ubun2

i am new to the linux world and in my endeavor to learn more i have been experementing with shell scripting.  i am following a tutorial at linuxcommand.org in which the author takes you through the process of writing a script that produces a HTML page with your system info.  at the part im at now the script makes use of the "du" command.

I want to set environment variable for example JAVA_HOME under my bash shell, please help
 
Running ant gives the following error
 
 
ml:255: Unable to find a javac compiler;
com.sun.tools.javac.Main is not on the classpath.
Perhaps JAVA_HOME does not point to the JDK.
It is currently set to "/usr/lib/jvm/java-6-openjdk/jre"