A deeper introduction to Unix DC

A deeper introduction to Unix DC(ben165.github.io)

72 points by ben165 5 years ago | 19 comments

arexxbifs 5 years ago |

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.

c0l0 5 years ago |

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? :)

em500 5 years ago | |

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.

c0l0 5 years ago | | |

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.

na85 5 years ago | |

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

kps 5 years ago | |

    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.)

m463 5 years ago | |

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

Hitton 5 years ago |

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

m463 5 years ago | |

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

seryoiupfurds 5 years ago |

    [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

azizsaya 5 years ago |

Aah! command I encounter and ignore when I mistype cd

yjftsjthsd-h 5 years ago | |

At least it's not sl ;)

082349872349872 5 years ago |

6581840dnP

kps 5 years ago | |

    156 is unimplemented

Is that a gnuism?

082349872349872 5 years ago | | |

Yes, sorry. Try:

    6582352
    dpP

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

[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