问题
EUID is not the same as UID. At what context are these both are used in the script?
I tried to get the values by echo "UID is $UID and EUID is $EUID", but only space came as output. My machine runs Ubuntu 12.04 LTS. Seen at some sites that this is usually used to check whether it is root user and all but not able to get proper difference.
回答1:
It only works on bash, not in dash (in Debian based distros as Ubuntu sh is usually a symlink to dash).
If you are running the script interactively you might not have bash configured as your default shell, run bash before trying.
If you are running it from console:
bash script.sh
If you are running it using its path (for example ./script.sh) ensure the first line of the script is:
#!/bin/bash
And not:
#!/bin/sh
For a more generic way to do it check: https://askubuntu.com/questions/15853/how-can-a-script-check-if-its-being-run-as-root
In that post the command id is mentioned, where:
id -u # is the EUID
id -u -r # is the UID
回答2:
They're different when a program is running set-uid. Effective UID is the user you changed to, UID is the original user.
来源：https://stackoverflow.com/questions/27669950/difference-between-euid-and-uid