History expansion allows you to use words from previous command lines in the command line you are typing. This simplifies spelling corrections and the repetition of complicated commands or arguments.
Immediately before execution, each command is saved in the history list,
the size of which is controlled by the HISTSIZE
parameter. The one
most recent command is always retained in any case. Each saved command in
the history list is called a history event and is assigned a number,
beginning with 1 (one) when the shell starts up. The history number that
you may see in your prompt (see
Prompt Expansion) is the number that is to be assigned to the next command.