I quite often need to be able to convert hex to binary for my MegaDrive assembly writing and a command line calculator would be useful for doing this - I've never really got on with BC.

I came across zcalc which is part of zsh. It can be enabled with

autoload …

So today I needed to replace a few hundred href link in varying content today.  Here's my take on solving it. This works in zsh.  I think for bash you need to add the do and done parts of the for loop, i'm not sure.

for file in `grep -lR …