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".