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HISTORY(3)                 Library Functions Manual                 HISTORY(3)



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  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.

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 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'.
       !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.  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 ex-
              pand 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.
       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 miss-
              ing, 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 following modifiers, each preceded by a `:'.  These mod-
       ify, 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 exclu-
              sive; 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  substi-
              tutions  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 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 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 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  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 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 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 (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 charac-
       ters.

       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), 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 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, double-quoted words are not scanned for the history expan-
       sion  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  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 8.1                  2020 July 17                       HISTORY(3)