Eternal plus per-directory bash history

Problems:

• Hate it when I can't find a useful command which was last executed too long ago and has "expired" from bash history
• bash history is too cluttered with commands from all over the whole system; I want a per-project history (project == directory, usually)
• but, I still want a global time-ordered history too (at least approximately)

There is a partial solution here upon which this is based.

Solution:

• redefine "cd" to save per-directory history inside the directory itself, and also append that to an ever-expanding ~/.bash_history
• replace in-memory history with the one from the CWD so that control-R searches don't find irrelevant commands
• redefine "history" to get the global history so that I can do comprehensive history | grep searches
• add a "chistory" command to get CWD-specific history only

If want to try it, stick this in your ~/.bashrc (and smoke it, or something):

# per-directory history
shopt -s histappend  # always append to history, don't replace
alias cd='cd_with_local_history'
alias chistory='builtin history'
alias history='cat $HOME/.bash_history'
export HISTFILE="$PWD/.bash_cwd_history"
function cd_with_local_history()
{
        export HISTFILE="$PWD/.bash_cwd_history"
        builtin history -w # write the local history file 
        cat $HOME/.bash_history .bash_cwd_history | uniq > .bash_cat_history
        mv .bash_cat_history $HOME/.bash_history
        builtin cd "$@" # do actual cd
        export HISTFILE="$PWD/.bash_cwd_history"
        builtin history -c # clear memory
        builtin history -r #read from current histfile
}

Disclaimer: I'm not responsible for your lost history! Please make a backup of your ~/.bash_history first, just in case.

Known remaining problems:

• ~/.bash_history will have accelerating growth because every time you cd out of a directory, it will concatenate the _entire_ CWD history into ~/.bash_history. This could be corrected with another temp file and a marker to separate new history from old history, some more scripting etc.
• If you exit from the shell it will only save the CWD history; the concatenation into ~/.bash_history only happens with the "cd" alias. (Is there an "onExit" hook of some sort I could use?)