How to show date and time in your history command using environment variable HISTTIMEFORMAT
It usually happens with me that I am trying out a cli based tool or learnt some new trick, it works fine then, but later I can hardly recall what I did 
. In such cases, all I remember is either a part of the command or the time while I was doing it. I always wondered if we could get more out of the history command - days, time etc. After searching a little, I found that it is actually possible and could be done pretty easily.
Its all in the genius of Bash 
. All you have to do is set the environment variable, HISTTIMEFORMAT, appropriately. Lets take an example where I just want to so the timestamp.
[shredder12]$ export HISTTIMEFORMAT="%T "
[shredder12]$ history
568 13:53:01 clear
569 13:53:03 top
570 13:53:07 sudo fdisk -l
571 13:53:16 free -m
572 13:53:17 cd
573 13:53:18 ls
574 13:53:22 cd Downloads/
Similary, for date you can use the following parameters
%d for Day
%m for Month
%y for Year
So, if you want both date and timestamp
[shredder12]$ export HISTTIMEFORMAT="%d/%m/%y %T "
[shredder12]$ history568 25/10/10 13:53:01 clear
569 25/10/10 13:53:03 top
570 25/10/10 13:53:07 sudo fdisk -l
571 25/10/10 13:53:16 free -m
572 25/10/10 13:53:17 cd
573 25/10/10 13:53:18 ls
574 25/10/10 13:53:22 cd Downloads/
Please note that, for a permanent setting you will have to append the "export" line in ~/.bashrc file.
1 Comment
Also note that the shredder12 is using the order customary in Europe, %d/%m. Americans may want to reverse this to %m/%d.
Further amusing question: is there an environment variable that contains the customary date format for the current locale? If it exists, you could use it in the definition of HISTTIMEFORMAT.
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