[[ ]] is effectively an entirely different parser than the surrounding shell, similar to (( )). so you can do things like [[ 1 < 2 ]] && echo true # where

[[ ]] is effectively an entirely different parser than the surrounding shell, similar to (( )). so you can do things like [[ 1 < 2 ]] && echo true # where < is now not redirect, like to (( 1 < 2 )) [[ "x" == 'y' || x == x ]] # note how || is not behaving the same as [ '' || 'y' ] `man 1 test` explains the more conventional `[ ]` where the bash man page would better explain the [[ case.