How to backup tcsh history periodically to a single file in chronological manner ?

Question

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:

1. My history buffer stores 2000 lines only

2. 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)!

3. 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 !!

Answer 1

never quite thought of doing this but the simplest way would be to write a cron job that appended the history file to another file. The problem with this would be that you would get duplicates unless you wrote the cron to clear the history file after it did the dump.

history is stored (as far as i am aware) by line number only so the numbers would repeat for each dump. but you cold add a marker line with the date of the dump.

Answer 2

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 :-)