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.

 - 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 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.

 - Function: int write_history (char *filename)
     Write the current history to FILENAME, overwriting FILENAME if
     necessary.  If FILENAME is `NULL', then write the history list to
     `~/.history'.  Values returned are as in `read_history ()'.

 - Function: int append_history (int nelements, char *filename)
     Append the last NELEMENTS of the history list to FILENAME.

 - Function: int history_truncate_file (char *filename, int nlines)
     Truncate the history file FILENAME, leaving only the last NLINES
     lines.