Work the Shell - Solve: a Command-Line Calculator Redux

Dave completes his explanation of writing a helpful interactive command-line calculator as a shell script.
The Full Script

Here's where the script stands at this point, in its entirety:


if [ $# -gt 0 ] ; then
bc << EOF
  /bin/echo -n "solve: "

  while read expression
    if [ "$expression" = "quit" -o 
         "$expression" = "exit" ] ; then
      exit 0
bc << EOF
    /bin/echo -n "solve: "

  echo ""
  echo "solved."

exit 0

Neat and darn useful, I'd say. If I were to continue hacking on it, the next thing I would do is write a simple help page that I'd store in some library folder and display on entry of ? or help. It simply would explain the syntax of the expressions understood by bc (though as we're invoking bc iteratively, we can't have persistent variables and so forth, so unfortunately, this approach won't let us access the full power of the binary calculator).

To learn what type of sophisticated expressions you can enter, simply type man bc. Then, let that be your inspiration for further tweaks and mods to this script!

Next month, I'll go back to the numerology script and see what strange things we can ascertain about the apparently benign world around us. Remember, just because I got out of sequence, doesn't mean we're not out to get you, dear reader!

Dave Taylor is a 26-year veteran of UNIX, creator of The Elm Mail System, and most recently author of both the best-selling Wicked Cool Shell Scripts and Teach Yourself Unix in 24 Hours, among his 16 technical books. His main Web site is at, and he also offers up tech support at


Dave Taylor has been hacking shell scripts for over thirty years. Really. He's the author of the popular "Wicked Cool Shell Scripts" and can be found on Twitter as @DaveTaylor and more generally at


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I use this great command

Mike 2009's picture

I use this great command line calculator

There is a windows version also that I use on my windows computer

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