Bash Check Username of User Running Script

gistfile1.sh

if [ "$(whoami)" != "username" ]; then
        echo "Script must be run as user: username"
        exit 255
fi

This came first on a search so I think despite the age it is worth noting that exit only accepts values 0-255. Any out of range values will be changed to 255. See here: https://www.tldp.org/LDP/abs/html/exitcodes.html

Couldn't you also just check $USER? That's faster than running $(whoami)..

if [ $USER != "username" ]; then
        echo "Script must be run as user: username"
        exit -1
fi

@HaoZeke
checking $USER is not working if the script is run with "sudo -u someuser", but whoami works correctly.

@HaoZeke
checking $USER is not working if the script is run with "sudo -u someuser", but whoami works correctly.

it works fine

[cade@db01 tmp]$ sudo /tmp/test.sh
Current user: [root]
[cade@db01 tmp]$ sudo -i /tmp/test.sh
Current user: [root]
[cade@db01 tmp]$ sudo -i -u oracle /tmp/test.sh
Current user: [oracle]
[cade@db01 tmp]$ sudo -u oracle /tmp/test.sh
Current user: [oracle]
[cade@db01 tmp]$ sudo -u grid /tmp/test.sh
Current user: [grid]
[cade@db01 tmp]$ sudo -i -u grid /tmp/test.sh
Current user: [grid]
[cade@db01 tmp]$ cat /tmp/test.sh
#!/usr/bin/env bash
echo "Current user: [$USER]"
exit

USER is set by the environment.
For example if you run bash in a clean environment (env -i bash) USER is not set.
If you are not sure about the environment is better to use whoami.

NOte, one of the sublt things with sudo and looking at environment variables in one line.

(root) $ sudo -u someuser echo ${USER}
root

Will always return 'root' since it ${USER} is value substituted before the call to sudo.

However, if you escape the $ symbol and pass the statement instead of value.
(root) $ sudo -u someuser bash -c "echo \${USER}"
someuser

Will more likely return what you intended.