Decide if a Bash Variable is Empty

If it’s worthwhile 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 referred to as VAR is ready, or empty.

What does this imply?

Unset signifies that the variable has not been set.

Empty signifies 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 resolution to get the variable worth

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

Take a look at if a variable is particularly unset

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

Take a look at the assorted prospects

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      |
+-----------------------+-------+-------+-----------+