpy (line, expansion, sizeof (line) - 1); 562 free (expansion); 563 @} 564 565 if (strcmp (line, "quit") == 0) 566 done = 1; 567 else if (strcmp (line, "save") == 0) 568 write_history ("history_file"); 569 else if (strcmp (line, "read") == 0) 570 read_history ("history_file"); 571 else if (strcmp (line, "list") == 0) 572 @{ 573 register HIST_ENTRY **the_list; 574 register int i; 575 576 the_list = history_list (); 577 if (the_list) 578 for (i = 0; the_list[i]; i++) 579 printf ("%d: %s\n", i + history_base, the_list[i]->line); 580 @} 581 else if (strncmp (line, "delete", 6) == 0) 582 @{ 583 int which; 584 if ((sscanf (line + 6, "%d", &which)) == 1) 585 @{ 586 HIST_ENTRY *entry = remove_history (which); 587 if (!entry) 588 fprintf (stderr, "No such entry %d\n", which); 589 else 590 @{ 591 free (entry->line); 592 free (entry); 593 @} 594 @} 595 else 596 @{ 597 fprintf (stderr, "non-numeric arg given to `delete'\n"); 598 @} 599 @} 600 @} 601@} 602@end smallexample 603