test_bash_set.sh

gistfile1.sh

#!/bin/bash

echo '          ${var-_}   ${var:-_}  $var       ${!var[@]}'

test_all()
{
    test "${var-_}" && echo -n 'T          ' || echo -n 'F          '
    test "${var:-_}" && echo -n 'T          ' || echo -n 'F          '
    test "$var" && echo -n 'T          ' || echo -n 'F          '
    [[ "${!var[@]}" ]] && echo 'T' || echo 'F'
}

declare var
echo -n 'unset     '
test_all

var=''
echo -n 'empty     '
test_all

var=' '
echo -n 'non-empty '
test_all

var=(var1 var2 var3)
echo -n 'array     '
test_all

In response to http://stackoverflow.com/questions/874389/bash-test-for-a-variable-unset-using-a-function/1469472#1469472