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