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    1: HISTORY(3)                 Library Functions Manual                 HISTORY(3)
    2: 
    3: 
    4: 
    5: NAME
    6:        history - GNU History Library
    7: 
    8: COPYRIGHT
    9:        The GNU History Library is Copyright (C) 1989-2020 by the Free Software
   10:        Foundation, Inc.
   11: 
   12: DESCRIPTION
   13:        Many programs read input from the user a line at a time.  The GNU  His-
   14:        tory  library is able to keep track of those lines, associate arbitrary
   15:        data with each line, and utilize information  from  previous  lines  in
   16:        composing new ones.
   17: 
   18: HISTORY EXPANSION
   19:        The  history library supports a history expansion feature that is iden-
   20:        tical to the history expansion in bash.  This  section  describes  what
   21:        syntax features are available.
   22: 
   23:        History expansions introduce words from the history list into the input
   24:        stream, making it easy to repeat commands, insert the  arguments  to  a
   25:        previous command into the current input line, or fix errors in previous
   26:        commands quickly.
   27: 
   28:        History expansion is usually performed  immediately  after  a  complete
   29:        line  is read.  It takes place in two parts.  The first is to determine
   30:        which line from the history list to use during substitution.  The  sec-
   31:        ond  is  to select portions of that line for inclusion into the current
   32:        one.  The line selected from the history is the event, and the portions
   33:        of  that  line  that  are  acted upon are words.  Various modifiers are
   34:        available to manipulate the selected words.  The line  is  broken  into
   35:        words in the same fashion as bash does when reading input, so that sev-
   36:        eral words that would otherwise be separated are  considered  one  word
   37:        when  surrounded  by  quotes (see the description of history_tokenize()
   38:        below).  History expansions are introduced by  the  appearance  of  the
   39:        history expansion character, which is ! by default.  Only backslash (\)
   40:        and single quotes can quote the history expansion character.
   41: 
   42:    Event Designators
   43:        An event designator is a reference to a command line entry in the  his-
   44:        tory  list.   Unless  the reference is absolute, events are relative to
   45:        the current position in the history list.
   46: 
   47:        !      Start a history substitution, except when followed by  a  blank,
   48:               newline, = or (.
   49:        !n     Refer to command line n.
   50:        !-n    Refer to the current command minus n.
   51:        !!     Refer to the previous command.  This is a synonym for `!-1'.
   52:        !string
   53:               Refer  to the most recent command preceding the current position
   54:               in the history list starting with string.
   55:        !?string[?]
   56:               Refer to the most recent command preceding the current  position
   57:               in  the  history  list containing string.  The trailing ? may be
   58:               omitted if string is followed  immediately  by  a  newline.   If
   59:               string  is  missing,  the  string from the most recent search is
   60:               used; it is an error if there is no previous search string.
   61:        ^string1^string2^
   62:               Quick substitution.  Repeat the last command, replacing  string1
   63:               with string2.  Equivalent to ``!!:s^string1^string2^'' (see Mod-
   64:               ifiers below).
   65:        !#     The entire command line typed so far.
   66: 
   67:    Word Designators
   68:        Word designators are used to select desired words from the event.  A  :
   69:        separates  the event specification from the word designator.  It may be
   70:        omitted if the word designator begins with a ^, $, *, -, or  %.   Words
   71:        are  numbered from the beginning of the line, with the first word being
   72:        denoted by 0 (zero).  Words are inserted into the  current  line  sepa-
   73:        rated by single spaces.
   74: 
   75:        0 (zero)
   76:               The zeroth word.  For the shell, this is the command word.
   77:        n      The nth word.
   78:        ^      The first argument.  That is, word 1.
   79:        $      The  last word.  This is usually the last argument, but will ex-
   80:               pand to the zeroth word if there is only one word in the line.
   81:        %      The first word matched by the most recent `?string?' search,  if
   82:               the  search  string  begins  with  a character that is part of a
   83:               word.
   84:        x-y    A range of words; `-y' abbreviates `0-y'.
   85:        *      All of the words but the zeroth.  This is a synonym  for  `1-$'.
   86:               It  is  not  an  error to use * if there is just one word in the
   87:               event; the empty string is returned in that case.
   88:        x*     Abbreviates x-$.
   89:        x-     Abbreviates x-$ like x*, but omits the last word.  If x is miss-
   90:               ing, it defaults to 0.
   91: 
   92:        If  a  word  designator is supplied without an event specification, the
   93:        previous command is used as the event.
