A deeper introduction to Unix DC (opens in new tab)

(ben165.github.io)

72 pointsben1655y ago19 comments

19 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.

c0l05y 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? :)

em5005y 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.

c0l05y 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.

3 more replies

na855y ago

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

kps5y 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.)

m4635y ago

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

Hitton5y ago

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

m4635y ago

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

seryoiupfurds5y 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

azizsaya5y ago

Aah! command I encounter and ignore when I mistype cd

yjftsjthsd-h5y ago

At least it's not sl ;)

0823498723498725y ago

6581840dnP

kps5y ago

    156 is unimplemented

Is that a gnuism?

0823498723498725y ago

Yes, sorry. Try:

    6582352
    dpP

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

j / k navigate · click thread line to collapse

19 comments

arexxbifs5y ago

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

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

staycoolboy5y ago

TIL this and a cool CSS trick.

c0l05y 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? :)

em5005y 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.

c0l05y 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.

3 more replies

na855y ago

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

kps5y 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.)

m4635y ago

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

Hitton5y ago

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

m4635y ago

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

seryoiupfurds5y 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

azizsaya5y ago

Aah! command I encounter and ignore when I mistype cd

yjftsjthsd-h5y ago

At least it's not sl ;)

0823498723498725y ago

6581840dnP

kps5y ago

    156 is unimplemented

Is that a gnuism?

0823498723498725y ago

Yes, sorry. Try:

    6582352
    dpP

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

j / k navigate · click thread line to collapse