...And removing one line only?

Greetings. This is a part of my "reading one line" message... If one would need to remove one line in a flatfile, how would it be done? I know there is no simple solution, and one is going to increment through the chosen file.. But how is it done? My programming skills are quite OK, but I am rather new to PHP and the for...loops doesnt work exactly the same way as in C++, thus that I have forgotten the way to read line in one file and in the same time iterate through another to write... Remove one line? Thanks, - Richard