   94: 
   95:    Modifiers
   96:        After the optional word designator, there may appear a sequence of  one
   97:        or more of the following modifiers, each preceded by a `:'.  These mod-
   98:        ify, or edit, the word or words selected from the history event.
   99: 
  100:        h      Remove a trailing file name component, leaving only the head.
  101:        t      Remove all leading file name components, leaving the tail.
  102:        r      Remove a trailing suffix of the form .xxx, leaving the basename.
  103:        e      Remove all but the trailing suffix.
  104:        p      Print the new command but do not execute it.
  105:        q      Quote the substituted words, escaping further substitutions.
  106:        x      Quote the substituted words as with q, but break into  words  at
  107:               blanks  and newlines.  The q and x modifiers are mutually exclu-
  108:               sive; the last one supplied is used.
  109:        s/old/new/
  110:               Substitute new for the first occurrence  of  old  in  the  event
  111:               line.  Any character may be used as the delimiter in place of /.
  112:               The final delimiter is optional if it is the last  character  of
  113:               the event line.  The delimiter may be quoted in old and new with
  114:               a single backslash.  If & appears in new, it is replaced by old.
  115:               A  single backslash will quote the &.  If old is null, it is set
  116:               to the last old substituted, or, if no previous history  substi-
  117:               tutions  took  place,  the last string in a !?string[?]  search.
  118:               If new is null, each matching old is deleted.
  119:        &      Repeat the previous substitution.
  120:        g      Cause changes to be applied over the entire event line.  This is
  121:               used  in  conjunction  with `:s' (e.g., `:gs/old/new/') or `:&'.
  122:               If used with `:s', any delimiter can be used in place of /,  and
  123:               the  final  delimiter is optional if it is the last character of
  124:               the event line.  An a may be used as a synonym for g.
  125:        G      Apply the following `s' or `&' modifier once to each word in the
  126:               event line.
  127: 
  128: PROGRAMMING WITH HISTORY FUNCTIONS
  129:        This  section  describes  how  to use the History library in other pro-
  130:        grams.
  131: 
  132:    Introduction to History
  133:        A programmer using the History library has available functions for  re-
  134:        membering  lines  on  a history list, associating arbitrary data with a
  135:        line, removing lines from the list, searching through the  list  for  a
  136:        line  containing  an arbitrary text string, and referencing any line in
  137:        the list directly.  In addition, a history expansion function is avail-
  138:        able  which  provides  for a consistent user interface across different
  139:        programs.
  140: 
  141:        The user using programs written with the History library has the  bene-
  142:        fit  of  a  consistent user interface with a set of well-known commands
  143:        for manipulating the text of previous lines and using that text in  new
  144:        commands.  The basic history manipulation commands are identical to the
  145:        history substitution provided by bash.
  146: 
  147:        The programmer can also use the Readline library, which  includes  some
  148:        history manipulation by default, and has the added advantage of command
  149:        line editing.
  150: 
  151:        Before declaring any functions using any functionality the History  li-
  152:        brary  provides in other code, an application writer should include the
  153:        file <readline/history.h> in any file that uses the  History  library's
  154:        features.   It  supplies  extern  declarations for all of the library's
  155:        public functions and variables, and declares all  of  the  public  data
  156:        structures.
  157: 
  158:    History Storage
  159:        The  history  list  is an array of history entries.  A history entry is
  160:        declared as follows:
  161: 
  162:        typedef void * histdata_t;
  163: 
  164:        typedef struct _hist_entry {
  165:          char *line;
  166:          char *timestamp;
  167:          histdata_t data;
  168:        } HIST_ENTRY;
  169: 
  170:        The history list itself might therefore be declared as
  171: 
  172:        HIST_ENTRY ** the_history_list;
  173: 
  174:        The state of the History library is encapsulated into a  single  struc-
  175:        ture:
  176: 
  177:        /*
  178:         * A structure used to pass around the current state of the history.
  179:         */
  180:        typedef struct _hist_state {
  181:          HIST_ENTRY **entries; /* Pointer to the entries themselves. */
  182:          int offset;           /* The location pointer within this array. */
  183:          int length;           /* Number of elements within this array. */
  184:          int size;             /* Number of slots allocated to this array. */
  185:          int flags;
  186:        } HISTORY_STATE;
  187: 
  188:        If the flags member includes HS_STIFLED, the history has been stifled.
  189: 
  190: History Functions
  191:        This  section  describes the calling sequence for the various functions
  192:        exported by the GNU History library.
  193: 
  194:    Initializing History and State Management
  195:        This section describes functions used  to  initialize  and  manage  the
  196:        state of the History library when you want to use the history functions
  197:        in your program.
