[Sanddancer]

File parsing is a pretty hard problem. Let's take for example a Microsoft .exe file. They all start with the string MZ. However, saying something is an executable file is just the start of the rabbit hole. Is it purely a DOS executable, or is it a windows PE executable? Or is it an OS/2 LE executable, or is it a wrapper around a COFF file created by DJGPP? Okay, now, we know it's a PE file. Is this PE file actually a self extracting archive file created by PKZIP? Or maybe RAR? All of those are also things which have definite headers and offsets that you have to look to, and which the file utility needs to know how to look for, and where things can quickly get complicated.