(via www.linuxjournal.com)
Have you ever wanted to change the names of many files at once? Or, have you ever needed to use a default value for a variable that has no value? These and many other options are available to you when you use string operators in bash and other Bourne-derived shells...
Bash Parameter Substitution
Bash Parameter Substitution
Variable Mangling in Bash with String Operators
http://linuxgazette.net/issue57/eyler.html