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HISTORY(3)                                                          HISTORY(3)

       history - GNU History Library

       The GNU History Library is Copyright (C) 1989-2002 by the Free Software Foundation, Inc.

       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  com-
       mands,  insert  the arguments to a previous command into the current input line, or fix errors in previous com-
       mands 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 expan-
       sion character.

   Event Designators
       An event designator is a reference to a command line entry 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 line minus n.
       !!     Refer to the previous command.  This is a synonym for '!-1'.
              Refer to the most recent command starting with string.
              Refer to the most recent command 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 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 num-
       bered 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 argument.
       %      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 single
              backslash will quote the &.  If old is null, it is set to the last old substituted, or, if  no  previous
              history substitutions took place, the last string in a !?string[?]  search.
       &      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      Apply the following 's' modifier once to each word in the event line.

       This section describes how to use the History library in other programs.

   Introduction to History
       The programmer using the History library has available functions for remembering lines on a history list, asso-
       ciating  arbitrary  data  with a line, removing lines from the list, searching through the list for a line con-
       taining an arbitrary text string, and referencing any line in the list directly.  In addition, a history expan-
       sion 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  applica-
       tion  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 structure:

        * A structure used to pass around the current state of the history.
       typedef struct _hist_state {
         HIST_ENTRY **entries; /* Pointer to the entries themselves. */
         int offset;           /* The location pointer within this array. */
         int length;           /* Number of elements within this array. */
         int size;             /* Number of slots allocated to this array. */
         int flags;

       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 string.

       HIST_ENTRY * remove_history (int which)
       Remove history entry at offset which from the history.  The removed element is returned so  you  can  free  the
       line, data, and containing structure.

       histdata_t free_history_entry (HIST_ENTRY *histent)
       Free  the  history entry histent and any history library private data associated with it.  Returns the applica-
       tion-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  dis-
       pose of any application-specific data.  In the case of an invalid which, a NULL pointer is returned.

       void clear_history (void)
       Clear the history list by deleting all the entries.

       void stifle_history (int max)
       Stifle the history list, remembering only the last max entries.

       int unstifle_history (void)
       Stop  stifling  the history.  This returns the previously-set maximum number of history entries (as set by sti-
       fle_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 history_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 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)
       Move  the current history offset forward to the next history entry, and return the a pointer to that entry.  If
       there is no next entry, return a NULL pointer.

   Searching the History List
       These functions allow searching of the history list for entries containing a specific string.  Searching may be
       performed  both  forward  and  backward from the current history position.  The search may be anchored, meaning
       that the string must match at the beginning of the history entry.

       int history_search (const char *string, int direction)
       Search the history for string, starting at the current history offset.  If direction is less than 0,  then  the
       search is through previous entries, otherwise through subsequent entries.  If string is found, then the current
       history index is set to that history entry, and the value returned is the offset in the line of the entry where
       string was found.  Otherwise, nothing is changed, and a -1 is returned.

       int history_search_prefix (const char *string, int direction)
       Search  the history for string, starting at the current history offset.  The search is 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 nega-
       tive, the search proceeds backward from pos, otherwise forward.  Returns the absolute index of the history ele-
       ment where string was found, or -1 otherwise.

   Managing the History File
       The History library can read the history from and write it to a file.  This section documents the functions for
       managing a history file.

       int read_history (const char *filename)
       Add  the  contents  of  filename  to  the  history list, a line at a time.  If filename is NULL, then read from
       ~/.history.  Returns 0 if successful, or errno if not.

       int read_history_range (const char *filename, int from, int to)
       Read a range of lines from filename, adding them to the history list.  Start reading at line from  and  end  at
       to.   If  from  is zero, start at the beginning.  If to is less than from, then read until the end of the file.
       If filename is NULL, then read from ~/.history.  Returns 0 if successful, or errno if not.

       int write_history (const char *filename)
       Write the current history to filename, overwriting filename if necessary.  If filename is NULL, then write  the
       history list to ~/.history.  Returns 0 on success, or errno on a read or write error.

       int append_history (int nelements, const char *filename)
       Append  the  last  nelements  of the history list to filename.  If filename is NULL, then append to ~/.history.
       Returns 0 on success, or errno on a read or write error.

       int history_truncate_file (const char *filename, int nlines)
       Truncate the history file filename, leaving only the last nlines lines.  If filename is NULL,  then  ~/.history
       is truncated.  Returns 0 on success, or errno on failure.

   History Expansion
       These functions implement history expansion.

       int history_expand (char *string, char **output)
       Expand string, placing the result into output, a pointer to a string.  Returns:
              0      If no expansions took place (or, if the only change in the text was the removal of escape charac-
                     ters 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 specifica-
       tion 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 charac-
       ters in the history_word_delimiters 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 stifle_history().

       int history_write_timestamps
       If  non-zero,  timestamps  are  written  to  the  history file, so they can be preserved between sessions.  The
       default value is 0, meaning that timestamps are not saved.

       char history_expansion_char
       The character that introduces a history event.  The default is !.  Setting this to 0  inhibits  history  expan-

       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, single-quoted words are not scanned for the history expansion 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.

              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 bug- or posted to the Usenet newsgroup gnu.bash.bug.

       Comments and bug reports concerning this manual page should be directed to chetATins.Edu.

GNU History 6.0                  2003 July 31                       HISTORY(3)