Simple shell calculator

I’ve made myself a simple command line calculator using bc. Since I almost always have a terminal open on my computer, it’s quicker to use than opening SpeedCrunch, a calculator app that I’ve liked for a long time but that has gotten kind of slow to launch.

My c calculator is just a shell function that handles piping the calculation into bc, ensures we get a reasonable number of decimal places if needed, and stores the result in an environment variable so it can be used in further calculations.

In bash, it looks like:

function c(){
    result=`echo $* | bc -l`
    if [ ! -z $result ]; then
        echo $C
        export C

I normally use fish though, where it looks like:

function c
    set result (echo $argv | bc -l)
    if test -n "$result"
        set -gx C (echo $argv | bc -l)
        echo $C

It can be used like c 3 + 36 / 3.5 or c "$C ^ 3 + 3 * 2". Some things have to be quoted because they would otherwise have special meaning in the shell.

bc doesn’t have the same built in functions with the same names that SpeedCrunch does, so it may not fully replace the app’s use. It does allow defining custom functions, so I may eventually add define calls to the front of the piped value with the functions I want, but that would take some work.

I’ve also played with using PHP with its -r flag, since it does have many math functions, usually with the same names as SpeedCrunch, and a full programming language that I’m used to to boot. This can be done by changing the calculation line to result=`php -r "echo ${*};"`. This works fairly well, but does have its own problems, such as ^ having different behavior, and the risk of being able to run non-math code that can mutate the file system, etc in a context where that may not be expected or desired.

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