# printing conditional commands for xtrace

set -x

# error
[[ -t X ]]
# null operand
[[ $b > 7 ]]

# successful unary operator
[[ -n X ]]

# successful binary operator
ivar=42
[[ $ivar -eq 42 ]]

# compound operator, displayed as two unary expressions

[[ -n a && -n b ]]