Hmm.. it's all about where you count. Clearly, he was working on it if the stubs is there. If the only difference between 3rd and 4th is the pipe code, then it would be fair to say that.

You might say something like: Pipe's were developed in a 3rd edition kernel, where there was is evidence of nascent idea (its has a name and there are subs for it), but the code to fully support it is lacking in the 3rd release. Pipes became a completed feature in the 4th edition.

On Tue, Jan 3, 2017 at 3:54 PM, Diomidis Spinellis <dds@aueb.gr> wrote:

Peter Salus writes "The other innovation present in the Third Edition was the pipe" ("A Quarter Century of Unix", p. 50). Yet, in the corresponding sys/ken/sysent.c, the pipe system call seems to be a stump.

1, &fpe, /* 40 = fpe */
0, &dup, /* 41 = dup */
0, &nosys, /* 42 = pipe */
1, &times, /* 43 = times */

On the other hand, the Fourth Edition manual documents the pipe system call, the construction of pipelines through the shell, and the use of wc as a filter (without an input file, as was required in the Second Edition).

Would it therefore be correct to say that pipes were introduced in the Fourth rather than the Third Edition?