History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly. History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event , and the portions of that line that are acted upon are called words .
Various modifiers are available to manipulate the selected words.
The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. If the histverify shell option is enabled, and Readline is being used, history substitutions are not immediately passed to the shell parser. Instead, the expanded line is reloaded into the Readline editing buffer for further modification. If Readline is being used, and the histreedit shell option is enabled, a failed history expansion will be reloaded into the Readline editing buffer for correction. This is most useful in conjunction with Readline.