Bash shell find out if a variable has NULL value OR not

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In Bash, you can use the -z operator to check if a variable has a NULL value or not. The -z operator returns true if the length of the string stored in the variable is zero. Here is an example:

# Declare a variable
myvar=""

# Check if the variable has a NULL value
if [ -z "$myvar" ]; then
echo "The variable is NULL"
else
echo "The variable has a value"
fi

You can also use the -v operator to check if a variable is set or not, regardless of its value:

# Declare a variable
myvar=""

# Check if the variable is set
if [ -v myvar ]; then
echo "The variable is set"
else
echo "The variable is not set"
fi

Another way is to check if the variable is empty or not

# Declare a variable
myvar=""

# Check if the variable is empty
if [ -z "${myvar}" ]; then
echo "The variable is empty"
else
echo "The variable is not empty"
fi

Please note that different ways of checking if a variable is null or not might have some slightly different behaviors, depending on the version of Bash and the specific use case.

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