(Poem #1419) Telnet Song There is a program called TELNET to get to another CPU. Control up-arrow is the escape; it's doubled to send it through, and "quit" is control up-arrow Q. A hacker once used TELNET to get to another CPU. He knew he could quit whenever he wanted to: all he had to do was type control up-arrow Q. Instead the hacker used TEL-NET to get to another CPU. He knew he could quit whenever he wanted to: all he had to do was type control up-arrow [at i-th time, repeat 2^i times] Q. [repeat verse n times; the choice of n is free] The hacker soon got bored with this, and wanted to get back. He sighed, and started the exponential popping of the stack: The hacked flushed the TEL-NET to the most distant CPU: He couldn't log out until he had killed them all, counting up powers of two: he typed control up-arrow [at i-th time, repeat 2^(n-i+1) times] Q. [repeat n times] Whew! The hacker's eyes were bloodshot; his fingers, black and blue; He wanted to log out and and go home to bed, and sleep for a day or two. He typed L O G O U T ... carriage return ... The hacker was on a network with only twenty CPU's. But if he had telnetted to them all, he would not yet be through with typing control up-arrow [repeat 7 times] Q! |
Note: This was written after an article by Donald E. Knuth, titled "The
Complexity of Songs":
D.E. Knuth, 'The Complexity of Songs', Communications of the ACM 27 (4)
pp. 345--348, April, 1984 (repetitions indicated; the song is only sung
correctly if the appropriate number of repetitions is used)
Some comments: Strictly speaking, the song is not part of the article;
it was appended afterwards. The composer and lyricist is Guy L. Steele,
Jr. The melody has a certain haunting quality that is quite hard to
convey in ASCII text. I don't know whether it has ever been played. The
composer has email, so it shouldn't be too hard to find out.
-- http://www.poppyfields.net/filks/00222.html
(Sitaram points out that that last bit is a dig at Knuth's refusal to use
email. :))
2^i is 2*2..*2 [i times], e.g. 2^5 = 2*2*2*2*2 = 32
I've explained the maths behind the song in a postscript (it gets long)
Two of the more delightful aspects of hacker culture [see links] are an
abundant and enthusiastic creativity, and a strong sense of play.
Unsurprisingly, these have combined to produce a large body of verse,
ranging from esoteric in-jokes to catchy and accessible song parodies, and
even some genuine "poetry". There is a marked, qualitative difference from
poems like yesterday's, though - this is not a case of poets embracing the
brave new world, but rather the denizens of that world embracing verse, a
look from the inside rather than from the outside. (There is a significant
overlap with science fiction fandom's filk music, not least because so many
fans are hackers and vice versa, but the two are nonetheless different
genres).
Today's song is definitely one of the classics of the genre, and not just
for its distinguished (if you'll forgive the understatement) authors -
Kunth's notion of song complexity has an irresistible combination of
quirkiness and serious academic value, and Steele's song highlights the
fun factor while providing a good intuitive grasp of Knuth's point. And
while the verse itself isn't as clever as some of the others out there, it
has a nicely hypnotic rhythm that fits the "trapped in an exponential loop"
nature of the song.
martin
[Links]
"Hacker" is used throughout in the original sense of the word - see
http://www.catb.org/~esr/jargon/html/H/hacker.html
[broken link] http://www.cs.sunysb.edu/~algorith/lectures-good/node2.html for some idea of
what is meant by "the complexity of songs".
[broken link] http://groups.google.com/groups?selm=ANDERS.90Jun7131354%40mago.uio.no lists
chords for the song
Biography of Steele:
[broken link] http://www.sls.csail.mit.edu/~hurley/guysteele.html
and of Knuth:
http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Knuth.html
The Jargon Files:
http://www.catb.org/~esr/jargon/
And a great collection of computer-related songs:
http://www.poppyfields.net/filks/fullindex.html
[PostScript]
A little digression into mathematics:
There is a program called TELNET to get to another CPU.
Control up-arrow is the escape; it's doubled to send it through,
An 'escape' is a character that sends the *next* character not to the
current session but to the one below it in the stack. So, say our intrepid
hacker logged in to machine A, telnetted to B, and from B telnetted to C
His stack now looks like this: [hacker -> C -> B -> A]. Anything he types
gets executed by machine C. Now supposing he wants to send a keystroke to
machine B instead? What he needs to do is to escape the keystroke. Escape,
here, is control-up arrow, so to type 'HELLO' on machine B, he needs to
type:
control-uparrow H control-uparrow E control-uparrow L control-uparrow
L control-uparrow O
or, using ^| as a shorthand for the control-up arrow key sequence,
^| H ^| E ^| L ^| L ^| O
for a total of 15 keystrokes (or 10 if you count ctrl-up arrow as one
keystroke even though it involves two physical keys).
Now supposing he wanted to send something to machine A? If he types ^|, the
keystrokes get sent to B - what he wants to do is type ^| on machine B, so
that the next character goes to machine A. But how does he type a ^| on B?
The song tells us that:
Control up-arrow is the escape; __it's doubled to send it through,__
so we type ^|^| to send a ^| to machine B. So to send, say, an "X" to
machine A, we need to type ^|^|X, right? Nope - because the ^|^| sends a ^|
to machine B, and then the X goes to *machine C*, the machine at the top of
the stack. To send the X to machine A, we need to send a ^|X to machine B.
And to do that, we need to send a ^|^| to C (which sends a ^| to B), and
then a ^|X to C (which sends an X to B), at which point we'll have sent a
^|X to B, which duly sends the X to A.
By this point, it should be clear how fast the number of keystrokes can blow
up as we add even one more machine to the stack. So let's go ahead and
complete the demonstration by logging out of A.
Press C B A
^| ^| C has a ^|, will pass the next key to B
^| ^| B has a ^|, will pass its next key to A
^| ^| ^| C has a ^|, will pass the next key to B
^|Q ^|Q the ^|Q gets passed to C which passes it to B
which passes it to A which logs out
Two telnet sessions (A->B and B->A), and a total of 4 (2^2) control-up arrows
before the Q, as Steele said. Logging out of four machines is left as an
exercise :)
(Note that I assume control-uparrow-Q is a single keystroke, rather than a
control-uparrow followed by a Q, otherwise the song doesn't work)
martin
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