I use tcsh at work - one of the features I use extensively is command-line history completion at the shell prompt. Currently, I've limited the size of my history file to 2000 (as I don't want to slow down the shell too much). However at times I need a command I know I've used a month or two back , but by now has been erased. So I want a system wherein:
My history buffer stores 2000 lines only
Instead of older commands getting erased , they should be saved into a "master" history file, ordered chronologically i.e if two shells were opened , then the commands entered in the history should be sorted as per the datestamp (not the order in which the shells were closed)!
It would be perfect , if this master history file could be auto-backed up, say per week basis.
I'm sure many of avid shell users have faced a situation like this - I'm hoping to get the answer from one of such users !!
2000 is pretty low. You could raise that a fair amount without suffering too much.
Next you probably want to store the history on logout, since this is when new commands are added to the .history file.
Create a file called .logout in your $HOME (for bash users, this file is .bash_logout). In this, copy the contents of the history to a permanent store. For example:
cat $HOME/.history >> $HOME/.ancient_history
This will append the history to a file ".ancient_history". For bash users, the file to copy is called .bash_history.
Then create a cron job that creates a back up of this every now and again. For starters here is one that moves the file to a filename with a date stamp at 5 minutes past midnight every day.
5 0 * * * mv $HOME/.ancient_history $HOME/.ancient_history_`date +%s`
There are probably more things you could do with this, but this is enough to get started. It's a pretty good idea that I hadn't thought of doing before either :-)