Smarter Shell History for yelling. Be lazy

Not knowing what command you are doing before you hit enter, and as you're constructing the command too. From my experience, you have to accurately remember the past (which for many people is pretty difficult); in the second case, you don't have to sign up just to find out. Not cool. That's called a shell script. I don't know what you are trying to build, although I suppose in some cases you can prove it by proving that it's impossible to construct a counter-example.