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HISTORY(3)                           Library Functions Manual                          HISTORY(3)

NAME
       history - GNU History Library

COPYRIGHT
       The GNU History Library is Copyright (C) 1989-2011 by the Free Software Foundation, Inc.

DESCRIPTION
       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  infor‐
       mation from previous lines in composing new ones.

HISTORY EXPANSION
       The  history library supports a history expansion feature that is identical to the history
       expansion in bash.  This section describes what syntax features are available.

       History expansions introduce words from the history list into the input stream, making  it
       easy to repeat commands, insert the arguments to a previous command into the current input
       line, or fix errors in previous commands quickly.

       History expansion is usually performed immediately after a  complete  line  is  read.   It
       takes  place  in two parts.  The first is to determine which line from the history list to
       use during substitution.  The second is to select portions of that line for inclusion into
       the  current  one.   The  line selected from the history is the event, and the portions of
       that line that are acted upon are words.  Various modifiers are  available  to  manipulate
       the  selected  words.  The line is broken into words in the same fashion as bash does when
       reading input, so that several words that would otherwise be separated are considered  one
       word when surrounded by quotes (see the description of history_tokenize() below).  History
       expansions are introduced by the appearance of the history expansion character, which is !
       by  default.  Only backslash (\) and single quotes can quote the history expansion charac‐
       ter.

   Event Designators
       An event designator is a reference to a command line entry in the  history  list.   Unless
       the  reference  is  absolute,  events  are relative to the current position in the history
       list.

       !      Start a history substitution, except when followed by a blank, newline, = or (.
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !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.
       ^string1^string2^
              Quick  substitution.   Repeat  the  last  command,  replacing string1 with string2.
              Equivalent to ``!!:s/string1/string2/'' (see Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word designators are used to select desired words from the event.  A : separates the event
       specification  from  the word designator.  It may be omitted if the word designator begins
       with a ^, $, *, -, or %.  Words are numbered from the beginning  of  the  line,  with  the
       first  word being denoted by 0 (zero).  Words are inserted into the current line separated
       by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last word.  This is usually the last argument, but will expand  to  the  zeroth
              word if there is only one word in the 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.

   Modifiers
       After the optional word designator, there may appear a sequence of one or more of the fol‐
       lowing 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.
       s/old/new/
              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 char‐
              acter  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 pre‐
              vious 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  conjunc‐
              tion  with  `:s'  (e.g., `:gs/old/new/') or `:&'.  If used with `:s', any delimiter
              can be used in place of /, and the final delimiter is optional if it  is  the  last
              character of the event line.  An a may be used as a synonym for g.
       G      Apply the following `s' modifier once to each word in the event line.

PROGRAMMING WITH HISTORY FUNCTIONS
       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, associating arbitrary data with a line,  removing  lines  from  the  list,
       searching through the list for a line containing an arbitrary text string, and referencing
       any line in the list directly.  In addition, a history  expansion  function  is  available
       which provides for a consistent user interface across different programs.

       The  user  using programs written with the History library has the benefit of a consistent
       user interface with a set of well-known commands for manipulating  the  text  of  previous
       lines  and  using  that text in new commands.  The basic history manipulation commands are
       identical to the history substitution provided by bash.

       If the programmer desires, he can use the Readline library, which  includes  some  history
       manipulation by default, and has the added advantage of command line editing.

       Before  declaring  any  functions  using any functionality the History library provides in
       other code, an application writer should include the file  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;
       } 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 inter‐
       active 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 application-specific data so the caller can dispose of it.

       HIST_ENTRY * replace_history_entry (int which, const char *line, histdata_t data)
       Make  the history entry at offset which have line and data.  This returns the old entry so
       the caller can dispose of any application-specific data.  In the case of an invalid which,
       a NULL pointer is 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 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.   Ele‐
       ment 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 suc‐
       cess, 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  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  docu‐
       ments 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  ~/.his‐
       tory.  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 characters preceding the history expansion character);
              1      if expansions did take place;
              -1     if there was an error in expansion;
              2      if the returned line should be displayed, but not executed, as with  the  :p
                     modifier.
       If an error ocurred in expansion, then output contains a descriptive error message.

       char * get_history_event (const char *string, int *cindex, int qchar)
       Returns  the text of the history event beginning at string + *cindex.  *cindex is modified
       to point to after the event specifier.  At function entry, cindex points to the index into
       string where the history event specification begins.  qchar is a character that is allowed
       to end the event specification in addition to the ``normal'' terminating characters.

       char ** history_tokenize (const char *string)
       Return an array of tokens parsed out of string, much as the shell might.  The  tokens  are
       split on the characters in the history_word_delimiters variable, and shell quoting conven‐
       tions 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_wite_timestamps
       If non-zero, timestamps are written to the history file, so they can be preserved  between
       sessions.   The  default  value  is 0, meaning that timestamps are not saved.  The current
       timestamp format uses the value of history_comment_char to delimit  timestamp  entries  in
       the  history  file.  If that variable does not have a value (the default), timestamps will
       not be written.

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

       char history_subst_char
       The character that invokes word substitution if found at the start of a line.  The default
       is ^.

       char history_comment_char
       During tokenization, if this character is seen as the first character of a word,  then  it
       and  all  subsequent characters up to a newline are ignored, suppressing history expansion
       for the remainder of the line.  This is disabled by default.

       char * history_word_delimiters
       The characters  that  separate  tokens  for  history_tokenize().   The  default  value  is
       " \t\n()<>;&|".

       char * history_no_expand_chars
       The list of characters which inhibit history expansion if found immediately following his‐
       tory_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.

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 appears in the latest version of the his‐
       tory library that you have.

       Once you have determined that a bug actually  exists,  mail  a  bug  report  to  bug-read‐
       line@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 6.3                            2013 June 27                                HISTORY(3)

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