I'm looking for some software that would be useful for giving demonstrations.

I regularly have to show the effects of scrips ect to classes while talking about their effects, and equaly regularly I have finger trouble and have to rewrite various commands - wasting class time and general energy.

I'd like to be able to record a sequence of commands in advance, and then play them back at the speed of my choosing.

So I might have a file that containes the commands:

echo "hello world!" 
ls ls -l  
ls -l | sort

I'd like to be able to play these commands back by typing similar ones in.

So I'd have a blinking command prompt and if I typed 'echo "hxxx' the command prompt would read

home$echo "hell

and if I typed any other letters the terminal would fill up with the remainder of the command until I press enter, when it executes the command. The point is that even if I screw up the command when typing it, the command that I'd prepared in advance would be executed.

My question is - does similar software exist for giving demonstrations? or even, is this an easy thing to script up...?

EDIT - two quick things first of all I'm on osx - but it would be nice to get a general solution for other people who arrive here from google. and second a lot of the comments/answers are concentrating on, in effect, making it fast and easy to enter long commands by means of hotkeys and the like. Actually I'd like it to at least look like I'm typing live - that's why I put in the bit about the one-to-one keymapping, but I don't think I explained that quite as well as I could have...