How can you concatenate two huge files with very little spare disk space? [closed]

Answer 1

Not very efficient, but I think it can be done.

Open the first file in append mode, and copy blocks from the second file to it until the disk is almost full. For the remainder of the second file, copy blocks from the point where you stopped back to the beginning of the file via random access I/O. Truncate the file after you've copied the last block. Repeat until finished.