What does Ritchie's 1979 PDP-11 `/usr/games/bcd` do?

Question

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?

score 28 · Accepted Answer · answered Dec 17 '12 at 03:42

28

The bcd command formats the output as a punch card, like this one:

enter image description here

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.

answered Dec 17 '12 at 03:42

Renan

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2

Since this appears to be a serious work tool I wonder why it was put in the games folder? – Dan Is Fiddling By Firelight Dec 17 '12 at 13:54
1

I don't really think this is a serious work tool; (I think that) in 1979 punch cards weren't used that much. – Renan Dec 17 '12 at 14:34
1

@DanNeely To make real punch cards, you need a card punch. printing them is just pretty. – hildred Dec 02 '13 at 02:41
I wonder which coding it uses... – sendmoreinfo Jul 04 '14 at 15:23
1

@sendmoreinfo: Probably [BCD coding](http://homepage.cs.uiowa.edu/~jones/cards/codes.html). – Dolda2000 Jul 11 '15 at 06:50

What does Ritchie's 1979 PDP-11 `/usr/games/bcd` do?

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