I recently tried the simh emulator pdp11.The disk image I used can be found on the internet, and instructions for booting it are here.Presumably it belonged to Dennis Ritchie, as the username is dmr.In the /usr/games folder are about 20 games and amusements for wasting expensive computing resources.One 'game' is called 'bcd'.If I run it by typing ./bcd, nothing happens. But then the next command I execute gets printed out as ascii art: ________________________________________________/WC -L *                                         || ]                                              ||   ]] ]                                         ||]                                               ||111111111111111111111111111111111111111111111111||222222222222222222222222222222222222222222222222||3]33]3333333333333333333333333333333333333333333||444444]44444444444444444444444444444444444444444||555555555555555555555555555555555555555555555555||]66666666666666666666666666666666666666666666666||777777777777777777777777777777777777777777777777||888888]88888888888888888888888888888888888888888||999999999999999999999999999999999999999999999999||________________________________________________| ________________________________________________/LS                                              ||                                                ||]                                               || ]                                              ||111111111111111111111111111111111111111111111111||2]2222222222222222222222222222222222222222222222||]33333333333333333333333333333333333333333333333||444444444444444444444444444444444444444444444444||555555555555555555555555555555555555555555555555||666666666666666666666666666666666666666666666666||777777777777777777777777777777777777777777777777||888888888888888888888888888888888888888888888888||999999999999999999999999999999999999999999999999||________________________________________________|Does anyone know what these represent?
What does Ritchie's 1979 PDP-11 `/usr/games/bcd` do?
history;games
The bcd command formats the output as a punch card, like this one:From the BSD games man page:bcd ppt morse - reformat input as punch cards, paper tape or morse code   The ] stands for where the holes would be.At first glance, it seems to do nothing because it's waiting for input from stdin. Try piping something into it (i.e. command | bcd) to see.