I love reading examples of these "great-great-grandparent" applications hidden in /bin. I've used dc in shell scripts for years, but for the simplest of simple computations (e.g., automating FDISK partitioning and doing sector math). Had no idea it could do this.
dc is worth having installed because of this CLI gem alone:
echo "[q]sa[ln0=aln256%Pln256/snlbx]sb729901041524823122snlbxq" | dc
I've never tried to understand what's really going on to produce the result, but also wouldn't really know where to start - maybe someone in HN's audience can enlighten me? :)
dc and bc are standard POSIX utils (and also part of busybox for embedded systems) so for most unix-like systems they're installed by default unless you take active measures to exclude them.
> Many GNU/Linux distros (at least Debian and RHEL) install neither `dc` nor `bc` by default, afaik.
Yeah, I recently wrote a script that used bc and immediately discovered that it didn't work on at least Arch Linux (and I think others, although I only seem to have added it to the Arch ansible config...); conveniently, I only needed the most trivial of calculations, so I just shifted to awk, which has better default availability.
[Monte Carlo approximation of Pi.
Registers:
u - routine : execute i if sum of squares less than 1
i - routine : increment register x
z - routine : iterator - execute u while n > m++
r - routine : RANDU PRNG
m - variable: number of samples
x - variable: number of samples inside circle
s - variable: seed for r
k - variable: scale for division
n - variable: number of iterations (user input)
]c
[lrx 2^ lrx 2^ + 1>i]su
[lx 1+ sx]si
[lu x lm 1+ d sm ln>z]sz
[0k ls 65539 * 2 31^ % d ss lkk 2 31 ^ /]sr
? sn
5dksk
1 ss
lzx
lx lm / 4*
p
$ dc pi.dc
100000
3.13372
[0] https://en.wikipedia.org/wiki/Bc_(programming_language)#Hist...