Objective: You wanted to run a command as root but you forgot to use sudo. There is a useful shell shortcut (using Event Designators) to re-run the previous command under sudo.
Let’s say you tried to cat the /etc/shadow file as a normal user.
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$ cat /etc/shadow cat: /etc/shadow: Permission denied |
You will get permission denied, because the shadow file is only readable by root. To repeat the last command with sudo, simply use the following syntax.
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$ sudo !! |
The ‘!!‘ syntax is a reference to a command line entry in the history list. It refers to the previous command. An alternative way to run the previous command is to use ‘!-1’.
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$ sudo !-1 |
The ‘!-1‘ syntax means refer to the previous command -n, where n is 1 in this case.