  198: 
  199:        void using_history (void)
  200:        Begin a session in which the history functions  might  be  used.   This
  201:        initializes the interactive variables.
  202: 
  203:        HISTORY_STATE * history_get_history_state (void)
  204:        Return a structure describing the current state of the input history.
  205: 
  206:        void history_set_history_state (HISTORY_STATE *state)
  207:        Set the state of the history list according to state.
  208: 
  209: 
  210:    History List Management
  211:        These  functions  manage individual entries on the history list, or set
  212:        parameters managing the list itself.
  213: 
  214:        void add_history (const char *string)
  215:        Place string at the end of the history list.  The associated data field
  216:        (if  any) is set to NULL.  If the maximum number of history entries has
  217:        been set using stifle_history(), and the new number of history  entries
  218:        would exceed that maximum, the oldest history entry is removed.
  219: 
  220:        void add_history_time (const char *string)
  221:        Change  the time stamp associated with the most recent history entry to
  222:        string.
  223: 
  224:        HIST_ENTRY * remove_history (int which)
  225:        Remove history entry at offset which from the history.  The removed el-
  226:        ement is returned so you can free the line, data, and containing struc-
  227:        ture.
  228: 
  229:        histdata_t free_history_entry (HIST_ENTRY *histent)
  230:        Free the history entry histent and any history library private data as-
  231:        sociated  with it.  Returns the application-specific data so the caller
  232:        can dispose of it.
  233: 
  234:        HIST_ENTRY * replace_history_entry (int which, const char *line,  hist-
  235:        data_t data)
  236:        Make  the  history  entry at offset which have line and data.  This re-
  237:        turns the old entry so the caller can dispose of  any  application-spe-
  238:        cific  data.   In  the  case of an invalid which, a NULL pointer is re-
  239:        turned.
  240: 
  241:        void clear_history (void)
  242:        Clear the history list by deleting all the entries.
  243: 
  244:        void stifle_history (int max)
  245:        Stifle the history list, remembering only the last  max  entries.   The
  246:        history list will contain only max entries at a time.
  247: 
  248:        int unstifle_history (void)
  249:        Stop  stifling  the  history.   This returns the previously-set maximum
  250:        number of history entries (as set by  stifle_history()).   history  was
  251:        stifled.  The value is positive if the history was stifled, negative if
  252:        it wasn't.
  253: 
  254:        int history_is_stifled (void)
  255:        Returns non-zero if the history is stifled, zero if it is not.
  256: 
  257: 
  258:    Information About the History List
  259:        These functions return information about the entire history list or in-
  260:        dividual list entries.
  261: 
  262:        HIST_ENTRY ** history_list (void)
  263:        Return a NULL terminated array of HIST_ENTRY * which is the current in-
  264:        put history.  Element 0 of this list is  the  beginning  of  time.   If
  265:        there is no history, return NULL.
  266: 
  267:        int where_history (void)
  268:        Returns the offset of the current history element.
  269: 
  270:        HIST_ENTRY * current_history (void)
  271:        Return  the  history  entry  at  the current position, as determined by
  272:        where_history().  If there is no entry there, return a NULL pointer.
  273: 
  274:        HIST_ENTRY * history_get (int offset)
  275:        Return the history entry at position offset.  The range of valid values
  276:        of  offset  starts  at history_base and ends at history_length - 1.  If
  277:        there is no entry there, or if offset is outside the valid  range,  re-
  278:        turn a NULL pointer.
  279: 
  280:        time_t history_get_time (HIST_ENTRY *)
  281:        Return  the  time stamp associated with the history entry passed as the
  282:        argument.
  283: 
  284:        int history_total_bytes (void)
  285:        Return the number of bytes that the primary history entries are  using.
  286:        This  function  returns  the sum of the lengths of all the lines in the
  287:        history.
  288: 
  289: 
  290:    Moving Around the History List
  291:        These functions allow the current index into the history list to be set
  292:        or changed.
  293: 
  294:        int history_set_pos (int pos)
  295:        Set the current history offset to pos, an absolute index into the list.
  296:        Returns 1 on success, 0 if pos is less than zero or  greater  than  the
  297:        number of history entries.
  298: 
  299:        HIST_ENTRY * previous_history (void)
  300:        Back  up  the current history offset to the previous history entry, and
  301:        return a pointer to that entry.  If there is no previous entry,  return
  302:        a NULL pointer.
