Quick, Linux-compatible unit-aware calculator

Question

I want to be able to press a keyboard combination, start typing a mathematical expression that includes units and slightly advanced math (not just a four-function calculator), and get a result immediately, in units that I specify, that I can copy and paste.

• Currently I open Firefox and press Ctrl+K, type in the search box, and it usually gives me a result in the drop-down from Google Calculator. It doesn't always, though, so I press "=" at the end, wait for a result, remove the equals, wait for a result, realize it doesn't understand the way I typed a unit, open the result in a new tab, etc. it sucks.
• Wolfram Alpha is smarter, but very much slower, and the output is all images, not text, and I don't have a quick widget for it, if such a thing could even exist.
• GNU units has a ton of units, which is great, and I can define my own units, which is great, but they have to be written in specific, unintuitive ways, it doesn't handle much advanced math, and I'd need to open a terminal, start units, etc. I hate the command line.

I wasted a lot of time trying to make front-ends for units in Deskbar and Launchy, but I'm not a real coder and I don't use either of those anymore.

Any other solutions or enhancements of these?

(Of course, something cross-platform would be even better, but Linux-only is fine.)

Answer 1

I'm very impressed with Qalculate!.

Answer 2

For a easily scriptable solution you might want to have a look a the sympy python module.

$ cat conv.py

#!/usr/bin/env python
import sys
from sympy.physics.units import *
from sympy.printing.pretty.pretty import pprint
from sympy.abc import x, y, z
from sympy import *

# adding extra units is easy
parsec = 3.26163626*ly

if __name__ == '__main__':
  s_input = sys.argv[1]
  s_unit  = sys.argv[2]
  input = eval(s_input)  # input string
  unit  = eval(s_unit)   # output unit

  print 'Converting:'
  pprint(input)
  print
  print str((input/unit).evalf()) +' '+ s_unit

which gives e.g. for some moderately ugly expression converted to mm:

$./conv.py 'tanh(3*m/(2*m))*sinh(60*deg)*1*parsec' 'mm'


Converting:
                           /π\
3.08574615554565e+16*m*sinh|--|*tanh(3/2)
                           \3 /

3.48955431541888e+19 mm

Of course this is really studpid code that does no checking thet unit compatibility of the input and output, so you might end up extra units in the result.

$./conv.py 'c' 'parsec'

Converting:
299792458*m
-----------
     s

9.71539598165644e-9/s parsec

Answer 3

Wolfram Alpha is capable of crunching math and doesn't require you to download or install anything.

Check here for how to use its math functions.