Test if a variable is set in bash when using “set -o nounset”

Question

The following code exits with a unbound variable error. How to fix this, while still using the set -o nounset option?

#!/bin/bash

set -o nounse         


        

Answer 1

You need to quote the variables if you want to get the result you expect:

check() {
    if [ -n "${WHATEVER-}" ]
    then
        echo 'not empty'
    elif [ "${WHATEVER+defined}" = defined ]
    then
        echo 'empty but defined'
    else
        echo 'unset'
    fi
}

Test:

$ unset WHATEVER
$ check
unset
$ WHATEVER=
$ check
empty but defined
$ WHATEVER='   '
$ check
not empty