history(3) — Linux manual page


HISTORY(3)                Library Functions Manual                HISTORY(3)

NAME         top

       history - GNU History Library

COPYRIGHT         top

       The GNU History Library is Copyright (C) 1989-2017 by the Free
       Software Foundation, Inc.

DESCRIPTION         top

       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.


       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.  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'.
              Refer to the most recent command preceding the current
              position in the history list starting with 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
              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 word.  This is usually the last argument, but will
              expand to the zeroth word if there is only one word in the
       %      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.

       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
       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.
              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[?]
       &      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' modifier once to each word in the
              event line.


       This section describes how to use the History library in other

   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:

       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

        * 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;

       If the flags member includes HS_STIFLED, the history has been

History Functions         top

       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.

       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.

   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

       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

       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 contain 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

       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 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)
       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

       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

       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.
              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.

       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

       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 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

       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, 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 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         top

              Default filename for reading and writing saved history

SEE ALSO         top

       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey

AUTHORS         top

       Brian Fox, Free Software Foundation

       Chet Ramey, Case Western Reserve University

BUG REPORTS         top

       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.ramey@case.edu.

COLOPHON         top

       This page is part of the readline (GNU Readline library) project.
       Information about the project can be found at 
       ⟨http://www.gnu.org/software/readline/⟩.  If you have a bug report for
       this manual page, see
       ⟨http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html#Bugs⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨git://git.savannah.gnu.org/readline.git⟩ on 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-02-07.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to man-pages@man7.org

GNU History 6.3                2017 October 8                     HISTORY(3)