General :: Edit Line In File From Terminal?

I don't really know where to put this topic but anyways my problem is that i need to edit a line in a file.

So i think of something like this

su
Cd /data/data/foldernameofapp/
Edit "file.dat"
Edit line 4 "text here 2"

i want it to edit like this "text here 3"

Change only the number. or replace the hole line with a new line where i only changed the number. btw the best is if the script can change a line and not find text and change. Because the number in the text i want to change can vary from different numbers.

P.S i can use root explorer and open the file with a text editor and change it, this works but takes forever P.S.S i got root