[built-in takes a series of arguments to perform one or more tests and return an exit status of zero (success) or non-zero (failure). Multiple expressions are separated by one or more
-o(OR) operators and can be grouped using parentheses (parentheses must be escaped or quoted to prevent interpolation).
stringis the same as if given
-n string. Combined with the unary NOT operator,
! stringis the same as
! stringinstead of
-z string, respectively.