Unique KSH history
Useful if you want each of your concurrent login sessions to have their own unique shell history.
Very useful if different people are logged in as the same user but doing different things (ie root user on a central system).
HISTFILE=$HOME/.ksh_hist`tty`
[ -d `dirname $HISTFILE` ] || mkdir -p `dirname $HISTFILE`
Works on Solaris' ksh and RedHat 8.0's pdksh