Ok .. So here's the breakup.
I have a text file filled with entries like :

"ABC","DEF","B","C:\Users\Dave\Documents";
[download]

The user inputs the following arguments: 1. The part of text to be replaced 2. The new text(to replace the substituted text)

So for eg: the User i/p for the text to be replaced(option1) is : C:\Users\Dave
and the I/p for option2 is : E:\Dave

the final output should be:
"ABC","DEF","B","E:\Dave\Documents";
Please help ..1!!