If you have to test if a bash variable is empty, or unset, then you should utilize the next code:
if [ -z "${VAR}" ];
The above code will test if a variable known as VAR is about, or empty.
What does this imply?
Unset implies that the variable has not been set.
Empty implies that the variable is about with an empty worth of "".
What’s the inverse of -z?
The inverse of -z is -n.
if [ -n "$VAR" ];
A brief answer 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, 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 |
+-----------------------+-------+-------+-----------+
