in reply to The easiest way to substitute a part of the content of a file.

Thank you for pointing that out :)

Unfortunately, Tilly, it's a program that needs to run more than once and is quite large. I didn't know that was possible though :).

Turnstep, it is indeed at the end of a file. Your example doesn't deviate much from my solution save for the fact that it doesn't put all that crap before the part to be substituted in memory. With 12 MB of RAM (edo!) in a crappy old machine I ought to replace it's quite important ;].

Anyways, thanks go to both of you.