A Weird Imagination

Impromptu dice

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Dice in shell

Today I was borrowing a board game from the lending library at Emerald City Comicon and it was missing its dice. We could have gotten some physical dice somewhere, but instead we decided to use the materials we had on hand. The people I was playing with agreed that we did not want to drain our phone batteries by using a dice app on our phones, but I had a laptop with me. So I wrote a dice app for the shell:

while true
    seq 1 6 | shuf -n1
    seq 1 6 | shuf -n1

This rolls two six-sided dice every time you hit enter and clears the screen before showing the result using reset.

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Reverse sequence for tr

The problem

If you take the word wizard, reverse the order of the letters and reverse the alphabet:

From: abcdefghijklmnopqrstuvwxyz

then you get the word wizard back, an observation made at least as early as 1972.

Now let's write a shell script to verify this so we can find other words with similar interesting properties. The obvious shell script to verify this

echo wizard | tr a-z z-a | rev

unfortunately fails with the error

tr: range-endpoints of 'z-a' are in reverse collating sequence order

The error is by design: it's not clear what a sequence in reverse order should mean, so POSIX actually requires that it not work.

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