history - GNU History Library


       The GNU History Library is Copyright (C) 1989-2014 by the Free Software
       Foundation, Inc.


       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  in
       composing new ones.


       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 line from the history list to use during substitution.  The  sec-
       ond  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  his-
       tory  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 newline.
              Quick substitution.  Repeat the last command, replacing  string1
              with string2.  Equivalent to ``!!:s/string1/string2/'' (see Mod-
              ifiers 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  sepa-
       rated 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 line.
       %      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 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.
              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 sin-
              gle backslash will quote the &.  If old is null, it  is  set  to
              the  last  old substituted, or, if no previous history substitu-
              tions took place, the last string in a !?string[?]  search.
       &      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


       This  section  describes  how  to use the History library in other pro-

   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 avail-
       able  which  provides  for a consistent user interface across different

       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.

       If the programmer desires, he  can  use  the  Readline  library,  which
       includes some history manipulation by default, and has the added advan-
       tage 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  pub-
       lic 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-

        * 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 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.

       void add_history_time (const char *string)
       Change the time stamp associated with the most recent history entry  to

       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, hist-
       data_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-spe-
       cific 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.

       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,  starting  from  his-
       tory_base.   If  there  is no entry there, or if offset is greater than
       the history length, 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

   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
       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  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 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 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 (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  exe-
                     cuted, 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  charac-

       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   his-
       tory_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_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-

       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 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), timestamps will
       not be written.

       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
       default 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, double-quoted words are not scanned for the history expan-
       sion  character or the history comment character.  The default value is

       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.


              Default filename for reading and writing saved history


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


       Brian Fox, Free Software Foundation

       Chet Ramey, Case Western Reserve University


       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   If  you have a fix, you are welcome to mail
       that as well!  Suggestions  and  `philosophical'  bug  reports  may  be
       mailed  to  or  posted  to  the  Usenet newsgroup

       Comments and bug reports concerning this manual page should be directed

GNU History 6.3                   2015 May 24                       HISTORY(3)

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