Re: Weekday abbreviations in output of cal(1)

["Jeremy C. Reed" <reed%reedmedia.net@localhost>]

Version 5 Unix:
https://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/source/s1/cal.c

char	dayw[]
{
	" S  M Tu  W Th  F  S"
};

Two decades later, 4.4BSD had
char *day_headings = " S  M Tu  W Th  F  S";

I find it interesting that the cal/ncal manual from a Ubuntu systems 
says "The output of the cal command is supposed to be bit for bit 
compatible to the original Unix cal command, because its output is 
processed by other programs ..."