[sillysaurus3]

Throw this in your ~/bin as a script named math:

  #!/bin/sh
  scale=4 # results will print to the 4th decimal
  echo "scale=$scale; $@" | bc -l

Now you can do math.

  $ math '1+1'
  2
  $ math '2/3'
  .6666

This is especially useful in shell scripts with interpolated variables:

  x=10
  x=`math $x - 1`

[xelxebar]

Alternatively, you could use an alias:

    # .bashrc
    alias bc='bc --mathlib'

and a .bcrc file:

    # .bcrc
    scale = 4

Actually, this is what my .bcrc looks like:

    scale = 39

    k_c = 299792458                   # Speed of Light
    k_g = 6.67384 * 10^-11            # Gravitation
    k_atm = 100325                    # Atmospheric pressure
    k_h = 6.62606957 * 10^-34         # Planck's constant
    k_hbar = 1.054571726 * 10^-34     # H Bar
    k_mu = 1.256637061 * 10^-6        # Vacuum permeability
    k_ep = 8.854187817 * 10^-12       # Vacuum permittivity
    k_epsilon = 8.854187817 * 10^-12  # Vacuum permittivity
    k_e = 1.602176565 * 10^-19        # Elementary charge
    k_coulomb = 8.987551787 * 10^9    # Coulomb's constant
    k_me = 9.10938294 * 10^-31        # Rest mass of an electron
    k_mp = 1.672621777 * 10^-27       # Rest mass of a proton
    k_n = 6.02214129 * 10^23          # Avogadro's number
    k_b = 1.3806488 * 10^-23          # Boltzmann's constant
    k_r = 8.3144621                   # Ideal gas constant
    k_si = 5.670373 * 10^-8           # Stefan-Boltzmann constant
    k_sigma = 5.670373 * 10^-8        # Stefan-Boltzmann constant
    k_mt = 5.97219^24                 # Mass of Earth (Tierra)
    k_rt = 6.371 * 10^6               # Mean radius of Earth (Tierra)

    pi = 3.1415926535897932384626433832795028841968

    # requires --mathlib
    define t(x) { return s(x)/c(x); }
    define as(x) { return 2*a(x/(1+sqrt(1-x^2))); }
    define ac(x) { return 2*a(sqrt(1-x^2)/(1+x)); }
    define at(x) { return a(x); }
    define csc(x) { return 1/s(x); }
    define sec(x) { return 1/c(x); }
    define cot(x) { return c(x)/s(x); }

[schoen]

It's not nearly as flexible as bc overall, but GNU units has lots more constants built-in and also trig functions.

I checked and it has all of the ones that you mentioned, sometimes under slightly different names. I was surprised that e is defined the elementary charge rather than Euler's constant!

[majewsky]

units(1) is my go-to calculator for everything. Really nice tool. I recommend

  alias units="units --verbose"

because the verbose output is much less ambiguous.

[schoen]

Nice, thanks for the suggestion.

[chubot]

That might be useful if you want floating point math, but most shell scripts can just use the integer math in shell:

    $ x=10
    $ echo $((x - 1))
    9

Though if I need to do a floating point calculation at the shell, I start python or R, which both have their own interactive shells (with the same readline interface, which I like).