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

Answer 1

Here's a slight improvement over my first answer.

If you have 100MB free, copy the last 100MB from the second file and create a third file. Truncate the second file so it is now 100MB smaller. Repeat this process until the second file has been completely decomposed into individual 100MB chunks.

Now each of those 100MB files can be appended to the first file, one at a time.