¿Cuáles son las 10 primeras cifras consecutivas no repetidas de los decimales de PI?
4592307816
echo "scale=100;a(1)*4" | bc -l | sed ':a;N;s/\\\n//;ta' | \
perl -pe 's/.*?(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2|\3)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\5|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9)(.).*/$1$2$3$4$5$6$7$8$9$10/'
perl -pe 's/.*?(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2|\3)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\5|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9)(.).*/$1$2$3$4$5$6$7$8$9$10/'
¿Dónde en las cifras de PI está escondida la frase ‘Hello world’?
21463853067
Pues
$ echo 21463853067 | tr 0-9 reHolwld\
Hello world
$
Hello world
$
echo "scale=4721;a(1)*4" | bc -l | sed ':a;N;s/\\\n//;ta' | \
perl -pe 's/.*?(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\5|\6|\7|\8|\9)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9|\10)(.).*/$1$2$3$4$5$6$7$8$9$10$11/' | \
tr 0-9 "reHolwld "
perl -pe 's/.*?(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\5|\6|\7|\8|\9)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9|\10)(.).*/$1$2$3$4$5$6$7$8$9$10$11/' | \
tr 0-9 "reHolwld "
O, para el debianita impaciente:
sudo apt-get -y install pi >/dev/null && pi 4721 | \
perl -pe 's/(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\5|\6|\7|\8|\9)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9|\10)(.).*/$1$2$3$4$5$6$7$8$9$10$11/' | \
tr 0-9 "reHolwld "
perl -pe 's/(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2)(.)(?!\1|\2|\3|\4)(.)(?!\1|\2|\3|\4|\5)(.)(?!\1|\2|\3|\4|\5|\6)(.)(?!\1|\2|\3|\4|\6|\7)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8)(.)(?!\1|\2|\5|\6|\7|\8|\9)(.)(?!\1|\2|\3|\4|\5|\6|\7|\8|\9|\10)(.).*/$1$2$3$4$5$6$7$8$9$10$11/' | \
tr 0-9 "reHolwld "
Now that we have pi installed, we can venture further:
pi 62999 | tr 0-9 del\ l\!owrH
[...] also: – this post. – More, diverse Bruce Schneier facts. – hello world, regex powered. ~$ pi –bibliography Recommended readings: "Pi", by Joerg Arndt and Christoph Haenel [...]