I couldn't tell from the man page (!) if it was kosher to use 'sed' on a binary file... so I went ahead and tried it, and it works fine. It works fine as far as substituting old_string for new_string, but the thing that's bugging me is that the new file always has one extra char, 0x0A, tacked onto the end. ( What the heck is 0x0A anyhow, it's not a newline??? ) Is there any way to prevent sed from adding that one char?