Re: [TUHS] Shell control through external commands

I remember reading about #! in the early 1980s, and having mixed feelings about it, as I still do. The basic idea is fine, if annoyingly limited; but that the kernel has to decide, in effect, whether to treat a header as binary or text bothers me. Were I designing a new system from scratch today, I'd just make the header all text; the small extra space and time for the kernel to parse that for binaries doesn't matter any more. It certainly did when #! was invented, though. I had the impression at the time that it came from Berkeley, but I think I later heard from the horse's mouth that it was originally Dennis's idea. I don't think anyone has yet laid out the complete story of what came before: 1. Originally, the shell would exec(file), and if exec returned ENOEXEC, would open the file and treat it as shell commands. 2. Then came the C shell, and a problem: did file contain commands for csh or sh? A hack emerged: if csh encountered a script file, it would read the first character; if that was '#' it was a csh script, otherwise it handed off to /bin/sh. None of this helped when some program other than the shell called exec on a shell script. That's one reason execlp and execvp appeared. (The other is that they observe $PATH if the command pathname has a single element.) I don't know offhand whether there was ever an execlp/vp that implemented the #-means-csh convention. Anyone else remember? Norman Wilson Toronto ON