Best kinds of conversations :) Set aside my mention of POSIX as a minor point. My basic claim is this: building a whole new shell is an ambitious act. Whether

Best kinds of conversations :) Set aside my mention of POSIX as a minor point. My basic claim is this: building a whole new shell is an ambitious act. Whether your goal is to create a better experience for others or just learn new skills, restricting yourself to what earlier shells happen to consider to be builtins is limiting ambition. Be more ambitious and rethink as much as you want. I'm not saying you have to rethink everything all at once all the way up from machine code (though I'm sympathetic to and experienced in that particular failure mode ^_^). I'm saying if you have an idea to improve 'cat' to fit better with your new shell, the fact that it's in coreutils shouldn't cause you pause. Who cares if it's a builtin in bash or not? Make it a builtin in your shell.