Solomon Boulos just pointed out the most useful bash feature I’ve found so far. Reverse-i-search! Like the emacs functionality, it autocompletes the command you’re typing in according to your history file, in the order of your history file.
Access this magic by hitting “Control-R”. Start typing a command and it will autocomplete it for you. Keep hitting Control-R and it will cycle through all possible matches. Incredibly useful! It’s like using ! except you can see what it’s going to execute.