writing a custom command file

[thomas]

Hi,

I would like to write a custom command file (say foo.el) that
interactively asks
for one argument (a string "s") and then executes a couple of
replace-regexp
commands, e.g.:

(replace-regexp "abc" "abc "+s)    ; + meaning string concatenation
(replace-regexp "def" "ghi")
(replace-regexp "123" "456")

Since i don't know anything about customizing emacs with Lisp
functions can anyone please tell me what the .el file for this would
look like?

Thanks a lot,

Thomas