> Note that [[ is actually a command/program that returns either 0 (true) or 1 (false). This is true for the [ command, which is the same as `test`, but the [[

> Note that [[ is actually a command/program that returns either 0 (true) or 1 (false). This is true for the [ command, which is the same as `test`, but the [[ ]] syntax is parsed directly by bash, as is (( )). In particular, [[ ]] is not subject to whitespace splitting, so you don't need to quote most variables. They mention $(( )), but don't go into (( )), which gives you very nice integer arithmetic and logic: for (( x = 0; x < 5; x += 2 )); do echo $x (( y = x * 10, z = y + 2 )) echo $y $z done