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.