One thing Bourne based shells and csh based shells share is that $? is the exit code of the previous command. But, we're talking about a UNIX Version 6 shell here; not a modern shell. I never used V6 much (although I worked on developing PWB UNIX and MERT both of which were derived from V6). I used the Mashey shell for a while and early versions of the Bourne shell (both of which were developed as replacements for the V6 shell). (As you can probably guess from current shells, the Mashey shell lost out to the Bourne shell; but some Mashey shell features were adopted by the Bourne shell.)

The V6 shell was VERY simple. (You can check out V6 utility man pages here.) Although there is no mention of shell variables or special parameters (e.g., $#, $?, and $!) on the V6 sh(1) man page and it is clear from the description of command execution that there was no $PATH variable, I think the special parameters listed above were provided with their current meanings. Positional parameters aren't even mentioned on the sh(1) man page, but $1 is mentioned on the goto(1) and shift(1) man pages. There were no loops (for, while, or until), but the the goto command could be used with the if command to produce loops. The only file descriptors you could redirect were standard input and standard output. (The BUGS section of the man page says it is a bug that diagnostic messages couldn't be redirected.) The Synopsis for the if command was:

Code:

if expr command [args...]

Note that there is no then, else, or fi here. And, as has been noted in this thread, if was a standalone utility; not a shell built-in. If I remember correctly, the only built-ins in V6 sh were chdir (there was no cd then), login, newgrp, shift, and probably exit.