!

Substitute with the previous command and run it with sudo

$ sudo !!

$ ![number]

$ !-[number]

$ ![string]

$ [command] !*

$ [command] !$

$ !:-

$ ![string]:p

!event-designator[:word-modifier][:history-modifier]

!!
    Expand to the last executed command.

!n
    Expand to command line n from history.

!-n
    Expand to nth command backward from current.

!string
    Most recent command starting with string.

!?string?
    Most recent command containing string.

!$
    Last argument of previous command.

!^
    First argument of previous command.

!*
    All arguments of previous command (except 0th).

!:N
    Nth argument of previous command.

!:N-M
    Arguments N through M of previous command.

The ! character in Linux shells like Bash enables history expansion, allowing quick reuse of previous commands or arguments without retyping. When the histexpand shell option is set (default for interactive non-login shells), the shell scans input lines for ! and expands them to historical events before execution or placement in the command history.

History expansion recognizes event designators to select commands (e.g., !! for the last command, !n for line n) and modifiers to alter the selected text (e.g., :p to print without executing, :h for head directory). This feature boosts efficiency for repetitive tasks but requires caution to avoid unintended expansions.

For example, typing ls !* expands !* to all arguments of the previous command. Expansion occurs after parsing but before execution, and quick substitution (^old^new^) provides a shorthand alternative. Disable with set +H if needed.

Expansions occur on unquoted !; use single quotes to prevent. Can cause syntax errors or security risks (e.g., command injection). Disabled in scripts by default. Use history -c to clear history.

:p print line without executing
:h remove trailing filename (/)
:t remove leading path
:r remove trailing suffix (.ext)
:e remove trailing suffix only
:x quote each word
:* all args from 1 to end
:% tail from unique arg.

Use history to list events. Expand with !# for current line, !?# for word at cursor.

Originated in Bill Joy's csh (1978) for C shell. Adopted by Bash (1989) with extensions; POSIX sh lacks it natively but supports via fc. Evolved with readline library for better completion.

bash(1), history(1), fc(1), csh(1)