GNU History Library Brian Fox Free Software Foundation Version 1.1 April 1991
This document describes the GNU History library, a programming tool that provides a consistent user interface for recalling lines of previously typed input.
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Copyright (C) 1989, 1991 Free Software Foundation, Inc.
This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the GNU History Library in your own programs, see section Programming with GNU History.
The History library provides a history expansion feature that is similar to the history expansion in Csh. The following text describes the sytax that you use to manipulate the history information.
History expansion takes place in two parts. The first is to determine which line from the previous history should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the previous history is called the event, and the portions of that line that are acted upon are called words. The line is broken into words in the same fashion that the Bash shell does, so that several English (or Unix) words surrounded by quotes are considered as one word.
An event designator is a reference to a command line entry in the history list.
!
!!
!-1.
!n
!-n
!string
!?string[?]
!#
^string1^string2^
!!:s^string1^string2^.
A : separates the event specification from the word designator. It can 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 a 0 (zero).
0 (zero)
n
^
$
%
?string? search.
x-y
-y abbreviates 0-y.
*
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.
After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a :.
h
r
e
t
p
s/old/new/
g
s, as in gs/old/new/.
This chapter describes how to interface the GNU History Library with programs that you write. It should be considered a technical guide. For information on the interactive use of GNU History, see section Using History Interactively.
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 making up new ones.
The programmer using the History library has available to him functions for remembering lines on a history stack, associating arbitrary data with a line, removing lines from the stack, searching through the stack for a line containing an arbitrary text string, and referencing any line on the stack directly. In addition, a history expansion function is available which provides for a consistent user interface across many different programs.
The end-user using programs written with the History library has the
benifit 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 similar to
the history substitution used by Csh.
If the programmer desires, he can use the Readline library, which includes some history manipulation by default, and has the added advantage of Emacs style command line editing.
typedef struct _hist_entry {
char *line;
char *data;
} HIST_ENTRY;
This section describes the calling sequence for the various functions present in GNU History.
Function: void using_history ()
Begin a session in which the history functions might be used. This just initializes the interactive variables.
Function: void add_history (char *string)
Place string at the end of the history list. The associated data
field (if any) is set to NULL.
Function: int where_history ()
Returns the number which says what history element we are now looking at.
Function: int history_set_pos (int pos)
Set the position in the history list to pos.
Function: int history_search_pos (char *string, int direction, int pos)
Search for string in the history list, starting at pos, an absolute index into the list. direction, if negative, says to search backwards from pos, else forwards. Returns the absolute index of the history element where string was found, or -1 otherwise.
Function: HIST_ENTRY *remove_history ();
Remove history element which from the history. The removed element is returned to you so you can free the line, data, and containing structure.
Function: void stifle_history (int max)
Stifle the history list, remembering only max number of entries.
Function: int unstifle_history ();
Stop stifling the history. This returns the previous amount the history was stifled by. The value is positive if the history was stifled, negative if it wasn't.
Function: int read_history (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.
Function: int read_history_range (char *filename, int from, int to)
Read a range of lines from filename, adding them to the history list.
Start reading at the from'th line and end at the to'th. 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.
Function: int write_history (char *filename)
Append the current history to filename. If filename is
NULL, then append the history list to `~/.history'. Values
returned are as in read_history ().
Function: int append_history (int nelements, char *filename)
Append nelement entries to filename. The entries appended are from the end of the list minus nelements up to the end of the list.
Function: HIST_ENTRY *replace_history_entry ()
Make the history entry at which have line and data.
This returns the old entry so you can dispose of the data. In the case
of an invalid which, a NULL pointer is returned.
Function: HIST_ENTRY *current_history ()
Return the history entry at the current position, as determined by
history_offset. If there is no entry there, return a NULL
pointer.
Function: HIST_ENTRY *previous_history ()
Back up history_offset to the previous history entry, and return a
pointer to that entry. If there is no previous entry, return a
NULL pointer.
Function: HIST_ENTRY *next_history ()
Move 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.
Function: HIST_ENTRY **history_list ()
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.
Function: int history_search (char *string, int direction)
Search the history for string, starting at history_offset.
If direction < 0, then the search is through previous entries,
else through subsequent. If string is found, then
current_history () is the history entry, and the value of this
function is the offset in the line of that history entry that the
string was found in. Otherwise, nothing is changed, and a -1 is
returned.
Function: int history_expand (char *string, char **output)
Expand string, placing the result into output, a pointer to a string. Returns:
0
1
-1
If an error ocurred in expansion, then output contains a descriptive error message.
Function: char *history_arg_extract (int first, int last, char *string)
Extract a string segment consisting of the first through last arguments present in string. Arguments are broken up as in the GNU Bash shell.
Function: int history_total_bytes ();
Return the number of bytes that the primary history entries are using.
This just adds up the lengths of the_history->lines.
This section describes the variables in GNU History that are externally visible.
For convenience only. You set this when interpreting history commands. It is the logical offset of the first history element.
The following snippet of code demonstrates simple use of the GNU History Library.
main ()
{
char line[1024], *t;
int done = 0;
line[0] = 0;
while (!done)
{
fprintf (stdout, "history%% ");
t = gets (line);
if (!t)
strcpy (line, "quit");
if (line[0])
{
char *expansion;
int result;
using_history ();
result = history_expand (line, &expansion);
strcpy (line, expansion);
free (expansion);
if (result)
fprintf (stderr, "%s\n", line);
if (result < 0)
continue;
add_history (line);
}
if (strcmp (line, "quit") == 0) done = 1;
if (strcmp (line, "save") == 0) write_history (0);
if (strcmp (line, "read") == 0) read_history (0);
if (strcmp (line, "list") == 0)
{
register HIST_ENTRY **the_list = history_list ();
register int i;
if (the_list)
for (i = 0; the_list[i]; i++)
fprintf (stdout, "%d: %s\n",
i + history_base, the_list[i]->line);
}
if (strncmp (line, "delete", strlen ("delete")) == 0)
{
int which;
if ((sscanf (line + strlen ("delete"), "%d", &which)) == 1)
{
HIST_ENTRY *entry = remove_history (which);
if (!entry)
fprintf (stderr, "No such entry %d\n", which);
else
{
free (entry->line);
free (entry);
}
}
else
{
fprintf (stderr, "non-numeric arg given to `delete'\n");
}
}
}
}