I really don't know what I'm doing here (my experience in shell scripting amounts to about two hours), but I put together this little script that will print out a random message each time you open a new bash window. Just copy this into your user's .bash_profile file, located in your user's home directory:
fn=/path/to/quotes.txt
cnt=$(wc -l $fn)
lns=${cnt:6:2}
if [ "$lns" = 0 ]; then
rnd=1
else
let "lns += 1"
rnd=$(expr $RANDOM % $lns)
let "rnd += 1"
fi
sed -n ${rnd}p $fn
Set the fn variable in the first line to the path and name of your quotes file. Each quote should be on its own line, with no extra lines between the quotes.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070508235210333