Command Substitution (Back Quotes)

# echo "Today is: `date`"
Today is: Tue Feb 5 05:48:51 EST 2013

# echo "Current working directory: `pwd`"
Current working directory: /tmp

# now=`date`
# echo $now
Tue Feb 5 05:52:11 EST 2013
# sleep 5
# echo $now
Tue Feb 5 05:52:11 EST 2013