A deeper introduction to Unix DC | Hacker News Reader

A deeper introduction to Unix DC

ben165.github.io

72 pointsben16519 comments

Related fun fact: bc is a dc preprocessor[0].

[0] https://en.wikipedia.org/wiki/Bc_(programming_language)#Hist...

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.

TIL this and a cool CSS trick.

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.

POSIX.1-2017 describes the `dc` program as "excluded" from the standard; check https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu... for details.

Many GNU/Linux distros (at least Debian and RHEL) install neither `dc` nor `bc` by default, afaik.

> 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.

Gentoo doesn't include it in the common 'stage3' tarball, either. Which is annoying because it's actually required to compile the linux kernel.

I stand corrected, only bc is included in POSIX.

https://stackoverflow.com/questions/37880810/how-come-is-thi...

    echo '1033333377708482P' | dc

produces the same output using Unix dc but not in the GNU near-clone. (To understand why, you have to R the P as well as the M.)

  echo 'EGSZ%%%'|tr 'E-Z%' 'R-ZA-M!'

Funny. Despite being long time Linux user this is the first time I remember hearing about dc. I only knew bc.

I have a way of looking at this. More people are familiar with apples than okra. (there's a reason for that)

    [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

Aah! command I encounter and ignore when I mistype cd

At least it's not sl ;)

6581840dnP

    156 is unimplemented

Is that a gnuism?

Yes, sorry. Try:

    6582352
    dpP

(at least we now know the error is old enough to be in octal)

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