HISTORY(3)                 Library Functions Manual                 HISTORY(3)

NAME
       history - GNU History Library

COPYRIGHT
       The GNU History Library is Copyright (C) 1989-2025 by the Free Software
       Foundation, Inc.

DESCRIPTION
       Many  programs read input from the user a line at a time.  The GNU His-
       tory library is able to keep track of those lines, associate  arbitrary
       data  with  each line, and utilize information from previous lines when
       composing new ones.

       The History library provides functions that allow applications to their
       history, the set of previously-typed lines, which it keeps in  a  list.
       Applications  can  choose  which lines to save into a history list, how
       many commands to save, save a history list to a file,  read  a  history
       list  from  a  file, and display lines from the history in various for-
       mats.

HISTORY EXPANSION
       The history library supports a history expansion feature that is  iden-
       tical  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  history list entry to use during substitution.  The second is to
       select portions of that entry to include into the current one.

       The entry selected from the history is the event, and the  portions  of
       that entry that are acted upon are words.  Various modifiers are avail-
       able  to  manipulate the selected words.  The entry is split 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).
       The event designator selects the event, the  optional  word  designator
       selects words from the event, and various optional modifiers are avail-
       able to manipulate the selected words.

       History  expansions are introduced by the appearance of the history ex-
       pansion character, which is ! by default.  History expansions  may  ap-
       pear anywhere in the input, but do not nest.

       Only  backslash  (\)  and single quotes can quote the history expansion
       character.

       There is a special abbreviation for substitution, active when the quick
       substitution character (default ^) is the first character on the  line.
       It  selects  the previous history list entry, using an event designator
       equivalent to !!, and substitutes one string for another in that entry.
       It is described below under Event Designators.  This is the  only  his-
       tory  expansion  that does not begin with the history expansion charac-
       ter.

   Event Designators
       An event designator is a reference to an entry  in  the  history  list.
       The event designator consists of the portion of the word beginning with
       the  history expansion character and ending with the word designator if
       present, or the end of the word.  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, carriage return, =, or (.
       !n     Refer to history list entry n.
       !-n    Refer to the current entry minus n.
       !!     Refer to the previous entry.  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, this uses the string  from  the  most  recent
              search; it is an error if there is no previous search string.
       ^string1^string2^
              Quick  substitution.   Repeat  the  previous  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.  They
       are optional; if the word designator isn't supplied, the history expan-
       sion uses the entire 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 in-
       serted into the current line separated by single spaces.

       0 (zero)
              The zeroth word.  For the shell, and  many  other  applications,
              this is the command word.
       n      The nth word.
       ^      The first argument: word 1.
       $      The  last  word.  This is usually the last argument, but expands
              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 begins with a character  that  is  part  of  a
              word.   By  default,  searches begin at the end of each line and
              proceed to the beginning, so the first word matched is  the  one
              closest to the end of the line.
       x-y    A range of words; "-y" abbreviates "0-y".
       *      All  of  the words but the zeroth.  This is a synonym for "1-$".
              It is not an error to use * if there is just  one  word  in  the
              event; it expands to the empty string in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.  If x is miss-
              ing, it defaults to 0.

       If  a  word  designator is supplied without an event specification, the
       previous command is used as the event, equivalent to !!.

   Modifiers
       After the optional word designator, the expansion  may  include  a  se-
       quence  of  one  or more of the following modifiers, each preceded by a
       ":".  These modify, or edit, the word or words selected from  the  his-
       tory event.

       h      Remove a trailing filename component, leaving only the head.
       t      Remove all leading filename 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  exclu-
              sive; expansion uses the last one supplied.
       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.  A single backslash quotes the delimiter in old
              and new.  If & appears in new, it is replaced with old.  A  sin-
              gle  backslash  quotes  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  pro-
       grams.

   Introduction to History
       A  programmer using the History library has available functions for re-
       membering 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 avail-
       able  which  provides  for a consistent user interface across different
       programs.

       The user using programs written with the History library has the  bene-
       fit  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  li-
       brary  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  struc-
       ture:

       /*
        * A structure used to pass around the current state of the history.
        */
       typedef struct _hist_state {
         HIST_ENTRY **entries; /* Pointer to entry records. */
         int offset;           /* The current record. */
         int length;           /* Number of records in list. */
         int size;             /* Number of records allocated. */
         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 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 el-
       ement is returned so you can free the line, data, and containing struc-
       ture.

       histdata_t free_history_entry (HIST_ENTRY *histent)
       Free the history entry histent and any history library private data as-
       sociated with it.  Returns the application-specific data so the  caller
       can dispose of it.

       HIST_ENTRY  * replace_history_entry (int which, const char *line, hist-
       data_t data)
       Make the history entry at offset which have line and  data.   This  re-
       turns  the  old entry so the caller can dispose of any application-spe-
       cific data.  In the case of an invalid which, a  NULL  pointer  is  re-
       turned.

       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 in-
       dividual list entries.

       HIST_ENTRY ** history_list (void)
       Return a NULL terminated array of HIST_ENTRY * which is the current in-
       put 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, re-
       turn 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  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,  incre-
       ment  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  con-
       taining a specific string.  Searching may be performed both forward and
       backward  from  the  current  history  position.  The search may be an-
       chored, meaning that the string must match at the beginning of the his-
       tory 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 en-
       tries, 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 the function returns -1.

       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 di-
       rection 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 the function returns -1.

       int history_search_pos (const char *string, int direction, int pos)
       Search for string in the history list, starting at pos, an absolute in-
       dex into the list.  If direction is negative, the search proceeds back-
       ward  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 neces-
       sary.  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  suc-
       cess, or errno on failure.

   History Expansion
       These functions implement history expansion.

       int history_expand (const 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  exe-
                     cuted, as with the :p modifier.
       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_de-
       limiters 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().

   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 sti-
       fle_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 time-
       stamps  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), the history li-
       brary will not write timestamps.

       char history_expansion_char
       The character that introduces a history event.  The default is !.  Set-
       ting 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 de-
       fault value is " \t\n()<>;&|".

       char * history_no_expand_chars
       The list of characters which inhibit history expansion if found immedi-
       ately 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, the history expansion code implements shell-like quoting:
       single-quoted words are not scanned for the history expansion character
       or the history comment character, and double-quoted words may have his-
       tory expansion performed, since single quotes are  not  special  within
       double quotes.  The default value is 0.

       int history_quoting_state
       An  application may set this variable to indicate that the current line
       being expanded is subject to existing quoting.  If set  to  ',  history
       expansion  assumes that the line is single-quoted and inhibit expansion
       until it reads an unquoted closing single quote; if set to  ",  history
       expansion  assumes the line is double quoted until it reads an unquoted
       closing double quote.  If set to zero, the default,  history  expansion
       assumes  the  line is not quoted and treats quote characters within the
       line as described above.  This is only effective if  history_quotes_in-
       hibit_expansion is set.

       rl_linebuf_func_t * history_inhibit_expansion_function
       This  should  be  set to the address of a function that takes two argu-
       ments: 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
       ~/.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)
       readline(3)

AUTHORS
       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet.ramey@case.edu

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  ap-
       pears 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.

GNU History 8.3                2024 December 31                     HISTORY(3)
