Integrated command line math | Hacker News Reader

Integrated command line math

danielcorin.github.io

39 pointsdanielcorin28 comments

Or, if you're on OS X, you can just use Spotlight. It includes trig functions, factorials, exponents, etc, and it's only a command-space away. The only downside is that it doesn't automatically copy the result into your clipboard.

An example: http://i.imgur.com/vaN7HfS.png

I'm surprised that pressing enter on the result in Spotlight doesn't copy it to the clipboard. Amusingly, it opens up the Calculator which I never need after getting the answer.

‘qalc’ is the command-line version of Qalculate![0] and runs both directly from the command line as well as interactively with tab-completion of variables (Planck mass, for example) and arbitrary unit conversion:

  $ qalc
  > 15 kilogram * (4 m/s)^2 / 2
  
    (15 * kilogram * (((4 * meter) / second)^2)) / 2 = 120((kg*m^2) / s^2)
  
  > convert best
  
    120((kg*m^2) / s^2) = 120 J
  
  > convert gTNT
  
    120 J = approx. 28.680688 mgTNT

[0] http://qalculate.sourceforge.net/

Thanks for sharing this

I have the GTK version of it bound to the blue ‘ThinkVantage’ key, it comes in more than handy multiple times a day :)

Or:

  echo "$1" | bc -l

No need to rev up python.

I thought the same thing until I got to the part where the author used

  from math import *

Which gives you significantly more options.

I love this idea, I have always found math in the command line to be clunky.

That is true, but I have found if I am doing calculations that need something like the full math library of python, it's not a one-off calculation, and I am typically on octave anyway.

In any case, since I have emacs open all time, I usually do

  M-x calc

for one-off calculations.

I just evaluate random lisp in my buffers, sometimes evaluating it to output directly there. Ah emacs!

I do that too, with textadept & Lua instead of Emacs & elisp.

A little syntactic sugar (in zsh):

  function calc {
    print $1 | bc -l
  }

Then:

  calc "(1+2)*3"
  9

zsh actually comes with its own little calculator:

  zcalc "(1+2)*3"
  1> 9
  2>

Among other things, it features "full command line editing, including the history of previous calculations".

minor nitpick, you don't need "echo"

    $ bc -l <<< 3+2
    5
    $

I don't quite understand the argument against bc in this case. 'echo "5 + 5" | bc' doesn't leave the command line.

bc is a little "obtuse". A bc replacement with BCD arithmetic and RPN entry would make me very happy :)

Actually, perhaps I should write one!

I think ``dc'' does what you want.

Wonderful! Thank you for posting. That's exactly what I wanted :)

Just a different way of approaching the problem

A probable improvement on this would be to leave bash out, and just put a python hash bang in the script directly.

I'll leave implementing it as an exercise to the reader. Personally I have found using Guake (http://guake.org/) with IPython as the shell a very nice way of solving this problem.

An even briefer improvement on this would be to remove the whole script and just alias/function the whole thing.

For example, my .bash_profile contains:

function scrub { ps -ef |grep $1 | grep -v grep | awk '{print $2}' | xargs kill }

mostly because I was too lazy to install pkill, but I can just do `scrub tomcat` and it works.

Also, don't alias a script path. Just add the script to the path.

While we're all about the options...you don't need a separate shell script for this, you can just do:

    qc() { python -c "from math import *; print $@" ; }

directly (or in your .bashrc)

For anyone who would like this in an Alfred workflow, make a Script Filter with the following python code (and uncheck all the escape character options):

  from math import *
  print '<?xml version="1.0"?><items>'
  print '<item uid="qcresult" valid="yes" autocomplete="">'
  print '<title>'+str({query})+'</title>'
  print '</item></items>'

Probably known to most, but your shell can also do simple arithmetic by itself.

  $ echo $((3**5))
  243

ksh and zsh support floating point, and ksh also has the usual math functions.

  $ echo $((2 * atan2(1, 0)))
  3.14159265358979324

In zsh you could use noglob to make this nicer:

  zmodload zsh/mathfunc
  _calc() { echo $[$*] }
  alias c='noglob _calc'

Then:

  % c 2 * atan(1, 0) 
  3.1415926535897931

(Although this works with any command, using an alias with qalc as pointed out above might be more useful.)

You can use xclip on Linux (presumably other X based systems) to write to the clipboard.

http://linux.die.net/man/1/xclip

If you are using Emacs, I find that having one buffer always open to R, and another open to shell, serves most of this need.

Great post, thanks.

a bit off topic: are there any calculators which support c like signed / unsigned binary representation? 2 -> 01 -2 -> FD ?

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