Please see the following for further reading relating to this chapter: http://tldp.org/LDP/abs/html/internalvariables.html http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-7.html http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_09_02.html http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_09_03.html http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_09_05.html