Steve Bourne wanted to use `od` to match Algol 68, but there was already an `od` utility for printing octal dumps.

The original bournegol macros for DO and OD were a bit different:

  #define DO ){
  #define OD ;}

https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh...