Event Designators (Bash Reference Manual)

An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.!

Start a history substitution, except when followed by a space, tab, the end of the line, ‘=’ or ‘(’ (when the extglob shell option is enabled using the shopt builtin).!n

Refer to command line n.!-n

Refer to the command n lines back.!!

Refer to the previous command. This is a synonym for ‘!-1’.!string

Refer to the most recent command preceding the current position in the history list starting with string.!?string[?]

Refer to the most recent command preceding the current position in the history list containing string. The trailing ‘?’ may be omitted if the string is followed immediately by a newline.^string1^string2^

Quick Substitution. Repeat the last command, replacing string1 with string2. Equivalent to !!:s/string1/string2/.!#

The entire command line typed so far.