If you asked for a big enough file of random bytes, eventually, chances are that the file would just happen to contain the substring "Xcat $1\nprintf X\ncat $0\

If you asked for a big enough file of random bytes, eventually, chances are that the file would just happen to contain the substring "Xcat $1\nprintf X\ncat $0\nexit\n". You then do the following: 1. Copy the part of the file preceding that substring to a file named "foo". 2. Take the rest of the file, including all of the substring EXCEPT for the initial X character, and put it in an executable file called "decompressor". When you run "./decompressor foo > out", you will then recreate the original file. The length of decompressor + foo will be one byte shorter than the original file.