Here’s how to check in Bash if a variable is empty or unset.
if [ -z "${VAR}" ]; then echo 'do something' else echo 'do another' fi |
One liner
if [ -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi |
The inverse
if [ ! -z "${VAR}" ]; then echo 'do something' else echo 'do another' fi |
if [ ! -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi |