When i was in college, i had a topic Regular Expression under the subject Formal system automata! At that time i was so confused with "What exactly this pattern matching is" never understood the concept just mugged up and passed!! After getting into the real world and for writing real application i have been forced to get back to REGEXP again!! Now, after writing few stuffs, i understood the basic concepts!! How powerful this pattern matching thing is!! I am giving an small example "To replace all hyphens with underscores". I have used CL-PPCRE library for this.

cl-user> (cl-ppcre:regex-replace-all "-" "foo-bar-bazz" "_") => "foo_bar_bazz"

w00t! this is really exciting!! one can do wonders by using regexp to get rid of major problems such as one of the problem we face is To split date "14/08/2008" as ("14" "08" "2008").

cl-user> (cl-ppcre:split "/" "14/08/2008") => ("28" "09" "2008")

These are few examples of REGEXP. I will add more of it soon :-)