arggggggggghhhhh

set_variables.sh

#!/usr/bin/env bash

#You need Bash >= 4.2.0 for this.
bash --version | head -n1

set -o errexit
set -o xtrace

unset my_var

if test -v "$my_var"; then
	echo "my_var is set"
else
	echo "my_var is not set"
fi

my_var=

if test -v "$my_var"; then
	echo "my_var is set"
else
	echo "my_var is not set"
fi

my_var="a string"

if test -v "$my_var"; then
	echo "my_var is set"
else
	echo "my_var is not set"
fi

unset my_var

echo ${my_var-default}

my_var="a string"

echo ${my_var-default}

if test -v "$my_var"; then
	echo "my_var is set"
else
	echo "my_var is not set"
fi

#Do not use parameter expansion!
if test -v my_var; then
	echo "my_var is set"
else
	echo "my_var is not set"
fi