Ok I have used it, but I think that my manner is not really elegant.

Do you know how to (by sed)...

overwrite a line which actually you only know how it begins but not how finishes?

I want to change a settings file... so I want to do something like that.

sed '49s/HorizSync[...]/HorizSync 30.0 - 83.0/g' xorg.conf

where [...] are characters which I don't know.

Thanks a lot!!