  303: 
  304:        HIST_ENTRY * next_history (void)
  305:        If  the  current history offset refers to a valid history entry, incre-
  306:        ment the current history offset.  If the  possibly-incremented  history
  307:        offset refers to a valid history entry, return a pointer to that entry;
  308:        otherwise, return a NULL pointer.
  309: 
  310: 
  311:    Searching the History List
  312:        These functions allow searching of the history list  for  entries  con-
  313:        taining a specific string.  Searching may be performed both forward and
  314:        backward from the current history position.   The  search  may  be  an-
  315:        chored, meaning that the string must match at the beginning of the his-
  316:        tory entry.
  317: 
  318:        int history_search (const char *string, int direction)
  319:        Search the history for string, starting at the current history  offset.
  320:        If  direction  is  less than 0, then the search is through previous en-
  321:        tries, otherwise through subsequent entries.  If string is found,  then
  322:        the  current  history index is set to that history entry, and the value
  323:        returned is the offset in the line of the entry where string was found.
  324:        Otherwise, nothing is changed, and a -1 is returned.
  325: 
  326:        int history_search_prefix (const char *string, int direction)
  327:        Search  the history for string, starting at the current history offset.
  328:        The search is anchored: matching lines must begin with string.  If  di-
  329:        rection  is  less  than 0, then the search is through previous entries,
  330:        otherwise through subsequent entries.  If string  is  found,  then  the
  331:        current  history index is set to that entry, and the return value is 0.
  332:        Otherwise, nothing is changed, and a -1 is returned.
  333: 
  334:        int history_search_pos (const char *string, int direction, int pos)
  335:        Search for string in the history list, starting at pos, an absolute in-
  336:        dex into the list.  If direction is negative, the search proceeds back-
  337:        ward from pos, otherwise forward.  Returns the absolute  index  of  the
  338:        history element where string was found, or -1 otherwise.
  339: 
  340: 
  341:    Managing the History File
  342:        The  History  library can read the history from and write it to a file.
  343:        This section documents the functions for managing a history file.
  344: 
  345:        int read_history (const char *filename)
  346:        Add the contents of filename to the history list, a line at a time.  If
  347:        filename  is NULL, then read from ~/.history.  Returns 0 if successful,
  348:        or errno if not.
  349: 
  350:        int read_history_range (const char *filename, int from, int to)
  351:        Read a range of lines from filename, adding them to the  history  list.
  352:        Start  reading  at  line from and end at to.  If from is zero, start at
  353:        the beginning.  If to is less than from, then read until the end of the
  354:        file.   If  filename  is NULL, then read from ~/.history.  Returns 0 if
  355:        successful, or errno if not.
  356: 
  357:        int write_history (const char *filename)
  358:        Write the current history to filename, overwriting filename  if  neces-
  359:        sary.   If filename is NULL, then write the history list to ~/.history.
  360:        Returns 0 on success, or errno on a read or write error.
  361: 
  362: 
  363:        int append_history (int nelements, const char *filename)
  364:        Append the last nelements of the history list to filename.  If filename
  365:        is  NULL, then append to ~/.history.  Returns 0 on success, or errno on
  366:        a read or write error.
  367: 
  368:        int history_truncate_file (const char *filename, int nlines)
  369:        Truncate the history file filename, leaving only the last nlines lines.
  370:        If  filename  is NULL, then ~/.history is truncated.  Returns 0 on suc-
  371:        cess, or errno on failure.
  372: 
  373: 
  374:    History Expansion
  375:        These functions implement history expansion.
  376: 
  377:        int history_expand (char *string, char **output)
  378:        Expand string, placing the result into output, a pointer to  a  string.
  379:        Returns:
  380:               0      If  no  expansions  took place (or, if the only change in
  381:                      the text was the removal of escape  characters  preceding
  382:                      the history expansion character);
  383:               1      if expansions did take place;
  384:               -1     if there was an error in expansion;
  385:               2      if  the  returned  line should be displayed, but not exe-
  386:                      cuted, as with the :p modifier.
  387:        If an error occurred in expansion, then output contains  a  descriptive
  388:        error message.
  389: 
  390:        char * get_history_event (const char *string, int *cindex, int qchar)
  391:        Returns  the  text  of the history event beginning at string + *cindex.
  392:        *cindex is modified to point to after the event specifier.  At function
  393:        entry,  cindex  points to the index into string where the history event
  394:        specification begins.  qchar is a character that is allowed to end  the
  395:        event  specification  in addition to the ``normal'' terminating charac-
  396:        ters.
