POSIX compliant way of writing conditional operators

Question

In bash you can do

if [ $(echo $UID) != 0 ]
then
    echo "Run as root"
    exit
fi

This returns an error message when I run the script with dash or other POSIX-compliant shells. How do you do this in POSIX?

Mathieu · Accepted Answer · 2020-01-14T10:10:11.883

2

UID is not defined for all shells (it's not a POSIX requirement)

You can use id -u instead:

#! /bin/sh

if [ "$(id -u)" != "0" ]
then
    echo "Run as root"
    exit
fi

edited Jan 14 '20 at 10:10

answered Jan 14 '20 at 09:01

Mathieu

Thank you! So it wasn't my operators after all. – opfez Jan 14 '20 at 09:42
And when it is defined, you don’t need the echo in the sub shell. – Warren Young Jan 14 '20 at 10:27
1

I would probably exit 1 as it's an error condition. – Kusalananda Jan 14 '20 at 10:36

1 Answers1