Tip: Shell aliases with sudo

Here is a quick tip for you.

Have you ever tried using your shell aliases in combination with the sudo command? Yeah, does not work. The reason being that shell aliases are a simple ‘text substitution’ mechanism and by default, only the first word in a command is checked to see if it has an alias. However, if the last character of an alias is a space, the following word is also checked for alias expansion.

The Trick

In order to use your aliases when using sudo, you need to create an alias for the sudo command itself. Aliasing it to sudo (that’s sudo + <space>) will force the following word to be evaluated as an alias as well.

alias sudo="sudo "

Example

$ alias show-logs="cat /var/log/nginx/access.log"

$ show-logs
cat: /var/log/nginx/access.log: Permission denied

$ sudo show-logs
sudo: show-logs: command not found

$ alias sudo="sudo "

$ sudo show-logs
20.20.20.20 - - [24/Jan/2018:22:48:12+0000] "GET / HTTP/1.1" 301 194 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36"
.
.
.

More detailed description of how alias expansion works can be found in the Bash Reference Manual.

Neat, right? That’s it. Bye bye 👋

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© 2018 Jerguš Lejko