TODO item: add \# which lists line numbers, and allows command execution

["Sibte Abbas" <sibtay(at)gmail(dot)com>]

Hi all,

Realizing that the mentioned TODO item discussed at http://archives.postgresql.org/pgsql-hackers/2006-12/msg00255.php
 can be useful for myself and others as well, I would like to go ahead and implement it.

Synopsis:
======

Sticking to the syntax and semantics which Joshua already mentioned in the thread:

\#: displays the command history. Like \s but prefixes the lines with line numbers

\# <line_no>: executes the command(if any) executed at the line specified by line_no


Display the history contents:
=================

Well the answer to this pretty much lies in the \s (without any filename) implementation. However \s simply writes the contents of the history to the TTY while \# would prefix all the history lines with their respective line numbers.

Because of this difference, we'll have to employ a more flexible approach rather than simply using the write_history() function.

A solution to this is to use history_list() function to get a list of HIST_ENTRY structures and simply display them as per our needs 
i.e. to prefix each line with incrementing numbers in our case.

Execute a line based on line number:
======================

For this we can simply use the history_get(int offset) function of the gnu history api to return a HIST_ENTRY structure corresponding to the given offset. 

The returned HIST_ENTRY can then be used to access the command that was executed at that specific line number.

Comments are welcomed.

regards,
-- 
Sibte Abbas