    Returns a status of 0 or 1 depending on the evaluation of the conditional
    expression EXPRESSION.  Expressions are composed of the same primaries used
    by the `test' builtin, and may be combined using the following operators
    
    	( EXPRESSION )	Returns the value of EXPRESSION
    	! EXPRESSION	True if EXPRESSION is false; else false
    	EXPR1 && EXPR2	True if both EXPR1 and EXPR2 are true; else false
    	EXPR1 || EXPR2	True if either EXPR1 or EXPR2 is true; else false
    
    When the `==' and `!=' operators are used, the string to the right of the
    operator is used as a pattern and pattern matching is performed.  The
    && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
    determine the expression's value.
