That feature already was in 6th edition UNIX, in 1975: <a href="http:&#x2F;&#x2F;man.cat-v.org&#x2F;unix-6th&#x2F;6&#x2F;cal" rel="nofollow">http:&#x2F;&#x2F;man.cat-v.org&#x2F;unix-6th&#x2F;6&#x2F;cal</a>.<p>I don&#x27;t think the 5th edition had <i>cal</i>.