Find out how to Decide if a Bash Variable is Empty

If you’ll want to examine if a bash variable is empty, or unset, then you should use the next code:

if [ -z "${VAR}" ];

The above code will examine if a variable known as VAR is about, or empty.

What does this imply?

Unset implies that the variable has not been set.

Empty implies that the variable is about with an empty worth of "".

What’s the inverse of -z?

The inverse of -z is -n.

if [ -n "$VAR" ];

A brief resolution to get the variable worth

VALUE="${1?"Utilization: $0 worth"}"

Check if a variable is particularly unset

if [[ -z ${VAR+x} ]]

Check the assorted potentialities

if [ -z "${VAR}" ]; then
    echo "VAR is unset or set to the empty string"
fi
if [ -z "${VAR+set}" ]; then
    echo "VAR is unset"
fi
if [ -z "${VAR-unset}" ]; then
    echo "VAR is about to the empty string"
fi
if [ -n "${VAR}" ]; then
    echo "VAR is about to a non-empty string"
fi
if [ -n "${VAR+set}" ]; then
    echo "VAR is about, presumably to the empty string"
fi
if [ -n "${VAR-unset}" ]; then
    echo "VAR is both unset or set to a non-empty string"
fi

This implies:

                        +-------+-------+-----------+
                VAR is: | unset | empty | non-empty |
+-----------------------+-------+-------+-----------+
| [ -z "${VAR}" ]       | true  | true  | false     |
| [ -z "${VAR+set}" ]   | true  | false | false     |
| [ -z "${VAR-unset}" ] | false | true  | false     |
| [ -n "${VAR}" ]       | false | false | true      |
| [ -n "${VAR+set}" ]   | false | true  | true      |
| [ -n "${VAR-unset}" ] | true  | false | true      |
+-----------------------+-------+-------+-----------+