Those features simply do not belong in a program whose purpose is to concatenate its input. If you want to number a file's lines, 'echo ,n | ed file | sed 1d' or 'awk ''{ print NR " " $0 }''' will do just fine. You could even wrap your ed or awk script into a shell script with a descriptive name like "lineno" rather than something silly like "cat -n". The reason GNU's is so complex is because it does many things and does them poorly. The V6 implementation does exactly what is says on the tin, does it well, and does nothing more: it catenates files.