Perhaps a marginally better title would be "EOF is not a character [on Unix]". There are some OS that have an explicit EOF character, but it seems to have been the less common approach historically. CP/M featured an explicit end of file marker because the file system didn't bother to handle the problem of files which were not block-aligned, so the application layer needed to detect where the actual end of the file was located (lest it read the contents of the rest of the block). This is a pretty unusual thing to do, and was definitely a hassle for developers, so CP/M descendants like MS-DOS fixed it.

It's just a convention, it isn't enforced by the OS. The C runtime for example will check for character 26 if you're reading a file opened in text mode but not in binary mode. The underlying OS call to read a file makes no distinction between text and binary.

I'm just reading up on this now. But according to Wikipedia "CP/M used the 7-bit ASCII set", so then character 26 would be the "SUB (substitute)" character. No?

EDIT: Seems like 26 = EOF is a DOS thing.

EDIT 2: Some confusing comments: https://www.perlmonks.org/bare/?node_id=228760

EDIT 3: A pretty good thread (read NigelQ's replay): http://forums.codeguru.com/showthread.php?181171-End-of-File...