I just went looking at the v6 source to confirm a memory, namely that cpp was only invoked if a # was the first character in the file. Hence, this: https://github.com/dspinellis/unix-history-repo/blob/Research-V6-Snapshot-Development/usr/source/c/c01.c#L1

People occasionally forgot this, and hilarity ensued.

Now I'm curious. Anyone know when that convention ended?

ron