How to find a string line in a txt file on SD-Card and replace

i want some code for sd card on ethernet shield to find a string in a txt file looks like

07836883,x 13108266,x 13033706,x 13056789,x

and then i can edit the value x after the comma

any help with code plz

I want peace on earth and a long life.

:o

ashrafh: :o

It means that you don't always get what you want without some effort.

What have you tried? What happened?