I have four text files A.txt, B.txt, C.txt and D.txt I have to perform a series of vim editing in all these files. Currently how I am doing is open each files and do the same vi
JimR and Ingo have provided excellent answers for your use case.
Just to add one more way to do it, however, you could use my vimrunner plugin to script the interaction in ruby: https://github.com/AndrewRadev/vimrunner.
Example:
vim = Vimrunner.start
vim.edit "file.txt"
vim.insert "Hello"
vim.write
vim.kill
This can be useful for more complicated interactions, since you get the full power of a programming language.