# phpman > man > HISTORY(3) [HISTORY(3)](https://www.chedong.com/phpMan.php/man/HISTORY/3/markdown) Library Functions Manual [HISTORY(3)](https://www.chedong.com/phpMan.php/man/HISTORY/3/markdown) ## NAME history - GNU History Library ## COPYRIGHT The GNU History Library is Copyright (C) 1989-2020 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 ex‐ pansion 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 sev‐ eral 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. Unless the reference is absolute, events are relative to the current position 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 minus _n_. **!!** Refer to the previous command. This is a synonym for `!-1'. **!**_string_ Refer to the most recent command preceding the current position in the history list starting with _string_. **!?**_string_**[?]** Refer to the most recent command preceding the current position in the history list containing _string_. The trailing **?** may be omitted if _string_ is followed immediately by a newline. If _string_ is missing, the string from the most recent search is used; it is an error if there is no previous search string. **^**_string1_**^**_string2_**^** Quick substitution. Repeat the last command, replacing _string1_ with _string2_. Equiva‐ lent 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 **^**, **$**, *****, **-**, or **%**. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spa‐ ces. ### 0 (zero) The zeroth word. For the shell, this is the command word. _n_ The _n_th word. **^** The first argument. That is, word 1. **$** The last word. This is usually the last argument, but will expand to the zeroth word if there is only one word in the line. **%** The first word matched by the most recent `?_string_?' search, if the search string be‐ gins with a character that is part of a word. _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 **x** is missing, it defaults to 0. 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 follow‐ ing modifiers, each preceded by a `:'. These modify, or edit, the word or words selected from the history event. **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. The **q** and **x** modifiers are mutually exclusive; the last one supplied is used. **s/**_old_**/**_new_**/** Substitute _new_ for the first occurrence of _old_ in the event line. Any character may be used as the delimiter 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. If _new_ is null, each matching _old_ is deleted. **&** 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**' or `**&**' 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 A 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**. The programmer can also 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 __ in any file that uses the History library's features. It supplies extern declarations for all of the li‐ brary'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: _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 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 li‐ brary 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 interac‐ tive 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 associated data field (if any) is set to **NULL**. If the maximum number of history entries has been set using **stifle**___**history()**, and the new number of history entries would exceed that maximum, the oldest history entry is removed. _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. Re‐ turns 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. The history list will con‐ tain only _max_ entries at a time. _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. ### Information About the History List 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_. The range of valid values of _offset_ starts at **history**___**base** and ends at **history**___**length** - 1. If there is no entry there, or if _offset_ is outside the valid range, 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 suc‐ cess, 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_) If the current history offset refers to a valid history entry, increment the current history offset. If the possibly-incremented history offset refers to a valid history entry, return a pointer to that entry; otherwise, 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. _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 an‐ chored: 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, noth‐ ing 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 managing 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 _~/.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. ### 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** mod‐ ifier. If an error occurred 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'' 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 conven‐ tions 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. The current time‐ stamp format uses the value of _history_comment_char_ to delimit timestamp entries in the his‐ tory 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 **his**‐‐ **tory**___**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, double-quoted words are not scanned for the history expansion character or the history comment 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 ex‐ pansion 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 _The_ _Gnu_ _History_ _Library_, Brian Fox and Chet Ramey [_bash_(1)](https://www.chedong.com/phpMan.php/man/bash/1/markdown) [_readline_(3)](https://www.chedong.com/phpMan.php/man/readline/3/markdown) ## AUTHORS Brian Fox, Free Software Foundation Chet Ramey, Case Western Reserve University ## 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** li‐ brary that you have. Once you have determined that a bug actually exists, mail a bug report to _bug-read__‐ <_line_@_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.ramey@case.edu_>. GNU History 8.1 2020 July 17 [HISTORY(3)](https://www.chedong.com/phpMan.php/man/HISTORY/3/markdown)