  397: 
  398:        char ** history_tokenize (const char *string)
  399:        Return an array of tokens parsed out  of  string,  much  as  the  shell
  400:        might.   The tokens are split on the characters in the history_word_de-
  401:        limiters variable, and shell quoting conventions are obeyed.
  402: 
  403:        char * history_arg_extract (int first, int last, const char *string)
  404:        Extract a string segment consisting of the first through last arguments
  405:        present in string.  Arguments are split using history_tokenize().
  406: 
  407: 
  408:    History Variables
  409:        This section describes the externally-visible variables exported by the
  410:        GNU History Library.
  411: 
  412:        int history_base
  413:        The logical offset of the first entry in the history list.
  414: 
  415:        int history_length
  416:        The number of entries currently stored in the history list.
  417: 
  418:        int history_max_entries
  419:        The maximum number of history entries.  This must be changed using sti-
  420:        fle_history().
  421: 
  422:        int history_write_timestamps
  423:        If non-zero, timestamps are written to the history file, so they can be
  424:        preserved between sessions.  The default value is 0, meaning that time-
  425:        stamps  are  not saved.  The current timestamp format uses the value of
  426:        history_comment_char to delimit timestamp entries in the history  file.
  427:        If  that  variable does not have a value (the default), timestamps will
  428:        not be written.
  429: 
  430:        char history_expansion_char
  431:        The character that introduces a history event.  The default is !.  Set-
  432:        ting this to 0 inhibits history expansion.
  433: 
  434:        char history_subst_char
  435:        The character that invokes word substitution if found at the start of a
  436:        line.  The default is ^.
  437: 
  438:        char history_comment_char
  439:        During tokenization, if this character is seen as the  first  character
  440:        of  a  word,  then it and all subsequent characters up to a newline are
  441:        ignored, suppressing history expansion for the remainder of  the  line.
  442:        This is disabled by default.
  443: 
  444:        char * history_word_delimiters
  445:        The  characters  that  separate tokens for history_tokenize().  The de-
  446:        fault value is " \t\n()<>;&|".
  447: 
  448:        char * history_no_expand_chars
  449:        The list of characters which inhibit history expansion if found immedi-
  450:        ately  following  history_expansion_char.   The  default is space, tab,
  451:        newline, \r, and =.
  452: 
  453:        char * history_search_delimiter_chars
  454:        The list of additional characters which can delimit  a  history  search
  455:        string,  in  addition to space, tab, : and ? in the case of a substring
  456:        search.  The default is empty.
  457: 
  458:        int history_quotes_inhibit_expansion
  459:        If non-zero, double-quoted words are not scanned for the history expan-
  460:        sion  character or the history comment character.  The default value is
  461:        0.
  462: 
  463:        rl_linebuf_func_t * history_inhibit_expansion_function
  464:        This should be set to the address of a function that  takes  two  argu-
  465:        ments:  a  char  *  (string) and an int index into that string (i).  It
  466:        should return a non-zero value if the  history  expansion  starting  at
  467:        string[i]  should  not  be  performed;  zero if the expansion should be
  468:        done.  It is intended for use by applications like bash  that  use  the
  469:        history  expansion character for additional purposes.  By default, this
  470:        variable is set to NULL.
  471: 
  472: FILES
  473:        ~/.history
  474:               Default filename for reading and writing saved history
  475: 
  476: SEE ALSO
  477:        The Gnu Readline Library, Brian Fox and Chet Ramey
  478:        The Gnu History Library, Brian Fox and Chet Ramey
  479:        bash(1)
  480:        readline(3)
  481: 
  482: AUTHORS
  483:        Brian Fox, Free Software Foundation
  484:        bfox@gnu.org
  485: 
  486:        Chet Ramey, Case Western Reserve University
  487:        chet.ramey@case.edu
  488: 
  489: BUG REPORTS
  490:        If you find a bug in the history library, you should  report  it.   But
  491:        first,  you  should  make sure that it really is a bug, and that it ap-
  492:        pears in the latest version of the history library that you have.
  493: 
  494:        Once you have determined that a bug actually exists, mail a bug  report
  495:        to  bug-readline@gnu.org.   If  you have a fix, you are welcome to mail
  496:        that as well!  Suggestions  and  `philosophical'  bug  reports  may  be
  497:        mailed  to  bug-readline@gnu.org  or  posted  to  the  Usenet newsgroup
  498:        gnu.bash.bug.
  499: 
  500:        Comments and bug reports concerning this manual page should be directed
  501:        to chet.ramey@case.edu.
  502: 
  503: 
  504: 
  505: GNU History 8.1                  2020 July 17                       HISTORY(3)