Function: _def_histfile
Class: default
Section: default
C-Name: sd_histfile
Prototype:
Help:
Doc: name of a file where
 \kbd{gp} will keep a history of all \emph{input} commands (results are
 omitted). If this file exists when the value of \kbd{histfile} changes,
 it is read in and becomes part of the session history. Thus, setting this
 default in your gprc saves your readline history between sessions. Setting
 this default to the empty string \kbd{""} changes it to
 \kbd{$<$undefined$>$}. Note that, by default, the number of history entries
 saved is not limited: set \kbd{history-size} in readline's \kbd{.inputrc}
 to limit the file size.

 The default value is \kbd{$<$undefined$>$} (no history file).
