Common If Conditions
Existence checks
Exists
# -n: return true when value is not empty.
if [[ -n "${X}" ]]; then
echo "X env variable not empty"
fi
Does not exist
# -z: returns true when value is empty.
if [[ -z "${X}" ]]; then
echo "true when value is empty"
fi
Numerical equality checks
Not Equal
# -ne: not equal operator
if [ "${X}" -ne 0 ]; then
echo "X is not equal to 0"
fi