The way to Decide if a Bash Variable is Empty

If you have to examine if a bash variable is empty, or unset, then you should utilize the next code:

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

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

What does this imply?

Unset implies that the variable has not been set.

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

What’s the inverse of -z?

The inverse of -z is -n.

if [ -n "$VAR" ];

A brief answer to get the variable worth

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

Check if a variable is particularly unset

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

Check the varied 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 "${VAR-unset}" ]; then
    echo "VAR is ready to the empty string"
fi
if [ -n "${VAR}" ]; then
    echo "VAR is ready to a non-empty string"
fi
if [ -n "${VAR+set}" ]; then
    echo "VAR is ready, probably to the empty string"
fi
if [ -n "${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      |
+-----------------------+-------+-------+-----------+